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  • Platformer gravity where gravity is greater than tile size

    - by Sara
    I am making a simple grid-tile-based platformer with basic physics. I have 16px tiles, and after playing with gravity it seems that to get a nice quick Mario-like jump feel, the player ends up moving faster than 16px per second at the ground. The problem is that they clip through the first layer of tiles before collisions being detected. Then when I move the player to the top of the colliding tile, they move to the bottom-most tile. I have tried limiting their maximum velocity to be less than 16px but it does not look right. Are there any standard approaches to solving this? Thanks.

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  • Rotating object along bezier curve: not rotating enough?

    - by Paul
    I tried to follow the instructions from the threads on the forum (Cocos2d rotating sprite while moving with CCBezierBy) with Unity, in order to rotate my object as it moves along a bezier curve. But it does not rotate enough, the angle is too low, it goes up to 6 instead of 90 for example, as you can see on this image (the y eulerAngle is at 6, I would expect it to be around 90 with this curve) : Would you know why it does this? And how to make the rotation toward the next point? Here is the code (in c# with Unity) : (I am comparing x and z to get the angle, and adding the angle to eulerAngles.y so that it rotates around the y axis) void Update () { if ( Input.GetKey("d") ) start = true; if ( start ){ myTime = Time.time; start = false; } float theTime = (Time.time - myTime) *0.5f; if ( theTime < 1 ) { car.position = Spline.Interp( myArray, theTime );//creates the bezier curve counterBezier += Time.deltaTime; //compare 2 positions after 0.1f if ( counterBezier > 0.1f ){ counterBezier = 0; cbDone = false; newpos = car.position; float angle = Mathf.Atan2(newpos.z - oldpos.z, newpos.x - oldpos.x); angle += car.eulerAngles.y; car.eulerAngles = new Vector3(0,angle,0); } else if ( counterBezier > 0 && !cbDone ){ oldpos = car.position; cbDone = true; } Thanks

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  • How can I implement collision detection for these tiles?

    - by Fiona
    I am wondering how this would be possible, if at all. In the image below: http://i.stack.imgur.com/d8cO3.png The light brows tiles are ground, while the dark brown is background, so the player can pass over those tiles. Here's the for loops that draws the level: float scale = 1f; for (row = 0; row < currentLevel.Rows; row++) { for (column = 0; column < currentLevel.Columns; column++) { Tile tile = (Tile)currentLevel.GetTile(row, column); if (tile == null) { continue; } Texture2D texture = tile.Texture; spriteBatch.Draw(texture, new Microsoft.Xna.Framework.Rectangle( (int)(column * currentLevel.CellSize.X * scale), (int)(row * currentLevel.CellSize.Y * scale), (int)(currentLevel.CellSize.X * scale), (int)(currentLevel.CellSize.Y * scale)), Microsoft.Xna.Framework.Color.White); } } Here's what I have so far to determine where to create a Rectangle: Microsoft.Xna.Framework.Rectangle[,,,] groundBounds = new Microsoft.Xna.Framework.Rectangle[?, ?, ?, ?]; int tileSize = 20; int screenSizeInTiles = 30; var tilePositions = new System.Drawing.Point[screenSizeInTiles, screenSizeInTiles]; for (int x = 0; x < screenSizeInTiles; x++) { for (int y = 0; y < screenSizeInTiles; y++) { tilePositions[x, y] = new System.Drawing.Point(x * tileSize, y * tileSize); groundBounds[x, y, tileSize, tileSize] = new Microsoft.Xna.Framework.Rectangle(x, y, 20, 20); } } First off, I'm not sure how to initialize the array groundBounds (I don't know how big to make it). Also, I'm not entirely sure how to go about adding information to groundBounds. I want to add a Rectangle for each tile in the level. Preferably I'd only make a Rectangle for those tiles accessible by the player, and not background tiles, but that's for a different day. FYI, the map was made with a freeware program called Realm Factory.

