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• How to fix bad Collada produced by FBX?

  - by David

  I tried to use the FBX SDK (2011.3.1) to load FBX files and save them as Collada files in order to be able to import FBX files in Panda3D. Unfortunately the resulting Collada files are not usable for several reasons, among them: There's a Maya specific extra technique diffuse <diffuse> <texture texture="Map__2-image" texcoord="CHANNEL0"> <extra> <technique profile="MAYA"> <wrapU sid="wrapU0">TRUE</wrapU> <wrapV sid="wrapV0">TRUE</wrapV> <blend_mode>ADD</blend_mode> </technique> </extra> </texture> </diffuse> It assigns a texcoord channel name that isn't referenced anywhere else in the file (in the previous code sample, no geometry uses "CHANNEL0"...) Every polygon is exported twice, a first time with a basic material (only diffuse color, specular color, etc.) and a second time with a textured material -- this doubles the number of polygons of each model without any valuable reason Anyway, the resulting Collada file cannot be opened correctly either with OpenCOLLADA or Panda3D's "dae2egg". Anyone has any experience on how to "fix" it and make it understandable by common and well-reputed Collada importers such as OpenCOLLADA?

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• Low coupling and tight cohesion

  - by hidayat

  Of course it depends on the situation. But when a lower lever object or system communicate with an higher level system, should callbacks or events be preferred to keeping a pointer to higher level object? For example, we have a world class that has a member variable vector<monster> monsters. When the monster class is going to communicate with the world class, should I prefer using a callback function then or should I have a pointer to the world class inside the monster class?

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• Producing a smooth mesh from density cloud and marching cubes

  - by Wardy

  Based on my results from this question I decided to build myself a 3D noise map containing float values in place of my existing boolean point values. The effect I'm trying to produce is something like this, rather than typical rolling hills; which should explain the "missing cubes" in the image below. If I render my density map in normal "minecraft mode" (1 block per point in the density map) varying the size of the cube based on the value in my density map (floats in the range 0 to 1) I get something like this: I'm now happy that I can produce a density map for the marching cubes algorithm (which will need a little tweaking) but for some reason when I run it through my implementation it's not producing what I expect. My problem is that I'm getting something like the first image in this answer to my previous question, when I want to achieve the effect in the second image. Upon further investigation I can't see how marching cubes does the "move vertex along the edge" type logic (i.e. the difference between the two images on my previous link). I see that it does do some interpolation, but I'm not convinced I have the correct understanding of what I think it should do, because the code in question appears to give the same result regardless of whether I use boolean or float values. I took the code from here which is a C# implementation of marching cubes, but instead of using the MarchingCubesPrimitive I modified it to accept an object of type IDrawable, containing lists for the various collections (vertices, normals, UVs, indices), the logic was otherwise untouched. My understanding is that given a very low isovalue the accuracy level of the surface being rendered should increase, so in short "less 45 degree slows more rolling hills" type mesh output. However this isn't what I'm seeing. Have I missed something or is the implementation flawed and need to be fixed? EDIT: A little more detail on what I am seeing when I "marching cube" the data. Ok so firstly, ignore the fact that the meshes created by the chunks don't "connect" (i'll probably raise another question about this later). Then look at the shaping of the island, it's too ... square, from the voxels rendered as boxes you get the impression there's a clean soft gradual hill and yet from the image there are sharp falling edges even in the most central areas where the gradient in the first image looks the most smooth. The data is "regenerated" each time I run this so no 2 islands come out the same, and it's purely random so not based on noise, but still, how can it look so smooth in 1 image and so not smooth in the other?

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• How can I implement 2D cel shading in XNA?

  - by Artii

  So I was just wondering on how to give a scene I am rendering a hand drawn look (like say Crayon Physics). I don't really want to preprocess the sprites and was thinking of using a shader. Cel shading supplies the effect I want to achieve, but I am only aware of the 3D instances for it. So I wanted to ask if anyone knew a way to get this effect in 2D, or if cel shading would work just as fine on 2D scenes?

