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• Testing of visualization projects

  - by paxRoman

  We develop small to large visualization projects for different tasks and industries and sometimes while rewriting them a couple of times in the process we hit walls because we discover that we need to add a lot of code to support new requirements. Now we have established a design process that seems to work well (at least we reduced the development time for each new project quite a bit), but we're still left scratching our heads around this question: what exactly should we test when testing visualizations? If everything that we want to explore is on the screen (bounded visualizations)? If the data is ok - if data is valid (that's one of the nice things about visualizations you can spot errors in your datasets)? Usability? User interaction? Code quality? I can tell you for sure that a simple check of the code quality is certainly not enough! Is there a classic paper / book about how to test visualizations? Also do you happen to know about classic design patterns for visualizations (except the obvious ones like Pub-Sub)?

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• Collision Attacks, Message Digests and a Possible solution

  - by Dominar

  I've been doing some preliminary research in the area of message digests. Specifically collision attacks of cryptographic hash functions such as MD5 and SHA-1, such as the Postscript example and X.509 certificate duplicate. From what I can tell in the case of the postscript attack, specific data was generated and embedded within the header of the postscript (which is ignored during rendering) which brought about the internal state of the md5 to a state such that the modified wording of the document would lead to a final MD equivalent to the original. The X.509 took a similar approach where by data was injected within the comment/whitespace of the certificate. Ok so here is my question, and I can't seem to find anyone asking this question: Why isn't the length of ONLY the data being consumed added as a final block to the MD calculation? In the case of X.509 - Why is the whitespace and comments being taken into account as part of the MD? Wouldn't a simple processes such as one of the following be enough to resolve the proposed collision attacks: MD(M + |M|) = xyz MD(M + |M| + |M| * magicseed_0 +...+ |M| * magicseed_n) = xyz where : M : is the message |M| : size of the message MD : is the message digest function (eg: md5, sha, whirlpool etc) xyz : is the acutal message digest value for the message M magicseed_{i}: Is a set random values generated with seed based on the internal-state prior to the size being added. This technqiue should work, as to date all such collision attacks rely on adding more data to the original message. In short, the level of difficulty involved in generating a collision message such that: It not only generates the same MD But is also comprehensible/parsible/compliant and is also the same size as the original message, is immensely difficult if not near impossible. Has this approach ever been discussed? Any links to papers etc would be nice.

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• How could I implement 3D player collision with rotation in LWJGL?

  - by Tinfoilboy

  I have a problem with my current collision implementation. Currently for player collision, I just use an AABB where I check if another AABB is in the way of the player, as shown in this code. (The code below is a sample of checking for collisions in the Z axis) for (int z = (int) (this.position.getZ()); z > this.position.getZ() - moveSpeed - boundingBoxDepth; z--) { // The maximum Z you can get. int maxZ = (int) (this.position.getZ() - moveSpeed - boundingBoxDepth) + 1; AxisAlignedBoundingBox aabb = WarmupWeekend.getInstance().currentLevel.getAxisAlignedBoundingBoxAt(new Vector3f(this.position.getX(), this.position.getY(), z)); AxisAlignedBoundingBox potentialCameraBB = new AxisAlignedBoundingBox(this, "collider", new Vector3f(this.position.getX(), this.position.getY(), z), boundingBoxWidth, boundingBoxHeight, boundingBoxDepth); if (aabb != null) { if (potentialCameraBB.colliding(aabb) && aabb.COLLIDER_TYPE.equalsIgnoreCase("collider")) { break; } else if (!potentialCameraBB.colliding(aabb) && z == maxZ) { if (this.grounded) { playFootstep(); } this.position.z -= moveSpeed; break; } } else if (z == maxZ) { if (this.grounded) { playFootstep(); } this.position.z -= moveSpeed; break; } } Now, when I tried to implement rotation to this method, everything broke. I'm wondering how I could implement rotation to this block (and as all other checks in each axis are the same) and others. Thanks in advance.

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• Do unit tests sometimes break encapsulation?