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  • extrapolating object state based on updates

    - by user494461
    I have a networked multi-user collaborative application. To maintain a consistent virtual world, I send updates for objects from a master peer to a guest peer. The update state contains x,y,z coordinates of object center and his rotation matrix(CHAI3d api used a 3x3 matrix) with 30Hz frequency. I want to reduce this update rate and want to send with a reduced update rate. I want a predictor on both peers. When the predicted value is outside, say a error value of 10% in comparison to master peers objects original state the master peer triggers a state update. Now for position I used velocity,position updates so that the guest peer can extrapolate position. Like velocity for position what parameter should I use for rotation extrapolition?

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  • Why does Farseer 2.x store temporaries as members and not on the stack? (.NET)

    - by Andrew Russell
    UPDATE: This question refers to Farseer 2.x. The newer 3.x doesn't seem to do this. I'm using Farseer Physics Engine quite extensively at the moment, and I've noticed that it seems to store a lot of temporary value types as members of the class, and not on the stack as one might expect. Here is an example from the Body class: private Vector2 _worldPositionTemp = Vector2.Zero; private Matrix _bodyMatrixTemp = Matrix.Identity; private Matrix _rotationMatrixTemp = Matrix.Identity; private Matrix _translationMatrixTemp = Matrix.Identity; public void GetBodyMatrix(out Matrix bodyMatrix) { Matrix.CreateTranslation(position.X, position.Y, 0, out _translationMatrixTemp); Matrix.CreateRotationZ(rotation, out _rotationMatrixTemp); Matrix.Multiply(ref _rotationMatrixTemp, ref _translationMatrixTemp, out bodyMatrix); } public Vector2 GetWorldPosition(Vector2 localPosition) { GetBodyMatrix(out _bodyMatrixTemp); Vector2.Transform(ref localPosition, ref _bodyMatrixTemp, out _worldPositionTemp); return _worldPositionTemp; } It looks like its a by-hand performance optimisation. But I don't see how this could possibly help performance? (If anything I think it would hurt by making objects much larger).

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  • Can not remove cube in UDK

    - by user32228
    For some reason, I can't move or remove an 'invisible' cube which is on my map. I searched on Google to find a solution but somehow I still can't remove it. The cube looks like this: http://screencloud.net/v/uNyz In Brush Wireframe: http://screencloud.net/v/3C0c In Wireframe: screencloud.net/v/oGBj As you can see, I want to delete the brown cube. Selecting it and pressing the DEL button won't do anything. So, how do you delete the brown cube? EDIT: Seriously, I wrote this post a few minutes ago and I found the solution. However, I still don't know how to delete the brown cube.

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  • How do you author HDR content?

    - by Nathan Reed
    How do you make it easy for your artists to author content for an HDR renderer? What kinds of tools should you provide, and what workflows need to change, in going from LDR to HDR? Note that I'm not asking about the technical aspects of implementing an HDR renderer, but about best practices for creating materials and lighting in HDR. I've googled around a bit, but there doesn't seem to be much about this topic on the web. Can anyone point me to some good resources on this, or share their own experiences? Some specific points: Lighting - how can lighting artists pick HDR light colors? Do they have a standard LDR color picker and then a multiplier? Is the multiplier in gamma or linear space? Maybe instead of a multiplier it's a log-luminance? Or a physical brightness level, like the number of lumens? How will they know what multiplier/luminance/brightness is "correct" for a given light? Materials - how can texture artists make emissive color maps, such as neon signs, TV screens, skyboxes, etc? Can you paint one as a regular LDR (8-bit-per-channel) image and apply a multiplier (or log-luminance, etc.)? Are there cases where it's necessary to actually paint HDR images? If so, how do you go about this in Photoshop (or other software)?

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  • Using Ogre particle point billboards with shaders

    - by Jay
    I'm learning about using Ogre particles and had some questions about how the point type particles work. Q. I believe point type particles are implemented as a single position. Is one single vertex is passed to the vertex shader? Q. If one vertex is passed to the vertex shader then what gets sent to the fragment shader? Q. Can I pass the particle size to the shader? Perhaps with a custom parameter?

