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• Create bullet physics rigid body along the vertices of a blender model

  - by Krishnabhadra

  I am working on my first 3D game, for iphone, and I am using Blender to create models, Cocos3D game engine and Bullet for physics simulation. I am trying to learn the use of physics engine. What I have done I have created a small model in blender which contains a Cube (default blender cube) at the origin and a UVSphere hovering exactly on top of this cube (without touching the cube) I saved the file to get MyModel.blend. Then I used File -> Export -> PVRGeoPOD (.pod/.h/.cpp) in Blender to export the model to .pod format to use along with Cocos3D. In the coding side, I added necessary bullet files to my Cocos3D template project in XCode. I am also using a bullet objective C wrapper. -(void) initializeScene { _physicsWorld = [[CC3PhysicsWorld alloc] init]; [_physicsWorld setGravity:0 y:-9.8 z:0]; /*Setup camera, lamp etc.*/ .......... ........... /*Add models created in blender to scene*/ [self addContentFromPODFile: @"MyModel.pod"]; /*Create OpenGL ES buffers*/ [self createGLBuffers]; /*get models*/ CC3MeshNode* cubeNode = (CC3MeshNode*)[self getNodeNamed:@"Cube"]; CC3MeshNode* sphereNode = (CC3MeshNode*)[self getNodeNamed:@"Sphere"]; /*Those boring grey colors..*/ [cubeNode setColor:ccc3(255, 255, 0)]; [sphereNode setColor:ccc3(255, 0, 0)]; float *cVertexData = (float*)((CC3VertexArrayMesh*)cubeNode.mesh).vertexLocations.vertices; int cVertexCount = (CC3VertexArrayMesh*)cubeNode.mesh).vertexLocations.vertexCount; btTriangleMesh* cTriangleMesh = new btTriangleMesh(); // for (int i = 0; i < cVertexCount * 3; i+=3) { // printf("\n%f", cVertexData[i]); // printf("\n%f", cVertexData[i+1]); // printf("\n%f", cVertexData[i+2]); // } /*Trying to create a triangle mesh that curresponds the cube in 3D space.*/ int offset = 0; for (int i = 0; i < (cVertexCount / 3); i++){ unsigned int index1 = offset; unsigned int index2 = offset+6; unsigned int index3 = offset+12; cTriangleMesh->addTriangle( btVector3(cVertexData[index1], cVertexData[index1+1], cVertexData[index1+2] ), btVector3(cVertexData[index2], cVertexData[index2+1], cVertexData[index2+2] ), btVector3(cVertexData[index3], cVertexData[index3+1], cVertexData[index3+2] )); offset += 18; } [self releaseRedundantData]; /*Create a collision shape from triangle mesh*/ btBvhTriangleMeshShape* cTriMeshShape = new btBvhTriangleMeshShape(cTriangleMesh,true); btCollisionShape *sphereShape = new btSphereShape(1); /*Create physics objects*/ gTriMeshObject = [_physicsWorld createPhysicsObjectTrimesh:cubeNode shape:cTriMeshShape mass:0 restitution:1.0 position:cubeNode.location]; sphereObject = [_physicsWorld createPhysicsObject:sphereNode shape:sphereShape mass:1 restitution:0.1 position:sphereNode.location]; sphereObject.rigidBody->setDamping(0.1,0.8); } When I run the sphere and cube shows up fine. I expect the sphere object to fall directly on top of the cube, since I have given it a mass of 1 and the physics world gravity is given as -9.8 in y direction. But What is happening the spere rotates around cube three or times and then just jumps out of the scene. Then I know I have some basic misunderstanding about the whole process. So my question is, how can I create a physics collision shape which corresponds to the shape of a particular mesh model. I may need complex shapes than cube and sphere, but before going into them I want to understand the concepts.

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• Swinging a sword in Xcode with Sprite Kit

  - by jking14

  I'm working on making an RPG in Xcode, and I'm having a major gameplay issue when it comes to having my character swing his sword in a way that is realistic and gameplay compatible. Right now, when the player taps the screen and the sword is in one of the player's hand, it rotates the upright sword 90 degrees. The sword which is a parent of the player floats in front of the player because of a collision issue I'm looking for any advice anyone can give on how to add a sword to the game and have it swing in a way that looks somewhat realistic and can damage enemies that are more than a single pixel away from the player

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• Collisions not working as intended