  - by user1288851

  I very often hear the following: "If you want to test private methods, you'd better put that in another class and expose it." While sometimes that's the case and we have a hiding concept inside our class, other times you end up with classes that have the same attributes (or, worst, every attribute of one class become a argument on a method in the other class) and exposes functionality that is, in fact, implementation detail. Specially on TDD, when you refactor a class with public methods out of a previous tested class, that class is now part of your interface, but has no tests to it (since you refactored it, and is a implementation detail). Now, I may be not finding an obvious better answer, but if my answer is the "correct", that means that sometimes writting unit tests can break encapsulation, and divide the same responsibility into different classes. A simple example would be testing a setter method when a getter is not actually needed for anything in the real code. Please when aswering don't provide simple answers to specific cases I may have written. Rather, try to explain more of the generic case and theoretical approach. And this is neither language specific. Thanks in advance. EDIT: The answer given by Matthew Flynn was really insightful, but didn't quite answer the question. Altough he made the fair point that you either don't test private methods or extract them because they really are other concern and responsibility (or at least that was what I could understand from his answer), I think there are situations where unit testing private methods is useful. My primary example is when you have a class that has one responsibility but the output (or input) that it gives (takes) is just to complex. For example, a hashing function. There's no good way to break a hashing function apart and mantain cohesion and encapsulation. However, testing a hashing function can be really tough, since you would need to calculate by hand (you can't use code calculation to test code calculation!) the hashing, and test multiple cases where the hash changes. In that way (and this may be a question worth of its own topic) I think private method testing is the best way to handle it. Now, I'm not sure if I should ask another question, or ask it here, but are there any better way to test such complex output (input)? OBS: Please, if you think I should ask another question on that topic, leave a comment. :)

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• No Gentle Galaxy Collision

  - by Akemi Iwaya

  It is hard to imagine a more cataclysmic event than the collision of two galaxies and the effect such an event has on each one as they are ripped apart. See the destructive power of collision at work in this video showing the latest Hubble imagery of Arp 142, a.k.a. the collision of NGC 2936 and NGC 2937. Note: The video also shows stunning imagery of other colliding galaxies. No Gentle Galaxy Collision [YouTube]     

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• Should adapters or wrappers be unit tested?

  - by m3th0dman

  Suppose that I have a class that implements some logic: public MyLogicImpl implements MyLogic { public void myLogicMethod() { //my logic here } } and somewhere else a test class: public MyLogicImplTest { @Test public void testMyLogicMethod() { /test my logic } } I also have: @WebService public MyWebServices class { @Inject private MyLogic myLogic; @WebMethod public void myLogicWebMethod() { myLogic.myLogicMethod(); } } Should there be a test unit for myLogicWebMethod or should the testing for it be handled in integration testing.

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• Unit Testing with NUnit and Moles Redux

  - by João Angelo

  Almost two years ago, when Moles was still being packaged alongside Pex, I wrote a post on how to run NUnit tests supporting moled types. A lot has changed since then and Moles is now being distributed independently of Pex, but maintaining support for integration with NUnit and other testing frameworks. For NUnit the support is provided by an addin class library (Microsoft.Moles.NUnit.dll) that you need to reference in your test project so that you can decorate yours tests with the MoledAttribute. The addin DLL must also be placed in the addins folder inside the NUnit installation directory. There is however a downside, since Moles and NUnit follow a different release cycle and the addin DLL must be built against a specific NUnit version, you may find that the release included with the latest version of Moles does not work with your version of NUnit. Fortunately the code for building the NUnit addin is supplied in the archive (moles.samples.zip) that you can found in the Documentation folder inside the Moles installation directory. By rebuilding the addin against your specific version of NUnit you are able to support any version. Also to note that in Moles 0.94.51023.0 the addin code did not support the use of TestCaseAttribute in your moled tests. However, if you need this support, you need to make just a couple of changes. Change the ITestDecorator.Decorate method in the MolesAddin class: Test ITestDecorator.Decorate(Test test, MemberInfo member) { SafeDebug.AssumeNotNull(test, "test"); SafeDebug.AssumeNotNull(member, "member"); bool isTestFixture = true; isTestFixture &= test.IsSuite; isTestFixture &= test.FixtureType != null; bool hasMoledAttribute = true; hasMoledAttribute &= !SafeArray.IsNullOrEmpty( member.GetCustomAttributes(typeof(MoledAttribute), false)); if (!isTestFixture && hasMoledAttribute) { return new MoledTest(test); } return test; } Change the Tests property in the MoledTest class: public override System.Collections.IList Tests { get { if (this.test.Tests == null) { return null; } var moled = new List<Test>(this.test.Tests.Count); foreach (var test in this.test.Tests) { moled.Add(new MoledTest((Test)test)); } return moled; } } Disclaimer: I only tested this implementation against NUnit 2.5.10.11092 version. Finally you just need to run the NUnit console runner through the Moles runner. A quick example follows: moles.runner.exe [Tests.dll] /r:nunit-console.exe /x86 /args:[NUnitArgument1] /args:[NUnitArgument2]

