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• Simplest way to render image over top of another with another image used as mask in OpenGL?

  - by Adam Naylor

  The effect I'm looking for is to have a single large background image that is always visible (at full alpha) and then show a second image (what I call a light map or specular map) that is partially shown over the top based on a third image (which is effectively a mask). The effect is similar to this effect except instead of simply darkening or lightening the background image using the third image it needs to mask the second without effecting the first at all. The third image is the only one that moves therefore hard baking the third images alpha into the second image isn't an option. If my explanation isn't clear I'll provide visual examples when I have more time. I'd prefer not to go down a shader route as I haven't taught myself this area yet so unless I have too I'd rather try to achieve this with simple alpha blending. Happy to use a shader approach. Cheers. Additional These third images are obviously light sources being cast onto the first image showing the specular information from the second image to simulate the light 'shining' off the objects in the first image. The solution I implement will need to allow two light sources to potentially overlap so my current thoughts are that the alpha values of the two images will need to be combined (Added?) to produce a final image which masks the second image? Don't worry about things like coloured lights. For this technique the lights are all considered white.

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• Generate texture for a heightmap

  - by James

  I've recently been trying to blend multiple textures based on the height at different points in a heightmap. However i've been getting poor results. I decided to backtrack and just attempt to recreate one single texture from an SDL_Surface (i'm using SDL) and just send that into opengl. I'll put my code for creating the texture and reading the colour values. It is a 24bit TGA i'm loading, and i've confirmed that the rest of my code works because i was able to send the surfaces pixels directly to my createTextureFromData function and it drew fine. struct RGBColour { RGBColour() : r(0), g(0), b(0) {} RGBColour(unsigned char red, unsigned char green, unsigned char blue) : r(red), g(green), b(blue) {} unsigned char r; unsigned char g; unsigned char b; }; // main loading code SDLSurfaceReader* reader = new SDLSurfaceReader(m_renderer); reader->readSurface("images/grass.tga"); // new texture unsigned char* newTexture = new unsigned char[reader->m_surface->w * reader->m_surface->h * 3 * reader->m_surface->w]; for (int y = 0; y < reader->m_surface->h; y++) { for (int x = 0; x < reader->m_surface->w; x += 3) { int index = (y * reader->m_surface->w) + x; RGBColour colour = reader->getColourAt(x, y); newTexture[index] = colour.r; newTexture[index + 1] = colour.g; newTexture[index + 2] = colour.b; } } unsigned int id = m_renderer->createTextureFromData(newTexture, reader->m_surface->w, reader->m_surface->h, RGB); // functions for reading pixels RGBColour SDLSurfaceReader::getColourAt(int x, int y) { Uint32 pixel; Uint8 red, green, blue; RGBColour rgb; pixel = getPixel(m_surface, x, y); SDL_LockSurface(m_surface); SDL_GetRGB(pixel, m_surface->format, &red, &green, &blue); SDL_UnlockSurface(m_surface); rgb.r = red; rgb.b = blue; rgb.g = green; return rgb; } // this function taken from SDL documentation // http://www.libsdl.org/cgi/docwiki.cgi/Introduction_to_SDL_Video#getpixel Uint32 SDLSurfaceReader::getPixel(SDL_Surface* surface, int x, int y) { int bpp = m_surface->format->BytesPerPixel; Uint8 *p = (Uint8*)m_surface->pixels + y * m_surface->pitch + x * bpp; switch (bpp) { case 1: return *p; case 2: return *(Uint16*)p; case 3: if (SDL_BYTEORDER == SDL_BIG_ENDIAN) return p[0] << 16 | p[1] << 8 | p[2]; else return p[0] | p[1] << 8 | p[2] << 16; case 4: return *(Uint32*)p; default: return 0; } } I've been stumped at this, and I need help badly! Thanks so much for any advice.

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• What is the practical use of IBOs / degenerate vertex in OpenGL?

  - by 0xFAIL

  Vertices in 3D models CAN get cut in the process of optimizing 3D geometry, (degenerate vertices) by 3D graphics software (Blender, ...) when exporting because they aren't needed when reusing a vertex for multiple triangles. (In the current case 3D data is exported from Blender as .ply and read by a simple application that displays the 3D model) Every vertex has a few attributes like position, color, normal, tangent,... But the data for each vertex that is cut through the vertex sharing is lost and is missing in the vertex shader. Modern shader techniques like Bump or Normal mapping require normals/tangents per vertex which are also cut. To use complex shader techniques IBOs must not be used? Or is there a way to use IBOs and retain the data per vertex that was origionally lost?

