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// conical gradient shader
#define M_PI 3.14159265358979323846
uniform sampler1D palette;
uniform float angle;
uniform vec3 inv_matrix_m0;
uniform vec3 inv_matrix_m1;
uniform vec3 inv_matrix_m2;
vec4 brush()
{
mat3 mat;
mat[0] = inv_matrix_m0;
mat[1] = inv_matrix_m1;
mat[2] = inv_matrix_m2;
vec3 hcoords = mat * vec3(gl_FragCoord.xy, 1);
vec2 A = hcoords.xy / hcoords.z;
/* float val = fmod((atan2(-A.y, A.x) + angle) / (2.0 * M_PI), 1); */
if (abs(A.y) == abs(A.x))
A.y += 0.002;
float t = (atan(-A.y, A.x) + angle) / (2.0 * M_PI);
float val = t - floor(t);
return texture1D(palette, val);
}
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