1 uniform sampler1D palette;

     2 uniform vec3 linear;

     3 uniform vec3 inv_matrix_m0;

     4 uniform vec3 inv_matrix_m1;

     5 uniform vec3 inv_matrix_m2;

     6 

     7 vec4 brush()

     8 {

     9     mat3 mat;

    10 

    11     mat[0] = inv_matrix_m0;

    12     mat[1] = inv_matrix_m1;

    13     mat[2] = inv_matrix_m2;

    14 

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

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

    17 

    18     float val = dot(linear.xy, A) * linear.z;

    19 

    20     return texture1D(palette, val);

    21 }

    22