1 uniform sampler1D palette;

     2 uniform vec2 fmp;

     3 uniform float fmp2_m_radius2;

     4 uniform vec3 inv_matrix_m0;

     5 uniform vec3 inv_matrix_m1;

     6 uniform vec3 inv_matrix_m2;

     7 

     8 vec4 brush()

     9 {

    10     mat3 mat;

    11 

    12     mat[0] = inv_matrix_m0;

    13     mat[1] = inv_matrix_m1;

    14     mat[2] = inv_matrix_m2;

    15 

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

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

    18     vec2 B = fmp;

    19 

    20     float a = fmp2_m_radius2;

    21     float b = 2.0*dot(A, B);

    22     float c = -dot(A, A);

    23 

    24     float val = (-b + sqrt(b*b - 4.0*a*c)) / (2.0*a);

    25 

    26     return texture1D(palette, val);

    27 }

    28