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• C# Collision test of a ship and asteriod, angle confusion

  - by Cherry

  We are trying to to do a collision detection for the ship and asteroid. If success than it should detect the collision before N turns. However it is confused between angle 350 and 15 and it is not really working. Sometimes it is moving but sometime it is not moving at all. On the other hand, it is not shooting at the right time as well. I just want to ask how to make the collision detection working??? And how to solve the angle confusion problem? // Get velocities of asteroid Console.WriteLine("lol"); // IF equation is between -2 and -3 if (equation1a <= -2) { // Calculate no. turns till asteroid hits float turns_till_hit = dx / vx; // Calculate angle of asteroid float asteroid_angle_rad = (float)Math.Atan(Math.Abs(dy / dx)); float asteroid_angle_deg = (float)(asteroid_angle_rad * 180 / Math.PI); float asteroid_angle = 0; // Calculate angle if asteroid is in certain positions if (asteroid.Y > ship.Y && asteroid.X > ship.X) { asteroid_angle = asteroid_angle_deg; } else if (asteroid.Y < ship.Y && asteroid.X > ship.X) { asteroid_angle = (360 - asteroid_angle_deg); } else if (asteroid.Y < ship.Y && asteroid.X < ship.X) { asteroid_angle = (180 + asteroid_angle_deg); } else if (asteroid.Y > ship.Y && asteroid.X < ship.X) { asteroid_angle = (180 - asteroid_angle_deg); } // IF turns till asteroid hits are less than 35 if (turns_till_hit < 50) { float angle_between = 0; // Calculate angle between if asteroid is in certain positions if (asteroid.Y > ship.Y && asteroid.X > ship.X) { angle_between = ship_angle - asteroid_angle; } else if (asteroid.Y < ship.Y && asteroid.X > ship.X) { angle_between = (360 - Math.Abs(ship_angle - asteroid_angle)); } else if (asteroid.Y < ship.Y && asteroid.X < ship.X) { angle_between = ship_angle - asteroid_angle; } else if (asteroid.Y > ship.Y && asteroid.X < ship.X) { angle_between = ship_angle - asteroid_angle; } // If angle less than 0, add 360 if (angle_between < 0) { //angle_between %= 360; angle_between = Math.Abs(angle_between); } // Calculate no. of turns to face asteroid float turns_to_face = angle_between / 25; if (turns_to_face < turns_till_hit) { float ship_angle_left = ShipAngle(ship_angle, "leftKey", 1); float ship_angle_right = ShipAngle(ship_angle, "rightKey", 1); float angle_between_left = Math.Abs(ship_angle_left - asteroid_angle); float angle_between_right = Math.Abs(ship_angle_right - asteroid_angle); if (angle_between_left < angle_between_right) { leftKey = true; } else if (angle_between_right < angle_between_left) { rightKey = true; } } if (angle_between > 0 && angle_between < 25) { spaceKey = true; } } }

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• Subdividing a polygon into boxes of varying size

  - by Michael Trouw

  I would like to be pointed to information / resources for creating algorithms like the one illustrated on this blog, which is a subdivision of a polygon (in my case a voronoi cell) into several boxes of varying size: http://procworld.blogspot.nl/2011/07/city-lots.html In the comments a paper by among others the author of the blog can be found, however the only formula listed is about candidate location suitability: http://www.groenewegen.de/delft/thesis-final/ProceduralCityLayoutGeneration-Preprint.pdf Any language will do, but if examples can be given Javascript is preferred (as it is the language i am currently working with) A similar question is this one: What is an efficient packing algorithm for packing rectangles into a polygon?

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• GLSL: Strange light reflections

