motion blur

[Barnes]

I tried to add a motion blur on the tutorial from Nvidia
http://http.developer.nvidia.com/GPUGem ... _ch27.html
problem - blurring the whole frame, Far plane more, looks like the depth of field, but with active blur of moving objects.



my code

setup matrix for motion blur

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Matrix4_Multiply(r_world_matrix, r_project_matrix, r_modelViewProjection);
InvertMatrix(r_modelViewProjection, r_modelViewProjectionInv);

render frame

setup 2d

postprocess

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void R_MotionBlur (void) {
   
   unsigned   defBits = 0;
   int         id;

    if (r_newrefdef.rdflags & RDF_NOWORLDMODEL)
            return;
   if (r_newrefdef.rdflags & RDF_IRGOGGLES)
            return;

   // setup program
   GL_BindProgram(motionBlurProgram, defBits);
   id = motionBlurProgram->id[defBits];
   qglUniformMatrix4fv(qglGetUniformLocation(id, "invMatrix"), 1, GL_FALSE, r_modelViewProjectionInv);
   qglUniformMatrix4fv(qglGetUniformLocation(id, "PrevMatrix"), 1, GL_FALSE, r_oldModelViewProjection);

   
   GL_SelectTexture      (GL_TEXTURE0_ARB);   
   GL_BindRect            (ScreenMap->texnum);
    qglCopyTexSubImage2D   (GL_TEXTURE_RECTANGLE_ARB, 0, 0, 0, 0, 0, vid.width, vid.height);
   qglUniform1i         (qglGetUniformLocation(id, "u_screenMap"), 0);

   GL_SelectTexture      (GL_TEXTURE1_ARB);   
   GL_BindRect            (depthMap->texnum);
    qglUniform1i         (qglGetUniformLocation(id, "u_depthMap"), 1);

   qglBegin(GL_QUADS);
    qglVertex2f(0, vid.height);
    qglVertex2f(vid.width, vid.height);
    qglVertex2f(vid.width, 0);
    qglVertex2f(0, 0);
    qglEnd();

   GL_BindNullProgram      ();
   GL_SelectTexture      (GL_TEXTURE0_ARB);   

}

after postprocess

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Matrix4_Copy(r_modelViewProjection, r_oldModelViewProjection);

shaders

vp

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void main ()
{
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}

fp

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uniform sampler2DRect u_depthMap;
uniform sampler2DRect u_screenMap;
uniform mat4 PrevMatrix;
uniform mat4 invMatrix;

void main(void)
{
vec4 zOverW = texture2DRect(u_depthMap, gl_FragCoord.xy);
// H is the viewport position at this pixel in the range -1 to 1.
vec4 H = vec4(gl_FragCoord.x * 2 - 1, (1 - gl_FragCoord.y) * 2 - 1, zOverW.g, 1);
// Transform by the view-projection inverse.
vec4 D = invMatrix * H;
// Divide by w to get the world position.
vec4 worldPos = D / vec4(D.w);

// Current viewport position
vec4 currentPos = H;
// Use the world position, and transform by the previous view-projection matrix.
vec4 previousPos = PrevMatrix * worldPos;
// Convert to nonhomogeneous points [-1,1] by dividing by w.
previousPos = previousPos / vec4(previousPos.w);
// Use this frame's position and last frame's to compute the pixel velocity.
vec2 velocity = vec2(currentPos.xy - previousPos.xy)/4000.0; // scale value for q2, was 2.0

// vec2 velocity = vec2(1.5, -0.5); //debug vector

   // Get the initial color at this pixel. 
   vec4 color = vec4(0.0, 0.0, 0.0, 0.0);
   
   for(int i = 1; i < 8; ++i) 
      { 
      // Sample the color buffer along the velocity vector. 
      vec4 currentColor = texture2DRect(u_screenMap, gl_FragCoord.xy + vec2(velocity)*i); 
      // Add the current color to our color sum. 
      color += currentColor; 
   } 
   // Average all of the samples to get the final blur color. 
   gl_FragColor = color / 8;
}


Any ideas?

[revelator]

sounds a bit like the same issue the last tenebrae had with postprocessing effects (also affected the entire screen) i newer quite figured out what goes wrong with it :S

[mh]

Looks like normal behaviour for this kind of effect. You're taking 8 samples, so for further objects those 8 samples will be from parts of them that are further apart in world-space, and so they'll blur more. It's likely also frame-rate dependent as it updates the blur every frame, so it will look very different running at 20 fps to how it would look at 200 fps.

One thing I would do with this kind of effect is fold the polyblend into it too - that way, if a polyblend is active, you get it (almost) for free rather than having to do another fillrate-intensive pass over the full screen.

[Barnes]

motion blur with polyblend (copy screen and draw up of frame) look so ugly