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This routine returns a short unsigned int (aka a color_t) corresponding to a color between red and blue.


short unsigned int heightcolor(float z, float z_min, float z_max) {
         float frac = ((z-z_min)/(z_max-z_min));
         float r = (0.25f)-frac;
         float g = (0.5f)-frac;
         float b = (0.75f)-frac;

         //calculate the R/G/B values
         r = (r>0.f)?r:-r; g = (g>0.f)?g:-g; b = (b>0.f)?b:-b;   //absolute value
         r = (0.25f)-r; g = (1.f/3.f)-g; b = (0.25f)-b;   //invert
         r = (r>0.f)?(6.f*r):0.f; g = (g>0.f)?(6.f*g):0.f; b = (b>0.f)?(6.f*b):0.f;   //scale the chromatic triangles
         r = (r>1.f)?1.f:r; g = (g>1.f)?1.f:g; b = (b>1.f)?1.f:b;   //clip the top of the chromatic triangles
         if (frac < 0.25f) r = (r+1.f)/2.f;   //adjust the bottom end of the scale so that z_min is red, not black
         if (frac > 0.75f) b = (b+1.f)/2.f;   //adjust the top end of the scale so that z_max is blue, not black
         return (short unsigned int)(0x0000ffff & (((int)(31.f*r) << 11) | ((int)(63.f*g) << 5) | ((int)(31.f*b))));   //put the bits together


  • float z: The current z value from which to get a color
  • float z_min: The minimum value for any z
  • float z_max: The maximum value for any z


A color between red and blue (with green in the middle)


Used in Graph3DP to determine the color of points in a 3D wireframe graph. Values near the minimum value are more red, and ones nearer to the top are blue. Very useful for color representations of a range or for 3D depth buffering.


Created by Christopher "Kerm Martian" Mitchell.