  - by Tom

  According to this tutorial I'm trying to make a normal mapping using GLSL, but something is wrong and I can't find the solution. The output render is in this image: Image1 in this image is a plane with two triangles and each of it is different illuminated (that is bad). The plane has 6 vertices. In the upper left side of this plane are 2 identical vertices (same in the lower right). Here are some vectors same for each vertice: normal vector = 0, 1, 0 (red lines on image) tangent vector = 0, 0,-1 (green lines on image) bitangent vector = -1, 0, 0 (blue lines on image) here I have one question: The two identical vertices does need to have the same tangent and bitangent? I have tried to make other values to the tangents but the effect was still similar. Here are my shaders Vertex shader: #version 130 // Input vertex data, different for all executions of this shader. in vec3 vertexPosition_modelspace; in vec2 vertexUV; in vec3 vertexNormal_modelspace; in vec3 vertexTangent_modelspace; in vec3 vertexBitangent_modelspace; // Output data ; will be interpolated for each fragment. out vec2 UV; out vec3 Position_worldspace; out vec3 EyeDirection_cameraspace; out vec3 LightDirection_cameraspace; out vec3 LightDirection_tangentspace; out vec3 EyeDirection_tangentspace; // Values that stay constant for the whole mesh. uniform mat4 MVP; uniform mat4 V; uniform mat4 M; uniform mat3 MV3x3; uniform vec3 LightPosition_worldspace; void main(){ // Output position of the vertex, in clip space : MVP * position gl_Position = MVP * vec4(vertexPosition_modelspace,1); // Position of the vertex, in worldspace : M * position Position_worldspace = (M * vec4(vertexPosition_modelspace,1)).xyz; // Vector that goes from the vertex to the camera, in camera space. // In camera space, the camera is at the origin (0,0,0). vec3 vertexPosition_cameraspace = ( V * M * vec4(vertexPosition_modelspace,1)).xyz; EyeDirection_cameraspace = vec3(0,0,0) - vertexPosition_cameraspace; // Vector that goes from the vertex to the light, in camera space. M is ommited because it's identity. vec3 LightPosition_cameraspace = ( V * vec4(LightPosition_worldspace,1)).xyz; LightDirection_cameraspace = LightPosition_cameraspace + EyeDirection_cameraspace; // UV of the vertex. No special space for this one. UV = vertexUV; // model to camera = ModelView vec3 vertexTangent_cameraspace = MV3x3 * vertexTangent_modelspace; vec3 vertexBitangent_cameraspace = MV3x3 * vertexBitangent_modelspace; vec3 vertexNormal_cameraspace = MV3x3 * vertexNormal_modelspace; mat3 TBN = transpose(mat3( vertexTangent_cameraspace, vertexBitangent_cameraspace, vertexNormal_cameraspace )); // You can use dot products instead of building this matrix and transposing it. See References for details. LightDirection_tangentspace = TBN * LightDirection_cameraspace; EyeDirection_tangentspace = TBN * EyeDirection_cameraspace; } Fragment shader: #version 130 // Interpolated values from the vertex shaders in vec2 UV; in vec3 Position_worldspace; in vec3 EyeDirection_cameraspace; in vec3 LightDirection_cameraspace; in vec3 LightDirection_tangentspace; in vec3 EyeDirection_tangentspace; // Ouput data out vec3 color; // Values that stay constant for the whole mesh. uniform sampler2D DiffuseTextureSampler; uniform sampler2D NormalTextureSampler; uniform sampler2D SpecularTextureSampler; uniform mat4 V; uniform mat4 M; uniform mat3 MV3x3; uniform vec3 LightPosition_worldspace; void main(){ // Light emission properties // You probably want to put them as uniforms vec3 LightColor = vec3(1,1,1); float LightPower = 40.0; // Material properties vec3 MaterialDiffuseColor = texture2D( DiffuseTextureSampler, vec2(UV.x,-UV.y) ).rgb; vec3 MaterialAmbientColor = vec3(0.1,0.1,0.1) * MaterialDiffuseColor; //vec3 MaterialSpecularColor = texture2D( SpecularTextureSampler, UV ).rgb * 0.3; vec3 MaterialSpecularColor = vec3(0.5,0.5,0.5); // Local normal, in tangent space. V tex coordinate is inverted because normal map is in TGA (not in DDS) for better quality vec3 TextureNormal_tangentspace = normalize(texture2D( NormalTextureSampler, vec2(UV.x,-UV.y) ).rgb*2.0 - 1.0); // Distance to the light float distance = length( LightPosition_worldspace - Position_worldspace ); // Normal of the computed fragment, in camera space vec3 n = TextureNormal_tangentspace; // Direction of the light (from the fragment to the light) vec3 l = normalize(LightDirection_tangentspace); // Cosine of the angle between the normal and the light direction, // clamped above 0 // - light is at the vertical of the triangle -> 1 // - light is perpendicular to the triangle -> 0 // - light is behind the triangle -> 0 float cosTheta = clamp( dot( n,l ), 0,1 ); // Eye vector (towards the camera) vec3 E = normalize(EyeDirection_tangentspace); // Direction in which the triangle reflects the light vec3 R = reflect(-l,n); // Cosine of the angle between the Eye vector and the Reflect vector, // clamped to 0 // - Looking into the reflection -> 1 // - Looking elsewhere -> < 1 float cosAlpha = clamp( dot( E,R ), 0,1 ); color = // Ambient : simulates indirect lighting MaterialAmbientColor + // Diffuse : "color" of the object MaterialDiffuseColor * LightColor * LightPower * cosTheta / (distance*distance) + // Specular : reflective highlight, like a mirror MaterialSpecularColor * LightColor * LightPower * pow(cosAlpha,5) / (distance*distance); //color.xyz = E; //color.xyz = LightDirection_tangentspace; //color.xyz = EyeDirection_tangentspace; } I have replaced the original color value by EyeDirection_tangentspace vector and then I got other strange effect but I can not link the image (not eunogh reputation) Is it possible that with this shaders is something wrong, or maybe in other place in my code e.g with my matrices? SOLVED Solved... 3 days needed for changing one letter from this: glBindBuffer(GL_ARRAY_BUFFER, vbo); glVertexAttribPointer ( 4, // attribute 3, // size GL_FLOAT, // type GL_FALSE, // normalized? sizeof(VboVertex), // stride (void*)(12*sizeof(float)) // array buffer offset ); to this: glBindBuffer(GL_ARRAY_BUFFER, vbo); glVertexAttribPointer ( 4, // attribute 3, // size GL_FLOAT, // type GL_FALSE, // normalized? sizeof(VboVertex), // stride (void*)(11*sizeof(float)) // array buffer offset ); see difference? :)