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• Simultaneous AI in turn based games

  - by Eduard Strehlau

  I want to hack together a roguelike. Now I thought about entity and world representation and got to a quite big problem. If you want all the AI to act simultaneously you would normally(in cellular automa for examble) just copy the cell buffer and let all action of indiviual cells depend on the copy. Actions which are not valid anymore after some cell before the cell you are currently operating on changed the original enviourment(blocking the path) are just ignored or reapplied with the "current"(between turns) environment. After all cells have acted you copy the current map to the buffer again. Now for an environment with complex AI and big(datawise) entities the copying would take too long. So I thought you could put every action and entity makes into a que(make no changes to the environment) and execute the whole que after everyone took their move. Every interaction on this que are realy interacting entities, so if a entity tries to attack another entity it sends a message to it, the consequences of the attack would be visible next turn, either by just examining the entity or asking the entity for data. This would remove problems like what happens if an entity dies middle in the cue but got actions or is messaged later on(all messages would go to null, and the messages from the entity would either just be sent or deleted(haven't decided yet) But what would happen if a monster spawns a fireball which by itself tracks the player(in the same turn). Should I add the fireball to the enviourment beforehand, so make a change to the environment before executing the action list or just add the ball to the "need updated" list as a special case so it doesn't exist in the environment and still operates on it, spawing after evaluating the action list? Are there any solutions or papers on this subject which I can take a look at? EDIT: I don't need information on writing a roguelike I need information on turn based ai in respective to a complex enviourment.

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• How to change speed without changing path travelled?

  - by Ben Williams

  I have a ball which is being thrown from one side of a 2D space to the other. The formula I am using for calculating the ball's position at any one point in time is: x = x0 + vx0*t y = y0 + vy0*t - 0.5*g*t*t where g is gravity, t is time, x0 is the initial x position, vx0 is the initial x velocity. What I would like to do is change the speed of this ball, without changing how far it travels. Let's say the ball starts in the lower left corner, moves upwards and rightwards in an arc, and finishes in the lower right corner, and this takes 5s. What I would like to be able to do is change this so it takes 10s or 20s, but the ball still follows the same curve and finishes in the same position. How can I achieve this? All I can think of is manipulating t but I don't think that's a good idea. I'm sure it's something simple, but my maths is pretty shaky.

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• Basic tutorial/introduction for 3d matrices, idealy in c++, without openGl or directX

  - by René Nyffenegger

  I am wondering if there is a simple tutorial that covers the basics of how to initialize rotation, translation and projection matrices, and how to multiply them, and how to get the screen coordinates afterwards for a 3d point. Idealy, the tutorial comes with compilable code and is not dependent on any 3rd party library. Searching the internet, I found lots of tutorials, so this is not the problem. Yet, it seemed all of these either covered openGl or directX, or they were theoretical in nature.

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• What could cause a pixel shader to paint outside the lines of the vertex shader output?

  - by Rei Miyasaka

  From what I understand, the pixels that a pixel shader operates on are specified implicitly by the SV_POSITION output (in DirectX) of the vertex shader. What then could cause a pixel shader to render in the middle of nowhere? I used the new Visual Studio 2012 graphics debugger to visualize my vertex and pixel shader output. This is the output from a DrawIndexed() call that draws a cube: The pink part is the rendered output of the pixel shader, which takes the cube on its left as its input. The vertex shader code: cbuffer Buf { float4x4 final; }; struct In { float4 pos:POSITION; float3 norm:NORMAL; float2 texuv:TEXCOORD; }; struct Out { float4 col:COLOR; float2 tex:TEXCOORD; float4 pos:SV_POSITION; }; Out main(In input) { Out output; output.pos = mul(input.pos, final); output.col = float4(1.0f, 0.5f, 0.5f, 1.0f); output.tex = input.texuv; return output; } And the pixel shader: struct In { float4 col:COLOR; float2 tex:TEXCOORD; float4 pos:SV_POSITION; }; float4 main(In input) : SV_TARGET { return input.col; } The raster stage is the only thing between the vertex shader and the pixel shader, so my suspicion is that it's some raster stage settings. But the raster stage shouldn't change the shape of the vertex shader output so drastically, should it?

