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• How do I accomplish fading texture trails in UDK?

  - by kdshay

  I would like to know how to leave a fading texture/material trail in udk. For example (I'm not sure if there is a special name for this effect): A character may leave footprints that fade after x number of seconds Or, a tank may leave a tracks trail as in Civilization IV. Here is another example of this type of effect. Skip to 1:00 and watch the green slime texture. http://www.youtube.com/watch?v=KdJIauWjE8s How do I accomplish this effect in UDK? Any good tutorials? Thank you.

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• How does opengl-es 2 assemble primitives?

  - by stephelton

  Two things I'm quite confused about. 1) OpenGL ES 2.0 creates primitives before the vertex shader is invoked. Why, then, does it not automatically provide the vertex shader the position of the vertex? 2) OpenGL ES 2.0 supports glDrawElements(), but it does not support glEnableClientState() or GL_VERTEX_ARRAY, so how can this call possibly be used to construct primitives? NOTE: this is OpenGL ES 2.0, NOT normal OpenGL! Thanks!

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• Building dynamic bounding box hierachies.

  - by adivasile

  I've been reading about collision detection and I saw that the first part was a coarse detection which generates possible contacts using bounding box hierarchies. I understand the concept of splitting up your objects in groups, to speed up the detection phase, but I'm a little confused on how do you actually build the hierachy, more so on what criteria is used to group them together. Do I iterate through all the objects in the scene, and check the distance between them to see where they should be inserted in the tree? Do you know some resources that may shed some light on this topic for me?

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• Dynamic Jump spot

  - by Pasquale Sada

  I have an initial velocity V(Vx,Vy,VZ) and a spot where he stands still at S(Sx,Sy,Sz). What I'm trying to achieve is a jump on a spot E(Ex,Ey,Ez) where you have clicked on(only lower or higher spot, because I've in place a simple steering behavior for even terrains). There are no obstacle around. I've implemented a formula that can make him jump in a precise way on a spot but you need to declare an angle: the problem arise when the selected spot is straight above your head. It' pretty lame that the char hang there and can reach a thing that is 1cm above is head. I'll share the code I'm using: Vector3 dir = target - transform.position; // get target direction float h = dir.y; // get height difference dir.y = 0; // retain only the horizontal direction float dist = dir.magnitude ; // get horizontal distance float a = angle * Mathf.Deg2Rad; // convert angle to radians dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle dist += h / Mathf.Tan(a); // correct for small height differences // calculate the velocity magnitude float vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 *a)); return vel * dir.normalized;

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• Octrees as data structure

  - by Christian Frantz

  In my cube world, I want to use octrees to represent my chunks of 20x20x20 cubes for frustum and occlusion culling. I understand how octrees work, I just dont know if I'm going about this the right way. My base octree class is taken from here: http://www.xnawiki.com/index.php/Octree What I'm wondering is how to apply occlusion culling using this class. Does it make sense to have one octree for each cube chunk? Or should I make the octree bigger? Since I'm using cubes, each cube should fit into a node without overlap so that won't be an issue

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• Rotate object Up/Down/Left/Right in any orientation

  - by George Duckett

  I'm rendering model at the origin with a fixed camera looking at it positioned on the z axis. I want to be able to rotate the model up/down and left/right. Currently I have 2 variables, HorizontalRotation and VerticalRotation. When calculating the world matrix I rotate about the Y axis by HorizontalRotation and about the X axis by VerticalRotation. The ..Rotation variables are controlled by pressing up/down/left/right arrow keys. The problem I'm having is that the rotations are happening relative to the object. Lets say it's a model of the world. Pressing Up a bit would let me look at the north pole. Currently when i press right the earth spins infront of the camera on its axis; I'm still looking at the north pole. How can i get it so that no matter what rotations are currently applied i can always rotate my model relative to the camera/world axis?

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• Calculating distance from viewer to object in a shader

  - by Jay

  Good morning, I'm working through creating the spherical billboards technique outlined in this paper. I'm trying to create a shader that calculates the distance from the camera to all objects in the scene and stores the results in a texture. I keep getting either a completely black or white texture. Here are my questions: I assume the position that's automatically sent to the vertex shader from ogre is in object space? The gpu interpolates the output position from the vertex shader when it sends it to the fragment shader. Does it do the same for my depth calculation or do I need to move that calculation to the fragment shader? Is there a way to debug shaders? I have no errors but I'm not sure I'm getting my parameters passed into the shaders correctly. Here's my shader code: void DepthVertexShader( float4 position : POSITION, uniform float4x4 worldViewProjMatrix, uniform float3 eyePosition, out float4 outPosition : POSITION, out float Depth ) { // position is in object space // outPosition is in camera space outPosition = mul( worldViewProjMatrix, position ); // calculate distance from camera to vertex Depth = length( eyePosition - position ); } void DepthFragmentShader( float Depth : TEXCOORD0, uniform float fNear, uniform float fFar, out float4 outColor : COLOR ) { // clamp output using clip planes float fColor = 1.0 - smoothstep( fNear, fFar, Depth ); outColor = float4( fColor, fColor, fColor, 1.0 ); } fNear is the near clip plane for the scene fFar is the far clip plane for the scene