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• Control convention for circular movement?

  - by Christian

  I'm currently doing a kind of training project in Unity (still a beginner). It's supposed to be somewhat like Breakout, but instead of just going left and right I want the paddle to circle around the center point. This is all fine and dandy, but the problem I have is: how do you control this with a keyboard or gamepad? For touch and mouse control I could work around the problem by letting the paddle follow the cursor/finger, but with the other control methods I'm a bit stumped. With a keyboard for example, I could either make it so that the Left arrow always moves the paddle clockwise (it starts at the bottom of the circle), or I could link it to the actual direction - meaning that if the paddle is at the bottom, it goes left and up along the circle or, if it's in the upper hemisphere, it moves left and down, both times toward the outer left point of the circle. Both feel kind of weird. With the first one, it can be counter intuitive to press Left to move the paddle right when it's in the upper area, while in the second method you'd need to constantly switch buttons to keep moving. So, long story short: is there any kind of existing standard, convention or accepted example for this type of movement and the corresponding controls? I didn't really know what to google for (control conventions for circular movement was one of the searches I tried, but it didn't give me much), and I also didn't really find anything about this on here. If there is a Question that I simply didn't see, please excuse the duplicate.

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• Opengl-es picking object

  - by lacas

  I saw a lot of picking code opengl-es, but nothing worked. Can someone give me what am I missing? My code is (from tutorials/forums) Vec3 far = Camera.getPosition(); Vec3 near = Shared.opengl().getPickingRay(ev.getX(), ev.getY(), 0); Vec3 direction = far.sub(near); direction.normalize(); Log.e("direction", direction.x+" "+direction.y+" "+direction.z); Ray mouseRay = new Ray(near, direction); for (int n=0; n<ObjectFactory.objects.size(); n++) { if (ObjectFactory.objects.get(n)!=null) { IObject obj = ObjectFactory.objects.get(n); float discriminant, b; float radius=0.1f; b = -mouseRay.getOrigin().dot(mouseRay.getDirection()); discriminant = b * b - mouseRay.getOrigin().dot(mouseRay.getOrigin()) + radius*radius; discriminant = FloatMath.sqrt(discriminant); double x1 = b - discriminant; double x2 = b + discriminant; Log.e("asd", obj.getName() + " "+discriminant+" "+x1+" "+x2); } } my camera vectors: //cam Vec3 position =new Vec3(-obj.getPosX()+x, obj.getPosZ()-0.3f, obj.getPosY()+z); Vec3 direction =new Vec3(-obj.getPosX(), obj.getPosZ(), obj.getPosY()); Vec3 up =new Vec3(0.0f, -1.0f, 0.0f); Camera.set(position, direction, up); and my picking code: public Vec3 getPickingRay(float mouseX, float mouseY, float mouseZ) { int[] viewport = getViewport(); float[] modelview = getModelView(); float[] projection = getProjection(); float winX, winY; float[] position = new float[4]; winX = (float)mouseX; winY = (float)Shared.screen.width - (float)mouseY; GLU.gluUnProject(winX, winY, mouseZ, modelview, 0, projection, 0, viewport, 0, position, 0); return new Vec3(position[0], position[1], position[2]); } My camera moving all the time in 3d space. and my actors/modells moving too. my camera is following one actor/modell and the user can move the camera on a circle on this model. How can I change the above code to working?