  - by Stan

  I'm making a game, it's a terraria-like game, with 20x20 blocks, and you can place and remove those blocks. Now, I am trying to write collisions, but it isn't working as I want, the collision succesfully stops the player from going through the ground, but, when I press a key like A + S, that means if I walk down and left (Noclip is on atm), my player will go into the ground, bug up, and exit the ground somewhere else in the level. I made a video of it. The red text means which buttons I am pressing. http://www.youtube.com/watch?v=mo4frZyNwOs You see, if I press A and S together, I go into the ground. Here is my collision code: Vector2 collisionDist, normal; private bool IsColliding(Rectangle body1, Rectangle body2) { normal = Vector2.Zero; Vector2 body1Centre = new Vector2(body1.X + (body1.Width / 2), body1.Y + (body1.Height / 2)); Vector2 body2Centre = new Vector2(body2.X + (body2.Width / 2), body2.Y + (body2.Height / 2)); Vector2 distance, absDistance; float xMag, yMag; distance = body1Centre - body2Centre; float xAdd = ((body1.Width) + (body2.Width)) / 2.0f; float yAdd = ((body1.Height) + (body2.Height)) / 2.0f; absDistance.X = (distance.X < 0) ? -distance.X : distance.X; absDistance.Y = (distance.Y < 0) ? -distance.Y : distance.Y; if (!((absDistance.X < xAdd) && (absDistance.Y < yAdd))) return false; xMag = xAdd - absDistance.X; yMag = yAdd - absDistance.Y; if (xMag < yMag) normal.X = (distance.X > 0) ? xMag : -xMag; else normal.Y = (distance.Y > 0) ? yMag : -yMag; return true; } private void PlayerCollisions() { foreach (Block blocks in allTiles) { collisionDist = Vector2.Zero; if (blocks.Texture != airTile && blocks.Texture != stoneDarkTexture && blocks.Texture != stoneDarkTextureSelected && blocks.Texture != airTileSelected && blocks.Texture != doorTexture && blocks.Texture != doorTextureSelected) { if (IsColliding(player.plyRect, blocks.tileRect)) { if (normal.Length() > collisionDist.Length()) { collisionDist = normal; } player.Position.X += collisionDist.X; player.Position.Y += collisionDist.Y; break; } } } } I got PlayerCollisions() running in my Update method. As you can see it works partly, but if it runs perfectly, it would be awesome, though I have no idea how to fix this problem. Help would be greatly appreciated. EDIT: If I remove the break; it works partly, then it is just the thing that it spasms when it hits two or more blocks at once, like, if I touch 2/3 blocks at once, it does twice the force up. How can I make it so that it only does the force for one block, so it stays correct, and does not spasm? Thanks.

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• A* Jump Point Search - how does pruning really work?

  - by DeadMG

  I've come across Jump Point Search, and it seems pretty sweet to me. However, I'm unsure as to how their pruning rules actually work. More specifically, in Figure 1, it states that we can immediately prune all grey neighbours as these can be reached optimally from the parent of x without ever going through node x However, this seems somewhat at odds. In the second image, node 5 could be reached by first going through node 7 and skipping x entirely through a symmetrical path- that is, 6 -> x -> 5 seems to be symmetrical to 6 -> 7 -> 5. This would be the same as how node 3 can be reached without going through x in the first image. As such, I don't understand how these two images are not entirely equivalent, and not just rotated versions of each other. Secondly, I'd like to understand how this algorithm could be generalized to a three-dimensional search volume.

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• How to impale and stack targets correctly according to the collider and its coordinate?

  - by David Dimalanta

  I'm making another simple game, a catch game, where a spawning target game object must be captured using a skewer to impale it. Here how: At the start, the falling object (in red) will fall in a vertical direction (in blue) When aimed properly, the target will fall down along the line of the skewer. (in blue) Then, another target is spawned and will fall vertically. (in red) When aimed successfully again in a streak, the second target will fall along the skewer and stacked. Same process over and over when another target is spawned. However, when I test run it on the scene tab in Unity, when impaled several targets, instead of a smooth flow and stacking it ended up overlaying it instead of stacking it up like a pancake. Here's what it look like: As I noticed when reaching the half-way of my progress, I tried to figure out how to deal with collider bodies without sticking each other so that it will actually stack like in the example of the image at no. 3. Here's the script code I added in the target game object: using UnityEngine; using System.Collections; public class ImpaleStateTest : MonoBehaviour { public GameObject target; public GameObject skewer; public bool drag = false; private float stack; private float impaleCount; void Start () { stack = 0; impaleCount = 0; } void Update () { if(drag) { target.transform.position = new Vector3 (DragTest.dir.transform.position.x, DragTest.dir.transform.position.y - 0.35f, 0); target.transform.rotation = DragTest.degrees; target.rigidbody2D.fixedAngle = true; target.rigidbody2D.isKinematic = true; target.rigidbody2D.gravityScale = 0; if(Input.GetMouseButton(0)) { Debug.Log ("Skewer: " + DragTest.dir.transform.position.x); Debug.Log ("Target: " + target.transform.position.x); } } } void OnTriggerEnter2D(Collider2D collider) { impaleCount++; Debug.Log ("Impaled " + impaleCount + " time(s)!"); drag = true; audio.Play (); } } Aside from that, I'm not sure if it's right but, the only way to stick the impaled targets while dragging the skewer left or right is to get the X coordinates from the skewer only. Is there something else to recommend it in order to improve this behavior as realistic as possible? Please help.

