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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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• Implementing Circle Physics in Java

  - by Shijima

  I am working on a simple physics based game where 2 balls bounce off each other. I am following a tutorial, 2-Dimensional Elastic Collisions Without Trigonometry, for the collision reactions. I am using Vector2 from the LIBGDX library to handle vectors. I am a bit confused on how to implement step 6 in Java from the tutorial. Below is my current code, please note that the code strictly follows the tutorial and there are redundant pieces of code which I plan to refactor later. Note: refrences to this refer to ball 1, and ball refers to ball 2. /* * Step 1 * * Find the Normal, Unit Normal and Unit Tangential vectors */ Vector2 n = new Vector2(this.position[0] - ball.position[0], this.position[1] - ball.position[1]); Vector2 un = n.normalize(); Vector2 ut = new Vector2(-un.y, un.x); /* * Step 2 * * Create the initial (before collision) velocity vectors */ Vector2 v1 = this.velocity; Vector2 v2 = ball.velocity; /* * Step 3 * * Resolve the velocity vectors into normal and tangential components */ float v1n = un.dot(v1); float v1t = ut.dot(v1); float v2n = un.dot(v2); float v2t = ut.dot(v2); /* * Step 4 * * Find the new tangential Velocities after collision */ float v1tPrime = v1t; float v2tPrime = v2t; /* * Step 5 * * Find the new normal velocities */ float v1nPrime = v1n * (this.mass - ball.mass) + (2 * ball.mass * v2n) / (this.mass + ball.mass); float v2nPrime = v2n * (ball.mass - this.mass) + (2 * this.mass * v1n) / (this.mass + ball.mass); /* * Step 6 * * Convert the scalar normal and tangential velocities into vectors??? */

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• OpenGL 2D Rasterization Sub-Pixel Translations

  - by Armin Ronacher

  I have a tile based 2D engine where the projection matrix is an orthographic view of the world without any scaling applied. Thus: one pixel texture is drawn on the screen in the same size. That all works well and looks nice but if the camera makes a sub-pixel movement small lines appear between the tiles. I can tell you in advance what does not fix the problem: GL_NEAREST texture interpolation GL_CLAMP_TO_EDGE What does “fix” the problem is anchoring the camera to the nearest pixel instead of doing a sub-pixel translation. I can live with that, but the camera movement becomes jerky. Any ideas how to fix that problem without resorting to the rounding trick I do currently?

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• Which game logic should run when doing prediction for PNP state updates

  - by spaceOwl

  We are writing a multiplayer game, where each game client (player) is responsible for sending state updates regarding its "owned" objects to other players. Each message that arrives to other (remote) clients is processed as such: Figure out when the message was sent. Create a diff between NOW and that time. Run game specific logic to bring the received state to "current" time. I am wondering which sort of logic should execute as part of step #3 ? Our game is composed of a physical update (position, speed, acceleration, etc) and many other components that can update an object's state and occur regularly (locally). There's a trade off here - Getting the new state quickly or remaining "faithful" to the true state representation and executing the whole thing to predict the "true" state when receiving state updates from remote clients. Which one is recommended to be used? and why?

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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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• 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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• Why am I getting a return value of zero from my position computation function?

  - by Hussain Murtaza

  Ok I have a Function int x(), which is used in new Rectangle(x(),a,a,a); in DrawMethod in XNA but when I use it I get x() = 0 as as the answer.Here is my CODE: int x() { int px = (128 * 5); int xx = 0; for (int i = 0; i < 6; i++) { if (Mouse.GetState().X > px) { //xx = Mouse.GetState().X; xx = px; break; } else { px -= 128; } } return xx; } Here is the DrawMethod Code: if (set) { spriteBatch.Draw(texture, new Rectangle(x(), y(), texture.Width, texture.Height), Color.White); textpositionX = x(); textpositionY = y(); set = false; select = false; place = true; } else if(select) { spriteBatch.Draw(texture, new Rectangle(Mouse.GetState().X - texture.Width / 2, Mouse.GetState().Y-texture.Height / 2, texture.Width, texture.Height), Color.White); } else if (place) { spriteBatch.Draw(texture, new Rectangle(textpositionX, textpositionY, texture.Width, texture.Height), Color.White); select = false; set = false; }

