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• AbstractMethodError on org.apache.xalan.processor.TransformerFactoryImpl

  - by JBristow

  With the following code: private Document transformDoc(Source source) throws TransformerException, IOException { Transformer xslTransformer = TransformerFactory.newInstance().newTransformer(new StreamSource(pdfTransformXslt.getInputStream())); xslTransformer.setParameter("http://apache.org/xml/features/nonvalidating/load-external-dtd", false); xslTransformer.setParameter("http://xml.org/sax/features/validation", false); JDOMResult result = new JDOMResult(); xslTransformer.transform(source, result); return result.getDocument(); } I'm getting the following error: java.lang.AbstractMethodError: org.apache.xalan.processor.TransformerFactoryImpl.setFeature(Ljava/lang/String;Z)V Why is this? Here's my Maven dependency tree: ------------------------------------------------------------------------ Building mc-hub-batch task-segment: [dependency:tree] ------------------------------------------------------------------------ snapshot com.billmelater:mc-test-support:2.0.0.11-SNAPSHOT: checking for updates from repository.jboss.org [dependency:tree {execution: default-cli}] com.billmelater:mc-hub-batch:jar:2.0.0.11-SNAPSHOT +- com.billmelater:mc-hub-core:jar:2.0.0.11-SNAPSHOT:compile | +- commons-lang:commons-lang:jar:2.4:compile | +- commons-collections:commons-collections:jar:3.2.1:compile | +- commons-beanutils:commons-beanutils:jar:1.8.0:compile | +- commons-digester:commons-digester:jar:2.0:compile | | +- (commons-beanutils:commons-beanutils:jar:1.8.0:compile - omitted for duplicate) | | \- (commons-logging:commons-logging:jar:1.1.1:compile - version managed from 1.0.4; omitted for duplicate) | \- (org.springframework.batch:spring-batch-core:jar:2.0.2.RELEASE:compile - omitted for duplicate) +- com.billmelater:mc-test-support:jar:2.0.0.11-SNAPSHOT:test | +- (com.billmelater:mc-hub-core:jar:2.0.0.11-SNAPSHOT:test - omitted for duplicate) | +- (org.springframework:spring:jar:2.5.6:test - omitted for duplicate) | +- org.springframework:spring-jdbc:jar:2.5.6.SEC01:test | | +- (commons-logging:commons-logging:jar:1.1.1:test - omitted for duplicate) | | +- (org.springframework:spring-beans:jar:2.5.6.SEC01:test - omitted for conflict with 2.5.6) | | +- (org.springframework:spring-context:jar:2.5.6.SEC01:test - omitted for conflict with 2.5.6) | | +- (org.springframework:spring-core:jar:2.5.6.SEC01:test - omitted for conflict with 2.5.6) | | \- (org.springframework:spring-tx:jar:2.5.6.SEC01:test - omitted for conflict with 2.5.6) | +- (org.dbunit:dbunit:jar:2.4.5:test - omitted for duplicate) | +- (log4j:log4j:jar:1.2.15:test - omitted for duplicate) | +- (org.slf4j:slf4j-api:jar:1.5.6:compile - version managed from 1.5.8; scope updated from test; omitted for duplicate) | +- (org.slf4j:slf4j-log4j12:jar:1.5.6:test - omitted for duplicate) | +- org.jboss.seam:jboss-seam:jar:2.2.0.GA:test | | +- xstream:xstream:jar:1.1.3:test | | +- (xpp3:xpp3_min:jar:1.1.3.4.O:compile - scope updated from test; omitted for duplicate) | | \- org.jboss.el:jboss-el:jar:1.0_02.CR4:test | +- (org.testng:testng:jar:jdk15:5.8:test - omitted for duplicate) | +- (org.hibernate:hibernate-core:jar:3.3.2.GA:test - version managed from 3.3.0.SP1; omitted for duplicate) | +- org.hibernate:hibernate-entitymanager:jar:3.4.0.GA:test | | +- (org.hibernate:ejb3-persistence:jar:1.0.2.GA:test - omitted for duplicate) | | +- (org.hibernate:hibernate-commons-annotations:jar:3.1.0.GA:test - omitted for duplicate) | | +- (org.hibernate:hibernate-annotations:jar:3.4.0.GA:test - omitted for duplicate) | | +- (org.hibernate:hibernate-core:jar:3.3.2.GA:test - version managed from 3.3.0.SP1; omitted for duplicate) | | +- (org.slf4j:slf4j-api:jar:1.5.6:test - version managed from 1.4.2; omitted for duplicate) | | +- (dom4j:dom4j:jar:1.6.1-jboss:test - version managed from 1.6.1; omitted for duplicate) | | +- (javax.transaction:jta:jar:1.0.1B:test - version managed from 1.1; omitted for duplicate) | | \- javassist:javassist:jar:3.4.GA:test | +- (org.hibernate:hibernate-validator:jar:3.1.0.GA:test - omitted for duplicate) | +- (org.apache.velocity:velocity:jar:1.6.2:test - omitted for duplicate) | \- (ojdbc:ojdbc:jar:14:test - omitted for duplicate) +- org.springframework:spring:jar:2.5.6:compile +- org.springframework.batch:spring-batch-core:jar:2.0.2.RELEASE:compile | +- org.springframework.batch:spring-batch-infrastructure:jar:2.0.2.RELEASE:compile | | +- (commons-logging:commons-logging:jar:1.1.1:compile - omitted for duplicate) | | +- (org.springframework:spring-core:jar:2.5.6:compile - omitted for duplicate) | | \- (stax:stax:jar:1.2.0:compile - omitted for duplicate) | +- org.aspectj:aspectjrt:jar:1.5.4:compile | +- org.aspectj:aspectjweaver:jar:1.5.4:compile | +- com.thoughtworks.xstream:xstream:jar:1.3:compile | | \- xpp3:xpp3_min:jar:1.1.4c:compile | +- org.codehaus.jettison:jettison:jar:1.0:compile | +- org.springframework:spring-aop:jar:2.5.6:compile | | +- aopalliance:aopalliance:jar:1.0:compile | | +- (commons-logging:commons-logging:jar:1.1.1:compile - omitted for duplicate) | | +- (org.springframework:spring-beans:jar:2.5.6:compile - omitted for duplicate) | | \- (org.springframework:spring-core:jar:2.5.6:compile - omitted for duplicate) | +- org.springframework:spring-beans:jar:2.5.6:compile | | +- (commons-logging:commons-logging:jar:1.1.1:compile - omitted for duplicate) | | \- (org.springframework:spring-core:jar:2.5.6:compile - omitted for duplicate) | +- org.springframework:spring-context:jar:2.5.6:compile | | +- (aopalliance:aopalliance:jar:1.0:compile - omitted for duplicate) | | +- (commons-logging:commons-logging:jar:1.1.1:compile - omitted for duplicate) | | +- (org.springframework:spring-beans:jar:2.5.6:compile - omitted for duplicate) | | \- (org.springframework:spring-core:jar:2.5.6:compile - omitted for duplicate) | +- org.springframework:spring-core:jar:2.5.6:compile | | \- (commons-logging:commons-logging:jar:1.1.1:compile - omitted for duplicate) | +- org.springframework:spring-tx:jar:2.5.6:compile | | +- (commons-logging:commons-logging:jar:1.1.1:compile - omitted for duplicate) | | +- (org.springframework:spring-beans:jar:2.5.6:compile - omitted for duplicate) | | +- (org.springframework:spring-context:jar:2.5.6:compile - omitted for duplicate) | | \- (org.springframework:spring-core:jar:2.5.6:compile - omitted for duplicate) | \- stax:stax:jar:1.2.0:compile | \- stax:stax-api:jar:1.0.1:compile +- commons-dbcp:commons-dbcp:jar:1.2.2:compile | \- commons-pool:commons-pool:jar:1.3:compile +- org.hibernate:hibernate-core:jar:3.3.2.GA:compile | +- antlr:antlr:jar:2.7.7:compile (version managed from 2.7.6) | +- dom4j:dom4j:jar:1.6.1-jboss:compile (version managed from 1.6.1) | +- javax.transaction:jta:jar:1.0.1B:compile (version managed from 1.1) | \- (org.slf4j:slf4j-api:jar:1.5.6:compile - version managed from 1.4.2; omitted for duplicate) +- org.hibernate:hibernate-validator:jar:3.1.0.GA:compile | +- (org.hibernate:hibernate-core:jar:3.3.2.GA:compile - version managed from 3.3.0.SP1; omitted for duplicate) | +- org.hibernate:hibernate-commons-annotations:jar:3.1.0.GA:compile | | \- (org.slf4j:slf4j-api:jar:1.5.6:compile - version managed from 1.4.2; omitted for duplicate) | \- (org.slf4j:slf4j-api:jar:1.5.6:compile - version managed from 1.4.2; omitted for duplicate) +- org.hibernate:hibernate-annotations:jar:3.4.0.GA:compile | +- org.hibernate:ejb3-persistence:jar:1.0.2.GA:compile | +- (org.hibernate:hibernate-commons-annotations:jar:3.1.0.GA:compile - omitted for duplicate) | +- (org.hibernate:hibernate-core:jar:3.3.2.GA:compile - version managed from 3.3.0.SP1; omitted for duplicate) | +- (org.slf4j:slf4j-api:jar:1.5.6:compile - version managed from 1.4.2; omitted for duplicate) | \- (dom4j:dom4j:jar:1.6.1-jboss:compile - version managed from 1.6.1; omitted for duplicate) +- ojdbc:ojdbc:jar:14:compile +- org.slf4j:slf4j-api:jar:1.5.6:compile +- org.slf4j:slf4j-log4j12:jar:1.5.6:compile | \- (org.slf4j:slf4j-api:jar:1.5.6:compile - version managed from 1.4.2; omitted for duplicate) +- log4j:log4j:jar:1.2.15:compile +- org.apache.velocity:velocity:jar:1.6.2:compile | +- (commons-collections:commons-collections:jar:3.2.1:compile - omitted for duplicate) | +- (commons-lang:commons-lang:jar:2.4:compile - omitted for duplicate) | \- oro:oro:jar:2.0.8:compile +- org.testng:testng:jar:jdk15:5.8:test +- org.dbunit:dbunit:jar:2.4.5:test | +- junit:junit:jar:4.7:test (version managed from 3.8.2) | +- (org.slf4j:slf4j-api:jar:1.5.6:test - version managed from 1.4.2; omitted for duplicate) | \- (commons-collections:commons-collections:jar:3.2.1:test - omitted for duplicate) +- hsqldb:hsqldb:jar:1.8.0.7:test +- jboss:javassist:jar:3.3.ga:provided +- org.jdom:jdom:jar:1.1:compile +- jaxen:jaxen:jar:1.1.1:provided +- org.apache.xmlgraphics:fop:jar:0.95:compile | +- (org.apache.xmlgraphics:xmlgraphics-commons:jar:1.3.1:compile - omitted for duplicate) | +- org.apache.xmlgraphics:batik-svg-dom:jar:1.7:compile | | +- (org.apache.xmlgraphics:batik-svg-dom:jar:1.7:compile - omitted for cycle) | | +- org.apache.xmlgraphics:batik-anim:jar:1.7:compile | | | +- (org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile - omitted for duplicate) | | | +- (org.apache.xmlgraphics:batik-dom:jar:1.7:compile - omitted for duplicate) | | | +- (org.apache.xmlgraphics:batik-ext:jar:1.7:compile - omitted for duplicate) | | | \- (org.apache.xmlgraphics:batik-parser:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile - omitted for duplicate) | | +- org.apache.xmlgraphics:batik-css:jar:1.7:compile | | | +- (org.apache.xmlgraphics:batik-ext:jar:1.7:compile - omitted for duplicate) | | | +- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | | | \- (xml-apis:xml-apis-ext:jar:1.3.04:compile - omitted for duplicate) | | +- org.apache.xmlgraphics:batik-dom:jar:1.7:compile | | | +- (org.apache.xmlgraphics:batik-css:jar:1.7:compile - omitted for duplicate) | | | +- (org.apache.xmlgraphics:batik-ext:jar:1.7:compile - omitted for duplicate) | | | +- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | | | +- (org.apache.xmlgraphics:batik-xml:jar:1.7:compile - omitted for duplicate) | | | +- (xalan:xalan:jar:2.6.0:compile - omitted for duplicate) | | | \- (xml-apis:xml-apis-ext:jar:1.3.04:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-ext:jar:1.7:compile - omitted for duplicate) | | +- org.apache.xmlgraphics:batik-parser:jar:1.7:compile | | | +- (org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile - omitted for duplicate) | | | +- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | | | \- (org.apache.xmlgraphics:batik-xml:jar:1.7:compile - omitted for duplicate) | | +- org.apache.xmlgraphics:batik-util:jar:1.7:compile | | \- xml-apis:xml-apis-ext:jar:1.3.04:compile | +- org.apache.xmlgraphics:batik-bridge:jar:1.7:compile | | +- (org.apache.xmlgraphics:batik-anim:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-css:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-dom:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-ext:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-bridge:jar:1.7:compile - omitted for cycle) | | +- (org.apache.xmlgraphics:batik-gvt:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-parser:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-bridge:jar:1.7:compile - omitted for cycle) | | +- org.apache.xmlgraphics:batik-script:jar:1.7:compile | | +- (org.apache.xmlgraphics:batik-svg-dom:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | | +- org.apache.xmlgraphics:batik-xml:jar:1.7:compile | | | \- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | | +- xalan:xalan:jar:2.6.0:compile | | \- (xml-apis:xml-apis-ext:jar:1.3.04:compile - omitted for duplicate) | +- org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile | | \- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | +- org.apache.xmlgraphics:batik-gvt:jar:1.7:compile | | +- (org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-gvt:jar:1.7:compile - omitted for cycle) | | +- (org.apache.xmlgraphics:batik-bridge:jar:1.7:compile - omitted for duplicate) | | \- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | +- org.apache.xmlgraphics:batik-transcoder:jar:1.7:compile | | +- (org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-bridge:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-dom:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-gvt:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-svg-dom:jar:1.7:compile - omitted for duplicate) | | +- org.apache.xmlgraphics:batik-svggen:jar:1.7:compile | | | +- (org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile - omitted for duplicate) | | | \- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-xml:jar:1.7:compile - omitted for duplicate) | | \- (xml-apis:xml-apis-ext:jar:1.3.04:compile - omitted for duplicate) | +- org.apache.xmlgraphics:batik-extension:jar:1.7:compile | | +- (org.apache.xmlgraphics:batik-awt-util:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-bridge:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-css:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-dom:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-ext:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-gvt:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-parser:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-svg-dom:jar:1.7:compile - omitted for duplicate) | | +- (org.apache.xmlgraphics:batik-util:jar:1.7:compile - omitted for duplicate) | | \- (xml-apis:xml-apis-ext:jar:1.3.04:compile - omitted for duplicate) | +- org.apache.xmlgraphics:batik-ext:jar:1.7:compile | +- commons-logging:commons-logging:jar:1.1.1:compile | +- commons-io:commons-io:jar:1.3.1:compile | \- org.apache.avalon.framework:avalon-framework-api:jar:4.3.1:compile +- org.apache.xmlgraphics:xmlgraphics-commons:jar:1.3.1:compile | +- (commons-io:commons-io:jar:1.3.1:compile - omitted for duplicate) | \- (commons-logging:commons-logging:jar:1.1.1:compile - version managed from 1.0.4; omitted for duplicate) +- org.easymock:easymock:jar:2.0:test \- org.easymock:easymockclassextension:jar:2.2:test +- (org.easymock:easymock:jar:2.2:test - omitted for conflict with 2.0) \- cglib:cglib-nodep:jar:2.2:test (version managed from 2.1_3) Can anyone tell me how to clear out intellij's classpath too?

