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

  - by Belgin

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

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• Masking OpenGL texture by a pattern

  - by user1304844

  Tiled terrain. User wants to build a structure. He presses build and for each tile there is an "allow" or "disallow" tile sprite added to the scene. FPS drops right away, since there are 600+ tiles added to the screen. Since map equals screen, there is no scrolling. I came to an idea to make an allow grid covering the whole map and mask the disallow fields. Approach 1: Create allow and disallow grid textures. Draw a polygon on screen. Pass both textures to the fragment shader. Determine the position inside the polygon and use color from allowTexture if the fragment belongs to the allow field, disallow otherwise Problem: How do I know if I'm on the field that isn't allowed if I cannot pass the matrix representing the map (enum FieldStatus[][] (Allow / Disallow)) to the shader? Therefore, inside the shader I don't know which fragments should be masked. Approach 2: Create allow texture. Create an empty texture buffer same size as the allow texture Memset the pixels of the empty texture to desired color for each pixel that doesn't allow building. Draw a polygon on screen. Pass both textures to the fragment shader. Use texture2 color if alpha 0, texture1 color otherwise. Problem: I'm not sure what is the right way to manipulate pixels on a texture. Do I just make a buffer with width*height*4 size and memcpy the color[] to desired coordinates or is there anything else to it? Would I have to call glTexImage2D after every change to the texture? Another problem with this approach is that it takes a lot more work to get a prettier effect since I'm manipulating the color pixels instead of just masking two textures. varying vec2 TexCoordOut; uniform sampler2D Texture1; uniform sampler2D Texture2; void main(void){ vec4 allowColor = texture2D(Texture1, TexCoordOut); vec4 disallowColor = texture2D(Texture2, TexCoordOut); if(disallowColor.a > 0){ gl_FragColor= disallowColor; }else{ gl_FragColor= allowColor; }} I'm working with OpenGL on Windows. Any other suggestion is welcome.

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• Drawing of a huge model - How to regain performance?

  - by marc wellman

  I have a huge model I want to draw in my XNA application but because of its size I am experiencing a tremendous loss of performance. The model has about ~50 000 000 edges and has a size on disk of 205 MB in DirectX Format. Please don't ask whether this model has to be that big - yes it has! Is there a way to transfer the model directly to my GPU in order to let the GPU do the drawing like when transferring a VertexBuffer like this: graphicsDevice.Vertices[1].SetSource(_instanceBuffers[i], 0, _sizeofMatrix); because when I try to fill a vertexBuffer with all the vertices I am getting a OutOfMemoryException.

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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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• Rotating multiple points at once in 2D

  - by Deukalion

  I currently have an editor that creates shapes out of (X, Y) coordinates and then triangulate that to make up a shape of those points. What will I have to do to rotate all of those points simultaneously? Say I click the screen in my editor, it locates the point where I've clicked and if I move the mouse up or down from that point it calculates rotation on X and Y axis depending on new position relevant to first position, say I move up 10 on the Y axis it rotates that way and the same way for X. Or simply, somehow to enter rotation degree: 90, 180, 270, 360, for example. I use VertexPositionColor at the moment. What are the best algorithms or methods that I can look at to rotate multiple points in 2D at once? Also: Since this is an editor I do now want to rotate it on the Matrix, so if I want to rotate the whole shape 180 degree that's the new "position" of all the points, so that's the new rotation = 0 for example. Later on I probably will use World Matrix rotation for this, but not now.

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• Directx and Open Libraries list? [closed]

  - by OVERTONE

  I've just been looking for comparissons between open and proprietary frameworks and libraries. More so just to get an idea of what exists than how they compare. For example: We have DirectX (graphics) and its open counterpart OpenGL DirectX (sound) and OpenAL But there are other DirectX libraries that I can't find open alternatives to such as DirectInput DXGI Direct2D DirectWrite Doe's anyone have any list's or Comparisons between Directx and their open counterparts?

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• Floodfill algorithm for GO

  - by user1048606

  The floodfill algorithm is used in the bucket tool in MS paint and photoshop, but it can also be used for GO and minesweeper. http://en.wikipedia.org/wiki/Flood_fill In go you can capture groups of stones, this website portrays it with two stones. http://www.connectedglobe.com/mindy/cap6.html This is my floodfill method in Java, it is not capturing a group of stones and I have no idea why because to me it makes sense. public void floodfill(int turn, int col, int row){ for(int a = col; a<19; a++){ for(int b = row; b<19; b++){ if(turn == black){ if(stones[col][row] == white){ stones[col][row] = 0; floodfill(black, col-1, row); floodfill(black, col+1, row); floodfill(black, col, row-1); floodfill(black, col, row+1); } } } } } It searches up, down, left, right for all the stones on the board. If the stones are white it captures them by making them 0, which represents empty.

