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  • Texture errors in CubeMap

    - by shade4159
    I am trying to apply this texture as a cubemap. This is my result: Clearly I am doing something with my texture coordinates, but I cannot for the life of me figure out what. I don't even see a pattern to the texture fragments. They just seem like a jumble of different faces. Can anyone shed some light on this? Vertex shader: #version 400 in vec4 vPosition; in vec3 inTexCoord; smooth out vec3 texCoord; uniform mat4 projMatrix; void main() { texCoord = inTexCoord; gl_Position = projMatrix * vPosition; } My fragment shader: #version 400 smooth in vec3 texCoord; out vec4 fColor; uniform samplerCube textures void main() { fColor = texture(textures,texCoord); } Vertices of cube: point4 worldVerts[8] = { vec4( 15, 15, 15, 1 ), vec4( -15, 15, 15, 1 ), vec4( -15, 15, -15, 1 ), vec4( 15, 15, -15, 1 ), vec4( -15, -15, 15, 1 ), vec4( 15, -15, 15, 1 ), vec4( 15, -15, -15, 1 ), vec4( -15, -15, -15, 1 ) }; Cube rendering: void worldCube(point4* verts, int& Index, point4* points, vec3* texVerts) { quadInv( verts[0], verts[1], verts[2], verts[3], 1, Index, points, texVerts); quadInv( verts[6], verts[3], verts[2], verts[7], 2, Index, points, texVerts); quadInv( verts[4], verts[5], verts[6], verts[7], 3, Index, points, texVerts); quadInv( verts[4], verts[1], verts[0], verts[5], 4, Index, points, texVerts); quadInv( verts[5], verts[0], verts[3], verts[6], 5, Index, points, texVerts); quadInv( verts[4], verts[7], verts[2], verts[1], 6, Index, points, texVerts); } Backface function (since this is the inside of the cube): void quadInv( const point4& a, const point4& b, const point4& c, const point4& d , int& Index, point4* points, vec3* texVerts) { quad( a, d, c, b, Index, points, texVerts, a.to_3(), b.to_3(), c.to_3(), d.to_3()); } And the quad drawing function: void quad( const point4& a, const point4& b, const point4& c, const point4& d, int& Index, point4* points, vec3* texVerts, const vec3& tex_a, const vec3& tex_b, const vec3& tex_c, const vec3& tex_d) { texVerts[Index] = tex_a.normalized(); points[Index] = a; Index++; texVerts[Index] = tex_b.normalized(); points[Index] = b; Index++; texVerts[Index] = tex_c.normalized(); points[Index] = c; Index++; texVerts[Index] = tex_a.normalized(); points[Index] = a; Index++; texVerts[Index] = tex_c.normalized(); points[Index] = c; Index++; texVerts[Index] = tex_d.normalized(); points[Index] = d; Index++; } Edit: I forgot to mention, in the image, the camera is pointed directly at the back face of the cube. You can kind of see the diagonals leading out of the corners, if you squint.

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  • Repeat a part of spritesheet as background

    - by Moiblpadde
    So I'm trying to repeat a part of my spritesheet as a background (js, canvas). My code so far: var canvas = $("#board")[0], ctx = canvas.getContext("2d"), sprite = new Image(); sprite.src = "spritesheet.png"; sprite.onload = function(){ ctx.fillStyle = ctx.createPattern(spriteBg, "repeat"); ctx.fillRect(0, 25, 500, 500); } This is fine, but as you can see, it repeat the whole sprite, not just a part of it, and I just can't figure out how to do it D:

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  • Linking one uniform variable to many shaders

    - by Winged
    Let's say, that I have 3 programs, and in each of those programs there is a view matrix uniform, which should be the same in all those programs. Right now, when my camera moves, I need to re-upload the modified matrix to every program separately. Is it possible to create some kind of global uniforms which are constant for all programs linked to it, so I could just upload the matrix once? I tried creating a globalUniforms object which looked kinda like this: var globalUniforms = { program: {}, // (...) vMatrixUniform: null, // (...) initialize: function() { vMatrixUniform = gl.getUniformLocation(this.program, 'uVMatrix'); } }; So I could just link it to proper programs like this: program.vMatrixUniform = globalUniforms.vMatrixUniform;, and then pass the matrix like this: if (camera.isDirty.viewMatrix !== false) { camera.isDirty.viewMatrix = false; gl.uniformMatrix4fv(globalUniforms.vMatrixUniform, false, camera.viewMatrix.element); } but unfortunately it throws an error: Uncaught exception: gl.INVALID_VALUE was caused by call to: getUniformLocation called from line 272, column 2 in () in mysite/js/mesh.js: vMatrixUniform = gl.getUniformLocation(this.program, 'uVMatrix'); Summing up: is there a more efficient way of managing shaders which follows my logic?