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  • Cocos2d-x 3.0 animation frame by frame

    - by Narek
    As I know animations are actions. Now I need to play animation frame by frame. Say I have an animation from N frames. each frame should be played after t delay. Now I want to play animation frame by frame, each frame advance the animation's state. How I can do this? And what about playing actions frame by frame advancing the state in general. I ask because I use ECS, and I deal with frames. P.S. I want to do something like this: Action * a = MoveTo(initialPoint, finalPoint, durationOfAnimation); a->play(0.001 seconds); a->play(0.003 seconds); a->play(0.02 seconds); a->play(0.67 seconds); a->play(0.06 seconds); And see the animation.

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  • SFML programs fails to debug with glslDevil

    - by Zhen
    I'm testing the glslDevil debugger with a simple (and working) SFML application in Linux + NVidia. But it always fails in the window creation step: W! Program Start | glXGetConfig(0x86a50b0, 0x86acef8, 4, 0xbf8228c4) | glXGetConfig(0x86a50b0, 0x86acef8, 5, 0xbf8228c8) | glXGetConfig(0x86a50b0, 0x86acef8, 8, 0xbf8228cc) | glXGetConfig(0x86a50b0, 0x86acef8, 9, 0xbf8228d0) | glXGetConfig(0x86a50b0, 0x86acef8, 10, 0xbf8228d4) | glXGetConfig(0x86a50b0, 0x86acef8, 11, 0xbf8228d8) | glXGetConfig(0x86a50b0, 0x86acef8, 12, 0xbf8228dc) | glXGetConfig(0x86a50b0, 0x86acef8, 13, 0xbf8228e0) | glXGetConfig(0x86a50b0, 0x86acef8, 100000, 0xbf8228e4) | glXGetConfig(0x86a50b0, 0x86acef8, 100001, 0xbf8228e8) | glXCreateContext(0x86a50b0, 0x86acef8, (nil), 1) E! Child process exited W! Program termination forced! And the code that fails: #include <SFML/Graphics.hpp> #define GL_GLEXT_PROTOTYPES 1 #define GL3_PROTOTYPES 1 #include <GL/gl.h> #include <GL/glu.h> #include <GL/glext.h> int main(){ sf::RenderWindow window{ sf::VideoMode(800, 600), "Test SFML+GL" }; bool running = true; while( running ){ sf::Event event; while( window.pollEvent(event) ){ if( event.type == sf::Event::Closed ){ running = false; }else if(event.type == sf::Event::Resized){ glViewport(0, 0, event.size.width, event.size.height); } } window.display(); } return 0; } Is It posible to solve this problem? or get around the problem to continue the gslsDevil use?.

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  • What is a better abstraction layer for D3D9 and OpenGL vertex data management?