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• Problems Rendering Text in OpenGL Using FreeType

  - by Sean M.

  I've been following both the FreeType2 tutorial and the WikiBooks tuorial, trying to combine things from them both in order to load and render fonts using the FreeType library. I used the font loading code from the FreeType2 tutorial and tried to implement the rendering code from the wikibooks tutorial (tried being the keyword as I'm still trying to learn model OpenGL, I'm using 3.2). Everything loads correctly and I have the shader program to render the text with working, but I can't get the text to render. I'm 99% sure that it has something to do with how I cam passing data to the shader, or how I set up the screen. These are the code segments that handle OpenGL initialization, as well as Font initialization and rendering: //Init glfw if (!glfwInit()) { fprintf(stderr, "GLFW Initialization has failed!\n"); exit(EXIT_FAILURE); } printf("GLFW Initialized.\n"); //Process the command line arguments processCmdArgs(argc, argv); //Create the window glfwWindowHint(GLFW_SAMPLES, g_aaSamples); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2); g_mainWindow = glfwCreateWindow(g_screenWidth, g_screenHeight, "Voxel Shipyard", g_fullScreen ? glfwGetPrimaryMonitor() : nullptr, nullptr); if (!g_mainWindow) { fprintf(stderr, "Could not create GLFW window!\n"); closeOGL(); exit(EXIT_FAILURE); } glfwMakeContextCurrent(g_mainWindow); printf("Window and OpenGL rendering context created.\n"); glClearColor(0.2f, 0.2f, 0.2f, 1.0f); //Are these necessary for Modern OpenGL (3.0+)? glViewport(0, 0, g_screenWidth, g_screenHeight); glOrtho(0, g_screenWidth, g_screenHeight, 0, -1, 1); //Init glew int err = glewInit(); if (err != GLEW_OK) { fprintf(stderr, "GLEW initialization failed!\n"); fprintf(stderr, "%s\n", glewGetErrorString(err)); closeOGL(); exit(EXIT_FAILURE); } printf("GLEW initialized.\n"); Here is the font file (it's slightly too big to post): CFont.h/CFont.cpp Here is the solution zipped up: [solution] (https://dl.dropboxusercontent.com/u/36062916/VoxelShipyard.zip), if anyone feels they need the entire solution. If anyone could take a look at the code, it would be greatly appreciated. Also if someone has a tutorial that is a little more user friendly, that would also be appreciated. Thanks.

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• How to make unit selection circles merge?

  - by MaT

  I would like to know how to make this effect of merged circle selection. Here are images to illustrate: Basically I'm looking for this effect: How the merge effect of the circles can be achieved ? I didn't found any explanation concerning this effect. I know that to project those texture I can develop a decal system but I don't know how to create the merging effect. If possible, I'm looking for purely shaders solution.

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• add collision detection to sprite?