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  • 3D rotation matrices deform object while rotating

    - by Kevin
    I'm writing a small 3D renderer (using an orthographic projection right now). I've run into some trouble with my 3D rotation matrices. They seem to squeeze my 3D object (a box primitive) at certain angles. Here's a live demo (only tested in Google Chrome): http://dl.dropbox.com/u/109400107/3D/index.html The box is viewed from the top along the Y axis and is rotating around the X and Z axis. These are my 3 rotation matrices (Only rX and rZ are being used): var rX = new Matrix([ [1, 0, 0], [0, Math.cos(radiants), -Math.sin(radiants)], [0, Math.sin(radiants), Math.cos(radiants)] ]); var rY = new Matrix([ [Math.cos(radiants), 0, Math.sin(radiants)], [0, 1, 0], [-Math.sin(radiants), 0, Math.cos(radiants)] ]); var rZ = new Matrix([ [Math.cos(radiants), -Math.sin(radiants), 0], [Math.sin(radiants), Math.cos(radiants), 0], [0, 0, 1] ]); Before projecting the verticies I multiply them by rZ and rX like so: vert1.multiply(rZ); vert1.multiply(rX); vert2.multiply(rZ); vert2.multiply(rX); vert3.multiply(rZ); vert3.multiply(rX); The projection itself looks like this: bX = (pos.x + (vert1.x*scale)); bY = (pos.y + (vert1.z*scale)); Where "pos.x" and "pos.y" is an offset for centering the box on the screen. I just can't seem to find a solution to this and I'm still relativly new to working with Matricies. You can view the source-code of the demo page if you want to see the whole thing.

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  • Correct use of VAO's in OpenGL ES2 for iOS?

    - by sak
    I'm migrating to OpenGL ES2 for one of my iOS projects, and I'm having trouble to get any geometry to render successfully. Here's where I'm setting up the VAO rendering: void bindVAO(int vertexCount, struct Vertex* vertexData, GLushort* indexData, GLuint* vaoId, GLuint* indexId){ //generate the VAO & bind glGenVertexArraysOES(1, vaoId); glBindVertexArrayOES(*vaoId); GLuint positionBufferId; //generate the VBO & bind glGenBuffers(1, &positionBufferId); glBindBuffer(GL_ARRAY_BUFFER, positionBufferId); //populate the buffer data glBufferData(GL_ARRAY_BUFFER, vertexCount, vertexData, GL_STATIC_DRAW); //size of verte position GLsizei posTypeSize = sizeof(kPositionVertexType); glVertexAttribPointer(kVertexPositionAttributeLocation, kVertexSize, kPositionVertexTypeEnum, GL_FALSE, sizeof(struct Vertex), (void*)offsetof(struct Vertex, position)); glEnableVertexAttribArray(kVertexPositionAttributeLocation); //create & bind index information glGenBuffers(1, indexId); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, *indexId); glBufferData(GL_ELEMENT_ARRAY_BUFFER, vertexCount, indexData, GL_STATIC_DRAW); //restore default state glBindVertexArrayOES(0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); glBindBuffer(GL_ARRAY_BUFFER, 0); } And here's the rendering step: //bind the frame buffer for drawing glBindFramebuffer(GL_FRAMEBUFFER, outputFrameBuffer); glClear(GL_COLOR_BUFFER_BIT); //use the shader program glUseProgram(program); glClearColor(0.4, 0.5, 0.6, 0.5); float aspect = fabsf(320.0 / 480.0); GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(65.0f), aspect, 0.1f, 100.0f); GLKMatrix4 modelViewMatrix = GLKMatrix4MakeTranslation(0.0f, 0.0f, -1.0f); GLKMatrix4 mvpMatrix = GLKMatrix4Multiply(projectionMatrix, modelViewMatrix); //glUniformMatrix4fv(projectionMatrixUniformLocation, 1, GL_FALSE, projectionMatrix.m); glUniformMatrix4fv(modelViewMatrixUniformLocation, 1, GL_FALSE, mvpMatrix.m); glBindVertexArrayOES(vaoId); glDrawElements(GL_TRIANGLE_FAN, kVertexCount, GL_FLOAT, &indexId); //bind the color buffer glBindRenderbuffer(GL_RENDERBUFFER, colorRenderBuffer); [context presentRenderbuffer:GL_RENDERBUFFER]; The screen is rendering the color passed to glClearColor correctly, but not the shape passed into bindVAO. Is my VAO being built correctly? Thanks!

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  • Is it ok to initialize an RB_ConstraintActor in PostBeginPlay?

