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• Correct way to handle path-finding collision matrix

  - by Xander Lamkins

  Here is an example of me utilizing path finding. The red grid represents the grid utilized by my A* library to locate a distance. This picture is only an example, currently it is all calculated on the 1x1 pixel level (pretty darn laggy). I want to make it so that the farther I click, the less accurate it will be (split the map into larger grid pieces). Edit: as mentioned by Eric, this is not a required game mechanic. I am perfectly fine with any method that allows me to make this accurate while still fast. This isn't the really the topic of this question though. The problem I have is, my current library uses a two dimensional grid of integers. The higher the number in a cell, the more resistance for that grid tile. Currently I'm setting all unwalkable spots to Integer Max. Here is an example of what I want: I'm just not sure how I should set up the arrays of integers of the grid. Every time an element is added/removed to/from the game, it's collision details are updated in the table. Here is a picture of what the map looks like on my collision layer: I probably shouldn't be creating new arrays every time I have to do a path find because my game needs to support tons of PF at the same time. Should I have multiple arrays that are all updated when the dynamic elements are updated (a building is built/a building is destroyed). The problem I see with this is that it will probably make the creation and destruction of buildings a little more laggy than I would want because it would be setting the collision grid for each built in accuracy level. I would also have to add more/remove some arrays if I ever in the future changed the map size. Should I generate the new array based on an accuracy value every time I need to PF? The problem I see with this is that it will probably make any form of PF just as laggy because it will have to search through a MapWidth x MapHeight number of cells to shrink it all down. Or is there a better way? I'm certainly not the best at optimizing really anything. I've just started dealing with XNA so I'm not used to having optimization code really doing much of an affect until now... :( If you need code examples, please ask. I'll add it as an edit. EDIT: While this doesn't directly relate to the question, I figure the more information I provide, the better. To keep your units from moving as accurately to the players desired position, I've decided that once the unit PFs over to the less accurate grid piece, it will then PF on a more accurate level to the exact position requested.

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• Keeping player aligned to grid in Pacman

  - by user17577

  I am making a Pacman game using XNA. The game is tile based, with each tile being 32 pixels. As the player moves, I need to know whenever it is perfectly on a tile (ie position of 32, 64, etc...) so that I can check to see if the next tile is free. I am using the following logic to test this. if (position.X % 32 == 0 && position.Y %32 == 0) { onTile = true; } I figure that I need to make the player's speed evenly divide 32. Everything works fine if I make the player's speed an integer such as 4 or 8. But if I make the speed something like 6.4, I end up with positions such as 64.00001, and my if statement no longer works correctly. How can I keep the player aligned with the grid, while allowing a wider range of player speeds than 1, 2, 4, 8, 16, and 32? Or is there some better way to go about this? Thanks

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• Good resources for JavaScript 2D game programming?

  - by DJCouchyCouch

  As an exercise, I've decided to look into JavaScript for game programming. While it's far from being the best language for that, I do like the idea that it's cross-platform and it's always available as a web page. So I thought I'd see what I could do with it. Specifically, I'd like to make a 2D tile-based game of some kind. Where can I find resources to do that? I'm sure this question's come up before, but I can't find any reference to it.

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• Object detection in bitmap JavaScript canvas

  - by fallenAngel

  I want to detect clicks on canvas elements which are drawn using paths. So far I have stored element paths in a JavaScript data structure and then check the coordinates of hits which match the element's coordinates. Rendering each element path and checking the hits would be inefficient when there are a lot of elements. I believe there must be an algorithm for this kind of coordinate search, can anyone help me with this?

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• Sprites rendering blurry with velocity

  - by ashes999

  After adding velocity to my game, I feel like my textures are twitching. I thought it was just my eyes, until I finally captured it in a screenshot: The one on the left is what renders in my game; the one on the right is the original sprite, pasted over. (This is a screenshot from Photoshop, zoomed in 6x.) Notice the edges are aliasing -- it looks almost like sub-pixel rendering. In fact, if I had not forced my sprites (which have position and velocity as ints) to draw using integer values, I would swear that MonoGame is drawing with floating point values. But it isn't. What could be the cause of these things appearing blurry? It doesn't happen without velocity applied. To be precise, my SpriteComponent class has a Vector2 Position field. When I call Draw, I essentially use new Vector2((int)Math.Round(this.Position.X), (int)Math.Round(this.Position.Y)) for the position. I had a bug before where even stationary objects would jitter -- that was due to me using the straight Position vector and not rounding the values to ints. If I use Floor/Ceiling instead of round, the sprite sinks/hovers (one pixel difference either way) but still draws blurry.