    - by Sam Hocevar
    My rendering code has always been OpenGL. I now need to support a platform that does not have OpenGL, so I have to add an abstraction layer that wraps OpenGL and Direct3D 9. I will support Direct3D 11 later. TL;DR: the differences between OpenGL and Direct3D cause redundancy for the programmer, and the data layout feels flaky. For now, my API works a bit like this. This is how a shader is created: Shader *shader = Shader::Create( " ... GLSL vertex shader ... ", " ... GLSL pixel shader ... ", " ... HLSL vertex shader ... ", " ... HLSL pixel shader ... "); ShaderAttrib a1 = shader->GetAttribLocation("Point", VertexUsage::Position, 0); ShaderAttrib a2 = shader->GetAttribLocation("TexCoord", VertexUsage::TexCoord, 0); ShaderAttrib a3 = shader->GetAttribLocation("Data", VertexUsage::TexCoord, 1); ShaderUniform u1 = shader->GetUniformLocation("WorldMatrix"); ShaderUniform u2 = shader->GetUniformLocation("Zoom"); There is already a problem here: once a Direct3D shader is compiled, there is no way to query an input attribute by its name; apparently only the semantics stay meaningful. This is why GetAttribLocation has these extra arguments, which get hidden in ShaderAttrib. Now this is how I create a vertex declaration and two vertex buffers: VertexDeclaration *decl = VertexDeclaration::Create( VertexStream<vec3,vec2>(VertexUsage::Position, 0, VertexUsage::TexCoord, 0), VertexStream<vec4>(VertexUsage::TexCoord, 1)); VertexBuffer *vb1 = new VertexBuffer(NUM * (sizeof(vec3) + sizeof(vec2)); VertexBuffer *vb2 = new VertexBuffer(NUM * sizeof(vec4)); Another problem: the information VertexUsage::Position, 0 is totally useless to the OpenGL/GLSL backend because it does not care about semantics. Once the vertex buffers have been filled with or pointed at data, this is the rendering code: shader->Bind(); shader->SetUniform(u1, GetWorldMatrix()); shader->SetUniform(u2, blah); decl->Bind(); decl->SetStream(vb1, a1, a2); decl->SetStream(vb2, a3); decl->DrawPrimitives(VertexPrimitive::Triangle, NUM / 3); decl->Unbind(); shader->Unbind(); You see that decl is a bit more than just a D3D-like vertex declaration, it kinda takes care of rendering as well. Does this make sense at all? What would be a cleaner design? Or a good source of inspiration?

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  • What tools do you use for 2D art/sprite creation?

    - by daemious
    What cheap/free tools do you use for 2D art and/or animation? I don't really like Gimp's interface, Paint.NET is limited and GraphicsGale is sort of archaic. Cosmigo ProMotion looks like it could be good, anyone use it? Seems a bit pricey at $78/92 but of course cheaper than Photoshop. I used to like Jasc Paint Shop Pro 7, but the newer versions Corel makes are more for photos. 2D Bones support would be handy also.

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  • Efficient visualization of a large voxelized volume

    - by Alejandro Piad
    Lets consider a large voxelized volume stored in an oct-tree or any other convenient structure. This volume represents, for instance, a landscape, where each block is either empty (air), or it has an specific material that will be later used to apply a texture. Voxels that are next to each other represent connected sections of the surface. What I need is an algorithm to generate a mesh from this voxels that represents the volume, with the following caracteristics: All the "holes" in the voxelized volume are correct. All the connections are correct, i.e. seamless. The surface appears smooth. In a broad sense, I want to somehow preserve the surface topology, meaning that connected sections remain connected in the resulting mesh and that the surface has a curvature that responds to the voxels topology. Imagine trying to render the Minecraft world but getting the mountain ladders to be smooth instead of blocky.

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  • How do I draw a scene with 2 nested frames