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• Collision detection of huge number of circles

  - by Tomek Tarczynski

  What is the best way to check collision of huge number of circles? It's very easy to detect collision between two circles, but if we check every combination then it is O(n^2) which definitely not an optimal solution. We can assume that circle object has following properties: -Coordinates -Radius -Velocity -Direction Velocity is constant, but direction can change. I've come up with two solutions, but maybe there are some better solutions. Solution 1 Divide whole space into overlapping squares and check for collision only with circles that are in the same square. Squares needs to overlap so there won't be a problem when circle moves from one square to another. Solution 2 At the beginning distances between every pair of circles need to be calculated. If the distance is small then these pair is stored in some list, and we need to check for collision in every update. If the distance is big then we store after which update there can be a collision (it can be calculated because we know the distance and velocitites). It needs to be stored in some kind of priority queue. After previously calculated number of updates distance needs to be checked again and then we do the same procedure - put it on the list or again in the priority queue.

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• implementing gravity to projectile - delta time issue

  - by Murat Nafiz

  I'm trying to implement a simple projectile motion in Android (with openGL). And I want to add gravity to my world to simulate a ball's dropping realistically. I simply update my renderer with a delta time which is calculated by: float deltaTime = (System.nanoTime()-startTime) / 1000000000.0f; startTime = System.nanoTime(); screen.update(deltaTime); In my screen.update(deltaTime) method: if (isballMoving) { golfBall.updateLocationAndVelocity(deltaTime); } And in golfBall.updateLocationAndVelocity(deltaTime) method: public final static double G = -9.81; double vz0 = getVZ0(); // Gets initial velocity(z) double z0 = getZ0(); // Gets initial height double time = getS(); // gets total time from act begin double vz = vz0 + G * deltaTime; // calculate new velocity(z) double z = z0 - vz0 * deltaTime- 0.5 * G * deltaTime* deltaTime; // calculate new position time = time + deltaTime; // Update time setS(time); //set new total time Now here is the problem; If I set deltaTime as 0.07 statically, then the animation runs normally. But since the update() method runs as faster as it can, the length and therefore the speed of the ball varies from device to device. If I don't touch deltaTime and run the program (deltaTime's are between 0.01 - 0.02 with my test devices) animation length and the speed of ball are same at different devices. But the animation is so SLOW! What am I doing wrong?

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• How do I implement a group of strings that starts randomly, but is bound by relevance upon selection?

  - by Freakishly

  Okay the title may be a little confusing, but here's what I'm trying to do :) I have a game in XNA where every tap from the user draws a moving circle on the screen. The circle has a tag, say 'dogs' displayed on it. So imagine multiple taps on the screen, and we have all these circles of various colors and sizes moving around the screen with different (but constant) velocities. Each circle with different tags: 'dogs', 'cats' and so on... Clicking on empty space generates a new circle at that point. Clicking on one of the circles "selects" it, turning it into a greeen shade and slowing its velocity down to a fraction of what it was. Clicking on it again "unselects" it, and restores its original color and velocity (trajectory does not change). With each circle comes a tag, and as of now I'm populating these tags randomly from a string array (which means there's a chance tags will repeat). I would like the tags for newly created circles to be relevant to previous "selected" tags. So when I click on 'dogs', I would like 'German Shepherd' but I would also like 'dog parks' and 'lemurs' assuming dogs get along well with lemurs. What would be the best way to approach this problem. In my head I have a massive many-to-many mapping, but I can't seem to translate it to code. Thanks for looking. FYI I'm using the sample project from here: http://mobile.tutsplus.com/tutorials/windows/introduction-to-xna-on-windows-phone-7/

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• The Product Owner

  - by Robert May

  In a previous post, I outlined the rules of Scrum.  This post details one of those rules. Picking a most important part of Scrum is difficult.  All of the rules are required, but if there were one rule that is “more” required that every other rule, its having a good Product Owner.  Simply put, the Product Owner can make or break the project. Duties of the Product Owner A Product Owner has many duties and responsibilities.  I’ll talk about each of these duties in detail below. A Product Owner: Discovers and records stories for the backlog. Prioritizes stories in the Product Backlog, Release Backlog and Iteration Backlog. Determines Release dates and Iteration Dates. Develops story details and helps the team understand those details. Helps QA to develop acceptance tests. Interact with the Customer to make sure that the product is meeting the customer’s needs. Discovers and Records Stories for the Backlog When I do Scrum, I always use User Stories as the means for capturing functionality that’s required in the system.  Some people will use Use Cases, but the same rule applies.  The Product Owner has the ultimate responsibility for figuring out what functionality will be in the system.  Many different mechanisms for capturing this input can be used.  User interviews are great, but all sources should be considered, including talking with Customer Support types.  Often, they hear what users are struggling with the most and are a great source for stories that can make the application easier to use. Care should be taken when soliciting user stories from technical types such as programmers and the people that manage them.  They will almost always give stories that are very technical in nature and may not have a direct benefit for the end user.  Stories are about adding value to the company.  If the stories don’t have direct benefit to the end user, the Product Owner should question whether or not the story should be implemented.  In general, technical stories should be included as tasks in User Stories.  Technical stories are often needed, but the ultimate value to the user is in user based functionality, so technical stories should be considered nothing more than overhead in providing that user functionality. Until the iteration prior to development, stories should be nothing more than short, one line placeholders. An exercise called Story Planning can be used to brainstorm and come up with stories.  I’ll save the description of this activity for another blog post. For more information on User Stories, please read the book User Stories Applied by Mike Cohn. Prioritizes Stories in the Product Backlog, Release Backlog and Iteration Backlog Prioritization of stories is one of the most difficult tasks that a Product Owner must do.  A key concept of Scrum done right is the need to have the team working from a single set of prioritized stories.  If the team does not have a single set of prioritized stories, Scrum will likely fail at your organization.  The Product Owner is the ONLY person who has the responsibility to prioritize that list.  The Product Owner must be very diplomatic and sincerely listen to the people around him so that he can get the priorities correct. Just listening will still not yield the proper priorities.  Care must also be taken to ensure that Return on Investment is also considered.  Ultimately, determining which stories give the most value to the company for the least cost is the most important factor in determining priorities.  Product Owners should be willing to look at cold, hard numbers to determine the order for stories.  Even when many people want a feature, if that features is costly to develop, it may not have as high of a return on investment as features that are cheaper, but not as popular. The act of prioritization often causes conflict in an environment.  Customer Service thinks that feature X is the most important, because it will stop people from calling.  Operations thinks that feature Y is the most important, because it will stop servers from crashing.  Developers think that feature Z is most important because it will make writing software much easier for them.  All of these are useful goals, but the team can have only one list of items, and each item must have a priority that is different from all other stories.  The Product Owner will determine which feature gives the best return on investment and the other features will have to wait their turn, which means that someone will not have their top priority feature implemented first. A weak Product Owner will refuse to do prioritization.  I’ve heard from multiple Product Owners the following phrase, “Well, it’s all got to be done, so what does it matter what order we do it in?”  If your product owner is using this phrase, you need a new Product Owner.  Order is VERY important.  In Scrum, every release is potentially shippable.  If the wrong priority items are developed, then the value added in each release isn’t what it should be.  Additionally, the Product Owner with this mindset doesn’t understand Agile.  A product is NEVER finished, until the company has decided that it is no longer a going concern and they are no longer going to sell the product.  