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D3DXMatrixDecompose gives different quaternion than D3DXQuaternionRotationMatrix

- by Fraser

In trying to solve this problem, I tracked down the problem to the conversion of the rotation matrix to quaternion. In particular, consider the following matrix: -0.02099178 0.9997436 -0.008475631 0 0.995325 0.02009799 -0.09446743 0 0.09427284 0.01041905 0.9954919 0 0 0 0 1 SlimDX.Quaternion.RotationMatrix (which calls D3DXQuaternionRotationMatrix gives a different answer than SlimDX.Matrix.Decompose (which uses D3DXMatrixDecompose). The answers they give (after being normalized) are: X Y Z W Quaternion.RotationMatrix -0.05244324 0.05137424 0.002209336 0.9972991 Matrix.Decompose 0.6989997 0.7135442 -0.03674842 -0.03006023 Which are totally different (note the signs of X, Z, and W are different). Note that these aren't q/-q (two quaternions that represent the same rotation); they face completely different directions. I've noticed that with matrices for rotations very close to that one (successive frames in the animation) that the Matrix.Decompose version gives a solution that flips around wildly and occasionally goes into the desired position, while the Quaternion.RotationMatrix version gives solutions that are stable but go in the wrong direction. This is only for the right arm in my animation -- for the left arm, both functions give the correct solution, which is the same quaternion within error tolerances. This makes me think that there's some sort of numeric instability or weird stuff with signs going on. I tried implementing this and then this, but both gave me a completely incorrect solution (even for the matricies where the SlimDX ones were working correctly) -- maybe the rows and columns are flipped?

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Viewport.Unproject - Checking if a model intersects a large sprite

- by Fibericon

Let's say I have a sprite, drawn like this: spriteBatch.Draw(levelCannons[i].texture, levelCannons[i].position, null, alpha, levelCannons[i].rotation, Vector2.Zero, scale, SpriteEffects.None, 0); Picture levelCannon as being a laser beam that goes across the entire screen. I need to see if my 3d model intersects with the screen space inhabited by the sprite. I managed to dig up Viewport.Unproject, but that seems to only be useful when dealing with a single point in 2d space, rather than an area. What can I do in my case?

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Camera placement sphere for an always fully visible object

- by BengtR

Given an object: With the bounds [x, y, z, width, height, depth] And an orthographic projection [left, right, bottom, top, near, far] I want to determine the radius of a sphere which allows me to randomly place my camera on so that: The object is fully visible from all positions on this sphere The sphere radius is the smallest possible value while still satisfying 1. Assume the object is centered around the origin. How can I find this radius? I'm currently using sqrt(width^2 + height^2 + depth^2) but I'm not sure that's the correct value, as it doesn't take the camera into account. Thanks for any advice. I'm sorry for confusing a few things here. My comments below should clarify what I'm trying to do actually.

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Checking for collisions on a 3D heightmap

- by Piku

I have a 3D heightmap drawn using OpenGL (which isn't important). It's represented by a 2D array of height data. To draw this I go through the array using each point as a vertex. Three vertices are wound together to form a triangle, two triangles to make a quad. To stop the whole mesh being tiny I scale this by a certain amount called 'gridsize'. This produces a fairly nice and lumpy, angular terrain kind of similar to something you'd see in old Atari/Amiga or DOS '3D' games (think Virus/Zarch on the Atari ST). I'm now trying to work out how to do collision with the terrain, testing to see if the player is about to collide with a piece of scenery sticking upwards or fall into a hole. At the moment I am simply dividing the player's co-ordinates by the gridsize to find which vertex the player is on top of and it works well when the player is exactly over the corner of a triangle piece of terrain. However... How can I make it more accurate for the bits between the vertices? I get confused since they don't exist in my heightmap data, they're a product of the GPU trying to draw a triangle between three points. I can calculate the height of the point closest to the player, but not the space between them. I.e if the player is hovering over the centre of one of these 'quads', rather than over the corner vertex of one, how do I work out the height of the terrain below them? Later on I may want the player to slide down the slopes in the terrain.