    - by Almo
    I have a KActorSpawnable subclass that acts weird. In PostBeginPlay, I initialize an RB_ConstraintActor; the default is not to allow rotation. If I create one in the editor, it's fine, and won't rotate. If I spawn one, it rotates. Here's the class: class QuadForceKActor extends KActorSpawnable placeable; var(Behavior) bool bConstrainRotation; var(Behavior) bool bConstrainX; var(Behavior) bool bConstrainY; var(Behavior) bool bConstrainZ; var RB_ConstraintActor PhysicsConstraintActor; simulated event PostBeginPlay() { Super.PostBeginPlay(); PhysicsConstraintActor = Spawn(class'RB_ConstraintActorSpawnable', self, '', Location, rot(0, 0, 0)); if(bConstrainRotation) { PhysicsConstraintActor.ConstraintSetup.bSwingLimited = true; PhysicsConstraintActor.ConstraintSetup.bTwistLimited = true; } SetLinearConstraints(bConstrainX, bConstrainY, bConstrainZ); PhysicsConstraintActor.InitConstraint(self, None); } function SetLinearConstraints(bool InConstrainX, bool InConstrainY, bool InConstrainZ) { if(InConstrainX) { PhysicsConstraintActor.ConstraintSetup.LinearXSetup.bLimited = 1; } else { PhysicsConstraintActor.ConstraintSetup.LinearXSetup.bLimited = 0; } if(InConstrainY) { PhysicsConstraintActor.ConstraintSetup.LinearYSetup.bLimited = 1; } else { PhysicsConstraintActor.ConstraintSetup.LinearYSetup.bLimited = 0; } if(InConstrainZ) { PhysicsConstraintActor.ConstraintSetup.LinearZSetup.bLimited = 1; } else { PhysicsConstraintActor.ConstraintSetup.LinearZSetup.bLimited = 0; } } DefaultProperties { bConstrainRotation=true bConstrainX=false bConstrainY=false bConstrainZ=false bSafeBaseIfAsleep=false bNoEncroachCheck=false } Here's the code I use to spawn one. It's a subclass of the one above, but it doesn't reference the constraint at all. local QuadForceKCreateBlock BlockActor; BlockActor = spawn(class'QuadForceKCreateBlock', none, 'PowerCreate_Block', BlockLocation(), m_PreparedRotation, , false); BlockActor.SetDuration(m_BlockDuration); BlockActor.StaticMeshComponent.SetNotifyRigidBodyCollision(true); BlockActor.StaticMeshComponent.ScriptRigidBodyCollisionThreshold = 0.001; BlockActor.StaticMeshComponent.SetStaticMesh(m_ValidCreationBlock.StaticMesh); BlockActor.StaticMeshComponent.AddImpulse(m_InitialVelocity); I used to initialize an RB_ConstraintActor where I spawned it from the outside. This worked, which is why I'm pretty sure it has nothing to do with the other code in QuadForceKCreateBlock. I then added the internal constraint in QuadForceKActor for other purposes. When I realized I had two constraints on the CreateBlock doing the same thing, I removed the constraint code from the place where I spawn it. Then it started rotating. Is there a reason I should not be initializing an RB_ConstraintActor in PostBeginPlay? I feel like there's some basic thing about how the engine works that I'm missing.

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  • SFX Played Once per Collision or Hit

    - by David Dimalanta
    I have a question about using Box2D (engine for LibGDX used to make realistic physics). I observed on the code that I've made for the physics here below: @Override public boolean touchUp(int screenX, int screenY, int pointer, int button) { // TODO Touch Up Event if(is_Next_Fruit_Touched) { BodyEditorLoader Fruit_Loader = new BodyEditorLoader(Gdx.files.internal("Shape_Physics/Fruity Physics.json")); Fruit_BD.type = BodyType.DynamicBody; Fruit_BD.position.set(x, y); FixtureDef Fruit_FD = new FixtureDef(); // --> Allows you to make the object's physics. Fruit_FD.density = 1.0f; Fruit_FD.friction = 0.7f; Fruit_FD.restitution = 0.2f; MassData mass = new MassData(); mass.mass = 5f; Fruit_Body[n] = world.createBody(Fruit_BD); Fruit_Body[n].setActive(true); // --> Let your dragon fall. Fruit_Body[n].setMassData(mass); Fruit_Body[n].setGravityScale(1.0f); System.out.println("Eggs... " + n); Fruit_Loader.attachFixture(Fruit_Body[n], Body, Fruit_FD, Fruit_IMG.getWidth()); Fruit_Origin = Fruit_Loader.getOrigin(Body, Fruit_IMG.getWidth()).cpy(); is_Next_Fruit_Touched = false; up = y; Gdx.app.log("Initial Y-coordinate", "Y at " + up); //Once it's touched, the next fruit will set to drag. if(n < 50) { n++; }else{ System.exit(0); } } return true; } Now, I'm thinking which part o line should I implement for the sound effects. My objectives to make SFX played once for every collision (Or should I say "SFX played once per collision"?) on the following: SFX played once if they hit on the objects of its kind. (e.g. apple vs. apple) SFX played once on a different sound when it hit on the ground. (e.g. apple land on the mud) Take note that I'm using Box2D for the Java programming version thanks to LibGDX via Box2D engine and I edited the physics body using Physics Body Editor before I implement it to code. I tried to check every available methods for body, fixture definition, or body definition to code for the SFX when hit but it seems only for the gravity and weight. Is there possibly available on the document for SFX played when collision happens if possible?

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  • OpenGL Learning Material (that's up to date)

    - by Sauron
    So im sure there are topics on this, but alot of them list older material. And the last book: http://www.amazon.com/OpenGL-SuperBible-Comprehensive-Tutorial-Reference/dp/0321712617/ref=sr_1_1?ie=UTF8&qid=1346116133&sr=8-1&keywords=opengl REALLY REALLY disappointed me. I DO NOT want to use someone else's library to learn this stuff, that bothers me SOOO much. So I was hoping there was a newer book that goes into detail, and doesn't use some sort of library "Hiding" everything from you. Or should I just look at older material? If so....anything thats not "too" out of date. Terrain tutorials are a plus (that's kinda my "goal"). Thanks

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  • Stop a rotating object at a specified angle?

    - by Krummelz
    I'm working in JavaScript with HTML5 and the canvas. I have an object which is rotating at a certain speed, and I need the object's rotation to slow down gradually and the front of the object to stop at a specified angle. (I'm using radians, not degrees.) I have a variable to keep track of the angle which the object is facing, as it rotates. How would I go about getting the object to come to rest, facing the direction I want it to?

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  • How can I determine if a cube is adjacent to another cube, and optimize its buffers if so?

    - by Christian Frantz
    I'm trying to optimize the rendering of a collection of cubes, (based on an answer I was given to another question I asked). I understand the logic behind occlusion culling, but I'm having trouble with the code. When I create a cube, I want to determine if that cube is touching another existing cube, and if so I don't want to generate the redundant data in my vertex or index buffers. I'm planning on making a method that I call from my cube constructor so that everytime I create a cube, these checks are made, and neither occluded face is ever drawn. How would I go about this?