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• Why doesn't Unity's OnCollisionEnter give me surface normals, and what's the most reliable way to get them?

  - by michael.bartnett

  Unity's on collision event gives you a Collision object that gives you some information about the collision that happened (including a list of ContactPoints with hit normals). But what you don't get is surface normals for the collider that you hit. Here's a screenshot to illustrate. The red line is from ContactPoint.normal and the blue line is from RaycastHit.normal. Is this an instance of Unity hiding information to provide a simplified API? Or do standard 3D realtime collision detection techniques just not collect this information? And for the second part of the question, what's a surefire and relatively efficient way to get a surface normal for a collision? I know that raycasting gives you surface normals, but it seems I need to do several raycasts to accomplish this for all scenarios (maybe a contact point/normal combination misses the collider on the first cast, or maybe you need to do some average of all the contact points' normals to get the best result). My current method: Back up the Collision.contacts[0].point along its hit normal Raycast down the negated hit normal for float.MaxValue, on Collision.collider If that fails, repeat steps 1 and 2 with the non-negated normal If that fails, try steps 1 to 3 with Collision.contacts[1] Repeat 4 until successful or until all contact points exhausted. Give up, return Vector3.zero. This seems to catch everything, but all those raycasts make me queasy, and I'm not sure how to test that this works for enough cases. Is there a better way?

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• Collision Detection - Java - Rectangle

  - by Trizicus

  I would like to know if this is a good idea that conforms to best practices that does not lead to obscenely confusing code or major performance hit(s): Make my own Collision detection class that extends Rectangle class. Then when instantiating that object doing something such as Collision col = new Rectangle(); <- Should I do that or is that something that should be avoided? I am aware that I 'can' but should I? I want to extend Rectangle class because of the contains() and intersects() methods; should I be doing that or should I be doing something else for 2D collision detection in Java?

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• What are some concise and comprehensive introductory guide to unit testing for a self-taught programmer [closed]