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• collision detection problems - Javascript/canvas game

  - by Tom Burman

  Ok here is a more detailed version of my question. What i want to do: i simply want the have a 2d array to represent my game map. i want a player sprite and i want that sprite to be able to move around my map freely using the keyboard and also have collisions with certain tiles of my map array. i want to use very large maps so i need a viewport. What i have: I have a loop to load the tile images into an array: /Loop to load tile images into an array var mapTiles = []; for (x = 0; x <= 256; x++) { var imageObj = new Image(); // new instance for each image imageObj.src = "images/prototype/"+x+".jpg"; mapTiles.push(imageObj); } I have a 2d array for my game map: //Array to hold map data var board = [ [1,2,3,4,3,4,3,4,5,6,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [17,18,19,20,19,20,19,20,21,22,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [33,34,35,36,35,36,35,36,37,38,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [49,50,51,52,51,52,51,52,53,54,1,1,1,1,1,1,1,1,1,1,1,1,1,197,198,199,1,1,1,1], [65,66,67,68,146,147,67,68,69,70,1,1,1,1,1,1,1,1,216,217,1,1,1,213,214,215,1,1,1,1], [81,82,83,161,162,163,164,84,85,86,1,1,1,1,1,1,1,1,232,233,1,1,1,229,230,231,1,1,1,1], [97,98,99,177,178,179,180,100,101,102,1,1,1,1,59,1,1,1,248,249,1,1,1,245,246,247,1,1,1,1], [1,1,238,1,1,1,1,239,240,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [216,217,254,1,1,1,1,255,256,1,204,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [232,233,1,1,1,117,118,1,1,1,220,1,1,119,120,1,1,1,1,1,1,1,1,1,1,1,119,120,1,1], [248,249,1,1,1,133,134,1,1,1,1,1,1,135,136,1,1,1,1,1,1,59,1,1,1,1,135,136,1,1], [1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [1,1,216,217,1,1,1,1,1,1,60,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [1,1,232,233,1,1,1,1,1,1,1,1,1,1,1,1,1,1,204,1,1,1,1,1,1,1,1,1,1,1], [1,1,248,249,1,1,1,1,1,1,1,1,1,1,1,1,1,1,220,1,1,1,1,1,1,216,217,1,1,1], [1,1,1,1,1,1,1,1,1,1,1,1,149,150,151,1,1,1,1,1,1,1,1,1,1,232,233,1,1,1], [12,12,12,12,12,12,12,13,1,1,1,1,165,166,167,1,1,1,1,1,1,119,120,1,1,248,249,1,1,1], [28,28,28,28,28,28,28,29,1,1,1,1,181,182,183,1,1,1,1,1,1,135,136,1,1,1,1,1,1,1], [44,44,44,44,44,15,28,29,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [1,1,1,1,1,27,28,29,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [1,1,1,1,1,27,28,29,1,1,1,1,1,1,1,1,1,59,1,1,197,198,199,1,1,1,1,119,120,1], [1,1,1,1,1,27,28,29,1,1,216,217,1,1,1,1,1,1,1,1,213,214,215,1,1,1,1,135,136,1], [1,1,1,1,1,27,28,29,1,1,232,233,1,1,1,1,1,1,1,1,229,230,231,1,1,1,1,1,1,1], [1,1,1,1,1,27,28,29,1,1,248,249,1,1,1,1,1,1,1,1,245,246,247,1,1,1,1,1,1,1], [1,1,1,197,198,199,28,29,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [1,1,1,213,214,215,28,29,1,1,1,1,1,60,1,1,1,1,204,1,1,1,1,1,1,1,1,1,1,1], [1,1,1,229,230,231,28,29,1,1,1,1,1,1,1,1,1,1,220,1,1,1,1,119,120,1,1,1,1,1], [1,1,1,245,246,247,28,29,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,135,136,1,1,60,1,1], [1,1,1,1,1,27,28,29,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1], [1,1,1,1,1,27,28,29,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1] ]; I have my loop to place the correct tile sin the correct positions: //Loop to place tiles onto screen in correct position for (x = 0; x <= viewWidth; x++){ for (y = 0; y <= viewHeight; y++){ var width = 32; var height = 32; context.drawImage(mapTiles[board[y+viewY][x+viewX]],x*width, y*height); } } I Have my player object : //Place player object context.drawImage(playerImg, (playerX-viewX)*32,(playerY-viewY)*32, 32, 32); I have my viewport setup: //Set viewport pos viewX = playerX - Math.floor(0.5 * viewWidth); if (viewX < 0) viewX = 0; if (viewX+viewWidth > worldWidth) viewX = worldWidth - viewWidth; viewY = playerY - Math.floor(0.5 * viewHeight); if (viewY < 0) viewY = 0; if (viewY+viewHeight > worldHeight) viewY = worldHeight - viewHeight; I have my player movement: canvas.addEventListener('keydown', function(e) { console.log(e); var key = null; switch (e.which) { case 37: // Left if (playerY > 0) playerY--; break; case 38: // Up if (playerX > 0) playerX--; break; case 39: // Right if (playerY < worldWidth) playerY++; break; case 40: // Down if (playerX < worldHeight) playerX++; break; } My Problem: I have my map loading an it looks fine, but my player position thinks it's on a different tile to what it actually is. So for instance, i know that if my player moves left 1 tile, the value of that tile should be 2, but if i print out the value it should be moving to (2), it comes up with a different value. How ive tried to solve the problem: I have tried swap X and Y values for the initialization of my player, for when my map prints. If i swap the x and y values in this part of my code: context.drawImage(mapTiles[board[y+viewY][x+viewX]],x*width, y*height); The map doesnt get draw correctly at all and tiles are placed all in random positions or orientations IF i sway the x and y values for my player in this line : context.drawImage(playerImg, (playerX-viewX)*32,(playerY-viewY)*32, 32, 32); The players movements are inversed, so up and down keys move my player left and right viceversa. My question: Where am i going wrong in my code, and how do i solve it so i have my map looking like it should and my player moving as it should as well as my player returning the correct tileID it is standing on or moving too. Thanks Again ALSO Here is a link to my whole code: prototype

