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• Coarse Collision Detection in highly dynamic environment

  - by Millianz

  I'm currently working a 3D space game with A LOT of dynamic objects that are all moving (there is pretty much no static environment). I have the collision detection and resolution working just fine, but I am now trying to optimize the collision detection (which is currently O(N^2) -- linear search). I thought about multiple options, a bounding volume hierarchy, a Binary Spatial Partitioning tree, an Octree or a Grid. I however need some help with deciding what's best for my situation. A grid seems unfeasible simply due to the space requirements and cache coherence problems. Since everything is so dynamic however, it seems to be that trees aren't ideal either, since they would have to be completely rebuilt every frame. I must admit I never implemented a physics engine that required spatial partitioning, do I indeed need to rebuild the tree every frame (assuming that everything is constantly moving) or can I update the trees after integrating? Advice is much appreciated - to give some more background: You're flying a space ship in an asteroid field, and there are lots and lots of asteroids and some enemy ships, all of which shoot bullets. EDIT: I came across the "Sweep an Prune" algorithm, which seems like the right thing for my purposes. It appears like the right mixture of fast building of the data structures involved and detailed enough partitioning. This is the best resource I can find: http://www.codercorner.com/SAP.pdf If anyone has any suggestions whether or not I'm going in the right direction, please let me know.

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• Find meeting point of 2 objects in 2D, knowing (constant) speed and slope

  - by Axonn

  I have a gun which fires a projectile which has to hit an enemy. The problem is that the gun has to be automatic, i.e. - choose the angle in which it has to shoot so that the projectile hits the enemy dead in the center. It's been a looooong time since school, and my physics skills are a bit rusty, but they're there. I've been thinking to somehow apply the v = d/t formula to find the time needed for the projectile or enemy to reach a certain point. But the problem is that I can't find the common point for both the projectile and enemy. Yes, I can find a certain point for the projectile, and another for the enemy, but I would need lots of tries to find where the point coincides, which is stupid. There has to be a way to link them together but I can't figure it out. I prepared some drawings and samples: A simple version of my Flash game, dumbed down to the basics, just some shapes: http://axonnsd.org/W/P001/MathSandBox.swf - click the mouse anywhere to fire a projectile. Or, here is an image which describes my problem: So... who has any ideas about how to find x3/y3 - thus leading me to find the angle in which the weapon has to tilt in order to fire a projectile to meet the enemy? EDIT I think it would be clearer if I also mention that I know: the speed of both Enemy and Projectile and the Enemy travels on a straight vertical line.

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• Hydraulics in game

  - by Mungoid

  I'm not completely sure if this would be better in the Physics site or not as this question is more about how hydraulics should work in game as opposed to how they really work (although that is taken into account) - So I apologize if this is in the wrong place. A project we are on, we have a machine with hydraulics that are powered (They don't just look like they move something, they are the only thing moving/turning/lifting something) - However, the hydraulic extends the same speed no matter what it is pushing. So, say there is a 10 ton object attached to one end of the hydraulic and the other end is attached to a plate on the ground. In real life it takes a few seconds to build up pressure depending on how heavy the object is, but in our project the hydraulics don't care about that. It will lift a 100 ton object the same speed as a 10 ton object. We have a way to fake the hydraulic pressurizing by reducing the 'drive amount' (how fast or slow the hydraulic extends) when we sense that it is touching the ground and that does a relatively decent job but we would like to be able to take other things into account like engine speed, ratios, loads, etc. but we aren't too sure what we need to think about. I'm kinda wondering if anyone here has any experience with this and could offer some suggestions on what to take into account?

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• Strange behavior of RigidBody with gravity and impulse applied

  - by Heisenbug

  I'm doing some experiments trying to figure out how physics works in Unity. I created a cube mesh with a BoxCollider and a RigidBody. The cuve is laying on a mesh plane with a BoxCollider. I'm trying to update the object position applying a force on its RigidBody. Inside script FixedUpdate function I'm doing the following: public void FixedUpdate() { if (leftButtonPressed()) this.rigidbody.AddForce( this.transform.forward * this.forceStrength, ForceMode.Impulse); } Despite the object is aligned with the world axis and the force is applied along Z axis, it performs a quite big rotation movement around its y axis. Since I didn't modify the center of mass and the BoxCollider position and dimension, all values should be fine. Removing gravity and letting the object flying without touching the plane, the problem doesn't show. So I suppose it's related to the friction between objects, but I can't understand exactly which is the problem. Why this? What's my mistake? How can I fix this, or what's the right way to do such a moving an object on a plane through a force impulse?