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  • XNA clip plane effect makes models black

    - by user1990950
    When using this effect file: float4x4 World; float4x4 View; float4x4 Projection; float4 ClipPlane0; void vs(inout float4 position : POSITION0, out float4 clipDistances : TEXCOORD0) { clipDistances.x = dot(position, ClipPlane0); clipDistances.y = 0; clipDistances.z = 0; clipDistances.w = 0; position = mul(mul(mul(position, World), View), Projection); } float4 ps(float4 clipDistances : TEXCOORD0) : COLOR0 { clip(clipDistances); return float4(0, 0, 0, 0); } technique { pass { VertexShader = compile vs_2_0 vs(); PixelShader = compile ps_2_0 ps(); } } all models using this are rendered black. Is it possible to render them correctly?

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  • Quake 3 Bot Programming Example

    - by Manni
    I would like to implement an intelligent bot for Quake-3. I downloaded the and built the code successfully under Linux. My problem is that I couldn't find any complete tutorial telling me how to build an agent; telling which files to use( as there are many files in the source code). Can you give me a website or piece of source code telling me how to start? Or something like an example source code for a bot.

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  • OpenGLES GLSL Shader attributes always bound to 0

    - by codemonkey
    So I have a very simple vertex shader as follows #version 120 attribute vec3 position; attribute vec3 inColor; uniform mat4 mvp; varying vec3 fragColor; void main(void){ fragColor = inColor; gl_Position = mvp * vec4(position, 1.0); } Which I load, as well as the fragment shader: #version 120 varying vec3 fragColor; void main(void) { gl_FragColor = vec4(fragColor,1.0); } Which I then load, compile, and link to my shader program. I check for link status using glGetProgramiv(shaderProgram, GL_LINK_STATUS, &shaderSuccess); which returns GL_TRUE so I think its ok. However, when I query the active attributes and uniforms using #ifdef DEBUG int totalAttributes = -1; glGetProgramiv(shaderProgram, GL_ACTIVE_ATTRIBUTES, &totalAttributes); for(int i=0; i<totalAttributes; ++i) { int name_len=-1, num=-1; GLenum type = GL_ZERO; char name[100]; glGetActiveAttrib(shaderProgram, GLuint(i), sizeof(name)-1, &name_len, &num, &type, name ); name[name_len] = 0; GLuint location = glGetAttribLocation(shaderProgram, name); fprintf(stderr, "Attribute %s is bound at %d\n", name, location); } int totalUniforms = -1; glGetProgramiv(shaderProgram, GL_ACTIVE_UNIFORMS, &totalUniforms); for(int i=0; i<totalUniforms; ++i) { int name_len=-1, num=-1; GLenum type = GL_ZERO; char name[100]; glGetActiveUniform(shaderProgram, GLuint(i), sizeof(name)-1, &name_len, &num, &type, name ); name[name_len] = 0; GLuint location = glGetUniformLocation(shaderProgram, name); fprintf(stderr, "Uniform %s is bound at %d\n", name, location); } #endif I get: Attribute inColor is bound at 0 Attribute position is bound at 1 Uniform mvp is bound at 0 Which leads to failure when trying to use the shader to render the objects. I have tried switching the order of declaration of position & inColor, but still, only position is bound with the other two giving 0 Can someone please explain why this is happening? Thanks

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  • How do GameEngines stop Pixel Seams appearing in adjacent mesh boundaries due to FP imprecision?

    - by ufomorace
    Graphics cards are mathematically imprecise. So when some meshes are joined by their borders, the graphics card often makes mistakes and decides that some pixels at the seam represent neither object, and unwanted pixels appear. It's a natural behaviour on all graphics cards. How are such worries avoided in Pro Games? Batching? Shaders? Different tangent vectors? Merging? Overlaping seams? Dark backgrounds? Extra vertices at borders? Z precision? Camera distance tweaks? Screencap of a fix that ended up not working:

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  • Inverse projection: question about w coordinate

    - by fayeWilly
    I have to perform in shader an inverse projection from a u/v of a render target. What I do is: Get NDC as 2*(u,v,depth) - 1 Then world space as tmp = (P*V)^-1 * (NDC,1.0); world space = tmp/tmp.w; This apparently works, but I am confused about the w division there. Why this work? Shouldn't be a multiplication by a w somewhere (as in the "forward" pipeline there is the perpsective division?) Thank you, Faye

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  • Importing 3d model with multiple skeletons

    - by Sweta Dwivedi
    I have created an animated butterfly in 3ds Max and try to export it in ".fbx" format to use in XNA, however as soon as I compile, i get the following Errors: Warning 1 Multiple skeletons were found in the file. The first skeleton, named "Left.Wing" has been moved to be a child of the scene root. The other, "Right.Wing", will be ignored. Fragment identifier "Right.Wing". Error 2 Vertex is bound to bone "Right.Wing", but this bone is not present in the skeleton. Which is confusing since I have the bone Right.Wing . . and I use it to animate the butterfly I have seen a few possible solution for Blender but none for 3Ds max it would be really helpful if someone could help me out with this

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  • libgdx actors and instant actions