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• Register Game Object Components in Game Subsystems? (Component-based Game Object design)

  - by topright

  I'm creating a component-based game object system. Some tips: GameObject is simply a list of Components. There are GameSubsystems. For example, rendering, physics etc. Each GameSubsystem contains pointers to some of Components. GameSubsystem is a very powerful and flexible abstraction: it represents any slice (or aspect) of the game world. There is a need in a mechanism of registering Components in GameSubsystems (when GameObject is created and composed). There are 4 approaches: 1: Chain of responsibility pattern. Every Component is offered to every GameSubsystem. GameSubsystem makes a decision which Components to register (and how to organize them). For example, GameSubsystemRender can register Renderable Components. pro. Components know nothing about how they are used. Low coupling. A. We can add new GameSubsystem. For example, let's add GameSubsystemTitles that registers all ComponentTitle and guarantees that every title is unique and provides interface to quering objects by title. Of course, ComponentTitle should not be rewrited or inherited in this case. B. We can reorganize existing GameSubsystems. For example, GameSubsystemAudio, GameSubsystemRender, GameSubsystemParticleEmmiter can be merged into GameSubsystemSpatial (to place all audio, emmiter, render Components in the same hierarchy and use parent-relative transforms). con. Every-to-every check. Very innefficient. con. Subsystems know about Components. 2: Each Subsystem searches for Components of specific types. pro. Better performance than in Approach 1. con. Subsystems still know about Components. 3: Component registers itself in GameSubsystem(s). We know at compile-time that there is a GameSubsystemRenderer, so let's ComponentImageRender will call something like GameSubsystemRenderer::register(ComponentRenderBase*). pro. Performance. No unnecessary checks as in Approach 1. con. Components are badly coupled with GameSubsystems. 4: Mediator pattern. GameState (that contains GameSubsystems) can implement registerComponent(Component*). pro. Components and GameSubystems know nothing about each other. con. In C++ it would look like ugly and slow typeid-switch. Questions: Which approach is better and mostly used in component-based design? What Practice says? Any suggestions about implementation of Approach 4? Thank you.

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• Delaying a Foreach loop half a second

  - by Sigh-AniDe

  I have created a game that has a ghost that mimics the movement of the player after 10 seconds. The movements are stored in a list and i use a foreach loop to go through the commands. The ghost mimics the movements but it does the movements way too fast, in split second from spawn time it catches up to my current movement. How do i slow down the foreach so that it only does a command every half a second? I don't know how else to do it. Please help this is what i tried : The foreach runs inside the update method DateTime dt = DateTime.Now; foreach ( string commandDirection in ghostMovements ) { int mapX = ( int )( ghostPostition.X / scalingFactor ); int mapY = ( int )( ghostPostition.Y / scalingFactor ); // If the dt is the same as current time if ( dt == DateTime.Now ) { if ( commandDirection == "left" ) { switch ( ghostDirection ) { case ghostFacingUp: angle = 1.6f; ghostDirection = ghostFacingRight; Program.form.direction = ""; dt.AddMilliseconds( 500 );// add half a second to dt break; case ghostFacingRight: angle = 3.15f; ghostDirection = ghostFacingDown; Program.form.direction = ""; dt.AddMilliseconds( 500 ); break; case ghostFacingDown: angle = -1.6f; ghostDirection = ghostFacingLeft; Program.form.direction = ""; dt.AddMilliseconds( 500 ); break; case ghostFacingLeft: angle = 0.0f; ghostDirection = ghostFacingUp; Program.form.direction = ""; dt.AddMilliseconds( 500 ); break; } } } }

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• (Abstract) Game engine design

  - by lukeluke

  I am writing a simple 2D game (for mobile platforms) for the first time. From an abstract point of view, i have the main player controlled by the human, the enemies, elments that will interact with the main player, other living elements that will be controlled by a simple AI (both enemies and non-enemies). The human player will be totally controlled by the player, the other actors will be controlled by AI. So i have a class CActor and a class CActorLogic to start with. I would define a CActor subclass CHero (the main player controlled with some input device). This class will probably implement some type of listener, in order to capture input events. The other players controlled by the AI will be probably a specific subclass of CActor (a subclass per-type, obviously). This seems to be reasonable. The CActor class should have a reference to a method of CActorLogic, that we will call something like CActorLogic::Advance() or similar. Actors should have a visual representation. I would introduce a CActorRepresentation class, with a method like Render() that will draw the actor (that is, the right frame of the right animation). Where to change the animation? Well, the actor logic method Advance() should take care of checking collisions and other things. I would like to discuss the design of a game engine (actors, entities, objects, messages, input handling, visualization of object states (that is, rendering, sound output and so on)) but not from a low level point of view, but from an high level point of view, like i have described above. My question is: is there any book/on line resource that will help me organize things (using an object oriented approach)? Thanks

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• Omni-directional light shadow mapping with cubemaps in WebGL