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• How to capture the screen in DirectX 9 to a raw bitmap in memory without using D3DXSaveSurfaceToFile

  - by cloudraven

  I know that in OpenGL I can do something like this glReadBuffer( GL_FRONT ); glReadPixels( 0, 0, _width, _height, GL_RGB, GL_UNSIGNED_BYTE, _buffer ); And its pretty fast, I get the raw bitmap in _buffer. When I try to do this in DirectX. Assuming that I have a D3DDevice object I can do something like this if (SUCCEEDED(D3DDevice->GetBackBuffer(0, 0, D3DBACKBUFFER_TYPE_MONO, &pBackbuffer))) { HResult hr = D3DXSaveSurfaceToFileA(filename, D3DXIFF_BMP, pBackbuffer, NULL, NULL); But D3DXSaveSurfaceToFile is pretty slow, and I don't need to write the capture to disk anyway, so I was wondering if there was a faster way to do this

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• Lighting with VBO

  - by nkint

  I'm using a Java JOGL wrapper called processing.org. I have coded some enviroment on it and I'm quite proud of it even if it has some ready stuffs that I didn't know anything about it (==LIGHTS). Then, for some geometry, I've decided to use a VBO. I had to pass in the hard way and recode all lights. But I can't achieve the same result. This is the original light system: And this with VBO: With this code: Vec3D l; gl.glEnable(GL.GL_LIGHTING); gl.glEnable(GL.GL_LIGHT0); gl.glEnable(GL.GL_COLOR_MATERIAL); gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL.GL_AMBIENT, new float[]{0.8f,0f,0f}, 0); l = new Vec3D(0,0,-10); gl.glColor3f(0.8f,0f,0f); gl.glLightfv(GL.GL_LIGHT0, GL.GL_POSITION, new float[] { l.x, l.y, l.z, 0 }, 0); gl.glLightfv(GL.GL_LIGHT0, GL.GL_SPOT_DIRECTION, new float[] { 1, 1, 1, 1 }, 0); I can't achive the same light, the same color material, and the same wireframe stuffs. If needed I can also post the code I use for VBO, but it is quite standard vertex array grabbed on the net that uses glDrawArrays

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• libgdx collision detection / bounding the object

  - by johnny-b

  i am trying to get collision detection so i am drawing a red rectangle to see if it is working, and when i do the code below in the update method. to check if it is going to work. the position is not in the right place. the red rectangle starts from the middle and not at the x and y point?Huh so it draws it wrong. i also have a getter method so nothing wrong there. bullet.set(getX(), getY(), getOriginX(), getOriginY()); this is for the render shapeRenderer.begin(ShapeType.Filled); shapeRenderer.setColor(Color.RED); shapeRenderer.rect(bullet.getX(), bullet.getY(), bullet.getOriginX(), bullet.getOriginY(), 15, 5, bullet.getRotation()); shapeRenderer.end(); i have tried to do it with a circle but the circle draws in the middle and i want it to be at the tip of the bullet. at the front of the bullet. x, y point. boundingCircle.set(getX() + getOriginX(), getY() + getOriginY(), 4.0f); shapeRenderer.begin(ShapeType.Filled); shapeRenderer.setColor(Color.RED); shapeRenderer.circle(bullet.getBoundingCircle().x, bullet.getBoundingCircle().y, bullet.getBoundingCircle().radius); shapeRenderer.end(); thank you need it to be of the x and y as the bullet is in the middle of the sprite when drawn originally via paint.