Therefore, prioritization isn’t an event, its something that continues every day.  The logical extension of the phrase “It’s all got to be done” is that you will never ship your product, since a product is never “done.”  Once stories have been prioritized, assigning them to the Release Backlog and the Iteration Backlog becomes relatively simple.  The top priority items are copied into the respective backlogs in order and the task is complete.  The team does have the right to shuffle things around a little in the iteration backlog.  For example, they may determine that working on story C with story A is appropriate because they’re related, even though story B is technically a higher priority than story C.  Or they may decide that story B is too big to complete in the time available after Story A has tasks created, so they’ll work on Story C since it’s smaller.  They can’t, however, go deep into the backlog to pick stories to implement.  The team and the Product Owner should work together to determine what’s best for the company. Prioritization is time consuming, but its one of the most important things a Product Owner does. Determines Release Dates and Iteration Dates Product owners are responsible for determining release dates for a product.  A common misconception that Product Owners have is that every “release” needs to correspond with an actual release to customers.  This is not the case.  In general, releases should be no more than 3 months long.  You  may decide to release the product to the customers, and many companies do release the product to customers, but it may also be an internal release. If a release date is too far away, developers will fall into the trap of not feeling a sense of urgency.  The date is far enough away that they don’t need to give the release their full attention.  Additionally, important tasks, such as performance tuning, regression testing, user documentation, and release preparation, will not happen regularly, making them much more difficult and time consuming to do.  The more frequently you do these tasks, the easier they are to accomplish. The Product Owner will be a key participant in determining whether or not a release should be sent out to the customers.  The determination should be made on whether or not the features contained in the release are valuable enough  and complete enough that the customers will see real value in the release.  Often, some features will take more than three months to get them to a state where they qualify for a release or need additional supporting features to be released.  The product owner has the right to make this determination. In addition to release dates, the Product Owner also will help determine iteration dates.  In general, an iteration length should be chosen and the team should follow that iteration length for an extended period of time.  If the iteration length is changed every iteration, you’re not doing Scrum.  Iteration lengths help the team and company get into a rhythm of developing quality software.  Iterations should be somewhere between 2 and 4 weeks in length.  Any shorter, and significant software will likely not be developed.  Any longer, and the team won’t feel urgency and planning will become very difficult. Iterations may not be extended during the iteration.  Companies where Scrum isn’t really followed will often use this as a strategy to complete all stories.  They don’t want to face the harsh reality of what their true performance is, and looking good is more important than seeking visibility and improving the process and team.  Companies like this typically don’t allow failure.  This is unhealthy.  Failure is part of life and unless we learn from it, we can’t improve.  I would much rather see a team push out stories to the next iteration and then have healthy discussions about why they failed rather than extend the iteration and not deal with the core problems. If iteration length varies, retrospectives become more difficult.  For example, evaluating the performance of the team’s estimation efforts becomes much more difficult if the iteration length varies.  Also, the team must have a velocity measurement.  If the iteration length varies, measuring velocity becomes impossible and upper management no longer will have the ability to evaluate the teams performance.  People external to the team will no longer have the ability to determine when key features are likely to be developed.  Variable iterations cause the entire company to fail and likely cause Scrum to fail at an organization. Develops Story Details and Helps the Team Understand Those Details A key concept in Scrum is that the stories are nothing more than a placeholder for a conversation.  Stories should be nothing more than short, one line statements about the functionality.  The team will then converse with the Product Owner about the details about that story.  The product owner needs to have a very good idea about what the details of the story are and needs to be able to help the team understand those details. Too often, we see this requirement as being translated into the need for comprehensive documentation about the story, including old fashioned requirements documentation.  The team should only develop the documentation that is required and should not develop documentation that is only created because their is a process to do so. In general, what we see that works best is the iteration before a team starts development work on a story, the Product Owner, with other appropriate business analysts, will develop the details of that story.  They’ll figure out what business rules are required, potentially make paper prototypes or other light weight mock-ups, and they seek to understand the story and what is implied.  Note that the time allowed for this task is deliberately short.  The Product Owner only has a single iteration to develop all of the stories for the next iteration. If more than one iteration is used, I’ve found that teams will end up with Big Design Up Front and traditional requirements documents.  This is a waste of time, since the team will need to then have discussions with the Product Owner to figure out what the requirements document says.  Instead of this, skip making the pretty pictures and detailing the nuances of the requirements and build only what is minimally needed by the team to do development.  If something comes up during development, you can address it at that time and figure out what you want to do.  The goal is to keep things as light weight as possible so that everyone can move as quickly as possible. Helps QA to Develop Acceptance Tests In Scrum, no story can be counted until it is accepted by QA.  Because of this, acceptance tests are very important to the team.  In general, acceptance tests need to be developed prior to the iteration or at the very beginning of the iteration so that the team can make sure that the tasks that they develop will fulfill the acceptance criteria. The Product Owner will help the team, including QA, understand what will make the story acceptable.  Note that the Product Owner needs to be careful about specifying that the feature will work “Perfectly” at the end of the iteration.  In general, features are developed a little bit at a time, so only the bit that is being developed should be considered as necessary for acceptance. A weak Product Owner will make statements like “Do it right the first time.”  Not only are these statements damaging to the team (like they would try to do it WRONG the first time . . .), they’re also ignoring the iterative nature of Scrum.  Additionally, a weak product owner will seek to add scope in the acceptance testing.  For example, they will refuse to determine acceptance at the beginning of the iteration, and then, after the team has planned and committed to the iteration, they will expand scope by defining acceptance.  This often causes the team to miss the iteration because scope that wasn’t planned on is included.  There are ways that the team can mitigate this problem.  For example, include extra “Product Owner” time to deal with the uncertainty that you know will be introduced by the Product Owner.  This will slow the perceived velocity of the team and is not ideal, since they’ll be doing more work than they get credit for. Interact with the Customer to Make Sure that the Product is Meeting the Customer’s Needs Once development is complete, what the team has worked on should be put in front of real live people to see if it meets the needs of the customer.  One of the great things about Agile is that if something doesn’t work, we can revisit it in a future iteration!  This frees up the team to make the best decision now and know that if that decision proves to be incorrect, the team can revisit it and change that decision. Features are about adding value to the customer, so if the customer doesn’t find them useful, then having the team make tweaks is valuable.  In general, most software will be 80 to 90 percent “right” after the initial round and only minor tweaks are required.  If proper coding standards are followed, these tweaks are usually minor and easy to accomplish.  Product Owners that are doing a good job will encourage real users to see and use the software, since they know that they are trying to add value to the customer. Poor product owners will think that they know the answers already, that their customers are silly and do stupid things and that they don’t need customer input.  If you have a product owner that is afraid to show the team’s work to real customers, you probably need a different product owner. Up Next, “Who Makes a Good Product Owner.” Followed by, “Messing with the Team.” Technorati Tags: Scrum,Product Owner