    - by Guido Granobles
    I have been trying for long time to figure out this: I have loaded a model from a directx file (I am using opengl and Java) the model have a hierarchical system of nested reference frames (there are not bones). There are just 2 frames, one of them is called x3ds_Torso and it has a child frame called x3ds_Arm_01. Each one of them has a mesh. The thing is that I can't draw the arm connected to the body. Sometimes the body is in the center of the screen and the arm is at the top. Sometimes they are both in the center. I know that I have to multiply the matrix transformation of every frame by its parent frame starting from the top to the bottom and after that I have to multiply every vertex of every mesh by its final transformation matrix. So I have this: public void calculeFinalMatrixPosition(Bone boneParent, Bone bone) { System.out.println("-->" + bone.name); if (boneParent != null) { bone.matrixCombined = bone.matrixTransform.multiply(boneParent.matrixCombined); } else { bone.matrixCombined = bone.matrixTransform; } bone.matrixFinal = bone.matrixCombined; for (Bone childBone : bone.boneChilds) { calculeFinalMatrixPosition(bone, childBone); } } Then I have to multiply every vertex of the mesh: public void transformVertex(Bone bone) { for (Iterator<Mesh> iterator = meshes.iterator(); iterator.hasNext();) { Mesh mesh = iterator.next(); if (mesh.boneName.equals(bone.name)) { float[] vertex = new float[4]; double[] newVertex = new double[3]; if (mesh.skinnedVertexBuffer == null) { mesh.skinnedVertexBuffer = new FloatDataBuffer( mesh.numVertices, 3); } mesh.vertexBuffer.buffer.rewind(); while (mesh.vertexBuffer.buffer.hasRemaining()) { vertex[0] = mesh.vertexBuffer.buffer.get(); vertex[1] = mesh.vertexBuffer.buffer.get(); vertex[2] = mesh.vertexBuffer.buffer.get(); vertex[3] = 1; newVertex = bone.matrixFinal.transpose().multiply(vertex); mesh.skinnedVertexBuffer.buffer.put(((float) newVertex[0])); mesh.skinnedVertexBuffer.buffer.put(((float) newVertex[1])); mesh.skinnedVertexBuffer.buffer.put(((float) newVertex[2])); } mesh.vertexBuffer = new FloatDataBuffer( mesh.numVertices, 3); mesh.skinnedVertexBuffer.buffer.rewind(); mesh.vertexBuffer.buffer.put(mesh.skinnedVertexBuffer.buffer); } } for (Bone childBone : bone.boneChilds) { transformVertex(childBone); } } I know this is not the more efficient code but by now I just want to understand exactly how a hierarchical model is organized and how I can draw it on the screen. Thanks in advance for your help.

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  • Sphere-Sphere intersection and Circle-Sphere intersection

    - by cagirici
    I have code for circle-circle intersection. But I need to expand it to 3-D. How do I calculate: Radius and center of the intersection circle of two spheres Points of the intersection of a sphere and a circle? Given two spheres (sc0,sr0) and (sc1,sr1), I need to calculate a circle of intersection whose center is ci and whose radius is ri. Moreover, given a sphere (sc0,sr0) and a circle (cc0, cr0), I need to calulate the two intersection points (pi0, pi1) I have checked this link and this link, but I could not understand the logic behind them and how to code them. I tried ProGAL library for sphere-sphere-sphere intersection, but the resulting coordinates are rounded. I need precise results.

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  • Trade offs of linking versus skinning geometry

    - by Jeff
    What are the trade offs between inherent in linking geometry to a node versus using skinned geometry? Specifically: What capabilities do you gain / lose from using each method? What are the performance impacts of doing one over the other? What are the specific situations where you would want to do one over the other? In addition, do the answers to these questions tend to be engine specific? If so, how much?

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  • Multiple Key Presses in XNA?

    - by Bryan Harrington
    I'm actually trying to do something fairly simple. I cannot get multiple key presses to work in XNA. I've tried the following pieces of code. else if (keyboardState.IsKeyDown(Keys.Down) && (keyboardState.IsKeyDown(Keys.Left))) { //Move Character South-West } and I tried. else if (keyboardState.IsKeyDown(Keys.Down)) { if (keyboardState.IsKeyDown(Keys.Left)) { //Move Character South-West } } Neither worked for me. Single presses work just fine. Any thoughts?

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  • 3DS Max exporting too many vertexes for model

    - by Juan Pablo
    I have a sample model of a cube and a buddha downloaded from internet in 3ds format which I can load correctly into my program and view them without problem, but wanted to try and create my own model. I created a simple box mesh in 3ds max, and exported it as .3ds (Converted to mesh - export as .3ds) When inspecting the .3ds file with a hex viewer, I was expecting to see 8 vertexes and 12 faces declared (as the model I downloaded from internet). But what i found was that it listed 26 vertexes, and 12 faces! And when I try to load that file with my .3ds viewer, my parser isn't detecting the face block (0x4120), which is strange because it worked for other objects downloaded from internet. Do I have to set any special property in order to export a 3ds file with minimum vertexes and a vertex-index list?