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• Architecture a for a central renderer rather than self-rendering

  - by The Communist Duck

  For the architectural side of rendering, there's two main ways: having each object render itself, and having a single renderer which renders everything. I'm currently aiming for the second idea, for the following reasons: The list can be sorted to only use shaders once. Else each object would have to bind the shader, because it's not sure if it's active. The objects could be sorted and grouped. Easier to swap APIs. With a few macro lines, it can be easy to swap between a DirectX renderer and an OpenGL renderer (not a reason for my project, but still a good point) Easier to manage rendering code Of course, if anyone has strong recommendations for the first method, I will listen to them. But I was wondering how make this work. First idea The renderer has a list of pointers to the renderable components of each entity, which register themselves on RenderCompoent creation. However, I'm worrying that this may end up as a lot of extra pointer weight. But I can sort the list of pointers every so often. Second idea The entire list of entities is passed to the renderer each render call. The renderer then sorts the list (each call, or maybe once?) and gets what it wants. That's a lot of passing and/or sorting, however. Other ideas ??? PROFIT Anyone got ideas? Thank you.

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• How to attach two XNA models together?

  - by jeangil

  I go back on unsolved question I asked about attaching two models together, could you give me some help on this ? For example, If I want to attach together Model1 (= Main model) & Model2 ? I have to get the transformation matrix of Model1 and after get the Bone index on Model1 where I want to attach Model2 and then apply some transformation to attach Model2 to Model1 I wrote some code below about this, but It does not work at all !! (6th line of my code seems to be wrong !?) Model1TransfoMatrix=New Matrix[Model1.Bones.Count]; Index=Model1.bone[x].Index; foreach (ModelMesh mesh in Model2.Meshes) { foreach(BasicEffect effect in mesh.effects) { matrix model2Transform = Matrix.CreateScale(0.1.0f)*Matrix.CreateFromYawPitchRoll(x,y,z); effect.World= model2Transform *Model1TransfoMatrix[Index]; effect.view = camera.View; effect.Projection= camera.Projection; } mesh.draw(); }

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• Why is my model's scale changing after rotating it?

  - by justnS

  I have just started a simple flight simulator and have implemented Roll and pitch. In the beginning, testing went very well; however, after about 15-20 seconds of constantly moving the thumbsticks in a random or circular motion, my model's scale begins to grow. At first I thought the model was moving closer to the camera, but i set break points when it was happening and can confirm the translation of my orientation matrix remains 0,0,0. Is this a result of Gimbal Lock? Does anyone see an obvious error in my code below? public override void Draw( Matrix view, Matrix projection ) { Matrix[] transforms = new Matrix[Model.Bones.Count]; Model.CopyAbsoluteBoneTransformsTo( transforms ); Matrix translateMatrix = Matrix.Identity * Matrix.CreateFromAxisAngle( _orientation.Right, MathHelper.ToRadians( pitch ) ) * Matrix.CreateFromAxisAngle( _orientation.Down, MathHelper.ToRadians( roll ) ); _orientation *= translateMatrix; foreach ( ModelMesh mesh in Model.Meshes ) { foreach ( BasicEffect effect in mesh.Effects ) { effect.World = _orientation * transforms[mesh.ParentBone.Index]; effect.View = view; effect.Projection = projection; effect.EnableDefaultLighting(); } mesh.Draw(); } } public void Update( GamePadState gpState ) { roll = 5 * gpState.ThumbSticks.Left.X; pitch = 5 * gpState.ThumbSticks.Left.Y; }

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• OpenGL error LNK2019

  - by Ghilliedrone

  I'm trying to compile a basic OpenGL program. I linked opengl32.lib and glu32.lib but I'm getting errors. The errors I get are: error LNK1120: 7 unresolved externals error LNK2019: unresolved external symbol _main referenced in function ___tmainCRTStartup error LNK2019: unresolved external symbol "public: float __thiscall GLWindow::getElapsedSeconds(void)" (?getElapsedSeconds@GLWindow@@QAEMXZ) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "public: bool __thiscall GLWindow::isRunning(void)" (?isRunning@GLWindow@@QAE_NXZ) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "public: void __thiscall GLWindow::attachExample(class Example *)" (?attachExample@GLWindow@@QAEXPAVExample@@@Z) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "public: void __thiscall GLWindow::destroy(void)" (?destroy@GLWindow@@QAEXXZ) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "public: __thiscall GLWindow::GLWindow(struct HINSTANCE__ *)" (??0GLWindow@@QAE@PAUHINSTANCE__@@@Z) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "private: void __thiscall GLWindow::setupPixelFormat(void)" (?setupPixelFormat@GLWindow@@AAEXXZ) referenced in function "public: long __stdcall GLWindow::WndProc(struct HWND__ *,unsigned int,unsigned int,long)" (?WndProc@GLWindow@@QAGJPAUHWND__@@IIJ@Z)