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• Finding the normals of an oriented bounding box?

  - by Milo

  Here is my problem. I'm working on the physics for my 2D game. All objects are oriented bounding boxes (OBB) based on the separate axis theorem. In order to do collision resolution, I need to be able to get an object out out of the object it is penetrating. To do this I need to find the normal of the face(s) that the other OBB is touching. Example: The small red OBB is a car lets say, and the big OBB is a static building. I need to determine the unit vector that is the normal of the building edge(s) the car is penetrating to get the car out of there. Here are my questions: How do I determine which edges the car is penetrating. I know how to determine the normal of an edge, but how do I know if I need (-dy, dx) or (dy, -dx)? In the case I'm demonstrating the car is penetrating 2 edges, which edge(s) do I use to get it out? Answers or help with any or all of these is greatly appreciated. Thank you

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• How do I get the compression on specific dynamic body

  - by Mike JM

  Sorry, I could not find any tag that would suit my question. Let me first show you the image and then write what I want to do: I'm using box2D. As you can see there are three dynamic bodies connected to each other (think of it as a table from front view).The LEG1 and LEG2 are connected to the static body. (it's the ground body). Another dynamic body is falling onto the table. I need to get the compression in the LEG1 and LEG2 separately. Joints have GetReactionForce() function which returns a b2Vec, which in turn has Length() and LengthSqd functions. This will give the total sum of the forces in any taken joint. But what I need is forces in individual bodies that are connected with joints. Once you connect several bodies with a single joint it again will show the sum of forces which is not useful.Here's the case iI'm talking about:

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• Finding the contact point with SAT

  - by Kai

  The Separating Axis Theorem (SAT) makes it simple to determine the Minimum Translation Vector, i.e., the shortest vector that can separate two colliding objects. However, what I need is the vector that separates the objects along the vector that the penetrating object is moving (i.e. the contact point). I drew a picture to help clarify. There is one box, moving from the before to the after position. In its after position, it intersects the grey polygon. SAT can easily return the MTV, which is the red vector. I am looking to calculate the blue vector. My current solution performs a binary search between the before and after positions until the length of the blue vector is known to a certain threshold. It works but it's a very expensive calculation since the collision between shapes needs to be recalculated every loop. Is there a simpler and/or more efficient way to find the contact point vector?

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• How do I detect multiple sprite collisions when there are >10 sprites?

  - by yao jiang

  I making a small program to animate the astar algorithm. If you look at the image, there are lots of yellow cars moving around. Those can collide at any moment, could be just one or all of them could just stupidly crash into each other. How do I detect all of those collisions? How do I find out which specific car has crash into which other car? I understand that pygame has collision function, but it only detects one collision at a time and I'd have to specify which sprites. Right now I am just trying to iterate through each sprite to see if there is collision: for car1 in carlist: for car2 in carlist: collide(car1, car2); This can't be the proper way to do it, if the car list goes to a huge number, a double loop will be too slow.

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• How to do reflective collisions with particles hitting background tiles?

  - by Shawn LeBlanc

  In my 2d pixel old-school platformer, I'm looking for methods for bouncing particles off of background tiles. Particles aren't affected by gravity and collisions are "reflective". By that I mean a particle hitting the side of a square tile at 45 degrees should bounce off at 45 degrees as well. We can assume that tiles will always be perfectly square. No slopes or anything. What are efficient methods and algorithms to do this? I'd be implementing this on a Sega Genesis.

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• AABB > AABB collision response?

  - by Levi

  I'm really confused about how to fix this in 3d? I want it so that I can slide along cubes but without getting caught if there's 2 adjacent cubes. I've gotten it so that I can do x collision, with sliding, and y, and z, but I can't do them together, probably because I don't know how to resolve it correctly. e.g. [] [] []^ []O [] O is the player, ^ is the direction the player is moving, with the methods which I was trying I would get stuck between the cubes because the z axis was responding and kicking me out :/. I don't know how to resolve this in all 3 direction, like how would I go about telling which direction I have to resolve in. My previous methods involved me checking 4 points in a axis aligned square around the player, I was checking if these points where inside the cubes and if they where fixing my position, but I couldn't get it working correctly. Help is appreciated. edit: pretend all the blocks are touching.