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• Offset Forward vector of object based on Rotation

  - by Taylor

  I'm using the Bullet 3D physics engine in a iOS application running openGL ES 1.1 Currently I'm accepting info from the gyroscope to allow the user to "look around" a 3d world that follows a bouncing ball (note: it only takes in the yaw to look around 360 degrees). Im also accepting information from the accelerometer based on the tilt to push the ball. As of right now, to move forward, the user tilts the devise forward (using the accelerometer); to move to the right, the user tilts the devise to the right and so on. The forward vector is currently along it's local Z-axis. The problem is that I want to change the ball bounce based on where the user has changed the view. If I change the view, the ball bounces in the fixed direction. I want to change the forward facing direction so that when a user changes the view (say to the look at the right of the world, the user rotates the device), tilting the devise forward will result in a forward force in that direction. Basically, I want the forward vector to take the rotation into consideration. Sorry if I didn't explain the issue well enough, its kind of confusing to write down.

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• Making particle bounce off a line with friction

  - by Dlaor

  So I'm making a game and I need a particle to bounce off a line. I've got this so far: public static Vector2f Reflect(this Vector2f vec, Vector2f axis) //vec is velocity { Vector2f result = vec - 2f * axis * axis.Dot(vec); return result; } Which works fine, but then I decided I wanted to be able to change the bounciness and friction of the bounce. I got bounciness down... public static Vector2f Reflect(this Vector2f vec, Vector2f axis, float bounciness) //Bounciness goes from 0 to 1, 0 being not bouncy and 1 being perfectly bouncy { var reflect = (1 + bounciness); //2f Vector2f result = vec - reflect * axis * axis.Dot(vec); return result; } But when I tried to add friction, everything went to hell and back... public static Vector2f Reflect(this Vector2f vec, Vector2f axis, float bounciness, float friction) //Does not work at all! { var reflect = (1 + bounciness); //2f Vector2f subtract = reflect * axis * axis.Dot(vec); Vector2f subtract2 = axis * axis.Dot(vec); Vector2f result = vec - subtract; result -= axis.PerpendicularLeft() * subtract2.Length() * friction; return result; } Any physics guys willing to help me out with this? (if you're not sure what I mean with the friction of a bounce see this: http://www.metanetsoftware.com/technique/diagrams/A-1_particle_collision.swf)

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• Dynamic Jump spot

  - by Pasquale Sada

  I have an initial velocity V(Vx,Vy,VZ) and a spot where he stands still at S(Sx,Sy,Sz). What I'm trying to achieve is a jump on a spot E(Ex,Ey,Ez) where you have clicked on(only lower or higher spot, because I've in place a simple steering behavior for even terrains). There are no obstacle around. I've implemented a formula that can make him jump in a precise way on a spot but you need to declare an angle: the problem arise when the selected spot is straight above your head. It' pretty lame that the char hang there and can reach a thing that is 1cm above is head. I'll share the code I'm using: Vector3 dir = target - transform.position; // get target direction float h = dir.y; // get height difference dir.y = 0; // retain only the horizontal direction float dist = dir.magnitude ; // get horizontal distance float a = angle * Mathf.Deg2Rad; // convert angle to radians dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle dist += h / Mathf.Tan(a); // correct for small height differences // calculate the velocity magnitude float vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 *a)); return vel * dir.normalized;

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• Simulate 'Shock absorbtion' with tire rubber in PhysX (2.8.x)