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• 3D Modeling Software for Programmer [closed]

  - by Pathachiever11

  I've recently learned how to make games for Unity3d, and now I want to start making games! I can't wait to start! However, before I can make 3D games, I need to learn 3D modeling for character design, level design, and some animation. What is the easiest 3D modeling software, compatible with Unity3d? I do not want to spend too much time learning the software. From what I've heard, Blender is a bit complicated to use. Maya and 3dsMax seem very powerful. Could someone point me in the right direction? I don't want to spend a lot of time learning. I know its not that easy, but you guys have experience, you guys probably know out of all which one is easier and powerful. Could you recommend a software? Many Thanks!

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• Render angles of a 3D model into 2D images?

  - by Ricket

  Is there a tool out there that you can give a 3D model file, and it will output 2D renders of it from various angles? For example if you were making a 2D RPG but you want to make your character look nice, you might make the character in 3D and then just render the character from 8 or more angles into images which then are used by the 2D engine to give a pseudo-3D look. Does such a tool exist or will it need to be custom-written or done manually?

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• write to depth buffer while using multiple render targets

  - by DocSeuss

  Presently my engine is set up to use deferred shading. My pixel shader output struct is as follows: struct GBuffer { float4 Depth : DEPTH0; //depth render target float4 Normal : COLOR0; //normal render target float4 Diffuse : COLOR1; //diffuse render target float4 Specular : COLOR2; //specular render target }; This works fine for flat surfaces, but I'm trying to implement relief mapping which requires me to manually write to the depth buffer to get correct silhouettes. MSDN suggests doing what I'm already doing to output to my depth render target - however, this has no impact on z culling. I think it might be because XNA uses a different depth buffer for every RenderTarget2D. How can I address these depth buffers from the pixel shader?

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• Make objects slide across the screen in random positions

  - by user3475907

  I want to make an object appear randomly at the right hand side of the screen and then slide across the screen and disapear at the left hand side. I am working with libgdx. I have this bit of code but it makes items fall from the top down. Please help. public EntityManager(int amount, OrthoCamera camera) { player = new Player(new Vector2(15, 230), new Vector2(0, 0), this, camera); for (int i = 0; i < amount; i++) { float x = MathUtils.random(0, MainGame.HEIGHT - TextureManager.ENEMY.getHeight()); float y = MathUtils.random(MainGame.WIDTH, MainGame.WIDTH * 10); float speed = MathUtils.random(2, 10); addEntity(new Enemy(new Vector2(x, y), new Vector2(-0, -speed))); }

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• How do I get my polygons to be lighted by either side?

  - by Molmasepic

  Okay, I am using Ogre3D and Gorilla(2D library for ogre3D) and I am making Gorilla::Screenrenderables in the open scene. The problem that I am having is that when I make a light and have my SR(screenrenderable) near it, it does not light up unless the face of the SR is facing the light... I am wondering if there is a way to maybe set the material or code(which would be harder) so the SR is lit up whether the vertices of the polygon are facing the light or not. I feel it is possible but the main obstacle is how I would go about doing this.

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• Does XNA/MonoGame have a text caching mechanism, or has an open source one been implemented?

  - by Casey

  I'm playing around with MonoGame, and I've noticed the SpriteFont class draws static text very inefficiently. Each time the text is drawn the spacing is recalculated. This isn't a big deal on my quad core PC, but on mobile applications it might be a problem. Before I go and program some text which caches the arrangement of its letters in an array and then feeds that array to the SpriteBatch, I would like to make sure there isn't something available to do this already, either in MonoGame itself or a class someone has implemented and made available for general use.

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• Why the clip space in OpenGL has 4 dimensions?