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• Checking whether a specific key was pressed in enchantJS

  - by MxyL

  I am using enchantJS and would like to use the letters and numbers as well as numpad on a keyboard to do different things (eg: hotkeys). From this page http://users.csc.calpoly.edu/~foaad/enchant/guide/playerInput.html By default, enchant.js provides input listeners for six buttons: UP, DOWN, LEFT, RIGHT, A, and B. By default, the directions are bound to the arrow keys. Any of the six buttons may also be bound to any key with an ASCII value. We’ll address that later. So enchant provides the ability to bind keys to different input such as up, down, left, right...but how can I simply check whether the D or X key was pressed, and if so, perform certain actions based on that event?

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• Surface normal to screen angle

  - by Tannz0rz

  I've been struggling to get this working. I simply wish to take a surface normal and convert it to a screen angle. As an example, assuming we're working with the highlighted surface on the sphere below, where the arrow is the normal, the 2D angle would obviously be PI/4 radians. Here's one of the many things I've tried to no avail: float4 A = v.vertex; float4 B = v.vertex + float4(v.normal, 0.0); A = mul(VP, A); B = mul(VP, B); A.xy = (0.5 * (A.xy / A.w)) + 0.5; B.xy = (0.5 * (B.xy / B.w)) + 0.5; o.theta = atan2(B.y - A.y, B.x - A.x); I'm finally at my wit's end. Thanks for any and all help.

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

  - by Adam Naylor

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

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• Low complexity shader to indicate the sides of a polyline

  - by Pris

  I have a bunch of polylines that I draw using GL_LINES. They can have thousands of points. They actually represent the separation of land and water on a map. I don't have complete polygons, just the ordered set of points. I'm looking for a neat but efficient way to visually convey Side A and Side B as being different. For example I could offset the polyline in one direction a few times and fade it out (but every offset is doubling the number of points), or offset it once to make a "ribbon" and give one side a 'glow' like effect to mimic the outer glow or shadow of a polygon). This is for a mobile application and I'm using OpenGL ES 2. I'd like to keep the effect as simple as possible from a complexity stand point. I'm looking for some additional ideas; maybe there's a clever shader technique out there or a visual effect I haven't considered.

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• Finding closest object to a location within a specific perpendicular distance to direction vector

  - by Sniper

  I have a location and a direction vector indicating facing, I want to find the closest object to that location that is within some tolerance distance (perpendicular distance) to the ray formed by the location and direction vector. Basically I want to get the object that is being aimed at. I have thought about finding all objects within a box and then finding the closest object to my vector from them results, but I am sure that there is a more efficient way. The Z axis is optional, the objects are most likely within a few meters of the search vector.

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• Inverse projection: question about w coordinate

  - by fayeWilly

  I have to perform in shader an inverse projection from a u/v of a render target. What I do is: Get NDC as 2*(u,v,depth) - 1 Then world space as tmp = (P*V)^-1 * (NDC,1.0); world space = tmp/tmp.w; This apparently works, but I am confused about the w division there. Why this work? Shouldn't be a multiplication by a w somewhere (as in the "forward" pipeline there is the perpsective division?) Thank you, Faye

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• What causes player box/world geometry glitches in old games?

  - by Alexander

  I'm looking to understand and find the terminology for what causes - or allows - players to interfere with geometry in old games. Famously, ID's Quake3 gave birth to a whole community of people breaking the physics by jumping, sliding, getting stuck and launching themselves off points in geometry. Some months ago (though I'd be darned if I can find it again!) I saw a conference held by Bungie's Vic DeLeon and a colleague in which Vic briefly discussed the issues he ran into while attempting to wrap 'collision' objects (please correct my terminology) around environment objects so that players could appear as though they were walking on organic surfaces, while not clipping through them or appear to be walking on air at certain points, due to complexities in the modeling. My aim is to compose a case study essay for University in which I can tackle this issue in games, drawing on early exploits and how techniques have changed to address such exploits and to aid in the gameplay itself. I have 3 current day example of where exploits still exist, however specifically targeting ID Software clearly shows they've massively improved their techniques between Q3 and Q4. So in summary, with your help please, I'd like to gain a slightly better understanding of this issue as a whole (its terminology mainly) so I can use terms and ask the right questions within the right contexts. In practical application, I know what it is, I know how to do it, but I don't have the benefit of level design knowledge yet and its technical widgety knick-knack terms =) Many thanks in advance AJ