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  • How to attach a sprite to a TMXTiledMap at a particular coordinate, in AndEngine?

    - by shailenTJ
    I am trying to add a sprite at a "grid" location on the tiled map. The TMX tiled Map is like a grid, and you can access the size of the grid by calling mTMXtiledMap.getTileRows() and mTMXtiledMap.getTileColumns(). I want to add an object at grid location, say (2, 5). My tileMap is of size (10,10). How can I do that? There is no function like mTMXTiledMap.addChild(int x, int y, Entity mEntity). I would appreciate any suggestions!

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  • Cocos2D 2.0 - masking a sprite

    - by Desperate Developer
    I have read this tutorial about how to mask sprites using Cocos2D 2.0. http://www.raywenderlich.com/4428/how-to-mask-a-sprite-with-cocos2d-2-0 But the author talks about OpenGL ES textures and vertices as they were common knowledge. My knowledge about OpenGl is zero raised to infinity. All I want is to use a rectangle to mask a sprite to it. How I would do in Photoshop using a rectangle as mask (yes, I want to clip a sprite to the rectangle bounds and no, I do not want to use the ClippingNode solution, that do not works for animation/scaling etc.). So, can you guys translate the klingon language used in this tutorial and tell how a solid rectangle can be used to mask a sprite in Cocos2D? I am desperate, as my username states. I am searching this for a week and have tried several solutions without satisfactory results. Please help me. Thanks!