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How should I choose quadtree depth?

- by Evpok

I'm using a quadtree to prune collision detection pairs in a 2d world. How should I choose to what depth said quadtree is calculated? The world is made mostly of moving objects1, so the cost of dispatching the objects between the quadtree cells matters. What is the relationship between the gain from less collision checking and the loss from more dispatching? How can I strike a balance that performs optimally? 1 To be completely explicit, they are autonomous self-replicating cells competing for food sources. This is an attempt to show my pupils predator-prey dynamics and genetic evolution at work.

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Collision 2D Quads

- by Vico Pelaez

I want to detect collision between two 2D squares, one square is static and the other one moves according to keyboard arrows. I have implemented some code, however nothing happens when they overlap each other and what I tried to achieve in the code was to detect an overlapping between them. I think I am either not understanding the concept really well or that because one of the squares is moving this is not working. Please I would really appreciate your help. Thank you! float x1=0.05 ,Y1=0.05; float x2=0.05 ,Y2=0.05; float posX1 =0.5, posY1 = 0.5; float movX2 = 0.0 , movY2 = 0.0; struct box{ int width=0.1; int heigth=0.1; }; void init(){ glClearColor(0.0, 0.0, 0.0, 0.0); glColor3f(1.0, 1.0, 1.0); } void quad1(){ glTranslatef(posX1, posY1, 0.0); glBegin(GL_POLYGON); glColor3f(0.5, 1.0, 0.5); glVertex2f(-x1, -Y1); glVertex2f(-x1, Y1); glVertex2f(x1,Y1); glVertex2f(x1,-Y1); glEnd(); } void quad2(){ glMatrixMode(GL_PROJECTION); glLoadIdentity(); glPushMatrix(); glTranslatef(movX2, movY2, 0.0); glBegin(GL_POLYGON); glColor3f(1.5, 1.0, 0.5); glVertex2f(-x2, -Y2); glVertex2f(-x2, Y2); glVertex2f(x2,Y2); glVertex2f(x2,-Y2); glEnd(); glPopMatrix(); } void reset(){ //Reset position of square??? movX2 = 0.0; movY2 = 0.0; collisionB = false; } bool collision(box A, box B){ int leftA, leftB; int rightA, rightB; int topA, topB; int bottomA, bottomB; //Calculate the sides of box A leftA = x1; rightA = x1 + A.width; topA = Y1; bottomA = Y1 + A.heigth; //Calculate the sides of box B leftB = x2; rightB = x2 + B.width; topB = Y1; bottomB = Y1+ B.heigth ; if( bottomA <= topB ) return false; if( topA >= bottomB ) return false; if( rightA <= leftB ) return false; if( leftA >= rightB ) return false; return true; } float move_unit = 0.1; void keyboardown(int key, int x, int y) { switch (key){ case GLUT_KEY_UP: movY2 += move_unit; break; case GLUT_KEY_RIGHT: movX2 += move_unit; break; case GLUT_KEY_LEFT: movX2 -= move_unit; break; case GLUT_KEY_DOWN: movY2 -= move_unit; break; default: break; } glutPostRedisplay(); } void display(){ glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glMatrixMode(GL_PROJECTION); glLoadIdentity(); cuad1(); if (!collision) { cuad2(); } else{ reset(); } glFlush(); } int main(int argc, char** argv){ glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize(500,500); glutInitWindowPosition(0, 0); glutCreateWindow("Collision Practice"); glutSpecialFunc(keyboardown); glutDisplayFunc(display); init(); glutMainLoop(); }

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Edge flicker when moving Camera (2D)

- by Matthias Reisner

I have a Orthographic camera. I have a fixed landscape texture and a texture for a moveable object. If the object moves to the right the camera will also move with the object. When I also draw an score text that should have fixed position on the screen, that score text position will be update too if the camera's position gets updated so that it looks like that it is fixed on the screen. But if I do that, I have some edge flickering at the text object. I'am using SpriteBatch! Is there another approach to implement a fixed positioned object on the screen?