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• Collision filtering techniques

  - by Griffin

  I was wondering what efficient techniques are out there for mapping collision filtering between various bodies, sub-bodies, and so forth. I'm familiar with the simple idea of having different layers of 2D bodies, but this is not sufficient for more complex mapping: (Think of having sub-bodies of a body, such as limbs, collide with each other by placing them on the same layer, and then wanting to only have the legs collide with the ground while the arms would not) This can be solved with a multidimensional layer setup, but I would probably end up just creating more and more layers to the point where the simplicity and efficiency of layer filtering would be gone. Are there any more complex ways to solve even more complex situations than this?

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• Java - 2d Array Tile Map Collision

  - by Corey

  How would I go about making certain tiles in my array collide with my player? Like say I want every number 2 in the array to collide. I am reading my array from a txt file if that matters and I am using the slick2d library. Here is my code if needed. public class Tiles { Image[] tiles = new Image[3]; int[][] map = new int[500][500]; Image grass, dirt, mound; SpriteSheet tileSheet; int tileWidth = 32; int tileHeight = 32; public void init() throws IOException, SlickException { tileSheet = new SpriteSheet("assets/tiles.png", tileWidth, tileHeight); grass = tileSheet.getSprite(0, 0); dirt = tileSheet.getSprite(7, 7); mound = tileSheet.getSprite(2, 6); tiles[0] = grass; tiles[1] = dirt; tiles[2] = mound; int x=0, y=0; BufferedReader in = new BufferedReader(new FileReader("assets/map.txt")); String line; while ((line = in.readLine()) != null) { String[] values = line.split(","); for (String str : values) { int str_int = Integer.parseInt(str); map[x][y]=str_int; //System.out.print(map[x][y] + " "); y=y+1; } //System.out.println(""); x=x+1; y = 0; } in.close(); } public void update() { } public void render(GameContainer gc) { for(int x = 0; x < 50; x++) { for(int y = 0; y < 50; y ++) { int textureIndex = map[y][x]; Image texture = tiles[textureIndex]; texture.draw(x*tileWidth,y*tileHeight); } } } } I tried something like this, but I it doesn't ever "collide". X and y are my player position. if (tiles.map[(int)x/32][(int)y/32] == 2) { System.out.println("Collided"); }

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• problem with frustum AABB culling in DirectX

  - by Matthew Poole

  Hi, I am currently working on a project with a few friends, and I am trying to get frustum culling working. Every single tutorial or article I go to shows that my math is correct and that this should be working. I thought maybe posting here, somebody would catch something I could not. Thank you. Here are the important code snippets /create the projection matrix void CD3DCamera::SetLens(float fov, float aspect, float nearZ, float farZ) { D3DXMatrixPerspectiveFovLH(&projMat, D3DXToRadian(fov), aspect, nearZ, farZ); } //build the view matrix after changes have been made to camera void CD3DCamera::BuildView() { //keep axes orthoganal D3DXVec3Normalize(&look, &look); //up D3DXVec3Cross(&up, &look, &right); D3DXVec3Normalize(&up, &up); //right D3DXVec3Cross(&right, &up, &look); D3DXVec3Normalize(&right, &right); //fill view matrix float x = -D3DXVec3Dot(&position, &right); float y = -D3DXVec3Dot(&position, &up); float z = -D3DXVec3Dot(&position, &look); viewMat(0,0) = right.x; viewMat(1,0) = right.y; viewMat(2,0) = right.z; viewMat(3,0) = x; viewMat(0,1) = up.x; viewMat(1,1) = up.y; viewMat(2,1) = up.z; viewMat(3,1) = y; viewMat(0,2) = look.x; viewMat(1,2) = look.y; viewMat(2,2) = look.z; viewMat(3,2) = z; viewMat(0,3) = 0.0f; viewMat(1,3) = 0.0f; viewMat(2,3) = 0.0f; viewMat(3,3) = 1.0f; } void CD3DCamera::BuildFrustum() { D3DXMATRIX VP; D3DXMatrixMultiply(&VP, &viewMat, &projMat); D3DXVECTOR4 col0(VP(0,0), VP(1,0), VP(2,0), VP(3,0)); D3DXVECTOR4 col1(VP(0,1), VP(1,1), VP(2,1), VP(3,1)); D3DXVECTOR4 col2(VP(0,2), VP(1,2), VP(2,2), VP(3,2)); D3DXVECTOR4 col3(VP(0,3), VP(1,3), VP(2,3), VP(3,3)); // Planes face inward frustum[0] = (D3DXPLANE)(col2); // near frustum[1] = (D3DXPLANE)(col3 - col2); // far frustum[2] = (D3DXPLANE)(col3 + col0); // left frustum[3] = (D3DXPLANE)(col3 - col0); // right frustum[4] = (D3DXPLANE)(col3 - col1); // top frustum[5] = (D3DXPLANE)(col3 + col1); // bottom // Normalize the frustum for( int i = 0; i < 6; ++i ) D3DXPlaneNormalize( &frustum[i], &frustum[i] ); } bool FrustumCheck(D3DXVECTOR3 max, D3DXVECTOR3 min, const D3DXPLANE* frustum) { // Test assumes frustum planes face inward. D3DXVECTOR3 P; D3DXVECTOR3 Q; bool ret = false; for(int i = 0; i < 6; ++i) { // For each coordinate axis x, y, z... for(int j = 0; j < 3; ++j) { // Make PQ point in the same direction as the plane normal on this axis. if( frustum[i][j] > 0.0f ) { P[j] = min[j]; Q[j] = max[j]; } else { P[j] = max[j]; Q[j] = min[j]; } } if(D3DXPlaneDotCoord(&frustum[i], &Q) < 0.0f ) ret = false; } return true; }