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• trouble running smooth animation in thread only when using key listener

  - by heysuse renard

  first time using a forum for coding help so sorry if i post this all wrong. i have more than a few classes i don't think screenManger or core holds the problem but i included them just incase. i got most of this code working through a set of tutorials. but a certain point started trying to do more on my own. i want to play the animation only when i'm moving my sprite. in my KeyTest class i am using threads to run the animation it used to work (poorly) but now not at all pluss it really gunks up my computer. i think it's because of the thread. im new to threads so i'm not to sure if i should even be using one in this situation or if its dangerous for my computer. the animation worked smoothly when i had the sprite bouce around the screen forever. the animation loop played with out stopping. i think the main problem is between the animationThread, Sprite, and keyTest classes, but itcould be more indepth. if someone could point me in the right direction for making the animation run smoothly when i push down a key and stop runing when i let off it would be greatly apriciated. i already looked at this Java a moving animation (sprite) obviously we were doing the same tutorial. but i feel my problem is slightly different. p.s. sorry for the typos. import java.awt.*; import java.awt.event.KeyEvent; import java.awt.event.KeyListener; import java.awt.image.BufferStrategy; import java.awt.image.BufferedImage; import java.util.ArrayList; import javax.swing.ImageIcon; import javax.swing.JFrame; public class KeyTest extends Core implements KeyListener { public static void main(String[] args) { new KeyTest().run(); } Sprite player1; Image hobo; Image background; animation hoboRun; animationThread t1; //init also calls init form superclass public void init() { super.init(); loadImages(); Window w = s.getFullScreenWindow(); w.setFocusTraversalKeysEnabled(false); w.addKeyListener(this); } //load method will go here. //load all pics need for animation and sprite public void loadImages() { background = new ImageIcon("\\\\STUART-PC\\Users\\Stuart\\workspace\\Gaming\\yellow square.jpg").getImage(); Image face1 = new ImageIcon("\\\\STUART-PC\\Users\\Stuart\\workspace\\Gaming\\circle.png").getImage(); Image face2 = new ImageIcon("\\\\STUART-PC\\Users\\Stuart\\workspace\\Gaming\\one eye.png").getImage(); hoboRun = new animation(); hoboRun.addScene(face1, 250); hoboRun.addScene(face2, 250); player1 = new Sprite(hoboRun); this.t1 = new animationThread(); this.t1.setAnimation(player1); } //key pressed public void keyPressed(KeyEvent e) { int keyCode = e.getKeyCode(); if (keyCode == KeyEvent.VK_ESCAPE) { stop(); } if (keyCode == KeyEvent.VK_RIGHT) { player1.setVelocityX(0.3f); try { this.t1.setRunning(true); Thread th1 = new Thread(this.t1); th1.start(); } catch (Exception ex) { System.out.println("noooo"); } } if (keyCode == KeyEvent.VK_LEFT) { player1.setVelocityX(-0.3f); try { this.t1.setRunning(true); Thread th1 = new Thread(this.t1); th1.start(); } catch (Exception ex) { System.out.println("noooo"); } } if (keyCode == KeyEvent.VK_DOWN) { player1.setVelocityY(0.3f); try { this.t1.setRunning(true); Thread th1 = new Thread(this.t1); th1.start(); } catch (Exception ex) { System.out.println("noooo"); } } if (keyCode == KeyEvent.VK_UP) { player1.setVelocityY(-0.3f); try { this.t1.setRunning(true); Thread th1 = new Thread(this.t1);; th1.start(); } catch (Exception ex) { System.out.println("noooo"); } } else { e.consume(); } } //keyReleased @SuppressWarnings("static-access") public void keyReleased(KeyEvent e) { int keyCode = e.getKeyCode(); if (keyCode == KeyEvent.VK_RIGHT || keyCode == KeyEvent.VK_LEFT) { player1.setVelocityX(0); try { this.t1.setRunning(false); } catch (Exception ex) { } } if (keyCode == KeyEvent.VK_UP || keyCode == KeyEvent.VK_DOWN) { player1.setVelocityY(0); try { this.t1.setRunning(false); } catch (Exception ex) { } } else { e.consume(); } } //last method from interface public void keyTyped(KeyEvent e) { e.consume(); } //draw public void draw(Graphics2D g) { Window w = s.getFullScreenWindow(); g.setColor(w.getBackground()); g.fillRect(0, 0, s.getWidth(), s.getHieght()); g.setColor(w.getForeground()); g.drawImage(player1.getImage(), Math.round(player1.getX()), Math.round(player1.getY()), null); } public void update(long timePassed) { player1.update(timePassed); } } abstract class Core { private static DisplayMode modes[] = { new DisplayMode(1600, 900, 64, 0), new DisplayMode(800, 600, 32, 0), new DisplayMode(800, 600, 24, 0), new DisplayMode(800, 600, 16, 0), new DisplayMode(800, 480, 32, 0), new DisplayMode(800, 480, 24, 0), new DisplayMode(800, 480, 16, 0),}; private boolean running; protected ScreenManager s; //stop method public void stop() { running = false; } public void run() { try { init(); gameLoop(); } finally { s.restoreScreen(); } } //set to full screen //set current background here public void init() { s = new ScreenManager(); DisplayMode dm = s.findFirstCompatibleMode(modes); s.setFullScreen(dm); Window w = s.getFullScreenWindow(); w.setFont(new Font("Arial", Font.PLAIN, 20)); w.setBackground(Color.GREEN); w.setForeground(Color.WHITE); running = true; } //main gameLoop public void gameLoop() { long startTime = System.currentTimeMillis(); long cumTime = startTime; while (running) { long timePassed = System.currentTimeMillis() - cumTime; cumTime += timePassed; update(timePassed); Graphics2D g = s.getGraphics(); draw(g); g.dispose(); s.update(); try { Thread.sleep(20); } catch (Exception ex) { } } } //update animation public void update(long timePassed) { } //draws to screen abstract void draw(Graphics2D g); } class animationThread implements Runnable { String name; boolean playing; Sprite a; //constructor takes input from keyboard public animationThread() { } //The run method for animation public void run() { long startTime = System.currentTimeMillis(); long cumTime = startTime; boolean test = getRunning(); while (test) { long timePassed = System.currentTimeMillis() - cumTime; cumTime += timePassed; test = getRunning(); } } public String getName() { return name; } public void setAnimation(Sprite a) { this.a = a; } public void setName(String name) { this.name = name; } public void setRunning(boolean running) { this.playing = running; } public boolean getRunning() { return playing; } } class animation { private ArrayList scenes; private int sceneIndex; private long movieTime; private long totalTime; //constructor public animation() { scenes = new ArrayList(); totalTime = 0; start(); } //add scene to ArrayLisy and set time for each scene public synchronized void addScene(Image i, long t) { totalTime += t; scenes.add(new OneScene(i, totalTime)); } public synchronized void start() { movieTime = 0; sceneIndex = 0; } //change scenes public synchronized void update(long timePassed) { if (scenes.size() > 1) { movieTime += timePassed; if (movieTime >= totalTime) { movieTime = 0; sceneIndex = 0; } while (movieTime > getScene(sceneIndex).endTime) { sceneIndex++; } } } //get animations current scene(aka image) public synchronized Image getImage() { if (scenes.size() == 0) { return null; } else { return getScene(sceneIndex).pic; } } //get scene private OneScene getScene(int x) { return (OneScene) scenes.get(x); } //Private Inner CLASS////////////// private class OneScene { Image pic; long endTime; public OneScene(Image pic, long endTime) { this.pic = pic; this.endTime = endTime; } } } class Sprite { private animation a; private float x; private float y; private float vx; private float vy; //Constructor public Sprite(animation a) { this.a = a; } //change position public void update(long timePassed) { x += vx * timePassed; y += vy * timePassed; } public void startAnimation(long timePassed) { a.update(timePassed); } //get x position public float getX() { return x; } //get y position public float getY() { return y; } //set x public void setX(float x) { this.x = x; } //set y public void setY(float y) { this.y = y; } //get sprite width public int getWidth() { return a.getImage().getWidth(null); } //get sprite height public int getHeight() { return a.getImage().getHeight(null); } //get horizontal velocity public float getVelocityX() { return vx; } //get vertical velocity public float getVelocityY() { return vx; } //set horizontal velocity public void setVelocityX(float vx) { this.vx = vx; } //set vertical velocity public void setVelocityY(float vy) { this.vy = vy; } //get sprite / image public Image getImage() { return a.getImage(); } } class ScreenManager { private GraphicsDevice vc; public ScreenManager() { GraphicsEnvironment e = GraphicsEnvironment.getLocalGraphicsEnvironment(); vc = e.getDefaultScreenDevice(); } //get all compatible DM public DisplayMode[] getCompatibleDisplayModes() { return vc.getDisplayModes(); } //compares DM passed into vc DM and see if they match public DisplayMode findFirstCompatibleMode(DisplayMode modes[]) { DisplayMode goodModes[] = vc.getDisplayModes(); for (int x = 0; x < modes.length; x++) { for (int y = 0; y < goodModes.length; y++) { if (displayModesMatch(modes[x], goodModes[y])) { return modes[x]; } } } return null; } //get current DM public DisplayMode getCurrentDisplayMode() { return vc.getDisplayMode(); } //checks if two modes match each other public boolean displayModesMatch(DisplayMode m1, DisplayMode m2) { if (m1.getWidth() != m2.getWidth() || m1.getHeight() != m2.getHeight()) { return false; } if (m1.getBitDepth() != DisplayMode.BIT_DEPTH_MULTI && m2.getBitDepth() != DisplayMode.BIT_DEPTH_MULTI && m1.getBitDepth() != m2.getBitDepth()) { return false; } if (m1.getRefreshRate() != DisplayMode.REFRESH_RATE_UNKNOWN && m2.getRefreshRate() != DisplayMode.REFRESH_RATE_UNKNOWN && m1.getRefreshRate() != m2.getRefreshRate()) { return false; } return true; } //make frame full screen public void setFullScreen(DisplayMode dm) { JFrame f = new JFrame(); f.setUndecorated(true); f.setIgnoreRepaint(true); f.setResizable(false); vc.setFullScreenWindow(f); if (dm != null && vc.isDisplayChangeSupported()) { try { vc.setDisplayMode(dm); } catch (Exception ex) { } } f.createBufferStrategy(2); } //sets graphics object = this return public Graphics2D getGraphics() { Window w = vc.getFullScreenWindow(); if (w != null) { BufferStrategy s = w.getBufferStrategy(); return (Graphics2D) s.getDrawGraphics(); } else { return null; } } //updates display public void update() { Window w = vc.getFullScreenWindow(); if (w != null) { BufferStrategy s = w.getBufferStrategy(); if (!s.contentsLost()) { s.show(); } } } //returns full screen window public Window getFullScreenWindow() { return vc.getFullScreenWindow(); } //get width of window public int getWidth() { Window w = vc.getFullScreenWindow(); if (w != null) { return w.getWidth(); } else { return 0; } } //get height of window public int getHieght() { Window w = vc.getFullScreenWindow(); if (w != null) { return w.getHeight(); } else { return 0; } } //get out of full screen public void restoreScreen() { Window w = vc.getFullScreenWindow(); if (w != null) { w.dispose(); } vc.setFullScreenWindow(null); } //create image compatible with monitor public BufferedImage createCopatibleImage(int w, int h, int t) { Window win = vc.getFullScreenWindow(); if (win != null) { GraphicsConfiguration gc = win.getGraphicsConfiguration(); return gc.createCompatibleImage(w, h, t); } return null; } }

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• Building the Elusive Windows Phone Panorama Control