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  • Off center projection

    - by N0xus
    I'm trying to implement the code that was freely given by a very kind developer at the following link: http://forum.unity3d.com/threads/142383-Code-sample-Off-Center-Projection-Code-for-VR-CAVE-or-just-for-fun Right now, all I'm trying to do is bring it in on one camera, but I have a few issues. My class, looks as follows: using UnityEngine; using System.Collections; public class PerspectiveOffCenter : MonoBehaviour { // Use this for initialization void Start () { } // Update is called once per frame void Update () { } public static Matrix4x4 GeneralizedPerspectiveProjection(Vector3 pa, Vector3 pb, Vector3 pc, Vector3 pe, float near, float far) { Vector3 va, vb, vc; Vector3 vr, vu, vn; float left, right, bottom, top, eyedistance; Matrix4x4 transformMatrix; Matrix4x4 projectionM; Matrix4x4 eyeTranslateM; Matrix4x4 finalProjection; ///Calculate the orthonormal for the screen (the screen coordinate system vr = pb - pa; vr.Normalize(); vu = pc - pa; vu.Normalize(); vn = Vector3.Cross(vr, vu); vn.Normalize(); //Calculate the vector from eye (pe) to screen corners (pa, pb, pc) va = pa-pe; vb = pb-pe; vc = pc-pe; //Get the distance;; from the eye to the screen plane eyedistance = -(Vector3.Dot(va, vn)); //Get the varaibles for the off center projection left = (Vector3.Dot(vr, va)*near)/eyedistance; right = (Vector3.Dot(vr, vb)*near)/eyedistance; bottom = (Vector3.Dot(vu, va)*near)/eyedistance; top = (Vector3.Dot(vu, vc)*near)/eyedistance; //Get this projection projectionM = PerspectiveOffCenter(left, right, bottom, top, near, far); //Fill in the transform matrix transformMatrix = new Matrix4x4(); transformMatrix[0, 0] = vr.x; transformMatrix[0, 1] = vr.y; transformMatrix[0, 2] = vr.z; transformMatrix[0, 3] = 0; transformMatrix[1, 0] = vu.x; transformMatrix[1, 1] = vu.y; transformMatrix[1, 2] = vu.z; transformMatrix[1, 3] = 0; transformMatrix[2, 0] = vn.x; transformMatrix[2, 1] = vn.y; transformMatrix[2, 2] = vn.z; transformMatrix[2, 3] = 0; transformMatrix[3, 0] = 0; transformMatrix[3, 1] = 0; transformMatrix[3, 2] = 0; transformMatrix[3, 3] = 1; //Now for the eye transform eyeTranslateM = new Matrix4x4(); eyeTranslateM[0, 0] = 1; eyeTranslateM[0, 1] = 0; eyeTranslateM[0, 2] = 0; eyeTranslateM[0, 3] = -pe.x; eyeTranslateM[1, 0] = 0; eyeTranslateM[1, 1] = 1; eyeTranslateM[1, 2] = 0; eyeTranslateM[1, 3] = -pe.y; eyeTranslateM[2, 0] = 0; eyeTranslateM[2, 1] = 0; eyeTranslateM[2, 2] = 1; eyeTranslateM[2, 3] = -pe.z; eyeTranslateM[3, 0] = 0; eyeTranslateM[3, 1] = 0; eyeTranslateM[3, 2] = 0; eyeTranslateM[3, 3] = 1f; //Multiply all together finalProjection = new Matrix4x4(); finalProjection = Matrix4x4.identity * projectionM*transformMatrix*eyeTranslateM; //finally return return finalProjection; } // Update is called once per frame public void FixedUpdate () { Camera cam = camera; //calculate projection Matrix4x4 genProjection = GeneralizedPerspectiveProjection( new Vector3(0,1,0), new Vector3(1,1,0), new Vector3(0,0,0), new Vector3(0,0,0), cam.nearClipPlane, cam.farClipPlane); //(BottomLeftCorner, BottomRightCorner, TopLeftCorner, trackerPosition, cam.nearClipPlane, cam.farClipPlane); cam.projectionMatrix = genProjection; } } My error lies in projectionM = PerspectiveOffCenter(left, right, bottom, top, near, far); The debugger states: Expression denotes a `type', where a 'variable', 'value' or 'method group' was expected. Thus, I changed the line to read: projectionM = new PerspectiveOffCenter(left, right, bottom, top, near, far); But then the error is changed to: The type 'PerspectiveOffCenter' does not contain a constructor that takes '6' arguments. For reasons that are obvious. So, finally, I changed the line to read: projectionM = new GeneralizedPerspectiveProjection(left, right, bottom, top, near, far); And the error I get is: is a 'method' but a 'type' was expected. With this last error, I'm not sure what it is I should do / missing. Can anyone see what it is that I'm missing to fix this error?

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  • How can I move a polygon edge 1 unit away from the center?

    - by Stephen
    Let's say I have a polygon class that is represented by a list of vector classes as vertices, like so: var Vector = function(x, y) { this.x = x; this.y = y; }, Polygon = function(vectors) { this.vertices = vectors; }; Now I make a polygon (in this case, a square) like so: var poly = new Polygon([ new Vector(2, 2), new Vector(5, 2), new Vector(5, 5), new Vector(2, 5) ]); So, the top edge would be [poly.vertices[0], poly.vertices[1]]. I need to stretch this polygon by moving each edge away from the center of the polygon by one unit, along that edge's normal. The following example shows the first edge, the top, moved one unit up: The final polygon should look like this new one: var finalPoly = new Polygon([ new Vector(1, 1), new Vector(6, 1), new Vector(6, 6), new Vector(1, 6) ]); It is important that I iterate, moving one edge at a time, because I will be doing some collision tests after moving each edge. Here is what I tried so far (simplified for clarity), which fails triumphantly: for(var i = 0; i < vertices.length; i++) { var a = vertices[i], b = vertices[i + 1] || vertices[0]; // in case of final vertex var ax = a.x, ay = a.y, bx = b.x, by = b.y; // get some new perpendicular vectors var a2 = new Vector(-ay, ax), b2 = new Vector(-by, bx); // make into unit vectors a2.convertToUnitVector(); b2.convertToUnitVector(); // add the new vectors to the original ones a.add(a2); b.add(b2); // the rest of the code, collision tests, etc. } This makes my polygon start slowly rotating and sliding to the left, instead of what I need. Finally, the example shows a square, but the polygons in question could be anything. They will always be convex, and always with vertices in clockwise order.

