Polar to Cartesian shader help...


    May 18 2007 | 11:33 pm
    Too much coffee is making me crazy, or.. well, maybe its not the
    coffee. ITS MY BRAIIIINNNNNNNNNnnnnn.
    I am attempting a Polar to Cartesian transform shader while fighting
    off my brains attempts to kill me.
    My thought is that I should be able to run cartopol shader and then a
    poltocar and get basically my same output minus weird edge pixels
    that the math messes up.
    However, I get nothing of the sort. I am obviously missing something.
    Ive looked at Wesleys poltocar code in the kaleidoscope shader
    mentioned here (second result in google for polar to cartesian glsl
    btw ;):
    "
    // polar to cartesian conversion
    vec2 no = vec2(-cos(foldtheta)*radius, -sin(foldtheta)*radius);
    no = no+0.5*sizea;
    "
    from: http://www.cycling74.com/forums/index.php?
    t=msg&goto=61224&rid=0&S=a3d1f2ed3cea8b2a7123521617329dc9
    The following is my fragment program in GLSL.
    What am I doing wrong?
    -----------
    // define our rectangular texture samplers
    uniform sampler2DRect tex0;
    // define our varying texture coordinates
    varying vec2 texcoord0;
    varying vec2 texdim0;
    void main (void)
    {
    const float pi=3.1415926;
    vec2 point = texcoord0/texdim0; //normalize coordinates
    vec2 normCoord = vec2(2.0) * (point - vec2(0.5)); // center point in
    texture
    float r = length(normCoord); // find hypot - seems nicer than other
    method.
    float phi = atan(normCoord.y, normCoord.x)+pi;
    vec2 frompol = vec2(r* cos(phi), r* sin(phi)); // this should be
    correct, yet I get an incorrect output ?
    vec2 outputCoord = (frompol/vec2(2.0) + vec2(0.5)) * texdim0; //
    unnormalize and remap to reg rect tex coords
    gl_FragColor = texture2DRect(tex0, outputCoord);
    }
    v a d e //
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