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• Blender - creating bones from transform matrices

  - by user975135

  Notice: this is for the Blender 2.5/2.6 API. Back in the old days in the Blender 2.4 API, you could easily create a bone from a transform matrix in your 3d file as EditBones had an attribute named "matrix", which was an armature-space matrix you could access and modify. The new 2.5+ API still has the "matrix" attribute for EditBones, but for some unknown reason it is now read-only. So how to create EditBones from transform matrices? I could only find one thing: a new "transform()" function, which takes a Matrix too. Transform the the bones head, tail, roll and envelope (when the matrix has a scale component). Perfect, but you already need to have some values (loc/rot/scale) for your bone, otherwise transforming with a matrix like this will give you nothing, your bone will be a zero-sized bone which will be deleted by Blender. if you create default bone values first, like this: bone.tail = mathutils.Vector([0,1,0]) Then transform() will work on your bone and it might seem to create correct bones, but setting a tail position actually generates a matrix itself, use transform() and you don't get the matrix from your model file on your EditBone, but the multiplication of your matrix with the bone's existing one. This can be easily proven by comparing the matrices read from the file with EditBone.matrix. Again it might seem correct in Blender, but now export your model and you see your animations are messed up, as the bind pose rotations of the bones are wrong. I've tried to find an alternative way to assign the transformation matrix from my file to my EditBone with no luck.

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• Why can't a blendShader sample anything but the current coordinate of the background image?

  - by Triynko

  In Flash, you can set a DisplayObject's blendShader property to a pixel shader (flash.shaders.Shader class). The mechanism is nice, because Flash automatically provides your Shader with two input images, including the background surface and the foreground display object's bitmap. The problem is that at runtime, the shader doesn't allow you to sample the background anywhere but under the current output coordinate. If you try to sample other coordinates, it just returns the color of the current coordinate instead, ignoring the coordinates you specified. This seems to occur only at runtime, because it works properly in the Pixel Bender toolkit. This limitation makes it impossible to simulate, for example, the Aero Glass effect in Windows Vista/7, because you cannot sample the background properly for blurring. I must mention that it is possible to create the effect in Flash through manual composition techniques, but it's hard to determine when it actually needs updated, because Flash does not provide information about when a particular area of the screen or a particular display object needs re-rendered. For example, you may have a fixed glass surface with objects moving underneath it that don't dispatch events when they move. The only alternative is to re-render the glass bar every frame, which is inefficient, which is why I am trying to do it through a blendShader so Flash determines when it needs rendered automatically. Is there a technical reason for this limitation, or is it an oversight of some sort? Does anyone know of a workaround, or a way I could provide my manual composition implementation with information about when it needs re-rendered? The limitation is mentioned with no explanation in the last note in this page: http://help.adobe.com/en_US/as3/dev/WSB19E965E-CCD2-4174-8077-8E5D0141A4A8.html It says: "Note: When a Pixel Bender shader program is run as a blend in Flash Player or AIR, the sampling and outCoord() functions behave differently than in other contexts.In a blend, a sampling function will always return the current pixel being evaluated by the shader. You cannot, for example, use add an offset to outCoord() in order to sample a neighboring pixel. Likewise, if you use the outCoord() function outside a sampling function, its coordinates always evaluate to 0. You cannot, for example, use the position of a pixel to influence how the blended images are combined."

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• How do I morph between meshes that have different vertex counts?

  - by elijaheac

  I am using MeshMorpher from the Unify wiki in my Unity project, and I want to be able to transform between arbitrary meshes. This utility works best when there are an equal number of vertices between the two meshes. Is there some way to equalize the vertex count between a set of meshes? I don't mean that this would reduce the vertex count of a mesh, but would rather add redundant vertices to any meshes with smaller counts. However, if there is an alternate method of handling this (other than increasing vertices), I would like to know.

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• Dynamic libraries are not allowed on iOS but what about this?