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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 can I draw an arrow at the edge of the screen pointing to an object that is off screen?

    - by Adam Henderson
    I am wishing to do what is described in this topic: http://www.allegro.cc/forums/print-thread/283220 I have attempted a variety of the methods mentioned here. First I tried to use the method described by Carrus85: Just take the ratio of the two triangle hypontenuses (doesn't matter which triagle you use for the other, I suggest point 1 and point 2 as the distance you calculate). This will give you the aspect ratio percentage of the triangle in the corner from the larger triangle. Then you simply multiply deltax by that value to get the x-coordinate offset, and deltay by that value to get the y-coordinate offset. But I could not find a way to calculate how far the object is away from the edge of the screen. I then tried using ray casting (which I have never done before) suggested by 23yrold3yrold: Fire a ray from the center of the screen to the offscreen object. Calculate where on the rectangle the ray intersects. There's your coordinates. I first calculated the hypotenuse of the triangle formed by the difference in x and y positions of the two points. I used this to create a unit vector along that line. I looped through that vector until either the x coordinate or the y coordinate was off the screen. The two current x and y values then form the x and y of the arrow. Here is the code for my ray casting method (written in C++ and Allegro 5) void renderArrows(Object* i) { float x1 = i->getX() + (i->getWidth() / 2); float y1 = i->getY() + (i->getHeight() / 2); float x2 = screenCentreX; float y2 = ScreenCentreY; float dx = x2 - x1; float dy = y2 - y1; float hypotSquared = (dx * dx) + (dy * dy); float hypot = sqrt(hypotSquared); float unitX = dx / hypot; float unitY = dy / hypot; float rayX = x2 - view->getViewportX(); float rayY = y2 - view->getViewportY(); float arrowX = 0; float arrowY = 0; bool posFound = false; while(posFound == false) { rayX += unitX; rayY += unitY; if(rayX <= 0 || rayX >= screenWidth || rayY <= 0 || rayY >= screenHeight) { arrowX = rayX; arrowY = rayY; posFound = true; } } al_draw_bitmap(sprite, arrowX - spriteWidth, arrowY - spriteHeight, 0); } This was relatively successful. Arrows are displayed in the bottom right section of the screen when objects are located above and left of the screen as if the locations of the where the arrows are drawn have been rotated 180 degrees around the center of the screen. I assumed this was due to the fact that when I was calculating the hypotenuse of the triangle, it would always be positive regardless of whether or not the difference in x or difference in y is negative. Thinking about it, ray casting does not seem like a good way of solving the problem (due to the fact that it involves using sqrt() and a large for loop). Any help finding a suitable solution would be greatly appreciated, Thanks Adam

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  • How to properly render a Frame Buffer to the BackBuffer in Stage3D / AGAL

    - by bigp
    After doing a render pass with RenderToTarget (RTT), how do you properly render that texture buffer to the screen while maintaining original scale / proportions so it doesn't stretch or lose quality? Can an AGAL VertexShader & FragmentShader be written so it's adaptable to any Texture size and Viewport dimensions? I find I'm getting some "blocky" effects in some of my first attempts at "ping-ponging" between two Texture buffers (to create trailing effects). Perhaps I'm not using the UVs correctly between the rendering-to-target and/or the backbuffer? Is there a simpler way just to "splash" the texture on the backbuffer, or is a Quad absolutely necessary (4 vertices, 2 triangles)? If it needs the Quad, should the Texture buffer be fully drawn (0.0 to 1.0 for vertical and horizontal UVs), or only a percentage of it should, like the example below? Texture Buffer U: 0.0 to viewport.width/texturebuffer.width; Texture Buffer V: 0.0 to viewport.height/texturebuffer.height; Thanks!

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