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• Which 3D file formats support multiple animations? [on hold]

  - by Justin

  I'm working on a 3D application that uses Assimp to import 3D models with animations. Personally, I use Blender to create the models and animations. I'm having trouble exporting multiple animations, however. For example, I'd like to have an idle animation, a walk animation, a run animation, etc. So far I've tried COLLADA and DirectX without much success. The COLLADA export will include the first animation, but not any of the others. The DirectX doesn't include any animation. Which 3D file formats support multiple animations? (Preferably one that Assimp can import. Also, the Assimp website says that it doesn't support .blend files with animation, otherwise I'd just do that.)

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• Grid Based Lighting in XNA/Monogame

  - by sm81095

  I know that questions like this have been asked many times, but I have not found one exactly like this yes. I have implemented a top-down grid based world in Monogame, and am starting on the lighting system soon. How I want to do lighting is to have a grid that is 4 times wider and higher, basically splitting each world tile into a 4x4 system of "subtiles". I would like to use a flow like system to spread light across the tiles by reducing the light by a small amount each time. This is kind of the effect I was going for: http://i.imgur.com/rv8LCxZ.png The black grid lines are the light grid, and the red lines are the actual tile grid, and the light drop-off is very exaggerated. I plan to render the world by drawing the unlit grid to a separate RenderTarget2D, then rendering the lighting grid to a separate target and overlaying the two. Basically, my questions are: What would be the algorithm for a flow style lighting system like this? Would there be a more efficient way of rendering this? How would I handle the darkening of the light with colors, reducing the RGB values in each grid, or reducing the alpha in each grid, assuming that I render the light map over the grid using blending? Even assuming the former are possible, what BlendState would I use for that?

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• want to build a replica of chartgame.com

  - by raj

  I want to develop a trading simulator based on technical analysis. my ideal application would exactly be chartgame.com currently chartgame.com doesnt have historical data for stocks beyond the year 2008 and I would like to have data until 2012 and have the capability to extend beyond if needed. what are the fundamentals to build an application like chartgame.com. If anyone here is willing to help I can arrange for the finances.let me know.

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• Leg animation not working

  - by Monacraft

  I am making a simple animation in XNA C# of a leg moving. This is the logic code for the thigh. It is meant to swing from 25' to 335'. However instead, it hits a point and then keeps on spinning in the other direction. Please help, here's the code: private void Thigh_method() { if (Legdata.Left == true) signvalue = -0.05f; else signvalue = 0.05f; if (Legdata.ToMid == true) Thighturn_ang += signvalue; if (Legdata.ToMid == false) Thighturn_ang -= signvalue; if (Thighturn_ang <= 25 || Thighturn_ang <= 335 && Thighturn_ang <= 180) Legdata.Left = true; if (Thighturn_ang >= 25 || Thighturn_ang >= 335 && Thighturn_ang >= 180) Legdata.Left = false; if (Thighturn_ang == 0) Legdata.ToMid = false; if (Math.Abs(Thighturn_ang) >= 25f) Legdata.ToMid = true; } Thanks in advance, Yours: Mona

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• Adding delay between damage

  - by iQue

  I have a bunch of enemies chasing my main-character, and if they intersect I want them to damage him and that's all good. The problem is that right now they damage him as long as they stand around him, every frame! and since it gets called every frame my character's HP reaches 0 almost instantly. I've tried adding delay and I've tried a timertask, but can't get it to work. This is the code I use to check for intersection: private void checkCollision(Canvas canvas) { synchronized (getHolder()) { Rect h1 = happy.getBounds(); for (int i = 0; i < enemies.size(); i++) { for (int j = 0; j < bullets.size(); j++) { Rect b1 = bullets.get(j).getBounds(); Rect e1 = enemies.get(i).getBounds(); if (b1.intersect(e1)) { enemies.get(i).damageHP(5); bullets.remove(j); } if(e1.intersect(h1)){ happy.damageHP(5); // this is the statement that needs some sort of delay, I want them to damage him every 2 seconds they intersect him. } if(enemies.get(i).getHP() <= 0){ enemies.get(i).death(canvas, enemies); score.incScore(5); break; } if(happy.getHP() <= 0){ score.incScore(-50); //end-screen } } } } } If anyone knows the logic to do this please do tell.