  - by xBroak

  bassically im trying to add collision detection to the sprite below, using the following: self.rect = bounds_rect collide = pygame.sprite.spritecollide(self, wall_list, False) if collide: # yes print("collide") However it seems that when the collide is triggered it continuously prints 'collide' over and over when instead i want them to simply not be able to walk through the object, any help? def update(self, time_passed): """ Update the creep. time_passed: The time passed (in ms) since the previous update. """ if self.state == Creep.ALIVE: # Maybe it's time to change the direction ? # self._change_direction(time_passed) # Make the creep point in the correct direction. # Since our direction vector is in screen coordinates # (i.e. right bottom is 1, 1), and rotate() rotates # counter-clockwise, the angle must be inverted to # work correctly. # self.image = pygame.transform.rotate( self.base_image, -self.direction.angle) # Compute and apply the displacement to the position # vector. The displacement is a vector, having the angle # of self.direction (which is normalized to not affect # the magnitude of the displacement) # displacement = vec2d( self.direction.x * self.speed * time_passed, self.direction.y * self.speed * time_passed) self.pos += displacement # When the image is rotated, its size is changed. # We must take the size into account for detecting # collisions with the walls. # self.image_w, self.image_h = self.image.get_size() global bounds_rect bounds_rect = self.field.inflate( -self.image_w, -self.image_h) if self.pos.x < bounds_rect.left: self.pos.x = bounds_rect.left self.direction.x *= -1 elif self.pos.x > bounds_rect.right: self.pos.x = bounds_rect.right self.direction.x *= -1 elif self.pos.y < bounds_rect.top: self.pos.y = bounds_rect.top self.direction.y *= -1 elif self.pos.y > bounds_rect.bottom: self.pos.y = bounds_rect.bottom self.direction.y *= -1 self.rect = bounds_rect collide = pygame.sprite.spritecollide(self, wall_list, False) if collide: # yes print("collide") elif self.state == Creep.EXPLODING: if self.explode_animation.active: self.explode_animation.update(time_passed) else: self.state = Creep.DEAD self.kill() elif self.state == Creep.DEAD: pass #------------------ PRIVATE PARTS ------------------# # States the creep can be in. # # ALIVE: The creep is roaming around the screen # EXPLODING: # The creep is now exploding, just a moment before dying. # DEAD: The creep is dead and inactive # (ALIVE, EXPLODING, DEAD) = range(3) _counter = 0 def _change_direction(self, time_passed): """ Turn by 45 degrees in a random direction once per 0.4 to 0.5 seconds. """ self._counter += time_passed if self._counter > randint(400, 500): self.direction.rotate(45 * randint(-1, 1)) self._counter = 0 def _point_is_inside(self, point): """ Is the point (given as a vec2d) inside our creep's body? """ img_point = point - vec2d( int(self.pos.x - self.image_w / 2), int(self.pos.y - self.image_h / 2)) try: pix = self.image.get_at(img_point) return pix[3] > 0 except IndexError: return False def _decrease_health(self, n): """ Decrease my health by n (or to 0, if it's currently less than n) """ self.health = max(0, self.health - n) if self.health == 0: self._explode() def _explode(self): """ Starts the explosion animation that ends the Creep's life. """ self.state = Creep.EXPLODING pos = ( self.pos.x - self.explosion_images[0].get_width() / 2, self.pos.y - self.explosion_images[0].get_height() / 2) self.explode_animation = SimpleAnimation( self.screen, pos, self.explosion_images, 100, 300) global remainingCreeps remainingCreeps-=1 if remainingCreeps == 0: print("all dead")

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• Implementing a multilanguage AI contest platform

  - by Alejandro Piad

  This is a followup to this question. To sum: I'm implementing an AI contest site, where each user may submit several AI implementations for different games. Think about Google AI Challenge but instead of just having a big event once a year, I would like it more on a league fashion, with all virtual players playing with each other every some close period of time. I want to support as many programming languages as possible. I've seen that contest sites (like codeforces) ask you to submit a source code and interact through stdin and stdout. The first question is: what is the best way of supporting multiple languages? As I see it, I can either ask people to upload some binary/script, and interact either through stdin/*stdout*, or sockets, or the file system; or ask people to submit source code, and wrap it with whatever is necessary for the interaction. I would like to skip the need to compile the code by myself (in the server, I mean), but I am willing to do it if its the "best" choice. I need to comunicate virtual players with each other, or even better, with some intermediary arbiter. The second question is regarding security. If I'm going to be running user code in my server, I want to ensure strict security conditions, like no file system access, no networking, etc. Otherwise it would be a safe heaven for hackers. I will be implementing the engine/arbiter in .NET. I would like to support at least C#, C++, Java and Python for the user's implementations. I'm willing to write interfaces for each of these languages to simplify the user interaction with the system. Thanks in advance.

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• GLSL, is it possible to offsetting vertices based on height map colour?