  - by Superbest

  I don't have much formal training in programming and I have learned most things by looking up solutions on the internet to practical problems I have. There are some areas which I think would be valuable to learn, but which ended up both being difficult to learn and easy to avoid learning for a self-taught programmer. Unit testing is one of them. Specifically, I am interested in tests in and for C#/.NET applications using Microsoft.VisualStudio.TestTools in Visual Studio 2010 and/or 2012, but I really want a good introduction to the principles so language and IDE shouldn't matter much. At this time I'm interested in relatively trivial tests for small or medium sized programs (development time of weeks or months and mostly just myself developing). I don't necessarily intend to do test-driven development (I am aware that some say unit testing alone is supposed to be for developing features in TDD, and not an assurance that there are no bugs in the software, but unit testing is often the only kind of testing for which I have resources). I have found this tutorial which I feel gave me a decent idea of what unit tests and TDD looks like, but in trying to apply these ideas to my own projects, I often get confused by questions I can't answer and don't know how to answer, such as: What parts of my application and what sorts of things aren't necessarily worth testing? How fine grained should my tests be? Should they test every method and property separately, or work with a larger scope? What is a good naming convention for test methods? (since apparently the name of the method is the only way I will be able to tell from a glance at the test results table what works in my program and what doesn't) Is it bad to have many asserts in one test method? Since apparently VS2012 reports only that "an Assert.IsTrue failed within method MyTestMethod", and if MyTestMethod has 10 Assert.IsTrue statements, it will be irritating to figure out why a test is failing. If a lot of the functionality deals with writing and reading data to/from the disk in a not-exactly trivial fashion, how do I test that? If I provide a bunch of files as input by placing them in the program's directory, do I have to copy those files to the test project's bin/Debug folder now? If my program works with a large body of data and execution takes minutes or more, should my tests have it do the whole use all of the real data, a subset of it, or simulated data? If latter, how do I decide on the subset or how to simulate? Closely related to the previous point, if a class is such that its main operation happens in a state that is arrived to by the program after some involved operations (say, a class makes calculations on data derived from a few thousands of lines of code analyzing some raw data) how do I test just that class without inevitably ending up testing that class and all the other code that brings it to that state along with it? In general, what kind of approach should I use for test initialization? (hopefully that is the correct term, I mean preparing classes for testing by filling them in with appropriate data) How do I deal with private members? Do I just suck it up and assume that "not public = shouldn't be tested"? I have seen people suggest using private accessors and reflection, but these feel like clumsy and unsuited for regular use. Are these even good ideas? Is there anything like design patterns concerning testing specifically? I guess the main themes in what I'd like to learn more about are, (1) what are the overarching principles that should be followed (or at least considered) in every testing effort and (2) what are popular rules of thumb for writing tests. For example, at one point I recall hearing from someone that if a method is longer than 200 lines, it should be refactored - not a universally correct rule, but it has been quite helpful since I'd otherwise happily put hundreds of lines in single methods and then wonder why my code is so hard to read. Similarly I've found ReSharpers suggestions on member naming style and other things to be quite helpful in keeping my codebases sane. I see many resources both online and in print that talk about testing in the context of large applications (years of work, 10s of people or more). However, because I've never worked on such large projects, this context is very unfamiliar to me and makes the material difficult to follow and relate to my real world problems. Speaking of software development in general, advice given with the assumptions of large projects isn't always straightforward to apply to my own, smaller endeavors. Summary So my question is: What are some resources to learn about unit testing, for a hobbyist, self-taught programmer without much formal training? Ideally, I'm looking for a short and simple "bible of unit testing" which I can commit to memory, and then apply systematically by repeatedly asking myself "is this test following the bible of testing closely enough?" and then amending discrepancies if it doesn't.

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• Testing sample code in python modules

  - by Andrew Walker

  I'm in the process of writing a python module that includes some samples. These samples aren't unit-tests, and they are too long and complex to be doctests. I'm interested in best practices for automatically checking that these samples run. My current project layout is pretty standard, except that there is an extra top level makefile that has build, install, unittest, coverage and profile targets, that delegate responsibility to setup.py and nose as required. projectname/ Makefile README setup.py samples/ foo-sample foobar-sample projectname/ __init__.py foo.py bar.py tests/ test-foo.py test-bar.py I've considered adding a sampletest module, or adding nose.tools.istest decorators to the entry-point functions of the samples, but for a small number of samples, these solutions sound a bit ugly. This question is similar to http://stackoverflow.com/questions/301365/automatically-unit-test-example-code, but I assume python best practices will differ from C#

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• What some good books on software testing/quality?

  - by mjh2007

  I'm looking for a good book on software quality. It would be helpful if the book covered: The software development process (requirements, design, coding, testing, maintenance) Testing roles (who performs each step in the process) Testing methods (white box and black box) Testing levels (unit testing, integration testing, etc) Testing process (Agile, waterfall, spiral) Testing tools (simulators, fixtures, and reporting software) Testing of embedded systems The goal here is to find an easy to read book that summarizes the best practices for ensuring software quality in an embedded system. It seems most texts cover the testing of application software where it is simpler to generate automated test cases or run a debugger. A book that provided solutions for improving quality in a system where the tests must be performed manually and therefore minimized would be ideal.