  - by Winged

  First of all I must say, that I have read a lot of posts describing an usage of cubemaps, but I'm still confused about how to use them. My goal is to achieve a simple omni-directional (point) light type shading in my WebGL application. I know that there is a lot more techniques (like using Two-Hemispheres or Camera Space Shadow Mapping) which are way more efficient, but for an educational purpose cubemaps are my primary goal. Till now, I have adapted a simple shadow mapping which works with spotlights (with one exception: I don't know how to cut off the glitchy part beyond the reach of a single shadow map texture): glitchy shadow mapping<<< So for now, this is how I understand the usage of cubemaps in shadow mapping: Setup a framebuffer (in case of cubemaps - 6 framebuffers; 6 instead of 1 because every usage of framebufferTexture2D slows down an execution which is nicely described here <<<) and a texture cubemap. Also in WebGL depth components are not well supported, so I need to render it to RGBA first. this.texture = gl.createTexture(); gl.bindTexture(gl.TEXTURE_CUBE_MAP, this.texture); gl.texParameteri(gl.TEXTURE_CUBE_MAP, gl.TEXTURE_MIN_FILTER, gl.LINEAR); gl.texParameteri(gl.TEXTURE_CUBE_MAP, gl.TEXTURE_MAG_FILTER, gl.LINEAR); for (var face = 0; face < 6; face++) gl.texImage2D(gl.TEXTURE_CUBE_MAP_POSITIVE_X + face, 0, gl.RGBA, this.size, this.size, 0, gl.RGBA, gl.UNSIGNED_BYTE, null); gl.bindTexture(gl.TEXTURE_CUBE_MAP, null); this.framebuffer = []; for (face = 0; face < 6; face++) { this.framebuffer[face] = gl.createFramebuffer(); gl.bindFramebuffer(gl.FRAMEBUFFER, this.framebuffer[face]); gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_CUBE_MAP_POSITIVE_X + face, this.texture, 0); gl.framebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.RENDERBUFFER, this.depthbuffer); var e = gl.checkFramebufferStatus(gl.FRAMEBUFFER); // Check for errors if (e !== gl.FRAMEBUFFER_COMPLETE) throw "Cubemap framebuffer object is incomplete: " + e.toString(); } Setup the light and the camera (I'm not sure if should I store all of 6 view matrices and send them to shaders later, or is there a way to do it with just one view matrix). Render the scene 6 times from the light's position, each time in another direction (X, -X, Y, -Y, Z, -Z) for (var face = 0; face < 6; face++) { gl.bindFramebuffer(gl.FRAMEBUFFER, shadow.buffer.framebuffer[face]); gl.viewport(0, 0, shadow.buffer.size, shadow.buffer.size); gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT); camera.lookAt( light.position.add( cubeMapDirections[face] ) ); scene.draw(shadow.program); } In a second pass, calculate the projection a a current vertex using light's projection and view matrix. Now I don't know If should I calculate 6 of them, because of 6 faces of a cubemap. ScaleMatrix pushes the projected vertex into the 0.0 - 1.0 region. vDepthPosition = ScaleMatrix * uPMatrixFromLight * uVMatrixFromLight * vWorldVertex; In a fragment shader calculate the distance between the current vertex and the light position and check if it's deeper then the depth information read from earlier rendered shadow map. I know how to do it with a 2D Texture, but I have no idea how should I use cubemap texture here. I have read that texture lookups into cubemaps are performed by a normal vector instead of a UV coordinate. What vector should I use? Just a normalized vector pointing to the current vertex? For now, my code for this part looks like this (not working yet): float shadow = 1.0; vec3 depth = vDepthPosition.xyz / vDepthPosition.w; depth.z = length(vWorldVertex.xyz - uLightPosition) * linearDepthConstant; float shadowDepth = unpack(textureCube(uDepthMapSampler, vWorldVertex.xyz)); if (depth.z > shadowDepth) shadow = 0.5; Could you give me some hints or examples (preferably in WebGL code) how I should build it?

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• AndEngine Box2d game

  - by OneMoreVladimir

  I'm developing a 2d survival shooter using Box2d extension and I've got some questions: I have two AnalogOnScreenControls. Their listeners modify both sprites and bodies. I receive TouchEventPool was exhausted and as their number grows the game crashes accidently. I've tried to put the modification of the bodies and sprites on the UpdateThread but that does not solve the problem. What could be the cause? I have a class that at the beginnig of the game loads all the textures. After I relaunch the game activity several times I receive Unable to find Phys Addr for and "green color" interface. But that doesn't happen if I clear the memory manually through the Task Manager before relaunch What could be the cause? I unload my atlas at the end of the game. The game sometimes crashes at start with NullPointerException in onResumeGame. The solution suggested is to set android:configChanges="orientation|screenSize" but my device is API 10 so it doesn't have screenSize property and orientation only does not seem to help, because the game starts in portrait mode at times (though landscape is set in the code)

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• Optimal Compression for Speech

  - by ashes999

  I'm designing a game that depends heavily on audio; I will have some 300+ speech files (most of them just a word or two long). This can very quickly escalate the size of my final game. What's the optimal way to encode/compress speech files to keep the size minimal without getting audio artifacts? Please address both per-file compression/encoding, and also zipping/compressing the set of all speech files together in your answer. Because I'm not sure which (or combination of both) factors will give me the best results. Edit: I need this to run in Silverlight and Android, so I'm presumably stuck with only MP3 as my option (other than uncompressed wave files).

