uniform sampler1D palette;

uniform vec2 fmp;

uniform float fmp2_m_radius2;

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;

    vec2 B = fmp;

    float a = fmp2_m_radius2;

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

    float c = -dot(A, A);

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

    return texture1D(palette, val);

}