  When the Windows Phone 7 Developer SDK was released a couple of weeks ago at MIX10 many people noticed the SDK doesnt include a template for a Panorama control.   Here at Clarity we decided to build our own Panorama control for use in some of our prototypes and I figured I would share what we came up with. There have been a couple of implementations of the Panorama control making their way through the interwebs, but I didnt think any of them really nailed the experience that is shown in the simulation videos.   One of the key design principals in the UX Guide for Windows Phone 7 is the use of motion.  The WP7 OS is fairly stripped of extraneous design elements and makes heavy use of typography and motion to give users the necessary visual cues.  Subtle animations and wide layouts help give the user a sense of fluidity and consistency across the phone experience.  When building the panorama control I was fairly meticulous in recreating the motion as shown in the videos.  The effect that is shown in the application hubs of the phone is known as a Parallax Scrolling effect.  This this pseudo-3D technique has been around in the computer graphics world for quite some time. In essence, the background images move slower than foreground images, creating an illusion of depth in 2D.  Here is an example of the traditional use: http://www.mauriciostudio.com/.  One of the animation gems I've learned while building interactive software is the follow animation.  The premise is straightforward: instead of translating content 1:1 with the interaction point, let the content catch up to the mouse or finger.  The difference is subtle, but the impact on the smoothness of the interaction is huge.  That said, it became the foundation of how I achieved the effect shown below.   Source Code Available HERE Before I briefly describe the approach I took in creating this control..and Ill add some **asterisks ** to the code below as my coding skills arent up to snuff with the rest of my colleagues.  This code is meant to be an interpretation of the WP7 panorama control and is not intended to be used in a production application.  1.  Layout the XAML The UI consists of three main components :  The background image, the Title, and the Content.  You can imagine each  these UI Elements existing on their own plane with a corresponding Translate Transform to create the Parallax effect.  2.  Storyboards + Procedural Animations = Sexy As I mentioned above, creating a fluid experience was at the top of my priorities while building this control.  To recreate the smooth scroll effect shown in the video we need to add some place holder storyboards that we can manipulate in code to simulate the inertia and snapping.  Using the easing functions built into Silverlight helps create a very pleasant interaction.    3.  Handle the Manipulation Events With Silverlight 3 we have some new touch event handlers.  The new Manipulation events makes handling the interactivity pretty straight forward.  There are two event handlers that need to be hooked up to enable the dragging and motion effects: the ManipulationDelta event :  (the most relevant code is highlighted in pink) Here we are doing some simple math with the Manipulation Deltas and setting the TO values of the animations appropriately. Modifying the storyboards dynamically in code helps to create a natural feel.something that cant easily be done with storyboards alone.   And secondly, the ManipulationCompleted event:  Here we take the Final Velocities from the Manipulation Completed Event and apply them to the Storyboards to create the snapping and scrolling effects.  Most of this code is determining what the next position of the viewport will be.  The interesting part (shown in pink) is determining the duration of the animation based on the calculated velocity of the flick gesture.  By using velocity as a variable in determining the duration of the animation we can produce a slow animation for a soft flick and a fast animation for a strong flick. Challenges to the Reader There are a couple of things I didnt have time to implement into this control.  And I would love to see other WPF/Silverlight approaches.  1.  A good mechanism for deciphering when the user is manipulating the content within the panorama control and the panorama itself.   In other words, being able to accurately determine what is a flick and what is click. 2.  Dynamically Sizing the panorama control based on the width of its content.  Right now each control panel is 400px, ideally the Panel items would be measured and then panorama control would update its size accordingly.  3.  Background and content wrapping.  The WP7 UX guidelines specify that the content and background should wrap at the end of the list.  In my code I restrict the drag at the ends of the list (like the iPhone).  It would be interesting to see how this would effect the scroll experience.     Well, Its been fun building this control and if you use it Id love to know what you think.  You can download the Source HERE or from the Expression Gallery  Erik Klimczak  | [email protected] | twitter.com/eklimczDid you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• RK4 Bouncing a Ball

  - by Jonathan Dickinson

  I am trying to wrap my head around RK4. I decided to do the most basic 'ball with gravity that bounces' simulation. I have implemented the following integrator given Glenn Fiedler's tutorial: /// <summary> /// Represents physics state. /// </summary> public struct State { // Also used internally as derivative. // S: Position // D: Velocity. /// <summary> /// Gets or sets the Position. /// </summary> public Vector2 X; // S: Position // D: Acceleration. /// <summary> /// Gets or sets the Velocity. /// </summary> public Vector2 V; } /// <summary> /// Calculates the force given the specified state. /// </summary> /// <param name="state">The state.</param> /// <param name="t">The time.</param> /// <param name="acceleration">The value that should be updated with the acceleration.</param> public delegate void EulerIntegrator(ref State state, float t, ref Vector2 acceleration); /// <summary> /// Represents the RK4 Integrator. /// </summary> public static class RK4 { private const float OneSixth = 1.0f / 6.0f; private static void Evaluate(EulerIntegrator integrator, ref State initial, float t, float dt, ref State derivative, ref State output) { var state = new State(); // These are a premature optimization. I like premature optimization. // So let's not concentrate on that. state.X.X = initial.X.X + derivative.X.X * dt; state.X.Y = initial.X.Y + derivative.X.Y * dt; state.V.X = initial.V.X + derivative.V.X * dt; state.V.Y = initial.V.Y + derivative.V.Y * dt; output = new State(); output.X.X = state.V.X; output.X.Y = state.V.Y; integrator(ref state, t + dt, ref output.V); } /// <summary> /// Performs RK4 integration over the specified state. /// </summary> /// <param name="eulerIntegrator">The euler integrator.</param> /// <param name="state">The state.</param> /// <param name="t">The t.</param> /// <param name="dt">The dt.</param> public static void Integrate(EulerIntegrator eulerIntegrator, ref State state, float t, float dt) { var a = new State(); var b = new State(); var c = new State(); var d = new State(); Evaluate(eulerIntegrator, ref state, t, 0.0f, ref a, ref a); Evaluate(eulerIntegrator, ref state, t + dt * 0.5f, dt * 0.5f, ref a, ref b); Evaluate(eulerIntegrator, ref state, t + dt * 0.5f, dt * 0.5f, ref b, ref c); Evaluate(eulerIntegrator, ref state, t + dt, dt, ref c, ref d); a.X.X = OneSixth * (a.X.X + 2.0f * (b.X.X + c.X.X) + d.X.X); a.X.Y = OneSixth * (a.X.Y + 2.0f * (b.X.Y + c.X.Y) + d.X.Y); a.V.X = OneSixth * (a.V.X + 2.0f * (b.V.X + c.V.X) + d.V.X); a.V.Y = OneSixth * (a.V.Y + 2.0f * (b.V.Y + c.V.Y) + d.V.Y); state.X.X = state.X.X + a.X.X * dt; state.X.Y = state.X.Y + a.X.Y * dt; state.V.X = state.V.X + a.V.X * dt; state.V.Y = state.V.Y + a.V.Y * dt; } } After reading over the tutorial I noticed a few things that just seemed 'out' to me. Notably how the entire simulation revolves around t at 0 and state at 0 - considering that we are working out a curve over the duration it seems logical that RK4 wouldn't be able to handle this simple scenario. Never-the-less I forged on and wrote a very simple Euler integrator: static void Integrator(ref State state, float t, ref Vector2 acceleration) { if (state.X.Y > 100 && state.V.Y > 0) { // Bounce vertically. acceleration.Y = -state.V.Y * t; } else { acceleration.Y = 9.8f; } } I then ran the code against a simple fixed-time step loop and this is what I got: 0.05 0.20 0.44 0.78 1.23 1.76 ... 74.53 78.40 82.37 86.44 90.60 94.86 99.23 103.05 105.45 106.94 107.86 108.42 108.76 108.96 109.08 109.15 109.19 109.21 109.23 109.23 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 ... As I said, I was expecting it to break - however I am unsure of how to fix it. I am currently looking into keeping the previous state and time, and working from that - although at the same time I assume that will defeat the purpose of RK4. How would I get this simulation to print the expected results?

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• Building the Elusive Windows Phone Panorama Control

  When the Windows Phone 7 Developer SDK was released a couple of weeks ago at MIX10 many people noticed the SDK doesnt include a template for a Panorama control.   Here at Clarity we decided to build our own Panorama control for use in some of our prototypes and I figured I would share what we came up with. There have been a couple of implementations of the Panorama control making their way through the interwebs, but I didnt think any of them really nailed the experience that is shown in the simulation videos.   One of the key design principals in the UX Guide for Windows Phone 7 is the use of motion.  The WP7 OS is fairly stripped of extraneous design elements and makes heavy use of typography and motion to give users the necessary visual cues.  Subtle animations and wide layouts help give the user a sense of fluidity and consistency across the phone experience.  When building the panorama control I was fairly meticulous in recreating the motion as shown in the videos.  The effect that is shown in the application hubs of the phone is known as a Parallax Scrolling effect.  This this pseudo-3D technique has been around in the computer graphics world for quite some time. In essence, the background images move slower than foreground images, creating an illusion of depth in 2D.  Here is an example of the traditional use: http://www.mauriciostudio.com/.  One of the animation gems I've learned while building interactive software is the follow animation.  The premise is straightforward: instead of translating content 1:1 with the interaction point, let the content catch up to the mouse or finger.  The difference is subtle, but the impact on the smoothness of the interaction is huge.  That said, it became the foundation of how I achieved the effect shown below.   Source Code Available HERE Before I briefly describe the approach I took in creating this control..and Ill add some **asterisks ** to the code below as my coding skills arent up to snuff with the rest of my colleagues.  This code is meant to be an interpretation of the WP7 panorama control and is not intended to be used in a production application.  1.  Layout the XAML The UI consists of three main components :  The background image, the Title, and the Content.  You can imagine each  these UI Elements existing on their own plane with a corresponding Translate Transform to create the Parallax effect.  2.  Storyboards + Procedural Animations = Sexy As I mentioned above, creating a fluid experience was at the top of my priorities while building this control.  To recreate the smooth scroll effect shown in the video we need to add some place holder storyboards that we can manipulate in code to simulate the inertia and snapping.  Using the easing functions built into Silverlight helps create a very pleasant interaction.    3.  Handle the Manipulation Events With Silverlight 3 we have some new touch event handlers.  The new Manipulation events makes handling the interactivity pretty straight forward.  There are two event handlers that need to be hooked up to enable the dragging and motion effects: the ManipulationDelta event :  (the most relevant code is highlighted in pink) Here we are doing some simple math with the Manipulation Deltas and setting the TO values of the animations appropriately. Modifying the storyboards dynamically in code helps to create a natural feel.something that cant easily be done with storyboards alone.   And secondly, the ManipulationCompleted event:  Here we take the Final Velocities from the Manipulation Completed Event and apply them to the Storyboards to create the snapping and scrolling effects.  Most of this code is determining what the next position of the viewport will be.  The interesting part (shown in pink) is determining the duration of the animation based on the calculated velocity of the flick gesture.  By using velocity as a variable in determining the duration of the animation we can produce a slow animation for a soft flick and a fast animation for a strong flick. Challenges to the Reader There are a couple of things I didnt have time to implement into this control.  And I would love to see other WPF/Silverlight approaches.  1.  A good mechanism for deciphering when the user is manipulating the content within the panorama control and the panorama itself.   In other words, being able to accurately determine what is a flick and what is click. 2.  Dynamically Sizing the panorama control based on the width of its content.  Right now each control panel is 400px, ideally the Panel items would be measured and then panorama control would update its size accordingly.  3.  Background and content wrapping.  The WP7 UX guidelines specify that the content and background should wrap at the end of the list.  In my code I restrict the drag at the ends of the list (like the iPhone).  It would be interesting to see how this would effect the scroll experience.     Well, Its been fun building this control and if you use it Id love to know what you think.  You can download the Source HERE or from the Expression Gallery  Erik Klimczak  | [email protected] | twitter.com/eklimczDid you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Welch's Juices-up Its Inventory Management with Oracle Supply Chain