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• Storing game objects with generic object information

  - by Mick

  In a simple game object class, you might have something like this: public abstract class GameObject { protected String name; // other properties protected double x, y; public GameObject(String name, double x, double y) { // etc } // setters, getters } I was thinking, since a lot of game objects (ex. generic monsters) will share the same name, movement speed, attack power, etc, it would be better to have all that information shared between all monsters of the same type. So I decided to have an abstract class "ObjectData" to hold all this shared information. So whenever I create a generic monster, I would use the same pre-created "ObjectData" for it. Now the above class becomes more like this: public abstract class GameObject { protected ObjectData data; protected double x, y; public GameObject(ObjectData data, double x, double y) { // etc } // setters, getters public String getName() { return data.getName(); } } So to tailor this specifically for a Monster (could be done in a very similar way for Npcs, etc), I would add 2 classes. Monster which extends GameObject, and MonsterData which extends ObjectData. Now I'll have something like this: public class Monster extends GameObject { public Monster(MonsterData data, double x, double y) { super(data, x, y); } } This is where my design question comes in. Since MonsterData would hold data specific to a generic monster (and would vary with what say NpcData holds), what would be the best way to access this extra information in a system like this? At the moment, since the data variable is of type ObjectData, I'll have to cast data to MonsterData whenever I use it inside the Monster class. One solution I thought of is this, but this might be bad practice: public class Monster extends GameObject { private MonsterData data; // <- this part here public Monster(MonsterData data, double x, double y) { super(data, x, y); this.data = data; // <- this part here } } I've read that for one I should generically avoid overwriting the underlying classes variables. What do you guys think of this solution? Is it bad practice? Do you have any better solutions? Is the design in general bad? How should I redesign this if it is? Thanks in advanced for any replies, and sorry about the long question. Hopefully it all makes sense!

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• I made a game in XNA - how can I share it with my friends?

  - by Raven Dreamer

  I've just finished programming a charming (albeit bare-bones) XNA version of arcade classic Tempest. Hooray! Given that this was a homework assignment, I'd like to be able to share it with my professor and my friends/classmates to solicit feedback. (And let's be honest - if I have a question about how to add in an additional feature, it might be nice to be able to share it with folks on this site as well.) Is there a better way of sharing an XNA game than by shuttling the visual studio - produced executable around? Some way to host it on a website would be ideal.

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• Isometric projection bad coordonate

  - by Christophe Debove

  I have a 2D map, for each element I apply this isometric projection to place my Sprite //Element e; float[] f= projection(e.getX(), e.getY() ,z); // x and y represent Sprite Coordonate (tile_width and height depend of my // camera size and the number of elements in x and in y float x = f[0]*tile_width; float y = f[1]*tile_height; public float[] projection(float x, float y, float z) { return new float[]{ (( x )-(y) ) , ((x/2) + (y/2) - z )}; } the sprite for one element : The result of my projection : The problem is I need to add an offset of tile_height/2 to the y and tile_width/2 to the x to have something like this (in the red rectangle I drawed with paint what I want) : Where did I make wrong? (I found the projection method in How should I sort images in an isometric game so that they appear in the correct order? )

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• Simple question about a cocos2d based game template

  - by Zishan

  I am learning a cocos2d based Game template tutorial from here and now I am at this point of the tutorial. My question is, how can i run 30 different scenes in 30 different levels of 5 chapter? Now I am using this switch (gameData.selectedLevel) { case 1: [SceneManager goChapter1Level1Scene]; break; (... snip a whole lot of lines...) case 30: [SceneManager goChapter5Level6Scene]; break; default: break; } in the "- (void) onPlay: (CCMenuItemImage*) sender" method. But it work only for 6 levels scene of chapter1. Other 4 chapters levels are show as same as 1st chapter levels scene. they are not show their own level scene. can any one please teach me, how can I do this stuff using this game template?

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• Tips for communication between JS browser game and node.js server?

  - by Petteri Hietavirta

  I am tinkering around with some simple Canvas based cave flyer game and I would like to make it multiplayer eventually. The plan is to use Node.js on the server side. The data sent over would consists of position of each player, direction, velocity and such. The player movements are simple force physics, so I should be able to extrapolate movements before next update from server. Any tips or best practices on the communications side? I guess web sockets are the way to go. Should I send information in every pass of the game loop or with specified intervals? Also, I don't mind if it doesn't work with older browsers.

