Of course! Thank you very much! Sometimes it's hard to see such easy things, I think this happens to other people too... Doesn't it? :-) Getting this answer was a perfect start of the working day. Now I feel very happy and will take further steps into the shader world. Asa
________________________________ Från: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] För Andreas Lindmark Skickat: den 3 november 2008 17:31 Till: OpenSceneGraph Users Ämne: Re: [osg-users] Varying shader variable /= 0 in vertex shader,is == 0 in fragment shader This line: vec2 displacementNDC = currentPosClip.xy/currentPosClip.w - previousPosClip.xy/previousPosClip.w; should be displacementNDC = currentPosClip.xy/currentPosClip.w - previousPosClip.xy/previousPosClip.w; Otherwise you will be declaring a new variable with the name displacementNDC the main function as scope. /Andreas 2008/11/3 Engvall Åsa <[EMAIL PROTECTED]> Hi osg-users! I'm trying to write my first shader, it is a very simple test program which sets the color on a sphere. The color depends on whether the sphere has moved relative to its position in the previous frame. I use two varying variables, which are set in the vertex shader, see the code below. If the sphere has moved, the variable called displacementNDC is /= 0. Then I expect that it should still be /= 0 in the fragment shader, but by some reason the value is == 0. The other varying variable, "green", does not change when going from vertex shader to fragment shader. (Just for test, I also tried to put the variable called currentPosClip in a varying variable. Testing for currentPosClip == 0 in the vertex shader returned false, but it returned true in the fragment shader.) Please, can anybody explain what is happening? Why are the values changing to zero? Regards, Asa -----------Vertex shader ------------------ uniform mat4 prevModelViewProjectionMatrix; varying vec2 displacementNDC; varying vec4 green; void main() { // Calculate the previous and current position in clip space. vec4 currentPosClip = gl_ModelViewProjectionMatrix*gl_Vertex; // Transforms vertex position vec4 previousPosClip = prevModelViewProjectionMatrix*gl_Vertex; // from object space to clip space. gl_Position = ftransform(); // Calculate displacement in NDC space. vec2 displacementNDC = currentPosClip.xy/currentPosClip.w - previousPosClip.xy/previousPosClip.w; // If the displacement is zero, varying variable "green" is set to the RGBA value for green. if (displacementNDC == vec2(0,0)) // Object has not moved. green = vec4(0, 1, 0, 0); else // Object has moved. green = vec4(0.0); } -----------End vertex shader ------------------ -----------Fragment shader ------------------ varying vec2 displacementNDC; varying vec4 green; void main() { if (displacementNDC == vec2(0,0)) gl_FragColor = vec4(1,0,0,1) + green; else gl_FragColor = vec4(0,0,1,1) + green; } -----------End fragment shader ------------------ When the sphere has moved, the resulting color should be blue. But it becomes red. _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
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