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• determine collision angle on a rotating body

  - by jorb

  update: new diagram and updated description I have a contact listener set up to try and determine the side that a collision happened at relative to the a bodies rotation. One way to solve this is to find the value of the yellow angle between the red and blue vectors drawn above. The angle can be found by taking the arc cosine of the dot product of the two vectors (Evan pointed this out). One of my points of confusion is the difference in domain of the atan2 function html canvas coordinates and the Box2d rotation information. I know I have to account for this somehow... SS below questions: Does Box2D provide these angles more directly in the collision information? Am I even on the right track? If so, any hints? I have the following javascript so far: Ship.prototype.onCollide = function (other_ent,cx,cy) { var pos = this.body.GetPosition(); //collision position relative to body var d_cx = pos.x - cx; var d_cy = pos.y - cy; //length of initial vector var len = Math.sqrt(Math.pow(pos.x -cx,2) + Math.pow(pos.y-cy,2)); //body angle - can over rotate hence mod 2*Pi var ang = this.body.GetAngle() % (Math.PI * 2); //vector representing body's angle - same magnitude as the first var b_vx = len * Math.cos(ang); var b_vy = len * Math.sin(ang); //dot product of the two vectors var dot_prod = d_cx * b_vx + d_cy * b_vy; //new calculation of difference in angle - NOT WORKING! var d_ang = Math.acos(dot_prod); var side; if (Math.abs(d_ang) < Math.PI/2 ) side = "front"; else side = "back"; console.log("length",len); console.log("pos:",pos.x,pos.y); console.log("offs:",d_cx,d_cy); console.log("body vec",b_vx,b_vy); console.log("body angle:",ang); console.log("dot product",dot_prod); console.log("result:",d_ang); console.log("side",side); console.log("------------------------"); }

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• Bounding volume hierarchy - linked nodes (linear model)

  - by teodron

  The scenario A chain of points: (Pi)i=0,N where Pi is linked to its direct neighbours (Pi-1 and Pi+1). The goal: perform efficient collision detection between any two, non-adjacent links: (PiPi+1) vs. (PjPj+1). The question: it's highly recommended in all works treating this subject of collision detection to use a broad phase and to implement it via a bounding volume hierarchy. For a chain made out of Pi nodes, it can look like this: I imagine the big blue sphere to contain all links, the green half of them, the reds a quarter and so on (the picture is not accurate, but it's there to help understand the question). What I do not understand is: How can such a hierarchy speed up computations between segments collision pairs if one has to update it for a deformable linear object such as a chain/wire/etc. each frame? More clearly, what is the actual principle of collision detection broad phases in this particular case/ how can it work when the actual computation of bounding spheres is in itself a time consuming task and has to be done (since the geometry changes) in each frame update? I think I am missing a key point - if we look at the picture where the chain is in a spiral pose, we see that most spheres are already contained within half of others or do intersect them.. it's odd if this is the way it should work.

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• Dynamic body implementation

  - by ArturoVM

  I am writing a 2D game where one of the characters has some very particular requirements. This character is a body with no particular shape (similar to a fluid, but not so much), it has to be able to grow and shrink (as in actually growing, not just scaling), and it has to have collision detection (even if it's basic). Because of this requirements, it obviously can't be based on a sprite, so direct rendering of the shape should be the logical thing to do. I assume this is no easy task, but I just couldn't find a good physics engine that covers these requirements (or at least no tutorial on how to do it; I particularly searched for Box2D tutorials). Is there a way of doing this with Box2D, SDL, or any other physics or game engine out there? If not, what's a good place to start? I am really clueless as far as soft-body physics are concerned.

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• Beginner question about vertex arrays in OpenGL

  - by MrDatabase

  Is there a special order in which vertices are entered into a vertex array? Currently I'm drawing single textures like this: glBindTexture(GL_TEXTURE_2D, texName); glVertexPointer(2, GL_FLOAT, 0, vertices); glTexCoordPointer(2, GL_FLOAT, 0, coordinates); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); where vertices has four "xy pairs". This is working fine. As a test I doubled the sizes of the vertices and coordinates arrays and changed the last line above to: glDrawArrays(GL_TRIANGLE_STRIP, 0, 8); since vertices now contains eight "xy pairs". I do see two textures (the second is intentionally offset from the first). However the textures are now distorted. I've tried passing GL_TRIANGLES to glDrawArrays instead of GL_TRIANGLE_STRIP but this doesn't work either. I'm so new to OpenGL that I thought it's best to just ask here :-) Cheers!

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• Pixmaps, ByteBuffers, and Textures....Oh my

  - by odaymichael

  My ultimate goal is to take a specific region of the screen, and redraw it somewhere else. For example, take a square from the upper left hand corner of the screen and redraw it on the lower right hand corner, so that it is basically a copy of that screen section; kind of like a minimap, but at the same scale as the original. I have looked in to pixmaps and bytebuffers. Also maybe copying that region from the backbuffer somehow. Wondering the best way to go about this. Any help is appreciated. I am using opengl es and libgdx for what it's worth.