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• Avoiding orbiting in pursuit steering behavior

  - by bobobobo

  I have a missile that does pursuit behavior to track (and try and impact) its (stationary) target. It works fine as long as you are not strafing when you launch the missile. If you are strafing, the missile tends to orbit its target. I fixed this by accelerating tangentially to the target first, killing the tangential component of the velocity first, then beelining for the target. So I accelerate in -vT until vT is nearly 0. Then accelerate in the direction of vN. While that works, I'm looking for a more elegant solution where the missile is able to impact the target without explicitly killing the tangential component first.

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• Smoothing rotation

  - by Lewis

  I've spent the last three days trying to work out how to rotate a sprite smoothly depending on the velocity.x value of the sprite. I'm using this: float Proportion = 9.5; float maxDiff = 200; float rotation = fmaxf(fminf(playerVelocity.x * Proportion, maxDiff), -maxDiff); player.rotation = rotation; The behaviour is what I required but if the velocity changes rapidly then it will look like the sprite will jump to face left or jump to face right. I'll go into the behaviour in a little more detail: 0 velocity = sprite faces forwards negative velocity = sprite faces left depending on value. positive velocity = sprite faces right (higher velocity the more it faces right) same as above. I've read about using interpolation rather than an absolute angle to rotate it to but I don't know how to implement that. I have a physics engine available. There is one other way to get around this: to use += on the rotation angle. The thing is that I would then have to change the equation to produce positive and negative values then to make sure the sprite faces 0 once it reaches 0 velocity again. If I add that in now, it keeps the previous angle even after the velocity has dropped / is dropping. Any ideas/code snippets would be greatly appreciated.

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• Mesh with Alpha Texture doesn't blend properly

  - by faulty

  I've followed example from various place regarding setting OutputMerger's BlendState to enable alpha/transparent texture on mesh. The setup is as follows: var transParentOp = new BlendStateDescription { SourceBlend = BlendOption.SourceAlpha, DestinationBlend = BlendOption.InverseDestinationAlpha, BlendOperation = BlendOperation.Add, SourceAlphaBlend = BlendOption.Zero, DestinationAlphaBlend = BlendOption.Zero, AlphaBlendOperation = BlendOperation.Add, }; I've made up a sample that display 3 mesh A, B and C, where each overlaps one another. They are drawn sequentially, A to C. Distance from camera where A is nearest and C is furthest. So, the expected output is that A see through and saw part of B and C. B will see through and saw part of C. But what I get was none of them see through in that order, but if I move C closer to the camera, then it will be semi transparent and see through A and B. B if move closer to camera will see A but not C. Sort of reverse. So it seems that I need to draw them in reverse order where furthest from camera is drawn first then nearest to camera is drawn last. Is it suppose to be done this way, or I can actually configure the blendstate so it works no matter in which order i draw them? Thanks

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• How to obtain window handle in SDL 2.0.3

  - by Diorthotis

  I need to obtain the handle of the window for SDL 2.0.3. I got the suggestion to use info.window after initializing SDL and filling the info variable with data by calling SDL_GetWindowWMInfo(); included in the header file SDL_syswm.h. My compiler (visual studio 2008 professional edition) gives the following error: 226) : error C2039: 'window' : is not a member of 'SDL_SysWMinfo' 1 include\sdl_syswm.h(173) : see declaration of 'SDL_SysWMinfo' Any help appreciated. Thanks. Nevermind, I needed to use "info.info.win.window". That seems a bit redundant, but whateves.

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• Lerping to a center point while in motion

  - by Fibericon

  I have an enemy that initially flies in a circular motion, while facing away from the center point. This is how I achieve that: position.Y = (float)(Math.Cos(timeAlive * MathHelper.PiOver4) * radius + origin.Y); position.X = (float)(Math.Sin(timeAlive * MathHelper.PiOver4) * radius + origin.X); if (timeAlive < 5) { angle = (float)Math.Atan((0 - position.X) / (0 - position.Y)); if (0 < position.Y) RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * Matrix.CreateRotationZ(-1 * angle); else RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * Matrix.CreateRotationZ(MathHelper.Pi - angle); } That part works just fine. After five seconds of this, I want the enemy to turn inward, facing the center point. However, I've been trying to lerp to that point, since I don't want it to simply jump to the new rotation. Here's my code for trying to do that: else { float newAngle = -1 * (float)Math.Atan((0 - position.X) / (0 - position.Y)); angle = MathHelper.Lerp(angle, newAngle, (float)gameTime.ElapsedGameTime.Milliseconds / 1000); if (0 < position.Y) RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * Matrix.CreateRotationZ(MathHelper.Pi - angle); else RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * Matrix.CreateRotationZ(-1 * angle); } That doesn't work so fine. It seems like it's going to at first, but then it just sort of skips around. How can I achieve what I want here?