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• Method for spawning enemies according to player score and game time

  - by Sun

  I'm making a top-down shooter and want to scale the difficulty of the game according to what the score is and how much time has Passed. Along with this, I want to spawn enemies in different patterns and increase the intervals at which these enemies are shown. I'm going for a similar effect to Geometry wars. However, I can think of a to do this other than have multiple if-else statments, e.g. : if (score > 1000) { //spawn x amount if enemies } else if (score > 10000) { //spawn x amount of enemy type 1 & 2 } else if (score > 15000) { //spawn x amount of enemy type 1 & 2 & 3 } else if (score > 25000) { //spawn x amount of enemy type 1 & 2 & 3 //create patterns with enemies } ...etc What would be a better method of spawning enemies as I have described?

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• Direct2D Transform

  - by James

  I have a beginner question about Direct2D transforms. I have a 20 x 10 bitmap that I would like to draw in different orientations. To start, I would like to draw it vertically with a destination rectangle of say: (left, top, right, bottom) (300, 300, 310, 320) The bitmap is wider than it is tall (20 x 10), but when I draw it vertically, it will be appear taller than it is wide (10 x 20). I know that I can use a rotation matrix like so: m_pRenderTarget->SetTransform( D2D1::Matrix3x2F::Rotation( 90.0f, D2D1::Point2F(<center of shape>)) ); But when I use this method to rotate my shape, the destination rectangle is still wider than it is tall. Maybe it would look something like this: (left, top, right, bottom) (280, 290, 300, 300) The destination rectangle is 20 x 10 but the bitmap appears on the screen as 10 x 20. I can't look at the destination rectangle in the debugger and compare it to: (left, top, right, bottom) (300, 300, 310, 320) Is there any simple way to say "I want to rotate it so that the image is rendered to exactly this destination rectangle after the rotation?" In this case, I would like to say "Please rotate the bitmap so that it appears on the screen at this location:" (left, top, right, bottom) (300, 300, 310, 320) If I can't do that, is there any way to find out the 10 x 20 destination rectangle where the bitmap is actually being rendered to the screen?

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• Weird rotation problem

  - by Phil

  I'm creating a simple tank game. No matter what I do, the turret keeps facing the target with it's side. I just can't figure out how to turn it 90 degrees in Y once so it faces it correctly. I've checked the pivot in Maya and it doesn't matter how I change it. This is the code I use to calculate how to face the target: void LookAt() { var forwardA = transform.forward; var forwardB = (toLookAt.transform.position - transform.position); var angleA = Mathf.Atan2(forwardA.x, forwardA.z) * Mathf.Rad2Deg; var angleB = Mathf.Atan2(forwardB.x, forwardB.z) * Mathf.Rad2Deg; var angleDiff = Mathf.DeltaAngle(angleA, angleB); //print(angleDiff.ToString()); if (angleDiff > 20) { //Rotate to transform.Rotate(new Vector3(0, (-turretSpeed * Time.deltaTime),0)); //transform.rotation = new Quaternion(transform.rotation.x, transform.rotation.y + adjustment, transform.rotation.z, transform.rotation.w); } else if (angleDiff < 20) { transform.Rotate(new Vector3(0, (turretSpeed * Time.deltaTime),0)); //transform.rotation = new Quaternion(transform.rotation.x, transform.rotation.y + adjustment, transform.rotation.z, transform.rotation.w); } else { } } I'm using Unity3d and would appreciate any help I can get! Thanks!

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• Manipulating Perlin Noise

  - by Numeri

  I've been learning about Procedurally Generated Content lately (in particular, Perlin noise). Perlin noise works great for making things like landscapes, height maps, and stuff like that. But now I am trying to generate structures more like mountain ranges (in 2D, as 3D would be way over my head right now) or underground veins of ores. I can't manage to manipulate Perlin Noise to do this. Making a cut off point (i.e. using only the tops of the 'mountains' of a heightmap) wouldn't work, because I would get lumps of mountains/veins. Any suggestions? Thanks, Numeri

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• How can I simulate objects floating on water without a physics engine?

  - by user1075940

  In my game the water movement is done in a shader using Gerstner equations. The water movement looks realistic enough for a school project but I encounter serious problem when I wanted to do sailing on waves (similar to this). I managed to do collision with land by calculating quad's vertices and normals beneath ship, however same method can not be applied to water because XZ are displaced and Y is calculated in a shader :( How to approach this problem ? Is it possible to retrieve transformed grid from shader? Unfortunately no external physics libraries can be used.