  - by Rob

  I am attempting to generate some terrain based upon a heightmap. I have generated a 32 x 32 grid and a corresponding height map - In my vertex shader I am trying to offset the position of the Y axis based upon the colour of the heightmap, white vertices being higher than black ones. //Vertex Shader Code #version 330 uniform mat4 modelMatrix; uniform mat4 viewMatrix; uniform mat4 projectionMatrix; uniform sampler2D heightmap; layout (location=0) in vec4 vertexPos; layout (location=1) in vec4 vertexColour; layout (location=3) in vec2 vertexTextureCoord; layout (location=4) in float offset; out vec4 fragCol; out vec4 fragPos; out vec2 fragTex; void main() { // Retreive the current pixel's colour vec4 hmColour = texture(heightmap,vertexTextureCoord); // Offset the y position by the value of current texel's colour value ? vec4 offset = vec4(vertexPos.x , vertexPos.y + hmColour.r, vertexPos.z , 1.0); // Final Position gl_Position = projectionMatrix * viewMatrix * modelMatrix * offset; // Data sent to Fragment Shader. fragCol = vertexColour; fragPos = vertexPos; fragTex = vertexTextureCoord; } However the code I have produced only creates a grid with none of the y vertices higher than any others.

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• Greiner-Hormann clipping problem

  - by Belgin

  I have a set of planar polygons in 3D space defined by their vertices in counterclockwise order. Let's define the 'positive face' as being the face of the 3D polygon such as when observed, the vertices appear in counterclockwise order, and the 'negative face', the face which when observed, the vertices appear in clockwise order. I'm doing perspective projection of the set of polygons onto a projection polygon defined by the points in this order: (0, h, 0), (0, 0, 0), (w, 0, 0), and (w, h, 0), where w and h are strictly positive integers. The positive face of this projection polygon is oriented towards positive Z, and the camera point is somewhere at (0, 0, d), where d is a strictly negative number. In order to 'clip' the projected polygons into the projection polygon, I'm applying the Greiner-Hormann (PDF) clipping algorithm, which requires that the clipper and the to-be-clipped polygons be in the same order (i.e. clockwise or counterclockwise). My question is the following: How can I determine whether the projected face of the 3D polygon is the negative or the positive one? Meaning, how do I find out if I have to work with the vertices in normal or inverted order for the algorithm to work? I noticed that only if the 3D polygon is facing the projection polygon with its negative face, both of them are in the same order (counterclockwise), otherwise, a modification needs to be done. Here is a picture (PNG) that illustrates this. Note that the planes described by the polygon from the set and the projection polygon may not always be parallel.

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• How do I make time?

  - by SystemNetworks

  I wanted to output a text for a certain amount of time. One way is to use threads. Are there any other ways? I can't use threads for slick2d. This is my code when I use threads for slick: package javagame; import org.newdawn.slick.GameContainer; import org.newdawn.slick.Graphics; import org.newdawn.slick.Image; import java.util.Random; import org.newdawn.slick.Input; import org.newdawn.slick.*; import org.newdawn.slick.state.*; import org.lwjgl.input.Mouse; public class thread1 implements Runnable { String showUp; int timeLeft; public thread1(String s) { s = showUp; } public void run(Graphics g) { try { g.drawString("%s is sleeping %d", 500, 500); Thread.sleep(timeLeft); g.drawString("%s is awake", 600,600); } catch(Exception e) { } } @Override public void run() { // TODO Auto-generated method stub run(); } } It auto generates a new run() And also when I call it to my main class it has stack overflow!

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• tunnel effect cocos2d

  - by samfisher

  I am looking to create a similar tunnel effect in COCOS2D (iOS). Could anyone suggest any pointers? ref Video 1 ref Video 2 Till now I have tried with several ring shape sprites with decreasing scale and positioned center to a same point and keeping Z decreasing as well for each smaller sprite. With that, animating it with CCScaleTo and changing the size to 2.0 with animation duration but it does not come anyway near to the tunnel effect shown in the reference. Thanks, sam