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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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• OpenGl / C++ and some strange light problem on half board

  - by mlodziaszka

  I have some problem with lights in my opengl "game". I have board with is square (-50,50), (50, 50), (50, -50), (-50,-50) x and z since y doesn't matter at all. I tried to make something like flashlight its moving and rotating with camera (me), but when i try to rotate more then 90 degree to left or right it just give diffrend light: http://imageshack.us/photo/my-images/688/lightij.jpg/ (left is spotlight, right point light) There is also a point light in the middle, but its working strange(not like a pointlight) it shines only on half of the board from (-50,50), (50, 50), (50, 0), (-50,-0) x and y: Link to my repo where u can find game exe in download and full code in source: https://bitbucket.org/mlodziaszka/my_game All more fragments of light: float gl_amb[] = { 0.2f, 0.2f, 0.2f, 1.0f }; glLightModelfv(GL_LIGHT_MODEL_AMBIENT, gl_amb); glEnable(GL_LIGHTING); // Wlaczenie oswietlenia glShadeModel(GL_SMOOTH); // Wybor techniki cieniowania glEnable(GL_LIGHT0); // Wlaczenie 0-go zrodla swiatla glEnable(GL_LIGHT1); Cubes parametri: float m1_amb[] = { 1.0f, 0.0f, 0.0f, 1.0f }; float m1_dif[] = { 1.0f, 0.0f, 0.0f, 1.0f }; float m1_spe[] = { 1.0f, 0.0f, 0.0f, 1.0f }; glMaterialfv(GL_FRONT, GL_AMBIENT, m1_amb); glMaterialfv(GL_FRONT, GL_DIFFUSE, m1_dif); glMaterialfv(GL_FRONT, GL_SPECULAR, m1_spe); glMaterialf(GL_FRONT, GL_SHININESS, 50.0f); Texture parametri: float m1_amb[] = { 1.0f, 1.0f, 1.0f, 1.0f }; float m1_dif[] = { 1.0f, 1.0f, 1.0f, 1.0f }; float m1_spe[] = { 1.0f, 1.0f, 1.0f, 1.0f }; glMaterialfv(GL_FRONT, GL_AMBIENT, m1_amb); glMaterialfv(GL_FRONT, GL_DIFFUSE, m1_dif); glMaterialfv(GL_FRONT, GL_SPECULAR, m1_spe); glMaterialf(GL_FRONT, GL_SHININESS, 0.0f); glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE ); Light0: //with some magic sn't working anyway float l0_amb[] = { 0.2f, 0.2f, 0.2f, 1.0f }; float l0_dif[] = { 1.0f, 1.0f, 1.0f, 1.0f }; float l0_spe[] = { 1.0f, 1.0f, 1.0f, 1.0f }; float l0_pos[] = { g_Camera.m_vPosition.x, g_Camera.m_vPosition.y, g_Camera.m_vPosition.z, 1.0f }; float temp = 0.0f, temp2 = 0.0f, temp3 = 0.0f; if(g_Camera.m_vView.z < g_Camera.m_vPosition.z) { temp = g_Camera.m_vView.x - g_Camera.m_vPosition.x; temp2 = g_Camera.m_vView.z - g_Camera.m_vPosition.z; } else { temp = g_Camera.m_vView.x - g_Camera.m_vPosition.x; temp2 = g_Camera.m_vView.z - g_Camera.m_vPosition.z; } float l0_pos1[] = {temp, 0.0f, temp2}; //float l0_pos1[] = {-1.0f, 0.0f, -1.0f}; glLightfv(GL_LIGHT0, GL_AMBIENT, l0_amb); glLightfv(GL_LIGHT0, GL_DIFFUSE, l0_dif); glLightfv(GL_LIGHT0, GL_SPECULAR, l0_spe); glLightfv(GL_LIGHT0, GL_POSITION, l0_pos); glLightf (GL_LIGHT0, GL_SPOT_CUTOFF, 15.0f); glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, l0_pos1); Light1: float l1_amb[] = { 0.2f, 0.2f, 0.2f, 1.0f }; float l1_dif[] = { 1.0f, 1.0f, 1.0f, 1.0f }; float l1_spe[] = { 1.0f, 1.0f, 1.0f, 1.0f }; float l1_pos[] = { 0.0f, 0.0f, 0.0f, 1.0f }; glLightfv(GL_LIGHT1, GL_AMBIENT, l1_amb); glLightfv(GL_LIGHT1, GL_DIFFUSE, l1_dif); glLightfv(GL_LIGHT1, GL_SPECULAR, l1_spe); glLightfv(GL_LIGHT1, GL_POSITION, l1_pos); I know that way I made this very old, but for now i want to keep this like that. I wouldbe realy gratefull if someone can tell me what is wrong with my lights xD full code: link up ^^