  - by tapirath

  I'm currently using LuaJIT and its FFI interface to call C functions from LUA scripts. What FFI does is to look at dynamic libraries' exported symbols and let the developer use it directly form LUA. Kind of like Python ctypes. Obviously using dynamic libraries is not permitted in iOS for security reasons. So in order to come up with a solution I found the following snippet. /* (c) 2012 +++ Filip Stoklas, aka FipS, http://www.4FipS.com +++ THIS CODE IS FREE - LICENSED UNDER THE MIT LICENSE ARTICLE URL: http://forums.4fips.com/viewtopic.php?f=3&t=589 */ extern "C" { #include <lua.h> #include <lualib.h> #include <lauxlib.h> } // extern "C" #include <cassert> // Please note that despite the fact that we build this code as a regular // executable (exe), we still use __declspec(dllexport) to export // symbols. Without doing that FFI wouldn't be able to locate them! extern "C" __declspec(dllexport) void __cdecl hello_from_lua(const char *msg) { printf("A message from LUA: %s\n", msg); } const char *lua_code = "local ffi = require('ffi') \n" "ffi.cdef[[ \n" "const char * hello_from_lua(const char *); \n" // matches the C prototype "]] \n" "ffi.C.hello_from_lua('Hello from LUA!') \n" // do actual C call ; int main() { lua_State *lua = luaL_newstate(); assert(lua); luaL_openlibs(lua); const int status = luaL_dostring(lua, lua_code); if(status) printf("Couldn't execute LUA code: %s\n", lua_tostring(lua, -1)); lua_close(lua); return 0; } // output: // A message from LUA: Hello from LUA! Basically, instead of using a dynamic library, the symbols are exported directly inside the executable file. The question is: is this permitted by Apple? Thanks.

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• Proper way to use a RenderTarget2D to draw multiple textures?

  - by TheBroodian

  In the process of trying to resolve a split screen issue, I've been trying to use a RenderTarget2D to draw a portion of my scene to a Texture2D, and then again to another Texture2D, but the end result of both Texture2D's is coming out the same. Can anybody tell me what I'm doing wrong? Texture2D camera1Render; Texture2D camera2Render; GraphicsDevice.SetRenderTarget(RenderTarget); GraphicsDevice.Clear(Color.Transparent); map.Draw(mapDisplayDevice, Camera1, new Location(0, 0), false); camera1Render = RenderTarget; GraphicsDevice.Clear(Color.Transparent); map.Draw(mapDisplayDevice, Camera2, new Location(0, 0), false); camera2Render = RenderTarget; SetRenderTarget(null);

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• I'm looking to learn how to apply traditional animation techniques to my graphics engine - are there any tutorials or online-resources that can help?

  - by blueberryfields

  There are many traditional animation techniques - such as blurring of motion, motion along an elliptical curve rather than a straight line, counter-motion before beginning of movement - which help with creating the appearance of a realistic 3D animated character. I'm looking to incorporate tools and short cuts for some of these into my graphics engine, to make it easier for my end users to use these techniques in their animations. Is there a good resource listing the techniques and the principles behind them, especially how they might apply to a graphics engine or 3D animation?

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• How does gluLookAt work?