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• Early Z culling - Ogre

  - by teodron

  This question is concerned with how one can enable this "pixel filter" to work within an Ogre based app. Simply put, one can write two passes, the first without writing any colour values to the frame buffer lighting off colour_write off shading flat The second pass is the one that employs heavy pixel shader computations, hence it would be really nice to get rid of those hidden surface patches and not process them pixel-wise. This approach works, except for one thing: objects with alpha, such as billboard trees suffer in a peculiar way - from one side, they seem to capture the sky/background within their alpha region and ignore other trees/houses behind them, while viewed from the other side, they exhibit the desired behavior. To tackle the issue, I thought I could write a custom vertex shader in the first pass and offset the projected Z component of the vertex a little further away from its actual position, so that in the second pass there is a need to recompute correctly the pixels of the objects closest to the camera. This doesn't work at all, all surfaces are processed in the pixel shader and there is no performance gain. So, if anyone has done a similar trick with Ogre and alpha objects, kindly please help.

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• If I use my own normal values, should I turn off winding order culling?

  - by Phil

  I've discovered that I managed to program a series of boxes with indexed vertices in such a way that every other triangle (Half of each face) has a backwards winding order. As a result, XNA is culling half of them. However, my Vertex objects contain normal data that I have explicitly set, and I am going to implement my own backface culling shortly to reduce the size of the VertexBuffer. Should I turn off winding order culling and manage it myself, or should I make sure the winding order is consistent and let XNA handle it?

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• My grid based collision detection is slow

  - by Fibericon

  Something about my implementation of a basic 2x4 grid for collision detection is slow - so slow in fact, that it's actually faster to simply check every bullet from every enemy to see if the BoundingSphere intersects with that of my ship. It becomes noticeably slow when I have approximately 1000 bullets on the screen (36 enemies shooting 3 bullets every .5 seconds). By commenting it out bit by bit, I've determined that the code used to add them to the grid is what's slowest. Here's how I add them to the grid: for (int i = 0; i < enemy[x].gun.NumBullets; i++) { if (enemy[x].gun.bulletList[i].isActive) { enemy[x].gun.bulletList[i].Update(timeDelta); int bulletPosition = 0; if (enemy[x].gun.bulletList[i].position.Y < 0) { bulletPosition = (int)Math.Floor((enemy[x].gun.bulletList[i].position.X + 900) / 450); } else { bulletPosition = (int)Math.Floor((enemy[x].gun.bulletList[i].position.X + 900) / 450) + 4; } GridItem bulletItem = new GridItem(); bulletItem.index = i; bulletItem.type = 5; bulletItem.parentIndex = x; if (bulletPosition > -1 && bulletPosition < 8) { if (!grid[bulletPosition].Contains(bulletItem)) { for (int j = 0; j < grid.Length; j++) { grid[j].Remove(bulletItem); } grid[bulletPosition].Add(bulletItem); } } } } And here's how I check if it collides with the ship: if (ship.isActive && !ship.invincible) { BoundingSphere shipSphere = new BoundingSphere( ship.Position, ship.Model.Meshes[0].BoundingSphere.Radius * 9.0f); for (int i = 0; i < grid.Length; i++) { if (grid[i].Contains(shipItem)) { for (int j = 0; j < grid[i].Count; j++) { //Other collision types omitted else if (grid[i][j].type == 5) { if (enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].isActive) { BoundingSphere bulletSphere = new BoundingSphere(enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].position, enemy[grid[i][j].parentIndex].gun.bulletModel.Meshes[0].BoundingSphere.Radius); if (shipSphere.Intersects(bulletSphere)) { ship.health -= enemy[grid[i][j].parentIndex].gun.damage; enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].isActive = false; grid[i].RemoveAt(j); break; //no need to check other bullets } } else { grid[i].RemoveAt(j); } } What am I doing wrong here? I thought a grid implementation would be faster than checking each one.