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• Implementing 2D CSG (for collision shapes)?

  - by bluescrn

  Are there any simple (or well documented) algorithms for basic CSG operations on 2D polygons? I'm looking for a way to 'add' a number of overlapping 2D collision shapes. These may be convex or concave, but will be closed shapes, defined as a set of line segments, with no self-intersections. The use of this would be to construct a clean set of collision edges, for use with a 2D physics engine, from a scene consisting of many arbitrarily placed (and frequently overlapping) objects, each with their own collision shape. To begin with, I only need to 'add' shapes, but the ability to 'subtract', to create holes, may also be useful.

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• How do I handle specific tile/object collisions?

  - by Thomas William Cannady

  What do I do after the bounding box test against a tile to determine whether there is a real collision against the contents of that tile? And if there is, how should I move the object in response to that collision? I have a small object, and test for collisions against the tiles that each corner of it is on. Here's my current code, which I run for each of those (up to) four tiles: // get the bounding box of the object, in world space objectBounds = object->bounds + object->position; if ( (objectBounds.right >= tileBounds.left) && (objectBounds.left <= tileBounds.right) && (objectBounds.top >= tileBounds.bottom) && (objectBounds.bottom <= tileBounds.top)) { // perform specific test to see if it's a left, top , bottom // or right collision. If so, I check to see the nature of it // and where I need to place the object to respond to that collision... // [THIS IS THE PART THAT NEEDS WORK] // if( lastkey==keydown[right] && ((objectBounds.right >= tileBounds.left) && (objectBounds.right <= tileBounds.right) && (objectBounds.bottom >= tileBounds.bottom) && (objectBounds.bottom <= tileBounds.top)) ) { object->position.x = tileBounds.left - objectBounds.width; } // etc.

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• SSIS Design Patterns Training in London 8-11 Sep!

  - by andyleonard

  A few seats remain for my course SQL Server Integration Services 2012 Design Patterns to be delivered in London 8-11 Sep 2014. Register today to learn more about: New features in SSIS 2012 and 2014 Advanced patterns for loading data warehouses Error handling The (new) Project Deployment Model Scripting in SSIS The (new) SSIS Catalog Designing custom SSIS tasks Executing, managing, monitoring, and administering SSIS in the enterprise Business Intelligence Markup Language (Biml) BimlScript ETL Instrumentation...(read more)

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• Finding Z given X & Y coordinates on terrain?