  - by user827992

  I will use this as a generic reference, but the more i browser online docs and books, the less i understand about this. const float vertexPositions[] = { 0.75f, 0.75f, 0.0f, 1.0f, 0.75f, -0.75f, 0.0f, 1.0f, -0.75f, -0.75f, 0.0f, 1.0f, }; in this online book there is an example about how to draw the first and classic hello world for OpenGL about making a triangle. The vertex structure for the triangle is declared as stated in the code above. The book, as all the other sources about this, stress the point that the Clip Space is a 4D structure that is used to basically decide what will be rasterized and rendered to the screen. Here I have my questions: i can't imagine something in 4D, i don't think that a human can do that, what is a 4D for this Clip space ? the most human-readable doc that i have read speaks about a camera, which is just an abstraction over the clipping concept, and i get that, the problem is, why not using the concept of a camera in the first place which is a more familiar 3D structure? The only problem with the concept of a camera is that you need to define the prospective in other way and so you basically have to add another statement about what kind of camera you wish to have. How i'm supposed to read this 0.75f, 0.75f, 0.0f, 1.0f ? All i get is that they are all float values and i get the meaning of the first 3 values, what does it mean the last one?

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• OpenGL ES 2. How do I Create a Basic Fading Streak Effect?

  - by dugla

  For the iPad app I am writing using OpenGL ES 2 I have a single quad - shaded using GLSL - that is dragged around the screen. Very basic. This works fine. But is rather boring. I want to increase the coolness a bit in the following way: when the user drags the quad it leaves a streak behind that fades over time. Continuous dragging would be a bit like a streaking comet across the night sky. What is the simplest way to implement this? Thanks.

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• Realtime rendering using a ray tracing engine

  - by Keyhan Asghari

  I want to render an object that has a mesh with one million hexagonal elements(100 * 100 * 100). Lights, shadows and textures is not important and each element has a solid color. and finally, the actions I want to have, is simply rotating the object, zooming and panning. I am wondering what ray tracing engine is better for my conditions. or, do I have to take another approach? any help will be appreciated.

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• Parenting Opengl with Groups in LibGDX

  - by Rudy_TM

  I am trying to make an object child of a Group, but this object has a draw method that calls opengl to draw in the screen. Its class its this public class OpenGLSquare extends Actor { private static final ImmediateModeRenderer renderer = new ImmediateModeRenderer10(); private static Matrix4 matrix = null; private static Vector2 temp = new Vector2(); public static void setMatrix4(Matrix4 mat) { matrix = mat; } @Override public void draw(SpriteBatch batch, float arg1) { // TODO Auto-generated method stub renderer.begin(matrix, GL10.GL_TRIANGLES); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y0, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y0, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y0, 0f); renderer.end(); } } In my screen class I have this, i call it in the constructor MyGroupClass spriteLab = new MyGroupClass(spriteSheetLab); OpenGLSquare square = new OpenGLSquare(); square.setX0(100); square.setY0(200); square.setX1(400); square.setY1(280); square.color.set(Color.BLUE); square.setSize(); //spriteLab.addActorAt(0, clock); spriteLab.addActor(square); stage.addActor(spriteLab); And the render in the screen I have @Override public void render(float arg0) { this.gl.glClear(GL10.GL_COLOR_BUFFER_BIT |GL10.GL_DEPTH_BUFFER_BIT); stage.draw(); stage.act(Gdx.graphics.getDeltaTime()); } The problem its that when i use opengl with parent, it resets all the other chldren to position 0,0 and the opengl renderer paints the square in the exact position of the screen and not relative to the parent. I tried using batch.enableBlending() and batch.disableBlending() that fixes the position problem of the other children, but not the relative position of the opengl drawing and it also puts alpha to the glDrawing. What am i doing wrong?:/

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• Triangle Picking Picking Back faces