  - by Mungoid

  This is a kinda tricky question and I fear there is no easy enough solution, but I figured I'd hit SE up before giving up on it and just doing what I can. A machine I am working on has no suspension or shocks or springs of any sort in the real machine, so you would think that when it drives over bumps, it would shake like crazy but because its tires (6 of them) are quite large they seem to absorb a lot of shock from the bumps. Part of this is because the machine is around 30k lbs and it just smashes/compresses any bumps in the ground down (This is another issue im still working on) and the other part is that the tires seem to have a lot of flex to them with a lot of air as well. So my current task is to simulate shock absorption in physx without visibly separating the tires from the spindle/axle.. I have been messing with all kinds of NxMaterial, NxSpring, Joints, etc. and have had no luck getting this to work. The main problem is that the spindle attached to the tire is directly in the center and the axle is basically solidly attached to the chassis, so if i give it any spring or suspension travel, that spindle on the tires will move upwards or downwards, looking very odd because now its not any longer in the center of the tire. I tried giving it a higher restitution but that just makes it bouncy without any shock absorption. Another avenue I am messing with is to actively smooth the terrain in front of the tires so that before it hits a bumpy patch, that patch is smoothed and it doesn't bounce. The only issue with this is that it is pretty expensive to do with 6 tires, high tesselation of the terrain and other complex things going on at the same time in this simulation. I am still working on this but I am hoping to mix and match a few different aspects to get the best possible outcome. This is a bit of a complex issue so I'm not expecting anyone to have a definitive answer, just hoping someone may think of something I haven't =-) -Side note: Yes i know PhysX 2.8.x is quite outdated but we have to stick with it for this implementation. We are in the process of going to another physics engine but it is out of scope to apply that engine to this project.

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• Transforms in Box2D

  - by user1264811

  I'm attempting to implement a camera in my game. I had it working for regular objects, but I began using Box2D and obviously things changed a bit. I have a Body object that I want to draw at the center of the screen. Basically what I'm doing is subtracting the viewportX and viewportY to the Body. I use this code that currently is not working as it should: public void paint(Graphics2D g, int viewportX, int viewportY) { Transform xf = new Transform(); // m_body is the Body object xf.set(m_body.getTransform()); // Here what I attemp to do is take the transform and alter it // by the viewportX and Y, which is something like **-240, -150**. // Why is it negative? Because an object has coordinates 500, 300 would be displayed // at 160, 150 when the subtraction is done. // With the DrawUtils.toScale(), it's just how I convert the units from JBox2D units // to my units. Vec2 v = Transform.mulTrans(xf, new Vec2(DrawUtils.toScale(-viewportX), DrawUtils.toScale(-viewportY))); // Set the new transform to the new vector. Keep the old angle. xf.set(v, xf.q.getAngle()); g.setColor(Color.white); // I know for a fact that the following method works 100%. It correctly displays // my object, just that it doesn't follow it. for (Fixture f = m_body.getFixtureList(); f != null; f = f.getNext()) DrawUtils.drawShape(f, xf); } Hopefully I didn't over comment this and you understand my problem. I don't want to alter the actual physics position of the object, I just want to display it in the center.

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• Can Google App Engine be used for "check for updated" and download binary file web service?

  - by Tofrizer

  Hi, I'm a Google App Engine newbie and would be grateful for any help. I have an iPhone app which sources data from an sqlite db stored localling on the device. I'd like to set up a Google App Engine web service which my iPhone client will talk to and check if there is a newer version of the sqlite database it needs to download. So iPhone client hits the web service with some kind of version number/timestamp and if there is a newer file, the App Engine will notify the client and the client will then request the new database to download which the App Engine will serve. Is it possible to set up a web service in Google App Engine to do this? Could anyone point me to any sample code / tutorials please? Many Thanks

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• How will you register a custom view engine where in the Areas will not be affected?

  - by Fleents

  I made a custom view engine for my application. ~/Themes/Default/Views.. And I have an Area called Admin. Area/Admin/Views.. I register my custom view engine in Global.asax : RegisterViewEngines(ViewEngines.Engines); AreaRegistration.RegisterAllAreas(); RegisterRoutes(RouteTable.Routes); When I browsed my admin site, it cant find the views.. I know its because of my custom view engine.. But how can you register new custom view engine without affecting the view engine of areas?

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• How to combine twill and python into one code that could be run on "Google App Engine"?