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InputLayout handling

- by Kikaimaru

Where are you supposed to store InputLayout? Suppose i have some basic structure like. class Mesh { List<MeshPart> MeshParts } class MeshPart { Effect Effect; VertexBufferBinding VertexBuffer; ... } Where should I store input layout? It's a connection between vertex buffer and specific pass, i can live with just 1 pass but I still have diffferent techniques so i need at least an array with some connection to effecttechniques, but I would appriciate something not crazy like dictionary. I could also create wrapper for Effect and EffectTechnique, but there must be some normal solution.

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Black or White Border/Shadow around PNGs in SDL/OPENGL

- by Dylan

having the same issue as this: Why do my sprites have a dark shadow/line/frame surrounding the texture? however, when I do the fix suggested there (changing GL_SRC_ALPHA to GL_ONE) it just replaces the black border with a white border on the images, and messes with my background color and some polygons I'm drawing (not all of them weirdly) by making them much lighter... any ideas? heres some of my relevant code. init: glMatrixMode(GL_PROJECTION); glLoadIdentity(); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glEnable(GL_DEPTH_TEST); glEnable(GL_MULTISAMPLE); glEnable(GL_TEXTURE_2D); glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); glAlphaFunc(GL_GREATER, 0.01); glEnable(GL_ALPHA_TEST); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); glEnable(GL_BLEND); when each texture is loaded: glGenTextures(1, &textureID); glBindTexture(GL_TEXTURE_2D, textureID); gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGBA, surface->w, surface->h, GL_BGRA, GL_UNSIGNED_BYTE, surface->pixels); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

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Threading iPhone

- by bobobobo

Say I have a group of large meshes that I have to intersect rays against. Assume also, for whatever reason, I cannot further simplify/reduce poly check count by spatial subdivisioning. I can do this in parallel: bool intersects( list of meshes ) // a mesh is a group of triangles { create n threads foreach mesh in meshes assign to a thread in threads wait until ( threads.run() ) ; // run asynchronously // when they're all done // pull out intersected triangles // from per-thread context data } Can you do this in ios for games? Or is the overhead of thread creation and mutex waiting going to beat-out the benefit of multithreading?

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OpenGL render to texture causing edge artifacts

- by mysticalOso

This is my first post here so any help would be massively appreciated :) I'm using C++ with SDL and OpenGL 3.3 When rendering directly to screen I get the following result And when I render to texture I this happens Anti-aliasing is turned off for both. I'm guessing this has something to do with depth buffer accuracy but I've tried a lot of different methods to improve the result but, no success :( I'm currently using the following code to set up my FBO: GLuint frameBufferID; glGenFramebuffers(1, &frameBufferID); glBindFramebuffer(GL_FRAMEBUFFER, frameBufferID); glGenTextures(1, &coloursTextureID); glBindTexture(GL_TEXTURE_2D, coloursTextureID); glTexImage2D(GL_TEXTURE_2D,0,GL_RGB,SCREEN_WIDTH,SCREEN_HEIGHT,0,GL_RGB,GL_UNSIGNED_BYTE,NULL); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); //Depth buffer setup GLuint depthrenderbuffer; glGenRenderbuffers(1, &depthrenderbuffer); glBindRenderbuffer(GL_RENDERBUFFER, depthrenderbuffer); glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, SCREEN_WIDTH,SCREEN_HEIGHT); glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthrenderbuffer); glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, coloursTextureID, 0); GLenum DrawBuffers[1] = {GL_COLOR_ATTACHMENT0}; glDrawBuffers(1, DrawBuffers); // if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) return false; Thank you so much for any help :)