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• Separate collision mesh model?

  - by Menno Gouw

  I want to have another go at 3D within XNA. What I have seen from some other games that they just have a separate very low poly model "cage" around the environment model. However I can not find any reference to this. I have not that much experience with XNA 3D either. Is it possible to have this cage within each of my environmental models already? Lets just say I call the mesh within the .FBX wall and col_wall. How would I call to these different meshes within XNA? The player would just have a tight collision cube around. To make it a bit more efficient I will be making divide the map up by cubes and only calculate collision if the player is in it. Question two: I can't find anywhere to do cube vs mesh collision. Is there a method for this? Or perhaps it is possible to build my collision cage out of cubes in the 3D app and on loading of the models in XNA replace them directly by cubes? So I could just do box to box collision which should be very cheap and still give the player the ability to move over ledges on the static models.

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• Maya is lagging in a specific way...?

  - by Aerovistae

  My Maya installation worked perfectly. It is not my computer. Something caused it to stop working overnight, somehow. When I try to drag a vertex or something like that, it moves the vertex, but then I have to click like 3 times somewhere outside the mesh before the actual mesh will catch up and follow the vertex. Until I do that, it just stays as it was, with a floating vertex somewhere inside it or outside it. It makes modeling borderline impossible and completely infuriating. What ought to be happening is what we're all used to-- as I move the vertex, the mesh follows it actively, so I can see what it looks like at every given moment until I release the vertex in its new position. Other weird thing: this only applies to complex meshes, like a couple thousand faces. A simple cube works fine. What gives?? Anybody?

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• HTML5 Canvas Converting between cartesian and isometric coordinates

  - by Amir

  I'm having issues wrapping my head around the Cartesian to Isometric coordinate conversion in HTML5 canvas. As I understand it, the process is two fold: (1) Scale down the y-axis by 0.5, i.e. ctx.scale(1,0.5); or ctx.setTransform(1,0,0,0.5,0,0); This supposedly produces the following matrix: [x; y] x [1, 0; 0, 0.5] (2) Rotate the context by 45 degrees, i.e. ctx.rotate(Math.PI/4); This should produce the following matrix: [x; y] x [cos(45), -sin(45); sin(45), cos(45)] This (somehow) results in the final matrix of ctx.setTransform(2,-1,1,0.5,0,0); which I cannot seem to understand... How is this matrix derived? I cannot seem to produce this matrix by multiplying the scaling and rotation matrices produced earlier... Also, if I write out the equation for the final transformation matrix, I get: newX = 2x + y newY = -x + y/2 But this doesn't seem to be correct. For example, the following code draws an isometric tile at cartesian coordinates (500, 100). ctx.setTransform(2,-1,1,0.5,0,0); ctx.fillRect(500, 100, width*2, height); When I check the result on the screen, the actual coordinates are (285, 215) which do not satisfy the equations I produced earlier... So what is going on here? I would be very grateful if you could: (1) Help me understand how the final isometric transformation matrix is derived; (2) Help me produce the correct equation for finding the on-screen coordinates of an isometric projection. Many thanks and kind regards

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• How can I render a semi transparent model with OpenGL correctly?