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• Which Graphics/Geometry abstraction to choose?

  - by Robz

  I've been thinking about the design for a browser app on the HTML5 canvas that simulates a 2D robot zooming around, sensing the world around it. I decided to do this from scratch just for fun. I need shapes, like polygons, circles, and lines in order to model the robot and the world it lives in. These shapes need to be drawn with different appearance attributes, like border/fill style/width/color. I also need to have geometry functions to detect intersections and containment for the robot's sensors and so that the robot doesn't go inside stuff. One idea for functions is to have two totally separate libraries, one to implement graphics (like drawShape(context, shape)) and one for geometry operations (like shapeIntersectsShape(shape1, shape2)). Or, in a more object-oriented approach, the shape objects themselves could implement methods to do their own graphics (shape.draw(context)) and geometry operations (shape1.intersects(shape2)). Then there is the data itself: whether the data to draw a shape and the data to do geometric operations on that shape should be encapsulated within the same object, or be separate structures (where one would contain the other, or both be contained inside another structure). How do existing applications that do graphics/geometry stuff deal with this? Is there one model that is best, or is each good for certain applications? Should the fact that I'm using Javascript instead of a more classical language change how I approach the design?

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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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• Scrolling Box2D DebugDraw

  - by onedayitwillmake

  I'm developing a game using Box2D (javascript implementation - Box2DWeb), and I would like to know how I can pan the debug draw. I know the usual answer is - don't use debug draw, it's just for debugging. I'm not, however not all my objects are on the same screen, and i'd like to see where they are in the physics representation. How can I pan the debug drawing? As you can see the debug draw stuff, is show on the top left, but it only shows a small part of the world. Here is an example of what I mean: http://onedayitwillmake.com/ChuClone/ The game is open source, If you'd like to poke through and note something that perhaps i'm doing something that is obviously wrong: https://github.com/onedayitwillmake/ChuClone Here's my hacky way that I'm using now to scroll the b2DebugDraw view, in which I added a property offsetX and offsetY into b2DebugDraw

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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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• 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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• 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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• How to make the Angry Birds "shot arch" dotted line? [duplicate]

  - by unexpected62

  This question already has an answer here: Show path of a body of where it should go after linear impulse is applied 2 answers I am making a game that includes 2D projectile flight paths like that of Angry Birds. Angry Birds employs the notion that a previous shot is shown with a dotted line "arch" showing the player where that last shot went. I think recording that data is simple enough once a shot is fired, but in my game, I want to show it preemptively, ie: before the shot. How would I go about calculating this dotted line? The other caveat is I have wind in my game. How can you determine a projectile preemptively when wind will affect it too? This seems like a pretty tough problem. My wind right now just applies a constant force every step of animation in the direction of the wind flow. I'm using Box2D and AndEngine if it matters.

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• Why won't my vertex buffer render in GLFW3?