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Binding BoundingSpheres to a world matrix in XNA

- by NDraskovic

I made a program that loads the locations of items on the scene from a file like this: using (StreamReader sr = new StreamReader(OpenFileDialog1.FileName)) { String line; while ((line = sr.ReadLine()) != null) { red = line.Split(','); model = row[0]; x = row[1]; y = row[2]; z = row[3]; elements.Add(Convert.ToInt32(model)); data.Add(new Vector3(Convert.ToSingle(x), Convert.ToSingle(y), Convert.ToSingle(z))); sfepheres.Add(new BoundingSphere(new Vector3(Convert.ToSingle(x), Convert.ToSingle(y), Convert.ToSingle(z)), 1f)); } I also have a list of BoundingSpheres (called spheres) that adds a new bounding sphere for each line from the file. In this program I have one item (a simple box) that moves (it has its world matrix called matrixBox), and other items are static entire time (there is a world matrix that holds those elements called simply world). The problem i that when I move the box, bounding spheres move with it. So how can I bind all BoundingSpheres (except the one corresponding to the box) to the static world matrix so that they stay in their place when the box moves?

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C++ Directx 11 D3DXVECTOR3 doesn't allow me to devide it

- by Miguel P

If i have a simple vector3 like this: D3DXVECTOR3 inversevector = D3DXVECTOR3( (pos+lookat_pos)); It works perfect! But let's say i wanted to multiply it by: Speed*(float) timeHandler.GetDelta() So: D3DXVECTOR3 inversevector = D3DXVECTOR3( (pos+lookat_pos) * Speed*(float) timeHandler.GetDelta()); Now this fails completely, i've used this snippet before, but for some wierd reason it simply won't work( The vector somehow leads x,y,z to 0 or almost, no idea why). Do you have any idea why?

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glTranslate, how exactly does it work?

- by mykk

I have some trouble understanding how does glTranslate work. At first I thought it would just simply add values to axis to do the transformation. However then I have created two objects that would load bitmaps, one has matrix set to GL_TEXTURE: public class Background { float[] vertices = new float[] { 0f, -1f, 0.0f, 4f, -1f, 0.0f, 0f, 1f, 0.0f, 4f, 1f, 0.0f }; .... private float backgroundScrolled = 0; public void scrollBackground(GL10 gl) { gl.glLoadIdentity(); gl.glMatrixMode(GL10.GL_MODELVIEW); gl.glTranslatef(0f, 0f, 0f); gl.glPushMatrix(); gl.glLoadIdentity(); gl.glMatrixMode(GL10.GL_TEXTURE); gl.glTranslatef(backgroundScrolled, 0.0f, 0.0f); gl.glPushMatrix(); this.draw(gl); gl.glPopMatrix(); backgroundScrolled += 0.01f; gl.glLoadIdentity(); } } and another to GL_MODELVIEW: public class Box { float[] vertices = new float[] { 0.5f, 0f, 0.0f, 1f, 0f, 0.0f, 0.5f, 0.5f, 0.0f, 1f, 0.5f, 0.0f }; .... private float boxScrolled = 0; public void scrollBackground(GL10 gl) { gl.glMatrixMode(GL10.GL_MODELVIEW); gl.glLoadIdentity(); gl.glTranslatef(0f, 0f, 0f); gl.glPushMatrix(); gl.glMatrixMode(GL10.GL_MODELVIEW); gl.glLoadIdentity(); gl.glTranslatef(boxScrolled, 0.0f, 0.0f); gl.glPushMatrix(); this.draw(gl); gl.glPopMatrix(); boxScrolled+= 0.01f; gl.glLoadIdentity(); } } Now they are both drawn in Renderer.OnDraw. However background moves exactly 5 times faster. If I multiply boxScrolled by 5 they will be in sinc and will move together. If I modify backgrounds vertices to be float[] vertices = new float[] { 1f, -1f, 0.0f, 0f, -1f, 0.0f, 1f, 1f, 0.0f, 0f, 1f, 0.0f }; It will also be in sinc with the box. So, what is going under glTranslate?