  - by mrky

  I need to know what the most efficient way of finding Z given X & Y coordinates on terrain. My terrain is set up as a grid, each grid block consisting of two triangles, which may be flipped in any direction. I want to move game objects smoothly along the floor of the terrain without "stepping." I'm currently using the following method with unexpected results: double mapClass::getZ(double x, double y) { int vertexIndex = ((floor(y))*width*2)+((floor(x))*2); vec3ray ray = {glm::vec3(x, y, 2), glm::vec3(x, y, 0)}; vec3triangle tri1 = { glmFrom(vertices[vertexIndex].v1), glmFrom(vertices[vertexIndex].v2), glmFrom(vertices[vertexIndex].v3) }; vec3triangle tri2 = { glmFrom(vertices[vertexIndex+1].v1), glmFrom(vertices[vertexIndex+1].v2), glmFrom(vertices[vertexIndex+1].v3) }; glm::vec3 intersect; if (!intersectRayTriangle(tri1, ray, intersect)) { intersectRayTriangle(tri2, ray, intersect); } return intersect.z; } intersectRayTriangle() and glmFrom() are as follows: bool intersectRayTriangle(vec3triangle tri, vec3ray ray, glm::vec3 &worldIntersect) { glm::vec3 barycentricIntersect; if (glm::intersectLineTriangle(ray.origin, ray.direction, tri.p0, tri.p1, tri.p2, barycentricIntersect)) { // Convert barycentric to world coordinates double u, v, w; u = barycentricIntersect.x; v = barycentricIntersect.y; w = 1 - (u+v); worldIntersect.x = (u * tri.p0.x + v * tri.p1.x + w * tri.p2.x); worldIntersect.y = (u * tri.p0.y + v * tri.p1.y + w * tri.p2.y); worldIntersect.z = (u * tri.p0.z + v * tri.p1.z + w * tri.p2.z); return true; } else { return false; } } glm::vec3 glmFrom(s_point3f point) { return glm::vec3(point.x, point.y, point.z); } My convenience structures are defined as: struct s_point3f { GLfloat x, y, z; }; struct s_triangle3f { s_point3f v1, v2, v3; }; struct vec3ray { glm::vec3 origin, direction; }; struct vec3triangle { glm::vec3 p0, p1, p2; }; vertices is defined as: std::vector<s_triangle3f> vertices; Basically, I'm trying to get the intersect of a ray (which is positioned at the x, and y coordinates specified facing pointing downwards toward the terrain) and one of the two triangles on the grid. getZ() rarely returns anything but 0. Other times, the numbers it generates seem to be completely off. Am I taking the wrong approach? Can anyone see a problem with my code? Any help or critique is appreciated!

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• ray collision with rectangle and floating point accuracy

  - by phq

  I'm trying to solve a problem with a ray bouncing on a box. Actually it is a sphere but for simplicity the box dimensions are expanded by the sphere radius when doing the collision test making the sphere a single ray. It is done by projecting the ray onto all faces of the box and pick the one that is closest. However because I'm using floating point variables I fear that the projected point onto the surface might be interpreted as being below in the next iteration, also I will later allow the sphere to move which might make that scenario more likely. Also the bounce coefficient might be as low as zero, making the sphere continue along the surface. So my naive solution is to project not only forwards but backwards to catch those cases. That is where I got into problems shown in the figure: In the first iteration the first black arrow is calculated and we end up at a point on the surface of the box. In the second iteration the "back projection" hits the other surface making the second black arrow bounce on the wrong surface. If there are several boxes close to each other this has further consequences making the sphere fall through them all. So my main question is how to handle possible floating point accuracy when placing the sphere on the box surface so it does not fall through. In writing this question I got the idea to have a threshold to only accept back projections a certain amount much smaller than the box but larger than the possible accuracy limitation, this would only cause the "false" back projection when the sphere hit the box on an edge which would appear naturally. To clarify my original approach, the arrows shown in the image is not only the path the sphere travels but is also representing a single time step in the simulation. In reality the time step is much smaller about 0.05 of the box size. The path traveled is projected onto possible sides to avoid traveling past a thinner object at higher speeds. In normal situations the floating point accuracy is not an issue but there are two situations where I have the concern. When the new position at the end of the time step is located very close to the surface, very unlikely though. When using a bounce factor of 0, here it happens every time the sphere hit a box. To add some loss of accuracy, the motivation for my concern, is that the sphere and box are in different coordinate systems and thus the sphere location is transformed for every test. This last one is why I'm not willing to stand on luck that one floating point value lying on top of the box always will be interpreted the same. I did not know voronoi regions by name, but looking at it I'm not sure how it would be used in a projection scenario that I'm using here.

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• Java 2D Rectangle Collision? [on hold]

  - by Andreas Elia

  I am just wanting to know of another (longer OR shorter) way of getting 100% effective collisions on a 2D plat-former. The current collision system that is in place works from coords on the level and does not always work reliably. Thank you in advance for any help/support. The current system draws a rectangle and is checking to see if any two points collide. From testing, the system can sometimes "glitch" and allow the player to collide into walls etc. Player Class http://pastebin.com/2zE8vz8R Main Class http://pastebin.com/A6Utb3ti

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• Setting up collision using a tilemap and cocos2d

  - by James

  I'm building my first platformer using cocos2d and a tilemap. I'm having trouble coming up with a decent way of determining if the character is colliding with an object. More specifically, in which direction is the character colliding with an object. Following the tutorial here, I have made a separate "meta" layer of collidable tiles. The problem is that unless the character is in the tile, you can't detect the collision. Also, there's no way of telling WHERE the collision is occurring. The best solution would be one that could tell me if a character is up against a wall, or walking on top of a platform. However, I can't seem to figure out a good technique for this.