  - by sm81095

  I have started to try to learn OpenGL, and I decided to use GLFW to assist in window creation. The problem is, since GLFW3 is so new, there are no tutorials on it or how to use it with modern OpenGL (3.3, specifically). Using the GLFW3 tutorial found on the website, which uses older OpenGL rendering (glBegin(GL_TRIANGLES), glVertex3f(), and such), I can get a triangle to render to the screen. The problem is, using new OpenGL, I can't get the same triangle to render to the screen. I am new to OpenGL, and GLFW3 is new to most people, so I may be completely missing something obvious, but here is my code: static const GLuint g_vertex_buffer_data[] = { -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f }; int main(void) { GLFWwindow* window; if(!glfwInit()) { fprintf(stderr, "Failed to initialize GLFW."); return -1; } glfwWindowHint(GLFW_SAMPLES, 4); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); window = glfwCreateWindow(800, 600, "Test Window", NULL, NULL); if(!window) { glfwTerminate(); fprintf(stderr, "Failed to create a GLFW window"); return -1; } glfwMakeContextCurrent(window); glewExperimental = GL_TRUE; GLenum err = glewInit(); if(err != GLEW_OK) { glfwTerminate(); fprintf(stderr, "Failed to initialize GLEW"); fprintf(stderr, (char*)glewGetErrorString(err)); return -1; } GLuint VertexArrayID; glGenVertexArrays(1, &VertexArrayID); glBindVertexArray(VertexArrayID); GLuint programID = LoadShaders("SimpleVertexShader.glsl", "SimpleFragmentShader.glsl"); GLuint vertexBuffer; glGenBuffers(1, &vertexBuffer); glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer); glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW); while(!glfwWindowShouldClose(window)) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glUseProgram(programID); glEnableVertexAttribArray(0); glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0); glDrawArrays(GL_TRIANGLES, 0, 3); glDisableVertexAttribArray(0); glfwSwapBuffers(window); glfwPollEvents(); } glDeleteBuffers(1, &vertexBuffer); glDeleteProgram(programID); glfwDestroyWindow(window); glfwTerminate(); exit(EXIT_SUCCESS); } I know it is not my shaders, they are super simple and I've checked them against GLFW 2.7 so I know that they work. I'm assuming that I've missed something crucial to using the OpenGL context with GLFW3, so any help locating the problem would be greatly appreciated.

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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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• Best way to load rigid bodies from file

  - by Mel

  I'm trying to switch to bullet for physics simulation. Lemme just say first that I am so pleased with bullet's accuracy and performance. After messing around it for a bit, I'm now trying to load rigid bodies from files. Most of my models are in blender and with some searching, I was able to export them in .bullet format. However, loading the files into bullet doesn't look like an easy task. I've come across this page that points me to a sample application that loads bullet files. But then it goes and says that this loader is just a starting point. Is there any open source library out there that will allow me to load rigid bodies from a file? I don't really wanna spend that much time trying to create my own loader.

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• Rope Colliding with a Rectangle

  - by Colton

  I have my rope, and I have my rectangles. The rope is similar to the implementation found here: http://nehe.gamedev.net/tutorial/rope_physics/17006/ Now, I want to make the rope properly collide with the rectangle such that the rope will not pass through a rectangle, and wrap around the rectangle and all that good stuff. Currently, I have it set so no rope node can pass through a rect (successfully), however, this means a rope segment can still pass through a block. Ex: So the question is, what can I do to fix this? What I have tried: I create a rectangle between two nodes of a rope, calculate rotation between the nodes, and get myself a transformed rectangle. I can successfully detect a collision between rope segments and a (non-transformed) rectangle. Create a new node or pivot point around the corner of the block, and rearrange nodes to point to the corner node. Trouble is determining what corner the rope segment is passing through. And then the current rope setup goes wonky (based on verlet integration, so a sudden change in position causes the rope to wiggle like a seismograph during a magnitude 8 earth quake.) Among other issues that might be solvable, but its turning into a case by case thing, which doesn't seem right. I think the best answer here would just be a link to a tutorial (I simply can't find any, most lead to box2D or farseer, but I want to at least learn how it works before I hide behind an engine).

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• Is there a good way to get pixel-perfect collision detection in XNA?

  - by ashes999

  Is there a well-known way (or perhaps reusable bit of code) for pixel-perfect collision detection in XNA? I assume this would also use polygons (boxes/triangles/circles) for a first-pass, quick-test for collisions, and if that test indicated a collision, it would then search for a per-pixel collision. This can be complicated, because we have to account for scale, rotation, and transparency. WARNING: If you're using the sample code from the link from the answer below, be aware that the scaling of the matrix is commented out for good reason. You don't need to uncomment it out to get scaling to work.