    - by vaati
    I'm having trouble with actors and actions. I have a list of actors, they all have either no action, or 1 sequence action This sequence action has either : a couple of actions (some are instant, some have duration 0) a couple of actions followed by a parallel action. My problem is the following: some of the instant actions are used to set the position and the alpha of the actor. So when one of the action is "move to x,y and set alpha to 0" the actor is visible for one frame at position 0,0 , move instantly to x,y for the next frame, and then disappears. Though this behaviours is to be expected, I want to avoid it. How can I achieve that? I tried to intercept the actions before I put actors in the stage but I need the stage width/height for some actions. So something like : Action actionSequence = actor.getActions().get(0); Array<Action> actions = ((SequenceAction) actionSequence).getActions(); for(Action act : actions){ if(act.act(0)) System.out.println("action " + act.toString() + " successfully run"); else System.out.println("action " + act.toString() + " wasn't instant"); } won't work. It gets even more complicated when an actor can also have a repeat action in stead of the sequence action (because you have to only run the actions that have duration 0 once without repeat, and then start the repeat). Any help is appreciated.

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  • Unrealscript splitting a string

    - by burntsugar
    Note, this is repost from stackoverflow - I have only just discovered this site :) I need to split a string in Unrealscript, in the same way that Java's split function works. For instance - return the string "foo" as an array of char. I have tried to use the SplitString function: array SplitString( string Source, optional string Delimiter=",", optional bool bCullEmpty ) Wrapper for splitting a string into an array of strings using a single expression. as found at http://udn.epicgames.com/Three/UnrealScriptFunctions.html but it returns the entire String. simulated function wordDraw() { local String inputString; inputString = "trolls"; local string whatwillitbe; local int b; local int x; local array<String> letterArray; letterArray = SplitString(inputString,, false); for (x = 0; x < letterArray.Length; x++) { whatwillitbe = letterArray[x]; `log('it will be '@whatwillitbe); b = letterarray.Length; `log('letterarray length is '@b); `log('letter number '@x); } } Output is: b returns: 1 whatwillitbe returns: trolls However I would like b to return 6 and whatwillitbe to return each character individually. I have had a few answers proposed, however, I would still like to properly understand how the SplitString function works. For instance, if the Delimiter parameter is optional, what does the function use as a delimiter by default?

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  • Building View Matrix in Direct3D11

    - by Balls
    Am I doing it right? I converted this. m_ViewMatrix = XMMatrixLookAtLH(XMLoadFloat3(&m_Position), lookAtVector, upVector); to this one. XMVECTOR vz = XMVector3Normalize( lookAtVector - XMLoadFloat3(&m_Position) ); XMVECTOR vx = XMVector3Normalize( XMVector3Cross( upVector, vz ) ); XMVECTOR vy = XMVector3Cross( vz, vx ); m_ViewMatrix.r[0] = vx; m_ViewMatrix.r[1] = vy; m_ViewMatrix.r[2] = vz; m_ViewMatrix.r[3] = XMLoadFloat3(&m_Position); m_ViewMatrix.r[0].m128_f32[3] = 0.0f; m_ViewMatrix.r[1].m128_f32[3] = 0.0f; m_ViewMatrix.r[2].m128_f32[3] = 0.0f; m_ViewMatrix.r[3].m128_f32[3] = 1.0f; m_ViewMatrix = XMMatrixInverse( &XMMatrixDeterminant(m_ViewMatrix), m_ViewMatrix ); Everything looks fine when I run it. Another question is, I saw on this site(http://webglfactory.blogspot.com/2011/06/how-to-create-view-matrix.html) that he subtracted lookat from position in his vector vz. I tried it but gave me wrong view matrix. Can anyone check my code. I'm studying linear algebra right now. Sucks my course doesn't have one. Thank you, Balls

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  • Simple 3D Physics engine as a part of graduation project [on hold]

    - by Eugene Kolesnikov
    I am working on my graduation project and one part of it is to simulate the motion of a rigid body in 3D space. I can use either already written physics engine or to write it myself. It's quite an interesting challenge for me, so I would like to do it myself. I am able to use either C++ or Java for programming (prefer C++). I am using Mac OS X and Debian 7. Could you suggest any guides or tutorials how to do it, can't find it anywhere... More precisely, I need a very simple engine, without collision detection, and many other things that I do not know, I just need to calculate the forces and move my body, depending on the resultant force. If you think that this task is still very difficult or there is no such tutorial, please suggest me some good and simple engine.

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  • Incorrect lighting results with deferred rendering

