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

[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