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• Moving in a diamond - enemy gets stuck

  - by Fibericon

  I have an enemy that I would like to move as follows: Start at (0, 200, 0) Move to (200, 0, 0) Move to (0, -200, 0) Move to (-200, 0, 0) Move to start point, repeat as long as it remains active. This is what I've done to achieve that: if (position.X < 200 && position.Y > 0) { Velocity = new Vector3(1, -1, 0) * speed; } else if (position.X >= 200 && position.Y <= 0 && position.Y > -200) { Velocity = new Vector3(-1, -1, 0) * speed; } else if (position.X <= 0 && position.Y <= -200) { Velocity = new Vector3(-1, 1, 0) * speed; } else { Velocity = new Vector3(1, 1, 0) * speed; } It moves to the second point, but then gets stuck and appears to vibrate in place. How should I be doing this?

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• Efficiently representing a dynamic transform hierarchy

  - by Mattia

  I'm looking for a way to represent a dynamic transform hierarchy (i.e. one where nodes can be inserted and removed arbitrarily) that's a bit more efficient than using a standard tree of pointers . I saw the answers to this question ( Efficient structure for representing a transform hierarchy. ), but as far as I can determine the tree-as-array approach only works for static hierarchies or dynamic ones where nodes have a fixed number of children (both deal-breakers for me). I'm probably wrong about that but could anyone point out how? If I'm not wrong are there other alternatives that work for dynamic hierarchies?

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• Procedural world generation oriented on gameplay features

  - by Richard Fabian

  In large procedural landscape games, the land seems dull, but that's probably because the real world is largely dull, with only limited places where the scenery is dramatic or tactical. Looking at world generation from this point of view, a landscape generator for a game (that is, not for the sake of scenery, but for the sake of gameplay) needs to not follow the rules of landscaping, but instead some rules married to the expectations of the gamer. For example, there could be a choke point / route generator that creates hills ravines, rivers and mountains between cities, rather than the natural way cities arise, scattered on the land based on resources or conditions generated by the mountains and rainfall patterns. Is there any existing work being done like this? Start with cities or population centres and then add in terrain afterwards? The reason I'm asking is that I'd previously pondered taking existing maps from fantasy fiction (my own and others), putting the information into the system as a base point, and then generating a good world to play in from it. This seems covered by existing technology, that is, where the designer puts in all the necessary information such as the city populations, resources, biomes, road networks and rivers, then allows the PCG fill in the gaps. But now I'm wondering if it may be possible to have a content generator generate also the overall design. Generate the cities and population centres, balancing them so that there is a natural seeming need of commerce, then generate the positions and connectivity, then from the type of city produce the list of necessary resources that must be nearby, and only then, maybe given some rules on how to make the journey between cities both believable and interesting, generate the final content including the roads, the choke points, the bridges and tunnels, ferries and the terrain including the biomes and coastline necessary. If this has been done before, I'd like to know, and would like to know what went wrong, and what went right.

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• How do I prevent other dynamic bodies from affecting the player's velocity with Box2D?

  - by Milo

  I'm working on my player object for my game. PhysicsBodyDef def; def.fixedRotation = true; def.density = 1.0f; def.position = Vec2(200.0f, 200.0f); def.isDynamic = true; def.size = Vec2(50.0f,200.0f); m_player.init(def,&m_physicsEngine.getWorld()); This is how he moves: b2Vec2 vel = getBody()->GetLinearVelocity(); float desiredVel = 0; if (m_keys[ALLEGRO_KEY_A] || m_keys[ALLEGRO_KEY_LEFT]) { desiredVel = -5; } else if (m_keys[ALLEGRO_KEY_D] || m_keys[ALLEGRO_KEY_RIGHT]) { desiredVel = 5; } else { desiredVel = 0; } float velChange = desiredVel - vel.x; float impulse = getBody()->GetMass() * velChange; //disregard time factor getBody()->ApplyLinearImpulse( b2Vec2(impulse,0), getBody()->GetWorldCenter(),true); This creates a few problems. First, to move the player at a constant speed he must be given a high velocity. The problem with this is if he just comes in contact with a small box, he makes it move a lot. Now, I can fix this by lowering his density, but then comes my main issue: I need other objects to be able to run into him, but when they do, he should be like a static wall and not move. I'm not sure how to do that without high density. I cannot use collision groups since I still need him to be solid toward other dynamic things. How can this be done? Essentially, how do I prevent other dynamic bodies from affecting the player's velocity?

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• Breakout... Getting the ball reflection X angle when htitting paddle / bricks

  - by Steven Wilson

  Im currently creating a breakout clone for my first ever C# / XNA game. Currently Ive had little trouble creating the paddle object, ball object, and all the bricks. The issue im currently having is getting the ball to bounce off of the paddle and bricks correctly based off of where the ball touches the object. This is my forumala thus far: if (paddleLocation.Intersects(ballLocation)) { position.Y = paddleLocation.Y - texture.Height; motion.Y *= -1; // determine X motion.X = 1 - 2 * (ballLocation.X - paddleLocation.X) / (paddleLocation.Width / 2); } The problem is, the ball goes the opposite direction then its supposed to. When the ball hits the left side of the paddle, instead of bouncing back to the left, it bounces right, and vise versa. Does anyone know what the math equation is to fix this?