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• Learning about tests for junior programmers

  - by RHaguiuda

  I`m not sure if its okay to ask it on stackoverflow. Ive been reading a log about tests, unit tests, tests frameworks, mocks and so on, but as a junior programmer I dont know anything about tests, not even where to start! Can anyone explain to young programmers about tests, how they`re run, where and what to test, what is unit testing, integration testing, automated tests? How much to test? And more important: how much test is enough? I belive this would be very helpfull. If possible indicate a few books too about these subjects. Thanks

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• Testing complex entities

  - by Carlos

  I've got a C# form, with various controls on it. The form controls an ongoing process, and there are many, many aspects that need to be right for the program to run correctly. Each part can be unit tested (for instance, loading some coefficients, drawing some diagnostics) but I often run into problems that are best described with an example: "If I click here, then here, then change this, then re-open the form, then click here, it crashes or produces an error" I've tried my best to use common code organisational ideas (inheritance, DRY, separation of concerns) but there never seems to be a way to test every single path, and inevitably, a form with several controls will have a huge number of ways to execute. What can I read (preferably online) that addresses this kind of issue, and is there a (non-generic) term for it. This isn't a specific problem I'm having, but one that creeps up on me, especially with WinForms.

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• How to get started with testing(jMock)

  - by London

  Hello, I'm trying to learn how to write tests. I'm also learning Java, I was told I should learn/use/practice jMock, I've found some articles online that help to certain extend like : http://www.theserverside.com/news/1365050/Using-JMock-in-Test-Driven-Development http://jeantessier.com/SoftwareEngineering/Mocking.html#jMock And most articles I found was about test driven development, write tests first then write code to make the test pass. I'm not looking for that at the moment, I'm trying to write tests for already existing code with jMock. The official documentation is vague to say the least and just too hard for me. Does anybody have better way to learn this. Good books/links/tutorials would help me a lot. thank you EDIT - more concrete question : http://jeantessier.com/SoftwareEngineering/Mocking.html#jMock - from this article Tried this to mock this simple class : import java.util.Map; public class Cache { private Map<Integer, String> underlyingStorage; public Cache(Map<Integer, String> underlyingStorage) { this.underlyingStorage = underlyingStorage; } public String get(int key) { return underlyingStorage.get(key); } public void add(int key, String value) { underlyingStorage.put(key, value); } public void remove(int key) { underlyingStorage.remove(key); } public int size() { return underlyingStorage.size(); } public void clear() { underlyingStorage.clear(); } } Here is how I tried to create a test/mock : public class CacheTest extends TestCase { private Mockery context; private Map mockMap; private Cache cache; @Override @Before public void setUp() { context = new Mockery() { { setImposteriser(ClassImposteriser.INSTANCE); } }; mockMap = context.mock(Map.class); cache = new Cache(mockMap); } public void testCache() { context.checking(new Expectations() {{ atLeast(1).of(mockMap).size(); will(returnValue(int.class)); }}); } } It passes the test and basically does nothing, what I wanted is to create a map and check its size, and you know work some variations try to get a grip on this. Understand better trough examples, what else could I test here or any other exercises would help me a lot. tnx

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• Simulating Ajax failures for QA testing

  - by womp

  Our first ASP.Net MVC/jQuery product is about to go to QA, and we're looking for a way for our QA guys to easily be able to simulate bad Ajax requests (without modifying the application code). A typical integration/UI test plan might be: Load page, click button "DoStuff" "DoStuff" fails Attempt button "DoStuff" again "DoStuff" succeeds Verify application state This is a simple test case - there will be cases with multiple failures and successes interspersed. Aside from "unplug your network cable" I'm looking for an easy way for our guys to simulate intermittent bad server responses. I'm open to any ideas so I won't go into too many details about our application setup or dependencies. How have you handled this?

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• JRuby-friendly method for parallel-testing Rails app

  - by Toby Hede

  I am looking for a system to parallelise a large suite of tests in a Ruby on Rails app (using rspec, cucumber) that works using JRuby. Cucumber is actually not too bad, but the full rSpec suite currently takes nearly 20 minutes to run. The systems I can find (hydra, parallel-test) look like they use forking, which isn't the ideal solution for the JRuby environment.

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• JRuby-friendly method for parallel-testing Ruby on Rails app

  - by Toby Hede

  I am looking for a system to parallelise my tests in a Ruby on Rails app (using rspec, cucumber) that works using JRuby. The systems I can find (hydra, parallel-test) look like they use forking, which is problematic in a JRuby environment.

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• Tools for website/web application load testing?

