1 // conical gradient shader

     2 #define M_PI  3.14159265358979323846

     3 uniform sampler1D palette;

     4 uniform float angle;

     5 uniform vec3 inv_matrix_m0;

     6 uniform vec3 inv_matrix_m1;

     7 uniform vec3 inv_matrix_m2;

     8 

     9 vec4 brush()

    10 {

    11     mat3 mat;

    12 

    13     mat[0] = inv_matrix_m0;

    14     mat[1] = inv_matrix_m1;

    15     mat[2] = inv_matrix_m2;

    16 

    17     vec3 hcoords = mat * vec3(gl_FragCoord.xy, 1);

    18     vec2 A = hcoords.xy / hcoords.z;

    19 

    20 /*     float val = fmod((atan2(-A.y, A.x) + angle) / (2.0 * M_PI), 1); */

    21     if (abs(A.y) == abs(A.x))

    22  	A.y += 0.002;

    23     float t = (atan(-A.y, A.x) + angle) / (2.0 * M_PI);

    24     float val = t - floor(t);

    25     return texture1D(palette, val);

    26 }

    27