  - by brilliant

  Hello everybody!!! I have installed twill on my computer (having previously installed Python 2.5) and have been using it recently. Python is installed on disk C on my computer: C:\Python25 And the twill folder (“twill-0.9”) is located here: E:\tmp\twill-0.9 Here is a code that I’ve been using in twill: go “some website’s sign-in page URL” formvalue 2 userid “my login” formvalue 2 pass “my password” submit go “URL of some other page from that website” save_html result.txt This code helps me to log in to one website, in which I have an account, record the HTML code of some other page of that website (that I can access only after logging in), and store it in a file named “result.txt” (of course, before using this code I firstly need to replace “my login” with my real login, “my password” with my real password, “some website’s sign-in page URL” and “URL of some other page from that website” with real URLs of that website, and number 2 with the number of the form on that website that is used as a sign-in form on that website’s log-in page) This code I store in “test.twill” file that is located in my “twill-0.9” folder: E:\tmp\twill-0.9\test.twill I run this file from my command prompt: python twill-sh test.twill Now, I also have installed “Google App Engine SDK” from “Google App Engine” and have also been using it for awhile. For example, I’ve been using this code: import hashlib m = hashlib.md5() m.update("Nobody inspects") m.update(" the spammish repetition ") print m.hexdigest() This code helps me transform the phrase “Nobody inspects the spammish repetition” into md5 digest. Now, how can I put these two pieces of code together into one python script that I could run on “Google App Engine”? Let’s say, I want my code to log in to a website from “Google App Engine”, go to another page on that website, record its HTML code (that’s what my twill code does) and than transform this HTML code into its md5 digest (that’s what my second code does). So, how can I combine those two codes into one python code? I guess, it should be done somehow by importing twill, but how can it be done? Can a python code - the one that is being run by “Google App Engine” - import twill from somewhere on the internet? Or, perhaps, twill is already installed on “Google App Engine”?

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• Can anyone get app-engine plugin working with Grails on mac os x?

  - by tim

  I have been trying for 4 days to get app-engine and grails working together on my mac to no avail. I am using latest groovy/grails and appengine sdk versions. Im following the app-engine plugin step by step on the grails site.. http://grails.org/plugin/app-engine Groovy Version: 1.7.1 JVM: 1.5.0_22 Grails 1.3.0.RC1 echo $APPENGINE_HOME reveals /Users/markstim/appengine-java-sdk-1.3.2 I perform the following steps 1. grails create-app myapp 2. cd myapp; grails list-plugins reveals hibernate 1.3.0.RC1 -- Hibernate for Grails tomcat 1.3.0.RC1 -- Apache Tomcat plugin for Grails add the following line to Config.groovy google.appengine.application="myapp" install the plugin for app-engine grails install-plugin app-engine and answer 'jpa' when asked (no errors yet) installed plugins list now looks like app-engine 0.8.9 -- Grails AppEngine plugin gorm-jpa 0.7.1 -- GORM-JPA Plugin then grails run-app and get this error as the server is coming up... [java] WARNING: Nested in org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.NewInstanceCreationException: Could not create a new instance of class [GormJpaGrailsPlugin]!: [java] java.lang.NoClassDefFoundError: org.grails.jpa.JpaPluginSupport then if i navigate to localhost:8080 I get HTTP ERROR: 503 Problem accessing /myapp. Reason: SERVICE_UNAVAILABLE Powered by Jetty://

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• Which techniques to study?

  - by Djentleman

  Just to give you some background info, I'm studying a programming major at a tertiary level and am in my third year, so I'm not a newbie off the street. However, I am still quite new to game programming as a subset of programming. One of my personal projects for next semester is to design and create a 2D platformer game with emphasis on procedural generation and "neato" effects (think metroidvania). I've written up a list of some techniques to help me improve my personal skills (using XNA for the time being). The list is as follows: QuadTrees: Build a basic program in XNA that moves basic 2D sprites (circles and squares) around a set path and speed and changes their colour when they collide. Add functionality to add and delete objects of different sizes (select a direction and speed when adding and just drag and drop them in). Particles: Build a basic program in XNA in which you can select different colours and create particle effects of those colours on screen by clicking and dragging the mouse around (simple particles emerging from where the mouse is clicked). Add functionality where you can change the amount of particles to be drawn and the speed at which they travel and when they expire. Possibly implement gravity and wind after part 3 is complete. Physics: Build a basic program in XNA where you have a ball in a set 2D environment, a wind slider, and a gravity slider (can go to negative for reverse gravity). You can click to drag the ball around and release to throw it and, depending on what you do, the ball interacts with the environment. Implement other shapes afterwards. Random 2D terrain generation: Build a basic program in XNA that randomly generates terrain (including hills, caves, etc) created from 2D tiles. Add functionality that draws the tiles from a tileset and places different tiles depending on where they lie on the y-axis (dirt on top, then rock, then lava, etc). Randomised objects: Build a basic program in XNA that, when a button is clicked, displays a randomised item sprite based on parameters (type, colour, etc) with the images pulled from tilesets. Add the ability to save the item as an object, which stores it in a side-pane where it can be selected for viewing. Movement: Build a basic program in XNA where you can move an object around in an environment (tile-based) with a camera that pans with it. No gravity. Implement gravity and wind, allow the character to jump and fall with some basic platforms. So my question is this: Are there any other commonly used techniques that I should research, and can I get some suggestions as to the effectiveness of the techniques I've chosen to work on (e.g., don't do QuadTree stuff because [insert reason here], or, do [insert technique here] before you start working on particles because [insert reason here])? I hope this is clear enough and please let me know if I can further clarify anything!