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• Meaning of offset in pygame Mask.overlap methods

  - by Alan

  I have a situation in which two rectangles collide, and I have to detect how much did they collide so so I can redraw the objects in a way that they are only touching each others edges. It's a situation in which a moving ball should hit a completely unmovable wall and instantly stop moving. Since the ball sometimes moves multiple pixels per screen refresh, it it possible that it enters the wall with more that half its surface when the collision is detected, in which case i want to shift it position back to the point where it only touches the edges of the wall. Here is the conceptual image it: I decided to implement this with masks, and thought that i could supply the masks of both objects (wall and ball) and get the surface (as a square) of their intersection. However, there is also the offset parameter which i don't understand. Here are the docs for the method: Mask.overlap Returns the point of intersection if the masks overlap with the given offset - or None if it does not overlap. Mask.overlap(othermask, offset) -> x,y The overlap tests uses the following offsets (which may be negative): +----+----------.. |A | yoffset | +-+----------.. +--|B |xoffset | | : :

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• How to fetch only the sprites in the player's range of motion for collision testing? (2D, axis aligned sprites)

  - by Twodordan

  I am working on a 2D sprite game for educational purposes. (In case you want to know, it uses WebGl and Javascript) I've implemented movement using the Euler method (and delta time) to keep things simple. Now I'm trying to tackle collisions. The way I wrote things, my game only has rectangular sprites (axis aligned, never rotated) of various/variable sizes. So I need to figure out what I hit and which side of the target sprite I hit (and I'm probably going to use these intersection tests). The old fashioned method seems to be to use tile based grids, to target only a few tiles at a time, but that sounds silly and impractical for my game. (Splitting the whole level into blocks, having each sprite's bounding box fit multiple blocks I might abide. But if the sprites change size and move around, you have to keep changing which tiles they belong to, every frame, it doesn't sound right.) In Flash you can test collision under one point, but it's not efficient to iterate through all the elements on stage each frame. (hence why people use the tile method). Bottom line is, I'm trying to figure out how to test only the elements within the player's range of motion. (I know how to get the range of motion, I have a good idea of how to write a collisionCheck(playerSprite, targetSprite) function. But how do I know which sprites are currently in the player's vicinity to fetch only them?) Please discuss. Cheers!

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• Camera Collision inside the room model

  - by sanddy

  I am having a problem in Calculating the camera collision for my Room model which consists of sofa, tables and other models. The users shall be moving the camera front, back, rotating so i need to make sure that the camera does not collide with any of the models with in the room. I have treated all my models inside the room by BoundingBox[] and the camera by BoundingSphere. So, far i have implemented collision by looking into the tutorial from http://www.toymaker.info/Games/XNA/html/xna_model_collisions.html which was great. But, I guess the problem lies in the Transformation part. I debugged and found some points to be at Vector(-XXX,-XXX,-XXX) where X is digit. Also i found my radius of some models where too large(in thousand, i just looked into its radius value before converting to BoundingBox). Do I need to scale the model for collision??? Below are my code:- On My LoadContent(): Matrix[] transforms = new Matrix[myModel.Bones.Count]; myModel.CopyAbsoluteBoneTransformsTo(transforms); int index = 0; box = new List<BoundingBox>(); BoundingBox worldModel = Utility.CalculateBoundingBox(myModel); foreach (ModelMesh mesh in myModel.Meshes) { Vector3[] obb = new Vector3[8]; worldModel.GetCorners(obb); Vector3[] asdf = (Vector3[])obb.Clone(); Vector3.Transform(obb, ref transforms[mesh.ParentBone.Index], obb); BoundingBox worldBox = BoundingBox.CreateFromPoints(obb); box.Add(worldBox); index++; } On CameraPosition Update: BoundingSphere bs = new BoundingSphere(this.cameraPos, 5.0f); if (RoomWalkthrough.Utility.CheckCollision(bs, bb)) { // Do Something } Please Help.