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• Alternatives to multiple sprite batches for achieving 2D particle system depth

  - by Ergwun

  In my 2D XNA game, I render all my sprites with a single sprite batch using SpriteSortMode.BackToFront and BlendState.AlphaBlend. I'm adding a particle system based on the App Hub particles sample. Since this uses SpriteSortMode.Deferred and BlendState.Additive, I will need to have two SpriteBatch.Begin / SpriteBatch.End pairs: one for 'regular' sprites, and one for particles. In my top-down shooter, If I want to have explosions appear under planes, but above the ground, then I believe I will have to have three Begin/End pairs, first to draw everything under the explosions, then to draw the explosions, then to draw everything above the explosions. If I want to have particle effects at multiple different depths, then I'm going to need even more Begin/Endpairs. This is all easy to code, but I'm wondering if there is an alternative way to handle this?

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• Annoying flickering of vertices and edges (possible z-fighting)

  - by Belgin

  I'm trying to make a software z-buffer implementation, however, after I generate the z-buffer and proceed with the vertex culling, I get pretty severe discrepancies between the vertex depth and the depth of the buffer at their projected coordinates on the screen (i.e. zbuffer[v.xp][v.yp] != v.z, where xp and yp are the projected x and y coordinates of the vertex v), sometimes by a small fraction of a unit and sometimes by 2 or 3 units. Here's what I think is happening: Each triangle's data structure holds the plane's (that is defined by the triangle) coefficients (a, b, c, d) computed from its three vertices from their normal: void computeNormal(Vertex *v1, Vertex *v2, Vertex *v3, double *a, double *b, double *c) { double a1 = v1 -> x - v2 -> x; double a2 = v1 -> y - v2 -> y; double a3 = v1 -> z - v2 -> z; double b1 = v3 -> x - v2 -> x; double b2 = v3 -> y - v2 -> y; double b3 = v3 -> z - v2 -> z; *a = a2*b3 - a3*b2; *b = -(a1*b3 - a3*b1); *c = a1*b2 - a2*b1; } void computePlane(Poly *p) { double x = p -> verts[0] -> x; double y = p -> verts[0] -> y; double z = p -> verts[0] -> z; computeNormal(p -> verts[0], p -> verts[1], p -> verts[2], &p -> a, &p -> b, &p -> c); p -> d = p -> a * x + p -> b * y + p -> c * z; } The z-buffer just holds the smallest depth at the respective xy coordinate by somewhat casting rays to the polygon (I haven't quite got interpolation right yet so I'm using this slower method until I do) and determining the z coordinate from the reversed perspective projection formulas (which I got from here: double z = -(b*Ez*y + a*Ez*x - d*Ez)/(b*y + a*x + c*Ez - b*Ey - a*Ex); Where x and y are the pixel's coordinates on the screen; a, b, c, and d are the planes coefficients; Ex, Ey, and Ez are the eye's (camera's) coordinates. This last formula does not accurately give the exact vertices' z coordinate at their projected x and y coordinates on the screen, probably because of some floating point inaccuracy (i.e. I've seen it return something like 3.001 when the vertex's z-coordinate was actually 2.998). Here is the portion of code that hides the vertices that shouldn't be visible: for(i = 0; i < shape.nverts; ++i) { double dist = shape.verts[i].z; if(z_buffer[shape.verts[i].yp][shape.verts[i].xp].z < dist) shape.verts[i].visible = 0; else shape.verts[i].visible = 1; } How do I solve this issue? EDIT I've implemented the near and far planes of the frustum, with 24 bit accuracy, and now I have some questions: Is this what I have to do this in order to resolve the flickering? When I compare the z value of the vertex with the z value in the buffer, do I have to convert the z value of the vertex to z' using the formula, or do I convert the value in the buffer back to the original z, and how do I do that? What are some decent values for near and far? Thanks in advance.

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• Can I use PBOs for textures in iOS?

  - by Radu

  As far as I can see, there is no GL_PIXEL_UNPACK_BUFFER. Also, the OpenGL ES 2.0 specification (and as far as I know, no iOS device currently supports OpenGL ES 2.0) states that glMapBufferOES() can only use GL_ARRAY_BUFFER as a target, yet glTexImage2D() and glTexSubImage2D() only seem to use PBOs if GL_PIXEL_UNPACK_BUFFER is bound. The OpenGL documentation for glBindBuffer() also states that: GL_PIXEL_PACK_BUFFER and GL_PIXEL_UNPACK_BUFFER are available only if the GL version is 2.1 or greater. So, can I use PBOs for textures? Am I missing something obvious?

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• Any ideas on reducing lag in terrain generation?