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• How to implement a simple bullet trajectory

  - by AirieFenix

  I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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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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• How to resolve concurrent ramp collisions in 2d platformer?

  - by Shaun Inman

  A bit about the physics engine: Bodies are all rectangles. Bodies are sorted at the beginning of every update loop based on the body-in-motion's horizontal and vertical velocity (to avoid sticky walls/floors). Solid bodies are resolved by testing the body-in-motion's new X with the old Y and adjusting if necessary before testing the new X with the new Y, again adjusting if necessary. Works great. Ramps (rectangles with a flag set indicating bottom-left, bottom-right, etc) are resolved by calculating the ratio of penetration along the x-axis and setting a new Y accordingly (with some checks to make sure the body-in-motion isn't attacking from the tall or flat side, in which case the ramp is treated as a normal rectangle). This also works great. Side-by-side ramps, eg. \/ and /\, work fine but things get jittery and unpredictable when a top-down ramp is directly above a bottom-up ramp, eg. < or > or when a bottom-up ramp runs right up to the ceiling/top-down ramp runs right down to the floor. I've been able to lock it down somewhat by detecting whether the body-in-motion hadFloor when also colliding with a top-down ramp or hadCeiling when also colliding with a bottom-up ramp then resolving by calculating the ratio of penetration along the y-axis and setting the new X accordingly (the opposite of the normal behavior). But as soon as the body-in-motion jumps the hasFloor flag becomes false, the first ramp resolution pushes the body into collision with the second ramp and collision resolution becomes jittery again for a few frames. I'm sure I'm making this more complicated than it needs to be. Can anyone recommend a good resource that outlines the best way to address this problem? (Please don't recommend I use something like Box2d or Chipmunk. Also, "redesign your levels" isn't an answer; the body-in-motion may at times be riding another body-in-motion, eg. a platform, that pushes it into a ramp so I'd like to be able to resolve this properly.) Thanks!

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• Best way to implement a simple bullet trajectory

  - by AirieFenix

  I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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• Movement prediction for non-shooters

  - by ShadowChaser

  I'm working on an isometric (2D) game with moderate-scale multiplayer - 20-30 players. I've had some difficulty getting a good movement prediction implementation in place. Right now, clients are authoritative for their own position. The server performs validation and broad-scale cheat detection, and I fully realize that the system will never be fully robust against cheating. However, the performance and implementation tradeoffs work well for me right now. Given that I'm dealing with sprite graphics, the game has 8 defined directions rather than free movement. Whenever the player changes their direction or speed (walk, run, stop), a "true" 3D velocity is set on the entity and a packet it sent to the server with the new movement state. In addition, every 250ms additional packets are transmitted with the player's current position for state updates on the server as well as for client prediction. After the server validates the packet, it gets automatically distributed to all of the other "nearby" players. Client-side, all entities with non-zero velocity (ie/ moving entities) are tracked and updated by a rudimentary "physics" system - basically nothing more than changing the position by the velocity according to the elapsed time slice (40ms or so). What I'm struggling with is how to implement clean movement prediction. I have the nagging suspicion that I've made a design mistake somewhere. I've been over the Unreal, Half-life, and all other movement prediction/lag compensation articles I could find, but they all seam geared toward shooters: "Don't send each control change, send updates every 120ms, server is authoritative, client predicts, etc". Unfortunately, that style of design won't work well for me - there's no 3D environment so each individual state change is important. 1) Most of the samples I saw tightly couple movement prediction right into the entities themselves. For example, storing the previous state along with the current state. I'd like to avoid that and keep entities with their "current state" only. Is there a better way to handle this? 2) What should happen when the player stops? I can't interpolate to the correct position, since they might need to walk backwards or another strange direction if their position is too far ahead. 3) What should happen when entities collide? If the current player collides with something, the answer is simple - just stop the player from moving. But what happens if two entities take up the same space on the server? What if the local prediction causes a remote entity to collide with the player or another entity - do I stop them as well? If the prediction had the misfortune of sticking them in front of a wall that the player has gone around, the prediction will never be able to compensate and once the error gets to high the entity will snap to the new position.