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• Center directional light shadow to the cameras eye

  - by Caesar

  I'm currently drawing my directional light shadow using this view and projection: XMFLOAT3 dir((float)pitch, (float)yaw, (float)roll); XMFLOAT3 center(0.0f, 0.0f, 0.0f); XMVECTOR lightDir = XMLoadFloat3(&dir); XMVECTOR lightPos = radius * lightDir; XMVECTOR targetPos = XMLoadFloat3(&center); XMVECTOR up = XMVectorSet(0.0f, 1.0f, 0.0f, 0.0f); XMMATRIX V = XMMatrixLookAtLH(lightPos, targetPos, up); // This is the view // Transform bounding sphere to light space. XMFLOAT3 sphereCenterLS; XMStoreFloat3(&sphereCenterLS, XMVector3TransformCoord(targetPos, V)); // Ortho frustum in light space encloses scene. float l = sphereCenterLS.x - radius; float b = sphereCenterLS.y - radius; float n = sphereCenterLS.z - radius; float r = sphereCenterLS.x + radius; float t = sphereCenterLS.y + radius; float f = sphereCenterLS.z + radius; XMMATRIX P = XMMatrixOrthographicOffCenterLH(l, r, b, t, n, f); // This is the projection Which works prefect if the center of my scene is at 0.0, 0.0, 0.0. What I would like to do is move the center of the scene relative to the cameras position. How can I do that?

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• Arcball 3D camera - how to convert from camera to object coordinates

  - by user38873

  I have checked multiple threads before posting, but i havent been able to figure this one out. Ok so i have been following this tutorial, but im not using glm, ive been implementing everything up until now, like lookat etc. http://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Arcball So i can rotate with the click and drag of the mouse, but when i rotate 90º degrees around Y and then move the mouse upwards or donwwards, it rotates on the wrong axis, this problem is demonstrated on this part of the tutorial An extra trick is converting the rotation axis from camera coordinates to object coordinates. It's useful when the camera and object are placed differently. For instace, if you rotate the object by 90° on the Y axis ("turn its head" to the right), then perform a vertical move with your mouse, you make a rotation on the camera X axis, but it should become a rotation on the Z axis (plane barrel roll) for the object. By converting the axis in object coordinates, the rotation will respect that the user work in camera coordinates (WYSIWYG). To transform from camera to object coordinates, we take the inverse of the MV matrix (from the MVP matrix triplet). What i have to do acording to the tutorial is convert my axis_in_camera_coordinates to object coordinates, and the rotation is done well, but im confused on what matrix i use to do just that. The tutorial talks about converting the axis from camera to object coordinates by using the inverse of the MV. Then it shows these 3 lines of code witch i havent been able to understand. glm::mat3 camera2object = glm::inverse(glm::mat3(transforms[MODE_CAMERA]) * glm::mat3(mesh.object2world)); glm::vec3 axis_in_object_coord = camera2object * axis_in_camera_coord; So what do i aply to my calculated axis?, the inverse of what, i supose the inverse of the model view? So my question is how do you transform camera axis to object axis. Do i apply the inverse of the lookat matrix? My code: if (cur_mx != last_mx || cur_my != last_my) { va = get_arcball_vector(last_mx, last_my); vb = get_arcball_vector( cur_mx, cur_my); angle = acos(min(1.0f, dotProduct(va, vb)))*20; axis_in_camera_coord = crossProduct(va, vb); axis.x = axis_in_camera_coord[0]; axis.y = axis_in_camera_coord[1]; axis.z = axis_in_camera_coord[2]; axis.w = 1.0f; last_mx = cur_mx; last_my = cur_my; } Quaternion q = qFromAngleAxis(angle, axis); Matrix m; qGLMatrix(q,m); vi = mMultiply(m, vi); up = mMultiply(m, up); ViewMatrix = ogLookAt(vi.x, vi.y, vi.z,0,0,0,up.x,up.y,up.z);

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• Missing z-axis rotation for transforming between two vectors