  - by zarko.susnjar

  Before going into production, our client demands actual numbers of how many users our web application can handle. We have all kinds of features implemented including asset management (file uploads/downloads), documents import/export, various statistics, web-services etc. Which tool (or set of tools) could do this? Application details: XHTML/jQuery Coldfusion 8 SQL Server 2008 Windows Server 2008

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• EBS 12.1.1 Test Starter Kit now Available for Oracle Application Testing Suite

  - by Steven Chan

  We've discussed automated testing tools for the E-Business Suite several times on this blog, since testing is such a key part of everyone's implementation lifecycle.  An important part of our testing arsenal in E-Business Suite Development is the Oracle Application Testing Suite.  The Oracle Automated Testing Suite (OATS) is built on the foundation of the e-TEST suite of products acquired from Empirix  in 2008.  The testing suite is comprised of:   1. Oracle Load Testing for scalability, performance, and load testing   2. Oracle Functional Testing for automated functional and regression testing   3. Oracle Test Manager for test process management, test execution, and defect trackingOracle Application Testing Suite 9.0 has been supported for use with the E-Business Suite since 2009.  I'm very pleased to let you know that our E-Business Suite Release 12.1.1 Test Starter Kit is now available for Oracle Application Testing Suite 9.1.  You can download it here:Oracle Application Testing Suite Downloads

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• Is there a name for a testing method where you compare a set of very different designs?

  - by DVK

  "A/B testing" is defined as "a method of marketing testing by which a baseline control sample is compared to a variety of single-variable test samples in order to improve response rates". The point here, of course, is to know which small single-variable changes are more optimal, with the goal of finding the local optimum. However, one can also envision a somewhat related but different scenario for testing the response rate of major re-designs: take a baseline control design, take one or more completely different designs, and run test samples on those redesigns to compare response rates. As a practical but contrived example, imagine testing a set of designs for the same website, one being minimalist "googly" design, one being cluttered "Amazony" design, and one being an artsy "designy" design (e.g. maximum use of design elements unlike Google but minimal simultaneously presented information, like Google but unlike Amazon) Is there an official name for such testing? It's definitely not A/B testing, since the main component of it (finding local optimum by testing single-variable small changes that can be attributed to response shift) is not present. This is more about trying to compare a set of local optimums, and compare to see which one works better as a global optimum. It's not a multivriable, A/B/N or any other such testing since you don't really have specific variables that can be attributed, just different designs.

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• Unit test SHA256 wrapper queries

  - by Sam Leach

  I am just beginning to write unit tests. So please bear with me. I have the following SHA256 wrapper. public static string SHA256(string plainText) { StringBuilder sb = new StringBuilder(); SHA256CryptoServiceProvider provider = new SHA256CryptoServiceProvider(); var hashedBytes = provider.ComputeHash(Encoding.UTF8.GetBytes(plainText)); for (int i = 0; i < hashedBytes.Length; i++) { sb.Append(hashedBytes[i].ToString("x2").ToLower()); } return sb.ToString(); } Do I want to be testing it? If so, what do you recommend? My thought process is as follows: What logic is there here. The answer is my for loop and ToString("x2") so from my understanding I want to be testing this part? I can assume Encoding.UTF8.GetBytes(plainText) works. Correct assumption? I can assume SHA256CryptoServiceProvider.ComputeHash() works. Correct assumption? I want to be only testing my logic. In this case is limited to the printing of hex encoded hash. Correct? Thanks.

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• How to unit test models in MVC / MVR app?

  - by BBnyc

  I'm building a node.js web app and am trying to do so for the first time in a test driven fashion. I'm using nodeunit for testing, which I find allows me to write tests quickly and painlessly. In this particular app, the heavy lifting primarily involves translating SQL data into complex Javascript object and serving them to the front-end via json. Likewise, the app also spends a great deal of code validating and translating complex, multidimensional Javascript objects it receives from the front-end into SQL rows. Hence I have used a fat model design for the app -- most of the real code resides in the models, where the data translation happens. What's the best approach to test such models with unit tests? I mean in particular the methods that have create javascript objects from the SQL rows and serve them to the front-end. Right now what I'm doing is making particular requests of my models with the unit tests and checking the returned data for all of the fields that should be there. However I have a suspicion that this is not the most robust kind of testing I could be doing. My current testing design also means I have to package my app code with some dummy data so that my tests can anticipate the kind of data that the app should be returning when tests run.

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• How can I convert a 2D bitmap (Used for terrain) to a 2D polygon mesh for collision?