    - by Lasse
    I am trying to render a light-pass to a texture which I will later apply on the scene. But I seem to calculate the light position wrong. I am working on view-space. In the image above, I am outputting the attenuation of a point light which is currently covering the whole screen. The light is at 0,10,0 position, and I transform it to view-space first: Vector4 pos; Vector4 tmp = new Vector4 (light.Position, 1); // Transform light position for shader Vector4.Transform (ref tmp, ref Camera.ViewMatrix, out pos); shader.SendUniform ("LightViewPosition", ref pos); Now to me that does not look as it should. What I think it should look like is that the white area should be on the center of the scene. The camera is at the corner of the scene, and it seems as if the light would move along with the camera. Here's the fragment shader code: void main(){ // default black color vec3 color = vec3(0); // Pixel coordinates on screen without depth vec2 PixelCoordinates = gl_FragCoord.xy / ScreenSize; // Get pixel position using depth from texture vec4 depthtexel = texture( DepthTexture, PixelCoordinates ); float depthSample = unpack_depth(depthtexel); // Get pixel coordinates on camera-space by multiplying the // coordinate on screen-space by inverse projection matrix vec4 world = (ImP * RemapMatrix * vec4(PixelCoordinates, depthSample, 1.0)); // Undo the perspective calculations vec3 pixelPosition = (world.xyz / world.w) * 3; // How far the light should reach from it's point of origin float lightReach = LightColor.a / 2; // Vector in between light and pixel vec3 lightDir = (LightViewPosition.xyz - pixelPosition); float lightDistance = length(lightDir); vec3 lightDirN = normalize(lightDir); // Discard pixels too far from light source //if(lightReach < lightDistance) discard; // Get normal from texture vec3 normal = normalize((texture( NormalTexture, PixelCoordinates ).xyz * 2) - 1); // Half vector between the light direction and eye, used for specular component vec3 halfVector = normalize(lightDirN + normalize(-pixelPosition)); // Dot product of normal and light direction float NdotL = dot(normal, lightDirN); float attenuation = pow(lightReach / lightDistance, LightFalloff); // If pixel is lit by the light if(NdotL > 0) { // I have moved stuff from here to above so I can debug them. // Diffuse light color color += LightColor.rgb * NdotL * attenuation; // Specular light color color += LightColor.xyz * pow(max(dot(halfVector, normal), 0.0), 4.0) * attenuation; } RT0 = vec4(color, 1); //RT0 = vec4(pixelPosition, 1); //RT0 = vec4(depthSample, depthSample, depthSample, 1); //RT0 = vec4(NdotL, NdotL, NdotL, 1); RT0 = vec4(attenuation, attenuation, attenuation, 1); //RT0 = vec4(lightReach, lightReach, lightReach, 1); //RT0 = depthtexel; //RT0 = 100 / vec4(lightDistance, lightDistance, lightDistance, 1); //RT0 = vec4(lightDirN, 1); //RT0 = vec4(halfVector, 1); //RT0 = vec4(LightColor.xyz,1); //RT0 = vec4(LightViewPosition.xyz/100, 1); //RT0 = vec4(LightPosition.xyz, 1); //RT0 = vec4(normal,1); } What am I doing wrong here?

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  • Efficiently separating Read/Compute/Write steps for concurrent processing of entities in Entity/Component systems

    - by TravisG
    Setup I have an entity-component architecture where Entities can have a set of attributes (which are pure data with no behavior) and there exist systems that run the entity logic which act on that data. Essentially, in somewhat pseudo-code: Entity { id; map<id_type, Attribute> attributes; } System { update(); vector<Entity> entities; } A system that just moves along all entities at a constant rate might be MovementSystem extends System { update() { for each entity in entities position = entity.attributes["position"]; position += vec3(1,1,1); } } Essentially, I'm trying to parallelise update() as efficiently as possible. This can be done by running entire systems in parallel, or by giving each update() of one system a couple of components so different threads can execute the update of the same system, but for a different subset of entities registered with that system. Problem In reality, these systems sometimes require that entities interact(/read/write data from/to) each other, sometimes within the same system (e.g. an AI system that reads state from other entities surrounding the current processed entity), but sometimes between different systems that depend on each other (i.e. a movement system that requires data from a system that processes user input). Now, when trying to parallelize the update phases of entity/component systems, the phases in which data (components/attributes) from Entities are read and used to compute something, and the phase where the modified data is written back to entities need to be separated in order to avoid data races. Otherwise the only way (not taking into account just "critical section"ing everything) to avoid them is to serialize parts of the update process that depend on other parts. This seems ugly. To me it would seem more elegant to be able to (ideally) have all processing running in parallel, where a system may read data from all entities as it wishes, but doesn't write modifications to that data back until some later point. The fact that this is even possible is based on the assumption that modification write-backs are usually very small in complexity, and don't require much performance, whereas computations are very expensive (relatively). So the overhead added by a delayed-write phase might be evened out by more efficient updating of entities (by having threads work more % of the time instead of waiting). A concrete example of this might be a system that updates physics. The system needs to both read and write a lot of data to and from entities. Optimally, there would be a system in place where all available threads update a subset of all entities registered with the physics system. In the case of the physics system this isn't trivially possible because of race conditions. So without a workaround, we would have to find other systems to run in parallel (which don't modify the same data as the physics system), other wise the remaining threads are waiting and wasting time. However, that has disadvantages Practically, the L3 cache is pretty much always better utilized when updating a large system with multiple threads, as opposed to multiple systems at once, which all act on different sets of data. Finding and assembling other systems to run in parallel can be extremely time consuming to design well enough to optimize performance. Sometimes, it might even not be possible at all because a system just depends on data that is touched by all other systems. Solution? In my thinking, a possible solution would be a system where reading/updating and writing of data is separated, so that in one expensive phase, systems only read data and compute what they need to compute, and then in a separate, performance-wise cheap, write phase, attributes of entities that needed to be modified are finally written back to the entities. The Question How might such a system be implemented to achieve optimal performance, as well as making programmer life easier? What are the implementation details of such a system and what might have to be changed in the existing EC-architecture to accommodate this solution?