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• How do I properly use multithreading with Nvidia PhysX?

  - by xcrypt

  I'm having a multithreading problem with Nvidia PhysX. the SDK requires that you call Simulate() (starts computing new physics positions within a new thread) and FetchResults() (waits 'till the physics computations are done). Inbetween Simulate() and FetchResults() you may not "compute new physics". It is proposed (in a sample) that we create a game loop as such: Logic (you may calculate physics here and other stuff) Render + Simulate() at start of Render call and FetchResults at end of Render() call However, this has given me various little errors that stack up: since you actually render the scene that was computed in the previous iteration in the game loop. Does anyone have a solution to this?

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• XNA Moddable Game - Architecture Design and Reflection

  - by David K

  I've decided to embark on an XNA moddable game project of a simple rogue style. For all purposes of this question, I'm going to not be using a scripting engine, but rather allow modders to directly compile assemblies that are loaded by the game at run time. I know about the security problems this may raise. So in order to expose the moddable content, I have gone about creating a generic project in XNA called MyModel. This contains a number of interfaces that all inherit from IPlugin, such as IGameSystem, IRenderingSystem, IHud, IInputSystem etc. Then I've created another project called MyRogueModel. This references MyModel project, and holds interfaces such as IMonster, IPlayer, IDungeonGenerator, IInventorySystem. More rogue specific interfaces, but again, all interfaces in this project inherit from IPlugin. Then finally, I've created another project called MyRogueGame, that references both MyModel and MyRogueModel projects. This project will be the game that you run and play. Here I have put the actual implementation of the Monster, DungeonGenerator, InputSystem and RenderingSystem classes. This project will also scan the mods directory during run time and load any IPlugins it finds using reflection and override anything it finds from the default. For example if it finds a new implementation of the DungeonGenerator it will use that one instead. Now my question is, in order to get this far, I have effectively 2 projects that contain nothing but interfaces... which seems a little... strange ? For people to create mods for the game, I would give them both the MyModel and MyRogueModel assemblies in which they would reference. I'm not sure whether this is the right way to do it, but my reasoning goes as follows : If I write 1 input system, I can use it in any game I write. If I create 3 rogue like games, and a modder writes 1 rendering system, that modder could use the rendering system for all 3 games, because it all comes from the MyModel project. I come from a more web based C# role, so having empty interface projects doesn't seem wrong, its just something I haven't done before. Before I embark on something that might be crazy, I'd just like to know whether this is a foolish idea and whether there's a better (or established) design principle I should be following ?

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• DX9 Deferred Rendering, GBuffer displays as clear color only

  - by Fire31

  I'm trying to implement Catalin Zima's Deferred Renderer in a very lightweight c++ DirectX 9 app (only renders a skydome and a model), at this moment I'm trying to render the gbuffer, but I'm having a problem, the screen shows only the clear color, no matter how much I move the camera around. However, removing all the render target operations lets the app render the scene normally, even if the models are being applied the renderGBuffer effect. Any ideas of what I'm doing wrong?

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• What is UVIndex and how do I use it on OpenGL?

  - by Delta

  I am a noob in OpenGL ES 2.0 (for WebGL) and I'm trying to draw a simple model I've made with a 3D tool and exported to .fbx format. I've been able to draw some models that only have: A vertex buffer, a index buffer for the vertices, a normal buffer and a texture coordinate buffer, but this model now has a "UVIndex" and I'm not sure where am I supposed to put this UVIndex. My code looks like this: GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.VertexBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["vPosition"],3,GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.NormalBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["vNormal"], 3, GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.TexCoordBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["TexCoord"], 2, GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ELEMENT_ARRAY_BUFFER, this.Model.House.IndexBuffer); GL.bindTexture(GL.TEXTURE_2D, this.Texture.HTex1); GL.activeTexture(GL.TEXTURE0); GL.drawElements(GL.TRIANGLES, this.Model.House.IndexBuffer.Length, GL.UNSIGNED_SHORT, 0); But my model renders totally incorrect and I think it has to do with the fact that I am ignoring this "UVIndex" in the .fbx file, since I've never drawn any model that uses this UVIndex I really have no clue on what to do with it. This is the json file containing the model's data: http://pastebin.com/raw.php?i=G294TVmz

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• Error in my Separating Axis Theorem collision code

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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