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03-13-2011, 09:55 AM

Hi,

I am trying to implement motion blur from "GPU Gems 3" as a post effect using a fragment shader.

(http://http.developer.nvidia.com/GPUGems3/gpugems3_ch27.html)

The sample code is in HLSL/Cg and I am having difficulties doing the conversion to GLSL right.

The "ViewProjectionMatrix" and it's reverse are the problem, I guess.

I am using gl_ModelViewProjectionMatrixInverse and as a uniform I upload the GL_MODELVIEW matrix.

Here is my fragment shader code:

(using OpenGL 2.0)

uniform sampler2D tex;

uniform sampler2D tex2;

uniform mat4 PrevMatrix;

varying vec2 vTexCoord;

void main(void)

{

vec4 color = texture2D(tex, vTexCoord);

vec4 zOverW = texture2D(tex2, vTexCoord);

// H is the viewport position at this pixel in the range -1 to 1.

vec4 H = vec4(vTexCoord.x * 2 - 1, (1 - vTexCoord.y) * 2 - 1, zOverW.g, 1);

// Transform by the view-projection inverse.

vec4 D = gl_ModelViewProjectionMatrixInverse * 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)/2.0;

//velocity = (velocity + 1.0 ) / 2.0;

gl_FragColor = vec4(velocity.x, velocity.y, color.g, 1.0);

}

here I set the previous frame's matrix:

GLint loc = glGetUniformLocation(program_object, "PrevMatrix" );

glUniformMatrix4fv( loc, 1, GL_FALSE, &prevMat[0]);

glGetFloatv(GL_MODELVIEW_MATRIX, prevMat);

Any help would be appreciated!

I am trying to implement motion blur from "GPU Gems 3" as a post effect using a fragment shader.

(http://http.developer.nvidia.com/GPUGems3/gpugems3_ch27.html)

The sample code is in HLSL/Cg and I am having difficulties doing the conversion to GLSL right.

The "ViewProjectionMatrix" and it's reverse are the problem, I guess.

I am using gl_ModelViewProjectionMatrixInverse and as a uniform I upload the GL_MODELVIEW matrix.

Here is my fragment shader code:

(using OpenGL 2.0)

uniform sampler2D tex;

uniform sampler2D tex2;

uniform mat4 PrevMatrix;

varying vec2 vTexCoord;

void main(void)

{

vec4 color = texture2D(tex, vTexCoord);

vec4 zOverW = texture2D(tex2, vTexCoord);

// H is the viewport position at this pixel in the range -1 to 1.

vec4 H = vec4(vTexCoord.x * 2 - 1, (1 - vTexCoord.y) * 2 - 1, zOverW.g, 1);

// Transform by the view-projection inverse.

vec4 D = gl_ModelViewProjectionMatrixInverse * 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)/2.0;

//velocity = (velocity + 1.0 ) / 2.0;

gl_FragColor = vec4(velocity.x, velocity.y, color.g, 1.0);

}

here I set the previous frame's matrix:

GLint loc = glGetUniformLocation(program_object, "PrevMatrix" );

glUniformMatrix4fv( loc, 1, GL_FALSE, &prevMat[0]);

glGetFloatv(GL_MODELVIEW_MATRIX, prevMat);

Any help would be appreciated!