  - by l5p4ngl312

  Ok so here's the deal. I've written an isometric engine that generates terrain based on camera values using 2D perlin noise. I planned on doing 3D but first I need to work out the lag issues I'm having. I will try to explain how I am doing this so that maybe someone can spot where I am going wrong. I know it should not be this laggy. There is the abstract class Block which right now just contains render(). BlockGrass, etc. extend this class and each has code in the render function to create a textured quad at the given position. Then there is the class Chunk which has the function Generate() and setBlocksInArea(). Generate uses 2D perlin noise to make a height map and stores the heights in a 2D array. It stores the positions of each block it generates in blockarray[x][y][z]. The chunks are 8x8x128. In the main game class there is a 3D array called blocksInArea. The blocks in this array are what gets rendered. When a chunk generates, it adds its blocks to this array at the correct index. It is like this so chunks can be saved to the hard drive (even though they aren't yet) but there can still be optimization with the rendering that you wouldn't have if you rendered each chunk separately. Here's where the laggy part comes in: When the camera moves to a new chunk, a row of chunks generates on the end of the axis that the camera moved on. But it still has to move the other chunks up/down in the blocksInArea (render) array. It does this by calculating the new position in the array and doing the Chunk.setBlocksInArea(): for(int x = 0; x < 8; x++){ for(int y = 0; y < 8; y++){ nx = x+(coordX - camCoordX)*8 ny = y+(coordY - camCoordY)*8 for(int z = 0; z < height[x][y]; z++){ blockarray[x][y][z] = Game.blocksInArea[nx][ny][z]; } } } My reasoning was that this would be much faster than doing the perlin noise all over again, but there are still little spikes of lag when you move in between chunks. Edit: Would it be possible to create a 3 dimensional array list so that shifting of chunks within the array would not be neccessary?

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• How to properly do weapon cool-down reload timer in multi-player laggy environment?

  - by John Murdoch

  I want to handle weapon cool-down timers in a fair and predictable way on both client on server. Situation: Multiple clients connected to server, which is doing hit detection / physics Clients have different latency for their connections to server ranging from 50ms to 500ms. They want to shoot weapons with fairly long reload/cool-down times (assume exactly 10 seconds) It is important that they get to shoot these weapons close to the cool-down time, as if some clients manage to shoot sooner than others (either because they are "early" or the others are "late") they gain a significant advantage. I need to show time remaining for reload on player's screen Clients can have clocks which are flat-out wrong (bad timezones, etc.) What I'm currently doing to deal with latency: Client collects server side state in a history, tagged with server timestamps Client assesses his time difference with server time: behindServerTimeNs = (behindServerTimeNs + (System.nanoTime() - receivedState.getServerTimeNs())) / 2 Client renders all state received from server 200 ms behind from his current time, adjusted by what he believes his time difference with server time is (whether due to wrong clocks, or lag). If he has server states on both sides of that calculated time, he (mostly LERP) interpolates between them, if not then he (LERP) extrapolates. No other client-side prediction of movement, e.g., to make his vehicle seem more responsive is done so far, but maybe will be added later So how do I properly add weapon reload timers? My first idea would be for the server to send each player the time when his reload will be done with each world state update, the client then adjusts it for the clock difference and thus can estimate when the reload will be finished in client-time (perhaps considering also for latency that the shoot message from client to server will take as well?), and if the user mashes the "shoot" button after (or perhaps even slightly before?) that time, send the shoot event. The server would get the shoot event and consider the time shot was made as the server time when it was received. It would then discard it if it is nowhere near reload time, execute it immediately if it is past reload time, and hold it for a few physics cycles until reload is done in case if it was received a bit early. It does all seem a bit convoluted, and I'm wondering whether it will work (e.g., whether it won't be the case that players with lower ping get better reload rates), and whether there are more elegant solutions to this problem.

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• ConsumeStructuredBuffer, what am I doing wrong?

  - by John

  I'm trying to implement the 3rd exercise in chapter 12 of Introduction to 3D Game Programming with DirectX 11, that is: Implement a Compute Shader to calculate the length of 64 vectors. Previous exercises ask you to do the same with typed buffers and regular structured buffers and I had no problems with them. For what I've read, [Consume|Append]StructuredBuffers are bound to the pipeline using UnorderedAccessViews (as long as they use the D3D11_BUFFER_UAV_FLAG_APPEND, and the buffers have both D3D11_BIND_SHADER_RESOURCE and D3D11_BIND_UNORDERED_ACCESS bind flags). Problem is: my AppendStructuredBuffer works, since I can append data to it and retrieve it from the application to write to a results file, but the ConsumeStructuredBuffer always returns zeroed data. Data is in the buffer, since if I change the UAV to a ShaderResourceView and to a StructuredBuffer in the HLSL side it works. I don't know what I am missing: Should I initialize the ConsumeStructuredBuffer on the GPU, or can I do it when I create the buffer (as I amb currently doing). Is it OK to bind the buffer with a UAV as described above? Do I need to bind it as a ShaderResourceView somehow? Maybe I am missing some step? This is the declaration of buffers in the Compute Shader: struct Data { float3 v; }; struct Result { float l; }; ConsumeStructuredBuffer<Data> gInput; AppendStructuredBuffer<Result> gOutput; And here the creation of the buffer and UAV for input data: D3D11_BUFFER_DESC inputDesc; inputDesc.Usage = D3D11_USAGE_DEFAULT; inputDesc.ByteWidth = sizeof(Data) * mNumElements; inputDesc.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_UNORDERED_ACCESS; inputDesc.CPUAccessFlags = 0; inputDesc.StructureByteStride = sizeof(Data); inputDesc.MiscFlags = D3D11_RESOURCE_MISC_BUFFER_STRUCTURED; D3D11_SUBRESOURCE_DATA vinitData; vinitData.pSysMem = &data[0]; HR(md3dDevice->CreateBuffer(&inputDesc, &vinitData, &mInputBuffer)); D3D11_UNORDERED_ACCESS_VIEW_DESC uavDesc; uavDesc.Format = DXGI_FORMAT_UNKNOWN; uavDesc.ViewDimension = D3D11_UAV_DIMENSION_BUFFER; uavDesc.Buffer.FirstElement = 0; uavDesc.Buffer.Flags = D3D11_BUFFER_UAV_FLAG_APPEND; uavDesc.Buffer.NumElements = mNumElements; md3dDevice->CreateUnorderedAccessView(mInputBuffer, &uavDesc, &mInputUAV); Initial data is an array of Data structs, which contain a XMFLOAT3 with random data. I bind the UAV to the shader using the Effects framework: ID3DX11EffectUnorderedAccessViewVariable* Input = mFX->GetVariableByName("gInput")->AsUnorderedAccessView(); Input->SetUnorderedAccessView(uav); // uav is mInputUAV Any ideas? Thank you.