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Questions before I revamp my rendering engine to use shaders (GLSL)

- by stephelton

I've written a fairly robust rendering engine using OpenGL ES 1.1 (fixed-function.) I've been looking into revamping the engine to use OpenGL ES 2.0, which necessitates that I use shaders. I've been absorbing information all day long and still have some questions. Firstly, lighting. The fixed-function pipeline is guaranteed to have at least 8 lights available. My current engine finds lights that are "close" to the primitives being drawn and enables them; I don't know how many lights are going to be enabled until I draw a given model. Nothing is dynamically allocated in GLSL, so I have to define in a shader some number of lights to be used, right? So if I want to stick with 8, should I write my general purpose shader to have 8 lights and then use uniforms to tell it how many / which lights to use? Which brings me to another question: should I be concerned with the amount of data I'm allocating in a shader? Recent video cards have hundreds of "stream processors." If I've got a fragment shader being used on some number of fragments in a given triangle, I assume they must each have their own stack to work on. Are read-only variables copied here, or read when needed? My initial goal is to rework my code so that it is virtually identical to the current implementation. What I have in mind is to create my own matrix stack so that I can implement something along the lines of push/popMatrix and apply all my translations, rotations, and scales to this matrix, then provide the matrix to the vertex shader so that it can make very quick vertex translations. Is this approach sound? Edit: My original intention was to ask if there was a tutorial that would explain the bare minimum necessary to jump from fixed-function to using shaders. Thanks!

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want to build a replica of chartgame.com

- by raj

I want to develop a trading simulator based on technical analysis. my ideal application would exactly be chartgame.com currently chartgame.com doesnt have historical data for stocks beyond the year 2008 and I would like to have data until 2012 and have the capability to extend beyond if needed. what are the fundamentals to build an application like chartgame.com. If anyone here is willing to help I can arrange for the finances.let me know.

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Changing coordinate system from Z-up to Y-up

- by Jari Komppa

Blender's coordinate system is different from what I'm used to, in that Z points upwards instead of Y. What would be the simplest way of converting all the world data (so that all animations, texture coordinates, etc still work) so that Y points upwards? Clarification: Object positions are defined as matrices, so just switching translation/rotation/scale information in matrices is not a trivial task.

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How to split a string with negative numbers using ActionScript 3.0

- by inzombiak

I'm having trouble loading my level. I'm using Ogmo to create my level then I import it. I have no problem converting 0's and 1's into an Array, but I can't figure out how to do the same for -1's. It separates the "-" and the "1". Any help would be great. I've posted my code and the XML files below levelXML = new XML(e.target.data); playerX = int(levelXML.Entities.Player.@x); playerY = int(levelXML.Entities.Player.@y); levelGrid = levelXML.Grid; levelGrid = levelGrid.split("\n").join(""); levelTiles = levelXML.Tiles; levelTiles = levelTiles.split("\n").join(""); levelTiles = levelTiles.split(",").join(""); tileArray = levelTiles.split(""); gridArray = levelGrid.split(""); for(i = 0; i <= 34; i++) { levelArray[i] = new Array(); for(j = 0; j <= 34; j++) { if(tileArray[j*35 + i] == 0) { gridArray[j*35+i] = -1; } var currentSymbol = gridArray[j*35+i]; levelArray[i][j] = currentSymbol; if(gridArray[j*35 + i] == 1) { wall = new Wall; addChild(wall); wall.x = i*20 + 10; wall.y = j*20 + 10; } else if(gridArray[j*35 + i] == -1) { pellet = new Pellet; addChild(pellet); pellet.x = i*20 + 10; pellet.y = j*20 + 10; } } } I know the code is very dirty, but I needed a quick fix. 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What is going on in this SAT/vector projection code?