  - by Tangeleno

  I'm having a bit of trouble with 3D picking, at first I thought my ray was inaccurate but it turns out that the picking is happening on faces facing the camera and faces facing away from the camera which I'm currently culling. Here's my ray creation code, I'm pretty sure the problem isn't here but I've been wrong before. private uint Pick() { Ray cursorRay = CalculateCursorRay(); Vector3? point = Control.Mesh.RayCast(cursorRay); if (point != null) { Tile hitTile = Control.TileMesh.GetTileAtPoint(point); return hitTile == null ? uint.MaxValue : (uint)(hitTile.X + hitTile.Y * Control.Generator.TilesWide); } return uint.MaxValue; } private Ray CalculateCursorRay() { Vector3 nearPoint = Control.Camera.Unproject(new Vector3(Cursor.Position.X, Control.ClientRectangle.Height - Cursor.Position.Y, 0f)); Vector3 farPoint = Control.Camera.Unproject(new Vector3(Cursor.Position.X, Control.ClientRectangle.Height - Cursor.Position.Y, 1f)); Vector3 direction = farPoint - nearPoint; direction.Normalize(); return new Ray(nearPoint, direction); } public Vector3 Camera.Unproject(Vector3 source) { Vector4 result; result.X = (source.X - _control.ClientRectangle.X) * 2 / _control.ClientRectangle.Width - 1; result.Y = (source.Y - _control.ClientRectangle.Y) * 2 / _control.ClientRectangle.Height - 1; result.Z = source.Z - 1; if (_farPlane - 1 == 0) result.Z = 0; else result.Z = result.Z / (_farPlane - 1); result.W = 1f; result = Vector4.Transform(result, Matrix4.Invert(ProjectionMatrix)); result = Vector4.Transform(result, Matrix4.Invert(ViewMatrix)); result = Vector4.Transform(result, Matrix4.Invert(_world)); result = Vector4.Divide(result, result.W); return new Vector3(result.X, result.Y, result.Z); } And my triangle intersection code. Ripped mainly from the XNA picking sample. public float? Intersects(Ray ray) { float? closestHit = Bounds.Intersects(ray); if (closestHit != null && Vertices.Length == 3) { Vector3 e1, e2; Vector3.Subtract(ref Vertices[1].Position, ref Vertices[0].Position, out e1); Vector3.Subtract(ref Vertices[2].Position, ref Vertices[0].Position, out e2); Vector3 directionCrossEdge2; Vector3.Cross(ref ray.Direction, ref e2, out directionCrossEdge2); float determinant; Vector3.Dot(ref e1, ref directionCrossEdge2, out determinant); if (determinant > -float.Epsilon && determinant < float.Epsilon) return null; float inverseDeterminant = 1.0f/determinant; Vector3 distanceVector; Vector3.Subtract(ref ray.Position, ref Vertices[0].Position, out distanceVector); float triangleU; Vector3.Dot(ref distanceVector, ref directionCrossEdge2, out triangleU); triangleU *= inverseDeterminant; if (triangleU < 0 || triangleU > 1) return null; Vector3 distanceCrossEdge1; Vector3.Cross(ref distanceVector, ref e1, out distanceCrossEdge1); float triangleV; Vector3.Dot(ref ray.Direction, ref distanceCrossEdge1, out triangleV); triangleV *= inverseDeterminant; if (triangleV < 0 || triangleU + triangleV > 1) return null; float rayDistance; Vector3.Dot(ref e2, ref distanceCrossEdge1, out rayDistance); rayDistance *= inverseDeterminant; if (rayDistance < 0) return null; return rayDistance; } return closestHit; } I'll admit I don't fully understand all of the math behind the intersection and that is something I'm working on, but my understanding was that if rayDistance was less than 0 the face was facing away from the camera, and shouldn't be counted as a hit. So my question is, is there an issue with my intersection or ray creation code, or is there another check I need to perform to tell if the face is facing away from the camera, and if so any hints on what that check might contain would be appreciated.

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• openGL Camera setup for Zoom in/out centered at point under cursor

  - by user3228921

  I am trying to implement a zoom in/out navigation mode in a openGL 3dViewer. I was able to implement zoom functionality centered at screen center just by moving eye towards the center in perspective mode. Now i am trying to do the zoom centered at arbitrary position under the cursor. I am unable to figure out how should i move my camera forward and backward such that point under cursor remains at the same screen coordinates after zoom in/out. Any help would be appreciated. Below are the images which show the desired effect. Just to mention, I am working in a perspective mode with eye target and up vectors to control camera. Same effect i found in google sketchup and 'zoom to mouse position' setting in blender.

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• How to attach an object to a rotating circle?

  - by armands

  I am trying to make an object get attached on a collision point to a circle that is rotating, but the player needs to get attached with a constant point on the player. For example the player is moving back and forth and when the user touches the screen and the player jumps up but what I need is that when the player collides with the circle it attaches it's legs to it and continues rotating with the circle. So I wanted to know how to make this kind of collision joint in Cocos2d Box2d?

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