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• Interpolating between two networked states?

  - by Vaughan Hilts

  I have many entities on the client side that are simulated (their velocities are added to their positions on a per frame basis) and I let them dead reckon themselves. They send updates about where they were last seen and their velocity changes. This works great and other players see this work find. However, after a while these players begin to desync after some time. This is because of latency. I'd like to know how I can interpolate between states so they appear to be in the correct position. I know where the player was LAST seen and their current velocity but interpolating to the last seen state causes the player to actually move -backwards-. I could not use velocity at all for other clients and simply 'lerp' them towards the appropriate direction but I feel this would cause jaggy movement. What are the alternatives?

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• Elliptical orbit modeling

  - by Nathon

  I'm playing with orbits in a simple 2-d game where a ship flies around in space and is attracted to massive things. The ship's velocity is stored in a vector and acceleration is applied to it every frame as appropriate given Newton's law of universal gravitation. The point masses don't move (there's only 1 right now) so I would expect an elliptical orbit. Instead, I see this: I've tried with nearly circular orbits, and I've tried making the masses vastly different (a factor of a million) but I always get this rotated orbit. Here's some (D) code, for context: void accelerate(Vector delta) { velocity = velocity + delta; // Velocity is a member of the ship class. } // This function is called every frame with the fixed mass. It's a // method of the ship's. void fall(Well well) { // f=(m1 * m2)/(r**2) // a=f/m // Ship mass is 1, so a = f. float mass = 1; Vector delta = well.position - loc; float rSquared = delta.magSquared; float force = well.mass/rSquared; accelerate(delta * force * mass); }

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• Loading levels from .txt or .XML for XNA

  - by Dave Voyles

  I'm attemptin to add multiple levels to my pong game. I'd like to simply exchange a few elements with each level, nothing crazy. Just the background texture, the color of the AI paddle (the one on the right side), and the music. It seems that the best way to go about this is by utilizing the StreamReader to read and write the files from XML. If there is a better, or more efficient alternative way then I'm all for it. In looking over the XNA Starter Platformer Kit provided by MS it seems that they've done it in this manner as well. I'm perplexed by a few things, however, namely parts within the Level class which aren't commented. /// <summary> /// Iterates over every tile in the structure file and loads its /// appearance and behavior. This method also validates that the /// file is well-formed with a player start point, exit, etc. /// </summary> /// <param name="fileStream"> /// A stream containing the tile data. /// </param> private void LoadTiles(Stream fileStream) { // Load the level and ensure all of the lines are the same length. int width; List<string> lines = new List<string>(); using (StreamReader reader = new StreamReader(fileStream)) { string line = reader.ReadLine(); width = line.Length; while (line != null) { lines.Add(line); if (line.Length != width) throw new Exception(String.Format("The length of line {0} is different from all preceeding lines.", lines.Count)); line = reader.ReadLine(); } } What does width = line.Length mean exactly? I mean I know how it reads the line, but what difference does it make if one line is longer than any of the others? Finally, their levels are simply text files that look like this: .................... .................... .................... .................... .................... .................... .................... .........GGG........ .........###........ .................... ....GGG.......GGG... ....###.......###... .................... .1................X. #################### It can't be that easy..... Can it?

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• Sprite transparency not effected libGDX

  - by Aon GoltzCrank

  I am making a game using libGDX and Tween Universal Engine. My problem is as follows: I have 2 screens so fars, a splash screen with the logo, and a second one which is the main menu. In the splash screen I use a SpriteBatch and a Sprite with the Texture of the image I want (which goes through some scaling.) Now I use the Tween engine, along with a created SpriteAccessor to control the alpha of the sprite. I fade the picture in, then fade it out, then change it to the next screen. In the next screen I have a single sprite, and a single, 3 slot, sprite array. In this screen I also use the tween engine, I fade the single sprite into the screen (it's the background image) then I try to, using the same method, (Tween.to) to change the alpah of the sprite array (each sprite by itself.), I first set it to 0 using Tween.set, then using the method I change it. This didn't work, after some tests I tried setting the alpha of a single sprite from the array to 0, and that didn't work. It's like the program is ignoring the alpha value, I even printed out the alpha value, it saying 0, but the sprite is visible. How can I fix this, or why might it be caused?

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