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  • The practical cost of swapping effects

    - by sebf
    Hello, I use XNA for my projects and on those forums I sometimes see references to the fact that swapping an effect for a mesh has a relatively high cost, which surprises me as I thought to swap an effect was simply a case of copying the replacement shader program to the GPU along with appropriate parameters. I wondered if someone could explain exactly what is costly about this process? And put, if possible, 'relatively' into context? For example say I wanted to use a short shader to help with picking, I would: Change the effect on every object, calculting a unique color to identify it and providing it to the shader. Draw all the objects to a render target in memory. Get the color from the target and use it to look up the selected object. What portion of the total time taken to complete that process would be spent swapping the shaders? My instincts would say that rendering the scene again, no matter how simple the shader, would be an order of magnitude slower than any other part of the process so why all the concern over effects?

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  • How to implement an intelligent enemy in a shoot-em-up?

    - by bummzack
    Imagine a very simple shoot-em-up, something we all know: You're the player (green). Your movement is restricted to the X axis. Our enemy (or enemies) is at the top of the screen, his movement is also restricted to the X axis. The player fires bullets (yellow) at the enemy. I'd like to implement an A.I. for the enemy that should be really good at avoiding the players bullets. My first idea was to divide the screen into discrete sections and assign weights to them: There are two weights: The "bullet-weight" (grey) is the danger imposed by a bullet. The closer the bullet is to the enemy, the higher the "bullet-weight" (0..1, where 1 is highest danger). Lanes without a bullet have a weight of 0. The second weight is the "distance-weight" (lime-green). For every lane I add 0.2 movement cost (this value is kinda arbitrary now and could be tweaked). Then I simply add the weights (white) and go to the lane with the lowest weight (red). But this approach has an obvious flaw, because it can easily miss local minima as the optimal place to go would be simply between two incoming bullets (as denoted with the white arrow). So here's what I'm looking for: Should find a way through bullet-storm, even when there's no place that doesn't impose a threat of a bullet. Enemy can reliably dodge bullets by picking an optimal (or almost optimal) solution. Algorithm should be able to factor in bullet movement speed (as they might move with different velocities). Ways to tweak the algorithm so that different levels of difficulty can be applied (dumb to super-intelligent enemies). Algorithm should allow different goals, as the enemy doesn't only want to evade bullets, he should also be able to shoot the player. That means that positions where the enemy can fire at the player should be preferred when dodging bullets. So how would you tackle this? Contrary to other games of this genre, I'd like to have only a few, but very "skilled" enemies instead of masses of dumb enemies.

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  • How to follow object on CatmullRomSplines at constant speed (e.g. train and train carriage)?