  - by Steve Baughman

  I'm trying to rotate a cube so that it's facing up, but am getting hung up on the final implementation details. It now reliably will rotate the x,y axis to the correct side, but the z-axis is never rotating (See photos of before and after rotation). When I'm using the code below I always get '0' for my rotationVector.z. What am I missing here? // Define lookAt vector lookAtVector = GLKVector3Make(0,0,1); // Define axes vectors axes[0] = GLKVector3Make(0,0,1); axes[1] = GLKVector3Make(-1,0,0); axes[2] = GLKVector3Make(0,1,0); axes[3] = GLKVector3Make(1,0,0); axes[4] = GLKVector3Make(0,-1,0); axes[5] = GLKVector3Make(0,0,-1); CGFloat highest_dot = -1.0; GLKVector3 closest_axis; for(int i = 0; i < 6; i++) { // multiply cube's axes by existing matrix GLKVector3 axis = GLKMatrix4MultiplyVector3(matrix, axes[i]); CGFloat dot = GLKVector3DotProduct(axis, lookAtVector); if(dot > highest_dot) { closest_axis = axis; highest_dot = dot; } } GLKVector3 rotationVector = GLKVector3CrossProduct(closest_axis, lookAtVector); // Get angle between vectors CGFloat angle = atan2(GLKVector3Length(rotationVector), GLKVector3DotProduct(closest_axis, lookAtVector)); // normalize the rotation vector rotationVector = GLKVector3Normalize(rotationVector); // Create transform CATransform3D rotationTransform = CATransform3DMakeRotation(angle, rotationVector.x, rotationVector.y, rotationVector.z); // add rotation transform to existing transformation baseTransform = CATransform3DConcat(baseTransform, rotationTransform); return baseTransform; Before 3d Rotation After 3d Rotation Implementation based on this post

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• Resources for 2D rendering using OpenGL?

  - by nightcracker

  I noticed that there is quite some difference between 3D and 2D rendering using OpenGL, the techniques are different - pixel-perfect placing is a lot more desirable, among other things. Are there any good (complete) references on using OpenGL for rendering 2D graphics? There are quite a few "tutorials" around on the net that help you open a window, set up a half-decent environment and draw a sprite, but no real good information on rotation, blending, lightning, drawing order, using the z-buffer, particles, "complex" primitives (circles, stars, cross symbols), ensuring pixel-perfect rendering, instancing and many other staple 2D effects/techniques. Any books, great blogs, anything? Any particular awesome libraries to read?

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• CreateRenderTarget returns 0x80070057 in big surface resolution

  - by senggen

  I have created the SLI merged desktop of three 1920x1680 monitors, so the desktop resolution is 5760x1080. There is a 0x80070057 error, while calling CreateRenderTarget to create the RT_Surface: IDirect3DSurface9* _render_surface; HRESULT hr = _device->CreateRenderTarget( _desktop_width * 2, _desktop_height + 1, D3DFMT_A8R8G8B8, D3DMULTISAMPLE_NONE, 0, TRUE, &_render_surface, NULL); It works OK with desktop resolution 1024x768, and the total resolution is 3072x768. In http://msdn.microsoft.com/en-us/library/windows/desktop/bb174361(v=vs.85).aspx, it says If the method succeeds, the return value is D3D_OK. If the method fails, the return value can be one of the following: D3DERR_NOTAVAILABLE, D3DERR_INVALIDCALL, D3DERR_OUTOFVIDEOMEMORY, E_OUTOFMEMORY. and no description about 0x80070057. HRESULT: 0x80070057 (2147942487) Name: E_INVALIDARG Description: An invalid parameter was passed to the returning function Somebody please help me.

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• How does flash store (represent) movieclips and sprites?

  - by humbleBee

  When we draw any object in flash and convert it into a movieclip or a sprite, how is it stored or represented in flash. I know in vector art it is stored or represented as line segments using formulae. Is there any way to get the vertices of the shape that was drawn? For example, lets say a simple rectangle is drawn and is converted to a movieclip. Is there anyway to obtain the vertices and the line segments from the sprite? So that its shape is obtained. Enough information should be obtained so that the shape can be replicated. That's the key - replication. In simple terms, where does flash store information about a shape that has been drawn so that we can obtain it and attempt to replicate the shape ourselves?

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