  - by [email protected]

  Supply & Demand Chain Executive published recently a great success story about Welch's implementation of "Take Supply Chain and G.SI to work with Oracle Process Manufacturing". The company says it's been able to improve operational control, inventory accuracy, visibility and order fulfillment by automating its processes across three production/warehousing locations nationwide. Improving warehouse and inventory management operations creates efficiencies across a high-velocity nationwide supply chain Welch's production facilities were collecting more information than ever before on the flow of materials and inventory, but the company needed an effective and accurate method to organize and manage these data.   Article found at: http://www.sdcexec.com/publication/article.jsp?pubId=1&id=12256&pageNum=2     

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• Welch's Juices-up Its Inventory Management with Oracle Supply Chain

  - by [email protected]

  Supply & Demand Chain Executive published recently a great success story about Welch's implementation of "Take Supply Chain and G.SI to work with Oracle Process Manufacturing". The company says it's been able to improve operational control, inventory accuracy, visibility and order fulfillment by automating its processes across three production/warehousing locations nationwide. Improving warehouse and inventory management operations creates efficiencies across a high-velocity nationwide supply chain Welch's production facilities were collecting more information than ever before on the flow of materials and inventory, but the company needed an effective and accurate method to organize and manage these data.   Article found at: http://www.sdcexec.com/publication/article.jsp?pubId=1&id=12256&pageNum=2     

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• Welch's Juices-up Its Inventory Management with Oracle Supply Chain

  - by [email protected]

  Supply & Demand Chain Executive published recently a great success story about Welch's implementation of "Take Supply Chain and G.SI to work with Oracle Process Manufacturing". The company says it's been able to improve operational control, inventory accuracy, visibility and order fulfillment by automating its processes across three production/warehousing locations nationwide. Improving warehouse and inventory management operations creates efficiencies across a high-velocity nationwide supply chain Welch's production facilities were collecting more information than ever before on the flow of materials and inventory, but the company needed an effective and accurate method to organize and manage these data.   Article found at: http://www.sdcexec.com/publication/article.jsp?pubId=1&id=12256&pageNum=2     

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• Swept AABB vs Line Segment 2D

  - by Larolaro

  I've really exhausted as much as Google has to give, I've spent a solid week googling every combination of words for an "AABBvsLine sweep", downloaded countless collision demos, dissected SAT intersection examples and an AABBvsAABB sweep trying to figure out how to approach this. I've not found a single thing covering this specific pairing. Can anyone shed any light on how to get the hit time of a swept AABB vs a Line segment in 2D? I'm still getting familiar with the SAT but I do know how to implement it to a degree, I'm just not sure how to extract the hit time from the velocity in the non axis aligned separating axes for the sweep. I really would appreciate anything at the moment, some code or even some helpful links, I'm at my wits end!

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• Game Maker Studio Gravity Problems

  - by Dusty

  I've started messing around with Game Maker Studio. The problem I'm having is trying to get a gravity code for orbiting. Here's how i did it in XNA foreach (GravItem Item in StarSystem.ActiveItems.OfType<GravItem>()) { if (this != Item) { Velocity += (10 * Vector2.Normalize(Item.Position - this.Position * (this.Mass * Item.Mass) / (Vector2.DistanceSquared(this.Position, Item.Position)) / (this.Mass)); } } Simple and works well, things or bit and everything is nice. but in Game maker i don't have the luxury of Vector2's or a For-each loop to loop threw all the objects that have a mass. I've tried a few different things but nothing seems to work distance = distance_to_object(obj_moon); //--Gravity hspeed += (0.5 * (distance) * (Mass * obj_moon.Mass) / (sqr(distance)) / Mass) vspeed += (0.5 * (distance) * (Mass * obj_moon.Mass) / (sqr(distance)) / Mass) thanks for the help

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• Platformer gravity where gravity is greater than tile size

  - by Sara

  I am making a simple grid-tile-based platformer with basic physics. I have 16px tiles, and after playing with gravity it seems that to get a nice quick Mario-like jump feel, the player ends up moving faster than 16px per second at the ground. The problem is that they clip through the first layer of tiles before collisions being detected. Then when I move the player to the top of the colliding tile, they move to the bottom-most tile. I have tried limiting their maximum velocity to be less than 16px but it does not look right. Are there any standard approaches to solving this? Thanks.

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• Software Management Tools for Agile Process Development

  - by Graviton

  We would like to implement the Agile/ Scrum process in our daily software management, so as to provide better progress visibility and feature managements, here are some of the activities that we want to do: Daily stand-up Release cycles of 6 weeks with 3 2-week iterations. Having a product back-log of tasks (integrate with bugzilla) and bugs estimated out. Printing a daily burn down to make velocity visible. When used as motivator, it's great. Easy feature development tracking and full blown visibility, especially for the sales and stake holders ( this means that it must be a web based tool). My team is distributed, so physical whiteboards aren't feasible. Is there such a web based tool that meets our needs? I heard icescrum may be one, but I've never used it so I don't know. There are a few more suggestions as here, but I've never heard of them, anyone cares to elaborate or suggest new tools?

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• Podcast Show Notes: The Role of the Cloud Architect

  - by Bob Rhubart

  Ron Batra James Baty If you want to understand what a cloud architect does, what better way than to talk to people in that role? In this program that’s exactly what we’ll do. Joining me for this conversation are cloud architects Ron Batra and Dr. James Baty. Ron is an Oracle ACE Director and product director for cloud computing at AT&T , and Jim is Vice President of Oracle’s Global Enterprise Architecture Program . This interview was recorded on June 12, 2012. The Conversation Listen to Part 1: How cloud computing is driving the supply-chaining of IT and the democratization of the activity of architecture. Listen to Part 2 (July 12): A discussion of DevOps, cloud computing, and the increasing velocity of IT. Listen to Part 3 (July 19): Why architects need to up their game to thrive and succeed in a cloud-driven world. Coming Soon A conversation about the International SOA, Cloud & Service Technology Symposium with a panel that features Thomas Erl and several Oracle community members who will be presenting at that event.

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• How to change speed without changing path travelled?

  - by Ben Williams

  I have a ball which is being thrown from one side of a 2D space to the other. The formula I am using for calculating the ball's position at any one point in time is: x = x0 + vx0*t y = y0 + vy0*t - 0.5*g*t*t where g is gravity, t is time, x0 is the initial x position, vx0 is the initial x velocity. What I would like to do is change the speed of this ball, without changing how far it travels. Let's say the ball starts in the lower left corner, moves upwards and rightwards in an arc, and finishes in the lower right corner, and this takes 5s. What I would like to be able to do is change this so it takes 10s or 20s, but the ball still follows the same curve and finishes in the same position. How can I achieve this? All I can think of is manipulating t but I don't think that's a good idea. I'm sure it's something simple, but my maths is pretty shaky.

