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/* Shader for performing initialization of the constant arrays b, c1 and c2
* as part of GVF initialization:
*
* Input: RED = dx gradient field.
* GREEN = dy gradient field.
*
* Output: RED = b = 1 - mag(dx,dy) field.
* GREEN = c1 = dx * mag field.
* BLUE = c2 = dy * mag field.
*
* (w)2006 by Mario Kleiner. Licensed under MIT license.
*/
#extension GL_ARB_texture_rectangle : enable
uniform sampler2DRect Image;
void main()
{
float m, c1, c2;
/* Read gradient - texel for position (x,y)==(s,t): */
vec2 g = texture2DRect(Image, gl_TexCoord[0].st).rg;
/* Compute magnitude m : */
m = (g.x * g.x + g.y * g.y);
/* b = 1-m to RED channel: */
gl_FragColor.r = 1.0 - m;
/* c1 = m * dx to GREEN channel: */
gl_FragColor.g = m * g.x;
/* c2 = m * dy to BLUE channel: */
gl_FragColor.b = m * g.y;
/* Ignore alpha channel: */
gl_FragColor.a = 0.0;
}
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