    - by Simon
    I have a CatmullRomSpline, and using the very good example at https://github.com/libgdx/libgdx/wiki/Path-interface-%26-Splines I have my object moving at an even pace over the spline. Using a simple train and carriage example, I now want to have the carriage follow the train at the same speed as the train (not jolting along as it does with my code below). This leads into my main questions: How can I make the carriage have the same constant speed as the train and make it non jerky (it has something to do with the derivative I think, I don't understand how that part works)? Why do I need to divide by the line length to convert to metres per second, and is that correct? It wasn't done in the linked examples? I have used the example I linked to above, and modified for my specific example: private void process(CatmullRomSpline catmullRomSpline) { // Render path with precision of 1000 points renderPath(catmullRomSpline, 1000); float length = catmullRomSpline.approxLength(catmullRomSpline.spanCount * 1000); // Render the "train" Vector2 trainDerivative = new Vector2(); Vector2 trainLocation = new Vector2(); catmullRomSpline.derivativeAt(trainDerivative, current); // For some reason need to divide by length to convert from pixel speed to metres per second but I do not // really understand why I need it, it wasn't done in the examples??????? current += (Gdx.graphics.getDeltaTime() * speed / length) / trainDerivative.len(); catmullRomSpline.valueAt(trainLocation, current); renderCircleAtLocation(trainLocation); if (current >= 1) { current -= 1; } // Render the "carriage" Vector2 carriageLocation = new Vector2(); float carriagePercentageCovered = (((current * length) - 1f) / length); // I would like it to follow at 1 metre behind carriagePercentageCovered = Math.max(carriagePercentageCovered, 0); catmullRomSpline.valueAt(carriageLocation, carriagePercentageCovered); renderCircleAtLocation(carriageLocation); } private void renderPath(CatmullRomSpline catmullRomSpline, int k) { // catMulPoints would normally be cached when initialising, but for sake of example... Vector2[] catMulPoints = new Vector2[k]; for (int i = 0; i < k; ++i) { catMulPoints[i] = new Vector2(); catmullRomSpline.valueAt(catMulPoints[i], ((float) i) / ((float) k - 1)); } SHAPE_RENDERER.begin(ShapeRenderer.ShapeType.Line); SHAPE_RENDERER.setColor(Color.NAVY); for (int i = 0; i < k - 1; ++i) { SHAPE_RENDERER.line((Vector2) catMulPoints[i], (Vector2) catMulPoints[i + 1]); } SHAPE_RENDERER.end(); } private void renderCircleAtLocation(Vector2 location) { SHAPE_RENDERER.begin(ShapeRenderer.ShapeType.Filled); SHAPE_RENDERER.setColor(Color.YELLOW); SHAPE_RENDERER.circle(location.x, location.y, .5f); SHAPE_RENDERER.end(); } To create a decent sized CatmullRomSpline for testing this out: Vector2[] controlPoints = makeControlPointsArray(); CatmullRomSpline myCatmull = new CatmullRomSpline(controlPoints, false); .... private Vector2[] makeControlPointsArray() { Vector2[] pointsArray = new Vector2[78]; pointsArray[0] = new Vector2(1.681817f, 10.379999f); pointsArray[1] = new Vector2(2.045455f, 10.379999f); pointsArray[2] = new Vector2(2.663636f, 10.479999f); pointsArray[3] = new Vector2(3.027272f, 10.700000f); pointsArray[4] = new Vector2(3.663636f, 10.939999f); pointsArray[5] = new Vector2(4.245455f, 10.899999f); pointsArray[6] = new Vector2(4.736363f, 10.720000f); pointsArray[7] = new Vector2(4.754545f, 10.339999f); pointsArray[8] = new Vector2(4.518181f, 9.860000f); pointsArray[9] = new Vector2(3.790908f, 9.340000f); pointsArray[10] = new Vector2(3.172727f, 8.739999f); pointsArray[11] = new Vector2(3.300000f, 8.340000f); pointsArray[12] = new Vector2(3.700000f, 8.159999f); pointsArray[13] = new Vector2(4.227272f, 8.520000f); pointsArray[14] = new Vector2(4.681818f, 8.819999f); pointsArray[15] = new Vector2(5.081817f, 9.200000f); pointsArray[16] = new Vector2(5.463636f, 9.460000f); pointsArray[17] = new Vector2(5.972727f, 9.300000f); pointsArray[18] = new Vector2(6.063636f, 8.780000f); pointsArray[19] = new Vector2(6.027272f, 8.259999f); pointsArray[20] = new Vector2(5.700000f, 7.739999f); pointsArray[21] = new Vector2(5.300000f, 7.440000f); pointsArray[22] = new Vector2(4.645454f, 7.179999f); pointsArray[23] = new Vector2(4.136363f, 6.940000f); pointsArray[24] = new Vector2(3.427272f, 6.720000f); pointsArray[25] = new Vector2(2.572727f, 6.559999f); pointsArray[26] = new Vector2(1.900000f, 7.100000f); pointsArray[27] = new Vector2(2.336362f, 7.440000f); pointsArray[28] = new Vector2(2.590908f, 7.940000f); pointsArray[29] = new Vector2(2.318181f, 8.500000f); pointsArray[30] = new Vector2(1.663636f, 8.599999f); pointsArray[31] = new Vector2(1.209090f, 8.299999f); pointsArray[32] = new Vector2(1.118181f, 7.700000f); pointsArray[33] = new Vector2(1.045455f, 6.880000f); pointsArray[34] = new Vector2(1.154545f, 6.100000f); pointsArray[35] = new Vector2(1.281817f, 5.580000f); pointsArray[36] = new Vector2(1.700000f, 5.320000f); pointsArray[37] = new Vector2(2.190908f, 5.199999f); pointsArray[38] = new Vector2(2.900000f, 5.100000f); pointsArray[39] = new Vector2(3.700000f, 5.100000f); pointsArray[40] = new Vector2(4.372727f, 5.220000f); pointsArray[41] = new Vector2(4.827272f, 5.220000f); pointsArray[42] = new Vector2(5.463636f, 5.160000f); pointsArray[43] = new Vector2(5.554545f, 4.700000f); pointsArray[44] = new Vector2(5.245453f, 4.340000f); pointsArray[45] = new Vector2(4.445455f, 4.280000f); pointsArray[46] = new Vector2(3.609091f, 4.260000f); pointsArray[47] = new Vector2(2.718181f, 4.160000f); pointsArray[48] = new Vector2(1.990908f, 4.140000f); pointsArray[49] = new Vector2(1.427272f, 3.980000f); pointsArray[50] = new Vector2(1.609090f, 3.580000f); pointsArray[51] = new Vector2(2.136363f, 3.440000f); pointsArray[52] = new Vector2(3.227272f, 3.280000f); pointsArray[53] = new Vector2(3.972727f, 3.340000f); pointsArray[54] = new Vector2(5.027272f, 3.360000f); pointsArray[55] = new Vector2(5.718181f, 3.460000f); pointsArray[56] = new Vector2(6.100000f, 4.240000f); pointsArray[57] = new Vector2(6.209091f, 4.500000f); pointsArray[58] = new Vector2(6.118181f, 5.320000f); pointsArray[59] = new Vector2(5.772727f, 5.920000f); pointsArray[60] = new Vector2(4.881817f, 6.140000f); pointsArray[61] = new Vector2(5.318181f, 6.580000f); pointsArray[62] = new Vector2(6.263636f, 7.020000f); pointsArray[63] = new Vector2(6.645453f, 7.420000f); pointsArray[64] = new Vector2(6.681817f, 8.179999f); pointsArray[65] = new Vector2(6.627272f, 9.080000f); pointsArray[66] = new Vector2(6.572727f, 9.699999f); pointsArray[67] = new Vector2(6.263636f, 10.820000f); pointsArray[68] = new Vector2(5.754546f, 11.479999f); pointsArray[69] = new Vector2(4.536363f, 11.599998f); pointsArray[70] = new Vector2(3.572727f, 11.700000f); pointsArray[71] = new Vector2(2.809090f, 11.660000f); pointsArray[72] = new Vector2(1.445455f, 11.559999f); pointsArray[73] = new Vector2(0.936363f, 11.280000f); pointsArray[74] = new Vector2(0.754545f, 10.879999f); pointsArray[75] = new Vector2(0.700000f, 9.939999f); pointsArray[76] = new Vector2(0.918181f, 9.620000f); pointsArray[77] = new Vector2(1.463636f, 9.600000f); return pointsArray; } Disclaimer: My math is very rusty, so please explain in lay mans terms....

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