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• Turning on collision crashes game

  - by MomentumGaming

  I am getting a null pointer excecption to both my sprite and level. I am working on my mob class, and when I try to move him and the move function is called, the game crashes after checking collision with a null pointer excecption. Taking out the one line that actually checks if the tile located in front of it fixes the problem. Also, if i keep collision ON but don't move the position of the mob (the spider) the game works fine. I will have collision, and the spider appears on the screen, only problem is, getting it to move causes this nasty error that i just can't fix. true Exception in thread "Display" java.lang.NullPointerException at com.apcompsci.game.entity.mob.Mob.collision(Mob.java:67) at com.apcompsci.game.entity.mob.Mob.move(Mob.java:38) at com.apcompsci.game.entity.mob.spider.update(spider.java:58) at com.apcompsci.game.level.Level.update(Level.java:55) at com.apcompsci.game.Game.update(Game.java:128) at com.apcompsci.game.Game.run(Game.java:106) at java.lang.Thread.run(Unknown Source) Here is my renderMob mehtod: public void renderMob(int xp,int yp,Sprite sprite,int flip) { xp -= xOffset; yp-=yOffset; for(int y = 0; y<32; y++) { int ya = y + yp; int ys = y; if(flip == 2||flip == 3)ys = 31-y; for(int x = 0; x<32; x++) { int xa = x + xp; int xs = x; if(flip == 1||flip == 3)xs = 31-x; if(xa < -32 || xa >=width || ya<0||ya>=height) break; if(xa<0) xa =0; int col = sprite.pixels[xs+ys*32]; if(col!= 0x000000) pixels[xa+ya*width] = col; } } } My spider class which determines the sprite and where I control movement, also rendering the spider onto the screen, when I increment ya to move the sprite, I get the crash, but without ya++, it runs flawlessly with a spider sprite on screen: package com.apcompsci.game.entity.mob; import com.apcompsci.game.entity.mob.Mob.Direction; import com.apcompsci.game.graphics.Screen; import com.apcompsci.game.graphics.Sprite; import com.apcompsci.game.level.Level; public class spider extends Mob{ Direction dir; private Sprite sprite; private boolean walking; public spider(int x, int y) { this.x = x <<4; this.y = y <<4; sprite = sprite.spider_forward; } public void update() { int xa = 0, ya = 0; ya++; if(ya<0) { sprite = sprite.spider_forward; dir = Direction.UP; } if(ya>0) { sprite = sprite.spider_back; dir = Direction.DOWN; } if(xa<0) { sprite = sprite.spider_side; dir = Direction.LEFT; } if(xa>0) { sprite = sprite.spider_side; dir = Direction.LEFT; } if(xa!= 0 || ya!= 0) { System.out.println("true"); move(xa,ya); walking = true; } else{ walking = false; } } public void render(Screen screen) { screen.renderMob(x, y, sprite, 0); } } This is th mob class that contains the move() method that is called in the spider class above. This move method calls the collision method. tile and sprite comes up null in the debugger: package com.apcompsci.game.entity.mob; import java.util.ArrayList; import java.util.List; import com.apcompsci.game.entity.Entity; import com.apcompsci.game.entity.projectile.DemiGodProjectile; import com.apcompsci.game.entity.projectile.Projectile; import com.apcompsci.game.graphics.Sprite; public class Mob extends Entity{ protected Sprite sprite; protected boolean moving = false; protected enum Direction { UP,DOWN,LEFT,RIGHT } protected Direction dir; public void move(int xa,int ya) { if(xa != 0 && ya != 0) { move(xa,0); move(0,ya); return; } if(xa>0) dir = Direction.RIGHT; if(xa<0) dir = Direction.LEFT; if(ya>0)dir = Direction.DOWN; if(ya<0)dir = Direction.UP; if(!collision(xa,ya)){ x+= xa; y+=ya; } } public void update() { } public void shoot(int x, int y, double dir) { //dir = Math.toDegrees(dir); Projectile p = new DemiGodProjectile(x, y,dir); level.addProjectile(p); } public boolean collision(int xa,int ya) { boolean solid = false; for(int c = 0; c<4; c++) { int xt = ((x+xa) + c % 2 * 14 - 8 )/16; int yt = ((y+ya) + c / 2 * 12 +3 )/16; if(level.getTile(xt, yt).solid()) solid = true; } return solid; } public void render() { } } Finally, here is the method in which i call the add() method for the spider to add it to the level: protected void loadLevel(String path) { try{ BufferedImage image = ImageIO.read(SpawnLevel.class.getResource(path)); int w = width =image.getWidth(); int h = height = image.getHeight(); tiles = new int[w*h]; image.getRGB(0, 0, w,h, tiles,0, w); } catch(IOException e){ e.printStackTrace(); System.out.println("Exception! Could not load level file!"); } add(new spider(20,45)); } I don't think i need to include the level class but just in case, I have provided a gistHub link for better context. It contains all of the full classes listed above , plus my entity class and maybe another. Thanks for the help if you decide to do so, much appreciated! Also, please tell me if i'm in the wrong section of stackeoverflow, i figured that since this is the gamign section that it belonged but debugging code normally goes into the general section.

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