- by ssb

I'm looking at the example XNA SAT collision code presented here: http://www.xnadevelopment.com/tutorials/rotatedrectanglecollisions/rotatedrectanglecollisions.shtml See the following code: private int GenerateScalar(Vector2 theRectangleCorner, Vector2 theAxis) { //Using the formula for Vector projection. Take the corner being passed in //and project it onto the given Axis float aNumerator = (theRectangleCorner.X * theAxis.X) + (theRectangleCorner.Y * theAxis.Y); float aDenominator = (theAxis.X * theAxis.X) + (theAxis.Y * theAxis.Y); float aDivisionResult = aNumerator / aDenominator; Vector2 aCornerProjected = new Vector2(aDivisionResult * theAxis.X, aDivisionResult * theAxis.Y); //Now that we have our projected Vector, calculate a scalar of that projection //that can be used to more easily do comparisons float aScalar = (theAxis.X * aCornerProjected.X) + (theAxis.Y * aCornerProjected.Y); return (int)aScalar; } I think the problems I'm having with this come mostly from translating physics concepts into data structures. For example, earlier in the code there is a calculation of the axes to be used, and these are stored as Vector2, and they are found by subtracting one point from another, however these points are also stored as Vector2s. So are the axes being stored as slopes in a single Vector2? Next, what exactly does the Vector2 produced by the vector projection code represent? That is, I know it represents the projected vector, but as it pertains to a Vector2, what does this represent? A point on a line? Finally, what does the scalar at the end actually represent? It's fine to tell me that you're getting a scalar value of the projected vector, but none of the information I can find online seems to tell me about a scalar of a vector as it's used in this context. I don't see angles or magnitudes with these vectors so I'm a little disoriented when it comes to thinking in terms of physics. If this final scalar calculation is just a dot product, how is that directly applicable to SAT from here on? Is this what I use to calculate maximum/minimum values for overlap? I guess I'm just having trouble figuring out exactly what the dot product is representing in this particular context. Clearly I'm not quite up to date on my elementary physics, but any explanations would be greatly appreciated.

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Why doesn't light continuous on my model?

- by nosferat

I created a basic textured cube model with Blender to practice modeling, and then I imported it into Unity. After I put up some lighting it looks pretty ugly. The light is not continuous on a row of textured cubes: What is more odd, the light on the blocks that makes up the floor is continuous. What am I doing wrong? UPDATE This is how it looks like without textures: https://dl.dropbox.com/u/45620018/without%20textures.PNG If I would not know that these are perfect cubes, I'd say there is a slight curve on surface. I also tried lightening the texture but it also didn't help: https://dl.dropbox.com/u/45620018/lighter%20texture.PNG I just simply exported the model from Blender and did not set up any normals or things like that. However I also did not do any special woth the floor brick model.

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How do I use unpackHalf2x16?

- by user1032861

I'm trying to use (un)packHalf2x16, without success so far. I'm drawing with: glVertexAttribIPointer(0, 2, GL_UNSIGNED_INT, 0, 0); glEnableVertexAttribArray(0); glBindBuffer(GL_ARRAY_BUFFER, vbo); glDrawArrays(GL_POINTS, 0, n_points); glDisableVertexAttribArray(0); and on the shader #version 330 core #extension GL_ARB_shading_language_packing : require in uvec2 A0; // (...) vec4 t = vec4(unpackHalf2x16(A0.x), unpackHalf2x16(A0.y)); But nothing gets drawn. I'm pretty sure buffer's content is right, and if I use vec4 t = vec4(0); I can see it's working properly. How is this packing / unpacking thing supposed to work? I can't find any example.