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• Collision Detection, player correction

  - by DoomStone

  I am having some problems with collision detection, I have 2 types of objects excluding the player. Tiles and what I call MapObjects. The tiles are all 16x16, where the MapObjects can be any size, but in my case they are all 16x16. When my player runs along the mapobjects or tiles, it get verry jaggy. The player is unable to move right, and will get warped forward when moving left. I have found the problem, and that is my collision detection will move the player left/right if colliding the object from the side, and up/down if collision from up/down. Now imagine that my player is sitting on 2 tiles, at (10,12) and (11,12), and the player is mostly standing on the (11,12) tile. The collision detection will first run on then (10,12) tile, it calculates the collision depth, and finds that is is a collision from the side, and therefore move the object to the right. After, it will do the collision detection with (11,12) and it will move the character up. So the player will not fall down, but are unable to move right. And when moving left, the same problem will make the player warp forward. This problem have been bugging me for a few days now, and I just can't find a solution! Here is my code that does the collision detection. public void ApplyObjectCollision(IPhysicsObject obj, List<IComponent> mapObjects, TileMap map) { PhysicsVariables physicsVars = GetPhysicsVariables(); Rectangle bounds = ((IComponent)obj).GetBound(); int leftTile = (int)Math.Floor((float)bounds.Left / map.GetTileSize()); int rightTile = (int)Math.Ceiling(((float)bounds.Right / map.GetTileSize())) - 1; int topTile = (int)Math.Floor((float)bounds.Top / map.GetTileSize()); int bottomTile = (int)Math.Ceiling(((float)bounds.Bottom / map.GetTileSize())) - 1; // Reset flag to search for ground collision. obj.IsOnGround = false; // For each potentially colliding tile, for (int y = topTile; y <= bottomTile; ++y) { for (int x = leftTile; x <= rightTile; ++x) { IComponent tile = map.Get(x, y); if (tile != null) { bounds = HandelCollision(obj, tile, bounds, physicsVars); } } } // Handel collision for all Moving objects foreach (IComponent mo in mapObjects) { if (mo == obj) continue; if (mo.GetBound().Intersects(((IComponent)obj).GetBound())) { bounds = HandelCollision(obj, mo, bounds, physicsVars); } } } private Rectangle HandelCollision(IPhysicsObject obj, IComponent objb, Rectangle bounds, PhysicsVaraibales physicsVars) { // If this tile is collidable, SpriteCollision collision = ((IComponent)objb).GetCollisionType(); if (collision != SpriteCollision.Passable) { // Determine collision depth (with direction) and magnitude. Rectangle tileBounds = ((IComponent)objb).GetBound(); Vector2 depth = bounds.GetIntersectionDepth(tileBounds); if (depth != Vector2.Zero) { float absDepthX = Math.Abs(depth.X); float absDepthY = Math.Abs(depth.Y); // Resolve the collision along the shallow axis. if (absDepthY <= absDepthX || collision == SpriteCollision.Platform) { // If we crossed the top of a tile, we are on the ground. if (obj.PreviousBound.Bottom <= tileBounds.Top) obj.IsOnGround = true; // Ignore platforms, unless we are on the ground. if (collision == SpriteCollision.Impassable || obj.IsOnGround) { // Resolve the collision along the Y axis. ((IComponent)obj).Position = new Vector2(((IComponent)obj).Position.X, ((IComponent)obj).Position.Y + depth.Y); // If we hit something about us, remove all velosity upwards if (depth.Y > 0 && obj.IsJumping) { obj.Velocity = new Vector2(obj.Velocity.X, 0); obj.JumpTime = physicsVars.MaxJumpTime; } // Perform further collisions with the new bounds. return ((IComponent)obj).GetBound(); } } else if (collision == SpriteCollision.Impassable) // Ignore platforms. { // Resolve the collision along the X axis. ((IComponent)obj).Position = new Vector2(((IComponent)obj).Position.X + depth.X, ((IComponent)obj).Position.Y); // Perform further collisions with the new bounds. return ((IComponent)obj).GetBound(); } } } return bounds; } Update: I have uploaded the source code, if you want to look that through. I think that my general approach might be wrong when i am working with small tiles, I have also be unable to find any good information on physics and collision detection in Platform games. http://dl.dropbox.com/u/3181816/Sogaard.Games.SuperMario.rar

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• Calculating instantaneous speed and acceleration for a simple Car software model

  - by Dylan

  I am trying to model a speedometer and tachometer for a simple software model of a car dashboard. I want this to be relatively simple, so for my purposes I won't likely simulate variables such as drag (or, assume that drag is a constant). But I would like to know the general formulas for: 1) Calculating the RPM, depending on a position of a graphical slider representing the accelerator. 2) Using this information to find the instantaneous speed (or, magnitude of instantaneous velocity?). I am not sure, in the case of 2), what other independent variables I need to consider. Do I need to consider the frequency of rotation of the wheels (assuming a fixed radius), in addition to the RPM? If anyone can give me a rough explanation plus relevant formulas, or alternatively direct me to other trusted resources online (I have had a hard time sifting through info and determining the accuracy), it would be much appreciated.

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• 2D SAT How to find collision center or point or area?

  - by Felipe Cypriano

  I've just implemented collision detection using SAT and this article as reference to my implementation. The detection is working as expected but I need to know where both rectangles are colliding. I need to find the center of the intersection, the black point on the image above. I've found some articles about this but they all involve avoiding the overlap or some kind of velocity, I don't need this. I just need to put a image on top of it. Like two cars crashed so I put an image on top of the collision. Any ideas? ## Update The information I've about the rectangles are the four points that represents them, the upper right, upper left, lower right and lower left coordinates. I'm trying to find an algorithm that can give me the intersection of these points.

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• Physics timestep questions

  - by SSL

  I've got a projectile working perfectly using the code below: //initialised in loading screen 60 is the FPS - projectilEposition and velocity are Vector3 types gravity = new Vector3(0, -(float)9.81 / 60, 0); //called every frame projectilePosition += projectileVelocity; This seems to work fine but I've noticed in various projectile examples I've seen that the elapsedtime per update is taken into account. What's the difference between the two and how can I convert the above to take into account the elapsedtime? (I'm using XNA - do I use ElapsedTime.TotalSeconds or TotalMilliseconds)? Edit: Forgot to add my attempt at using elapsedtime, which seemed to break the physics: projectileVelocity.Y += -(float)((9.81 * gameTime.ElapsedGameTime.TotalSeconds * gameTime.ElapsedGameTime.TotalSeconds) * 0.5f); Thanks for the help

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• TFS vs. Star Team comparison

  - by ryanabr

  I have a sales call today in which the person that I am talking to is interested in what TFS would give them over Star Team, The first thing I believe that I can say is that TFS is cheaper! Especially if you are doing MSFT development already and your team members have MSDN subscriptions as the CALs for TFS are covered in the MSDN subscription. The other thing that I noticed about Star Team was all of the references to ‘readiness’ and ‘integration’. While that is great, that means that other tools will be needed to provide the features that are already bundled with TFS like, SharePoint integration, as well as Analysis Services and Reporting Services to provide visibility on the web with reports on project health, and team velocity. Below is a quick table that I was able to throw together to answer some high level questions: Feature TFS Star Team Work Items X X Work Item custom Queries X X Customizable Work Items X Web Portal View X X Reporting X Integration Version Control X X Build Management X Integration Integrated Test Suite X Integration Cost Free for first 5 / MSDN Sub covers others $7500 / seat

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• Continuous Movement of gun bullet

  - by Siddharth

  I was using box2d for the movement of the body. When I apply gravity (0,0) the bullet continuously move but when I change gravity to the earth the behavior was changed. I also try to apply continuous force to the bullet body but the behavior was not so good. So please provide any suggestion to continuously move bullet body in earth gravity. currentVelocity = bulletBody.getLinearVelocity(); if (currentVelocity.len() < speed|| currentVelocity.len() > speed + 0.25f) { velocityChange = Math.abs(speed - currentVelocity.len()); currentVelocity.set(currentVelocity.x* velocityChange, currentVelocity.y*velocityChange); bulletBody.applyLinearImpulse(currentVelocity,bulletBody.getWorldCenter()); } I apply above code for the continuous velocity of the body. And also I did not able to find any setGravityScale method in the library.

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• How to handle estimates for programmers joining the team?

  - by Jordan

  Iteration has already started, new programmer joins the team, task X has already been estimated to be 30 hours by a different developer. What is the best practice in this situation? new developer runs with the given estimate (the idea being that any discrepancy will be corrected for when velocity is calculated?) new developer re-estimates task? (if so, what if it's significantly higher and no longer fits in the iteration?) throw our hands up and go back to waterfall? something else entirely?

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