  - by Megadanxzero

  So I'm making an artillery type game, sort of similar to Worms with all the usual stuff like destructible terrain etc... and while I could use per-pixel collision that doesn't give me collision normals or anything like that. Converting it all to a mesh would also mean I could use an existing physics library, which would be better than anything I can make by myself. I've seen people mention doing this by using Marching Squares to get contours in the bitmap, but I can't find anything which mentions how to turn these into a mesh (Unless it refers to a 3D mesh with contour lines defining different heights, which is NOT what I want). At the moment I can get a basic Marching Squares contour which looks something like this (Where the grid-like lines in the background would be the Marching Squares 'cells'): That needs to be interpolated to get a smoother, more accurate result but that's the general idea. I had a couple ideas for how to turn this into a mesh, but many of them wouldn't work in certain cases, and the one which I thought would work perfectly has turned out to be very slow and I've not even finished it yet! Ideally I'd like whatever I end up using to be fast enough to do every frame for cases such as rapidly-firing weapons, or digging tools. I'm thinking there must be some kind of existing algorithm/technique for turning something like this into a mesh, but I can't seem to find anything. I've looked at some things like Delaunay Triangulation, but as far as I can tell that won't correctly handle concave shapes like the above example, and also wouldn't account for holes within the terrain. I'll go through the technique I came up with for comparison and I guess I'll see if anyone has a better idea. First of all interpolate the Marching Squares contour lines, creating vertices from the line ends, and getting vertices where lines cross cell edges (Important). Then, for each cell containing vertices create polygons by using 2 vertices, and a cell corner as the 3rd vertex (Probably the closest corner). Do this for each cell and I think you should have a mesh which accurately represents the original bitmap (Though there will only be polygons at the edges of the bitmap, and large filled in areas in between will be empty). The only problem with this is that it involves lopping through every pixel once for the initial Marching Squares, then looping through every cell (image height + 1 x image width + 1) at least twice, which ends up being really slow for any decently sized image...

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• Physics Engine [Collision Response, 2-dimensional] experts, help!! My stack is unstable!

  - by Register Sole

  Previously, I struggle with the sequential impulse-based method I developed. Thanks to jedediah referring me to this paper, I managed to rebuild the codes and implement the simultaneous impulse based method with Projected-Gauss-Seidel (PGS) iterative solver as described by Erin Catto (mentioned in the reference of the paper as [Catt05]). So here's how it currently is: The simulation handles 2-dimensional rotating convex polygons. Detection is using separating-axis test, with a SKIN, meaning closest points between two polygons is detected and determined if their distance is less than SKIN. To resolve collision, simultaneous impulse-based method is used. It is solved using iterative solver (PGS-solver) as in Erin Catto's paper. Error-correction is implemented using Baumgarte's stabilization (you can refer to either paper for this) using J V = beta/dt*overlap, J is the Jacobian for the constraints, V the matrix containing the velocities of the bodies, beta an error-correction parameter that is better be < 1, dt the time-step taken by the engine, and overlap, the overlap between the bodies (true overlap, so SKIN is ignored). However, it is still less stable than I expected :s I tried to stack hexagons (or squares, doesn't really matter), and even with only 4 to 5 of them, they hardly stand still! Also note that I am not looking for a sleeping scheme. But I would settle if you have any explicit scheme to handle resting contacts. That said, I would be more than happy if you have a way of treating it generally (as continuous collision, instead of explicitly as a special state). Ideas I have: I would try adding a damping term (proportional to velocity) to the Baumgarte. Is this a good idea in general? If not I would not want to waste my time trying to tune the parameter hoping it magically works. Ideas I have tried: Using simultaneous position based error correction as described in the paper in section 5.3.2, turned out to be worse than the current scheme. If you want to know the parameters I used: Hexagons, side 50 (pixels) gravity 2400 (pixels/sec^2) time-step 1/60 (sec) beta 0.1 restitution 0 to 0.2 coeff. of friction 0.2 PGS iteration 10 initial separation 10 (pixels) mass 1 (unit is irrelevant for now, i modified velocity directly<-impulse method) inertia 1/1000 Thanks in advance! I really appreciate any help from you guys!! :)

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