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applyAngularVelocity causes error when called right after object instantiation

- by Appeltaart

I'm trying to make a physicsBody rotate as soon as it is instantiated. CCNode* ball = [CCBReader load:@"Ball"]; [ball.physicsBody applyForce:force]; [ball.physicsBody applyAngularImpulse:arc4random_uniform(360) - 180]; Applying force works fine, the last line however throws an error in cpBody.c line 123: cpAssertHard(body->w == body->w && cpfabs(body->w) != INFINITY, "Body's angular velocity is invalid."); When I don't apply force and merely rotate the problem persists. If I send applyAngularImpulse at some later point (in this case on a touch) it does work. Is this function not supposed to be called right after instantiation, or is this a bug?

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Collision detection - player gets stuck in platform when jumping

- by Sun

So I'm having some problems with my collision detection with my platformer. Take the image below as an example. When I'm running right I am unable to go through the platform, but when I hold my right key and jump, I end up going through the object as shown in the image, below is the code im using: if(shapePlatform.intersects(player.getCollisionShape())){ Vector2f vectorSide = new Vector2f(shapePlatform.getCenter()[0] - player.getCollisionShape().getCenter()[0], shapePlatform.getCenter()[1] - player.getCollisionShape().getCenter()[1]); player.setVerticleSpeed(0f); player.setJumping(false); if(vectorSide.x > 0 && !(vectorSide.y > 0)){ player.getPosition().set(player.getPosition().x-3, player.getPosition().y); }else if(vectorSide.y > 0){ player.getPosition().set(player.getPosition().x, player.getPosition().y); }else if(vectorSide.x < 0 && !(vectorSide.y > 0)){ player.getPosition().set(player.getPosition().x+3, player.getPosition().y); } } I'm basically getting the difference between the centre of the player and the centre of the colliding platform to determine which side the player is colliding with. When my player jumps and walks right on the platform he goes right through. The same can also be observed when I jump on the actual platform, should I be resetting the players y in this situation?

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How do I draw a dotted or dashed line?

- by Gagege

I'm trying to draw a dashed or dotted line by placing individual segments(dashes) along a path and then separating them. The only algorithm I could come up with for this gave me a dash length that was variable based on the angle of the line. Like this: private function createDashedLine(fromX:Float, fromY:Float, toX:Float, toY:Float):Sprite { var line = new Sprite(); var currentX = fromX; var currentY = fromY; var addX = (toX - fromX) * 0.0075; var addY = (toY - fromY) * 0.0075; line.graphics.lineStyle(1, 0xFFFFFF); var count = 0; // while line is not complete while (!lineAtDestination(fromX, fromY, toX, toY, currentX, currentY)) { /// move line draw cursor to beginning of next dash line.graphics.moveTo(currentX, currentY); // if dash is even if (count % 2 == 0) { // draw the dash line.graphics.lineTo(currentX + addX, currentY + addY); } // add next dash's length to current cursor position currentX += addX; currentY += addY; count++; } return line; } This just happens to be written in Haxe, but the solution should be language neutral. What I would like is for the dash length to be the same no matter what angle the line is. As is, it's just adding 75 thousandths of the line length to the x and y, so if the line is and a 45 degree angle you get pretty much a solid line. If the line is at something shallow like 85 degrees then you get a nice looking dashed line. So, the dash length is variable, and I don't want that. How would I make a function that I can pass a "dash length" into and get that length of dash, no matter what the angle is? If you need to completely disregard my code, be my guest. I'm sure there's a better solution.

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Set Position of multiple bodies

- by philipp

I have a character composed of five bodies which are tied together by a lot of joints. On of them is the overall chassis, to which all forces and impulses are applied to move the whole Character. All in all that works very fine, except one thing: I need to set the Position of the Character so that it get Beamed from one place to the other in one single frame. Unfortunately I cannot get this to work. I tried the following code, without any success… playerbodies.forEach(function (bd) { bd.SetLinearVelocity(new b2.Vec2()); var t = bd.GetTransform(); t.p.x -= 10; bd.SetTransform(t, bd.GetAngle()); }); How can I make that happen?

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