  - by Chan

  From my understanding, gluLookAt( eye_x, eye_y, eye_z, center_x, center_y, center_z, up_x, up_y, up_z ); is equivalent to: glRotatef(B, 0.0, 0.0, 1.0); glRotatef(A, wx, wy, wz); glTranslatef(-eye_x, -eye_y, -eye_z); But when I print out the ModelView matrix, the call to glTranslatef() doesn't seem to work properly. Here is the code snippet: #include <stdlib.h> #include <stdio.h> #include <GL/glut.h> #include <iomanip> #include <iostream> #include <string> using namespace std; static const int Rx = 0; static const int Ry = 1; static const int Rz = 2; static const int Ux = 4; static const int Uy = 5; static const int Uz = 6; static const int Ax = 8; static const int Ay = 9; static const int Az = 10; static const int Tx = 12; static const int Ty = 13; static const int Tz = 14; void init() { glClearColor(0.0, 0.0, 0.0, 0.0); glEnable(GL_DEPTH_TEST); glShadeModel(GL_SMOOTH); glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); GLfloat lmodel_ambient[] = { 0.8, 0.0, 0.0, 0.0 }; glLightModelfv(GL_LIGHT_MODEL_AMBIENT, lmodel_ambient); } void displayModelviewMatrix(float MV[16]) { int SPACING = 12; cout << left; cout << "\tMODELVIEW MATRIX\n"; cout << "--------------------------------------------------" << endl; cout << setw(SPACING) << "R" << setw(SPACING) << "U" << setw(SPACING) << "A" << setw(SPACING) << "T" << endl; cout << "--------------------------------------------------" << endl; cout << setw(SPACING) << MV[Rx] << setw(SPACING) << MV[Ux] << setw(SPACING) << MV[Ax] << setw(SPACING) << MV[Tx] << endl; cout << setw(SPACING) << MV[Ry] << setw(SPACING) << MV[Uy] << setw(SPACING) << MV[Ay] << setw(SPACING) << MV[Ty] << endl; cout << setw(SPACING) << MV[Rz] << setw(SPACING) << MV[Uz] << setw(SPACING) << MV[Az] << setw(SPACING) << MV[Tz] << endl; cout << setw(SPACING) << MV[3] << setw(SPACING) << MV[7] << setw(SPACING) << MV[11] << setw(SPACING) << MV[15] << endl; cout << "--------------------------------------------------" << endl; cout << endl; } void reshape(int w, int h) { float ratio = static_cast<float>(w)/h; glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(45.0, ratio, 1.0, 425.0); } void draw() { float m[16]; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glGetFloatv(GL_MODELVIEW_MATRIX, m); gluLookAt( 300.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f ); glColor3f(1.0, 0.0, 0.0); glutSolidCube(100.0); glGetFloatv(GL_MODELVIEW_MATRIX, m); displayModelviewMatrix(m); glutSwapBuffers(); } int main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH); glutInitWindowSize(400, 400); glutInitWindowPosition(100, 100); glutCreateWindow("Demo"); glutReshapeFunc(reshape); glutDisplayFunc(draw); init(); glutMainLoop(); return 0; } No matter what value I use for the eye vector: 300, 0, 0 or 0, 300, 0 or 0, 0, 300 the translation vector is the same, which doesn't make any sense because the order of code is in backward order so glTranslatef should run first, then the 2 rotations. Plus, the rotation matrix, is completely independent of the translation column (in the ModelView matrix), then what would cause this weird behavior? Here is the output with the eye vector is (0.0f, 300.0f, 0.0f) MODELVIEW MATRIX -------------------------------------------------- R U A T -------------------------------------------------- 0 0 0 0 0 0 0 0 0 1 0 -300 0 0 0 1 -------------------------------------------------- I would expect the T column to be (0, -300, 0)! So could anyone help me explain this? The implementation of gluLookAt from http://www.mesa3d.org void GLAPIENTRY gluLookAt(GLdouble eyex, GLdouble eyey, GLdouble eyez, GLdouble centerx, GLdouble centery, GLdouble centerz, GLdouble upx, GLdouble upy, GLdouble upz) { float forward[3], side[3], up[3]; GLfloat m[4][4]; forward[0] = centerx - eyex; forward[1] = centery - eyey; forward[2] = centerz - eyez; up[0] = upx; up[1] = upy; up[2] = upz; normalize(forward); /* Side = forward x up */ cross(forward, up, side); normalize(side); /* Recompute up as: up = side x forward */ cross(side, forward, up); __gluMakeIdentityf(&m[0][0]); m[0][0] = side[0]; m[1][0] = side[1]; m[2][0] = side[2]; m[0][1] = up[0]; m[1][1] = up[1]; m[2][1] = up[2]; m[0][2] = -forward[0]; m[1][2] = -forward[1]; m[2][2] = -forward[2]; glMultMatrixf(&m[0][0]); glTranslated(-eyex, -eyey, -eyez); }

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• Stop a rotating object at a specified angle?

  - by Krummelz

  I'm working in JavaScript with HTML5 and the canvas. I have an object which is rotating at a certain speed, and I need the object's rotation to slow down gradually and the front of the object to stop at a specified angle. (I'm using radians, not degrees.) I have a variable to keep track of the angle which the object is facing, as it rotates. How would I go about getting the object to come to rest, facing the direction I want it to?