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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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• Using two joysticks in Cocos2D

  - by Blade

  Here is what I am trying to do: With the left joystick the player can steer the figure and with the right joystick it can attack. Problem is that the left joystick seems to get all the input, the right one does not even register anything. I enabled multipletouch after the eagleView and gone thoroughly over the code. But I seem to miss something. I initiliaze both sticks and it shows me both of them in game, but like I said, only the left one works. I initialize them both. From the h. file: SneakyJoystick *joystick; SneakyJoystick *joystickRight; And in m.file I synthesize, deallocate and initialize them. In order to use one for controlling and the other for attacking I put this: -(void)updateStateWithDeltaTime:(ccTime)deltaTime andListOfGameObjects:(CCArray*)listOfGameObjects { if ((self.characterState == kStateIdle) || (self.characterState == kStateWalkingBack) || (self.characterState == kStateWalkingLeft) || (self.characterState == kStateWalkingRight)|| (self.characterState == kStateWalkingFront) || (self.characterState == kStateAttackingFront) || (self.characterState == kStateAttackingBack)|| (self.characterState == kStateAttackingRight)|| (self.characterState == kStateAttackingLeft)) { if (joystick.degrees > 60 && joystick.degrees < 120) { if (self.characterState != kStateWalkingBack) [self changeState:kStateWalkingBack]; }else if (joystick.degrees > 1 && joystick.degrees < 59) { if (self.characterState != kStateWalkingRight) [self changeState:kStateWalkingRight]; } else if (joystick.degrees > 211 && joystick.degrees < 300) { if (self.characterState != kStateWalkingFront) [self changeState:kStateWalkingFront]; } else if (joystick.degrees > 301 && joystick.degrees < 360){ if (self.characterState != kStateWalkingRight) [self changeState:kStateWalkingRight]; } else if (joystick.degrees > 121 && joystick.degrees < 210) { if (self.characterState != kStateWalkingLeft) [self changeState:kStateWalkingLeft]; } if (joystickRight.degrees > 60 && joystickRight.degrees < 120) { if (self.characterState != kStateAttackingBack) [self changeState:kStateAttackingBack]; }else if (joystickRight.degrees > 1 && joystickRight.degrees < 59) { if (self.characterState != kStateAttackingRight) [self changeState:kStateAttackingRight]; } else if (joystickRight.degrees > 211 && joystickRight.degrees < 300) { if (self.characterState != kStateAttackingFront) [self changeState:kStateAttackingFront]; } else if (joystickRight.degrees > 301 && joystickRight.degrees < 360){ if (self.characterState != kStateAttackingRight) [self changeState:kStateAttackingRight]; } else if (joystickRight.degrees > 121 && joystickRight.degrees < 210) { if (self.characterState != kStateAttackingLeft) [self changeState:kStateAttackingLeft]; } [self applyJoystick:joystick forTimeDelta:deltaTime]; [self applyJoystick:joystickRight forTimeDelta:deltaTime]; } Maybe it has something to do with putting them both to time delta? I tried working around it, but it did not work. So I am thankful for any input you guys can give me :)

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• How to model interentity membership in entity-component architecture?

  - by croxis

  I'm falling in love with simple grace of entity-component design, although I still have issues breaking from MVC and OOP practices. Some of my game entities have membership relationships with each other (ex: a player is a member of a city, a city is a member of a nation), and I am unsure on the best way to implement it. My initial reaction is to have a a MemberOfCity component that points to the appropriate city component, but components are suppose to have no references to each other. My other option is to have a System do it, but that would require the system to persist data outside of a component. Is there a clean way to do this in an entity-component design, or am I trying to use a hammer on a screw and should use a hybrid/another approach?

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• How does a collision engine work?

  - by JXPheonix

  Original question: Click me How exactly does a collision engine work? This is an extremely broad question. What code keeps things bouncing against each other, what code makes the player walk into a wall instead of walk through the wall? How does the code constantly refresh the players position and objects position to keep gravity and collision working as it should? If you don't know what a collision engine is, basically it's generally used in platform games to make the player acutally hit walls and the like. There's the 2D type and the 3D type, but they all accomplish the same thing: collision. So, what keeps a collision engine ticking?

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