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• Good Open souce game engines for making MMO game

  - by Call Me Dummy

  I am interested in making a MMO game but I am not sure where to start. I am looking for an open source game engine which is simple to use and allows me to concentrate on the game design and architecture. I have some basic C,C++,C# knowledge. After lots of searching in google I was going to start out with Ogre3D but soon realized that it is a rendering engine and does not include physics engine. I have not tried it yet since in many forums it says they don't have a good documentation. So is there any good open source game engine good for fast game developing ? Some key features I want include basic requirements like collision detection, object to object collision detection, physics etc.

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• How can I use multiple meshes per entity without breaking one component of a single type per entity?

  - by Mathias Hölzl

  We are just switching from a hierarchy based game engine to a component based game engine. My problem is that when I load a model which has has a hierarchy of meshes and the way I understand is that a entity in a component based system can not have multiple components of the same type, but I need a "meshComponent" for each mesh in a model. So how could I solve this problem. On this side they implemented a Component based game engine: http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy/

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• How to list my blog to google search

  - by messy123

  Hi, i had created a blog in blogspot.com, after few days later i updated. but my blog is not appearing in google search. even if i give the full link of blog its not coming.. i have some other blogs, it works well.. i dont no whats wrong with new one.. can any one know what to do

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• How to fo fluid dynamics like Where's My Water?

  - by Edgar Miranda

  There is a game on the app store called "Where's My Water" that is really fun and uses fluid dynamics in it's gameplay. You can check out a video of the game play here... http://www.youtube.com/watch?v=UnFFWnwOohk. You use your finger to remove dirt from the screen, and then the water just flows to the new area. Anyone know what engine this was made in and how they where able to get the fluid dynamics in there? I'm using the Corona SDK for mobile development and want to do something similar like this (a game with fluid dynamics).

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• What's a good Game development platform for a platformer game with these characteristics?

  - by Joe

  Yes, I know, the best way to make an indie game is to learn to code. I've got some scripting experience, but I want to do worldbuilding with already-existing tools (and communities surrounding those tools), and I've been really impressed with games like An Untitled Story that were made with pre-packaged toolsets at their core, like Game Maker. :) So I'm planning to make my game using either Game Maker or something like it. The basic parameters of my planned game: -2D platformer. -Physics/speed akin to Sonic the Hedgehog. -Large, non-linear world, flowing as seamlessly as possible -- think Super Metroid, but without the forced screen transitions. The first two points have me leaning toward Game Maker -- Plenty of 2D platformers have been made with it, and there are serviceable, openly available Sonic-the-Hedgehog-style physics engines for it that could be adapted to my needs with minimal muss and fuss. But the third makes me antsy -- from what limited information I hear, Game Maker has problems with large levels/boards/screens/whateveryoucallthem, thus necessitating transitions between screens. I want to avoid that if at all possible -- it would, I believe, fundamentally alter the flow of the game. I understand that generally speaking, the more you have loaded into memory the more things are going to chug (especially for a one-size-fits-all game development platform that isn't a model of efficient coding), but I'm hoping there are systems that can un-load objects that are sufficiently far offscreen and thus better produce seamlessness. Any thoughts, people? :) The sooner I can get a basic pre-fab physics engine and world-building program up and running, the sooner I can start prototyping areas and generally tooling around. Should I be looking at Game Maker, or elsewhere? (My current plan is to more-or-less build the game prototype-style, then worry about art and sound at the very end once the damn thing is playable.)

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• 3D/perspective Top down shooter bullet issues

  - by Tseng

  I'm developing a top-down shooter with multiple levels (ground for ground units, middle level for buildings, top level for air unity). The problem is the collision. Though I can make the collider box of a bullet be long enough to reach the ground (and collide with it), the real issue is optical. When the bullet is fired from a aircraft and collides with some object on the ground (building, ground unit) it will be optically offset due to the perspective camera, because it looks like the shot "by-passed" the target as seen below Is there any way to make the bullets collide perspectively correct? I'm using Unity3d Engine and it offers only simple colliders (box, sphere, cylinder, mesh and wheel), though I don't think a cone-formed collider would solve this issue. I'd need a (cheap) way to check if it's overlapping a destructible object? I thought of casting a ray from the camera through the bullet and if it hits something destructible, trigger an action, but that's quite punctual and maybe to performance heavy on certain number of bullets

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