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• Error X3650 when compiling shader in XNA

  - by Saikai

  I'm attempting to convert the XBDEV.NET Mosaic Shader for use in my XNA project and having trouble. The compiler errors out because of the half globals. At first I tried replacing the globals and just writing the variables explicitly in the code, but that garbles the Output. Next I tried replacing all the half with float vars, but that still garbles the resulting Image. I call the effect file from SpriteBatch.Begin(). Is there a way to convert this shader to the new pixel shader conventions? Are there any good tutorials for this topic? Here is the shader file for reference: /*****************************************************************************/ /* File: tiles.fx Details: Modified version of the NVIDIA Composer FX Demo Program 2004 Produces a tiled mosaic effect on the output. Requires: Vertex Shader 1.1 Pixel Shader 2.0 Modified by: [email protected] (www.xbdev.net) */ /*****************************************************************************/ float4 ClearColor : DIFFUSE = { 0.0f, 0.0f, 0.0f, 1.0f}; float ClearDepth = 1.0f; /******************************** TWEAKABLES *********************************/ half NumTiles = 40.0; half Threshhold = 0.15; half3 EdgeColor = {0.7f, 0.7f, 0.7f}; /*****************************************************************************/ texture SceneMap : RENDERCOLORTARGET < float2 ViewportRatio = { 1.0f, 1.0f }; int MIPLEVELS = 1; string format = "X8R8G8B8"; string UIWidget = "None"; >; sampler SceneSampler = sampler_state { texture = <SceneMap>; AddressU = CLAMP; AddressV = CLAMP; MIPFILTER = NONE; MINFILTER = LINEAR; MAGFILTER = LINEAR; }; /***************************** DATA STRUCTS **********************************/ struct vertexInput { half3 Position : POSITION; half3 TexCoord : TEXCOORD0; }; /* data passed from vertex shader to pixel shader */ struct vertexOutput { half4 HPosition : POSITION; half2 UV : TEXCOORD0; }; /******************************* Vertex shader *******************************/ vertexOutput VS_Quad( vertexInput IN) { vertexOutput OUT = (vertexOutput)0; OUT.HPosition = half4(IN.Position, 1); OUT.UV = IN.TexCoord.xy; return OUT; } /********************************** pixel shader *****************************/ half4 tilesPS(vertexOutput IN) : COLOR { half size = 1.0/NumTiles; half2 Pbase = IN.UV - fmod(IN.UV,size.xx); half2 PCenter = Pbase + (size/2.0).xx; half2 st = (IN.UV - Pbase)/size; half4 c1 = (half4)0; half4 c2 = (half4)0; half4 invOff = half4((1-EdgeColor),1); if (st.x > st.y) { c1 = invOff; } half threshholdB = 1.0 - Threshhold; if (st.x > threshholdB) { c2 = c1; } if (st.y > threshholdB) { c2 = c1; } half4 cBottom = c2; c1 = (half4)0; c2 = (half4)0; if (st.x > st.y) { c1 = invOff; } if (st.x < Threshhold) { c2 = c1; } if (st.y < Threshhold) { c2 = c1; } half4 cTop = c2; half4 tileColor = tex2D(SceneSampler,PCenter); half4 result = tileColor + cTop - cBottom; return result; } /*****************************************************************************/ technique tiles { pass p0 { VertexShader = compile vs_1_1 VS_Quad(); ZEnable = false; ZWriteEnable = false; CullMode = None; PixelShader = compile ps_2_0 tilesPS(); } }

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• Is a Single Texture Cube Map Possible?

  - by smoth190

  I'm currently developing a test project to explore OpenGL 3 texturing abilities. I have a simple cube, made of 8 vertices and 36 indices. I want each of the cubes faces to have a different texture, so I devised this texture: I made it obvious which sections I want visible (I hope...). In Direct3D, I once made a skybox, and I used a cubemap. However, I had to split it into 6 different textures. This is annoying and hard to manage, it would be nice to have just one texture. Is this even possible? I read somewhere that I could do this by duplicating vertices, is that a good idea? Someone else said I could do it in the shader, but that also baffles me...

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• Dynamic Quad/Oct Trees

  - by KKlouzal

  I've recently discovered the power of Quadtrees and Octrees and their role in culling/LOD applications, however I've been pondering on the implementations for a Dynamic Quad/Oct Tree. Such tree would not require a complete rebuild when some of the underlying data changes (Vertex Data). Would it be possible to create such a tree? What would that look like? Could someone point me in the correct direction to get started? The application here would, in my scenario, be used for a dynamically changing spherical landscape with over 10,000,000 verticies. The use of Quad/Oct Trees is obvious for Culling & LOD as well as the benefits from not having to completely recompute the tree when the underlying data changes.

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