  - by phobitor

  I'm using OpenGL ES 2 and I want to render a simple model with some level of transparency. I'm just starting out with shaders, and I wrote a simple diffuse shader for the model without any issues but I don't know how to add transparency to it. I tried to set my fragment shader's output (gl_FragColor) to a non opaque alpha value but the results weren't too great. It sort of works, but it looks like certain model triangles are only rendered based on the camera position... It's really hard to describe what's wrong so please watch this short video I recorded: http://www.youtube.com/watch?v=s0JqA0rZabE I thought this was a depth testing issue so I tried playing around with enabling/disabling depth testing and back face culling. Enabling back face culling changes the output slightly but the problem in the video is still there. Enabling/disabling depth testing doesn't seem to do anything. Could anyone explain what I'm seeing and how I can add some simple transparency to my model with the shader? I'm not looking for advanced order independent transparency implementations. edit: Vertex Shader: // color varying for fragment shader varying mediump vec3 LightIntensity; varying highp vec3 VertexInModelSpace; void main() { // vec4 LightPosition = vec4(0.0, 0.0, 0.0, 1.0); vec3 LightColor = vec3(1.0, 1.0, 1.0); vec3 DiffuseColor = vec3(1.0, 0.25, 0.0); // find the vector from the given vertex to the light source vec4 vertexInWorldSpace = gl_ModelViewMatrix * vec4(gl_Vertex); vec3 normalInWorldSpace = normalize(gl_NormalMatrix * gl_Normal); vec3 lightDirn = normalize(vec3(LightPosition-vertexInWorldSpace)); // save vertexInWorldSpace VertexInModelSpace = vec3(gl_Vertex); // calculate light intensity LightIntensity = LightColor * DiffuseColor * max(dot(lightDirn,normalInWorldSpace),0.0); // calculate projected vertex position gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex; } Fragment Shader: // varying to define color varying vec3 LightIntensity; varying vec3 VertexInModelSpace; void main() { gl_FragColor = vec4(LightIntensity,0.5); }

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• Zooming to point of interest

  - by user1010005

  I have the following variables: Point of interest which is the position(x,y) in pixels of the place to focus. Screen width,height which are the dimensions of the window. Zoom level which sets the zoom level of the camera. And this is the code I have so far. void Zoom(int pointOfInterestX,int pointOfInterstY,int screenWidth, int screenHeight,int zoomLevel) { glTranslatef( (pointOfInterestX/2 - screenWidth/2), (pointOfInterestY/2 - screenHeight/2),0); glScalef(zoomLevel,zoomLevel,zoomLevel); } And I want to do zoom in/out but keep the point of interest in the middle of the screen. but so far all of my attempts have failed and I would like to ask for some help.

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• Black or White Border/Shadow around PNGs in SDL/OPENGL

  - by Dylan

  having the same issue as this: Why do my sprites have a dark shadow/line/frame surrounding the texture? however, when I do the fix suggested there (changing GL_SRC_ALPHA to GL_ONE) it just replaces the black border with a white border on the images, and messes with my background color and some polygons I'm drawing (not all of them weirdly) by making them much lighter... any ideas? heres some of my relevant code. init: glMatrixMode(GL_PROJECTION); glLoadIdentity(); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glEnable(GL_DEPTH_TEST); glEnable(GL_MULTISAMPLE); glEnable(GL_TEXTURE_2D); glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); glAlphaFunc(GL_GREATER, 0.01); glEnable(GL_ALPHA_TEST); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); glEnable(GL_BLEND); when each texture is loaded: glGenTextures(1, &textureID); glBindTexture(GL_TEXTURE_2D, textureID); gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGBA, surface->w, surface->h, GL_BGRA, GL_UNSIGNED_BYTE, surface->pixels); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

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• OpenGL Application displays only 1 frame

  - by Avi

  EDIT: I have verified that the problem is not the VBO class or the vertex array class, but rather something else. I have a problem where my vertex buffer class works the first time its called, but displays nothing any other time its called. I don't know why this is, and it's also the same in my vertex array class. I'm calling the functions in this order to set up the buffers: enable client states bind buffers set buffer / array data unbind buffers disable client states Then in the draw function, that's called every frame: enable client states bind buffers set pointers unbind buffers bind index buffer draw elements unbind index buffer disable client states Is there something wrong with the order in which I'm calling the functions, or is it a more specific code error? EDIT: here's some of the code Code for setting pointers: //element is the vertex attribute being drawn (e.g. normals, colors, etc.) static void makeElementPointer(VertexBufferElements::VBOElement element, Shader *shade, void *elementLocation) { //elementLocation is BUFFER_OFFSET(n) if a buffer is bound switch (element) { .... glVertexPointer(3, GL_FLOAT, 0, elementLocation); //changes based on element .... //but I'm only dealing with } //vertices for now } And that's basically all the code that isn't just a straight OpenGL function call.

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• Where have the Direct3D 11 tutorials on MSDN have gone?

  - by Cam Jackson

  I've had this tutorial bookmarked for ages. I've just decided to give DX11 a real go, so I've gone through that tutorial, but I can't find where the next one in the series is! There are no links from that page to either the next in the series, or back up to the table of contents that lists all of the tutorials. These are just companion tutorials to the samples that come with the SDK, but I find them very helpful. Searching MSDN from google and the MSDN Bing search box has turned up nothing, it's like they've removed all links to these tutorials, but the pages are still there if you have the URLs. Unfortunately, MSDN URLs are akin to youtube URLs, so I can't just guess the URL of the next tutorial. Anyone have any idea what happened to these tutorials, or how I can find the others?

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