source: trunk/src/opengl/util/ellipse_functions.glsl@ 376

uniform vec3 inv_matrix_m0;
uniform vec3 inv_matrix_m1;
uniform vec3 inv_matrix_m2;

uniform vec2 ellipse_offset;

float ellipse()
{
    vec2 st = gl_TexCoord[0].st;

    if (dot(st, st) > 1)
        discard;

    return 1.0;
}

// ellipse equation

// s^2/a^2 + t^2/b^2 = 1
//
// implicit equation:
// g(s,t) = 1 - s^2/r_s^2 - t^2/r_t^2

// distance from ellipse:
// grad = [dg/dx dg/dy]
// d(s, t) ~= g(s, t) / |grad|

// dg/dx = dg/ds * ds/dx + dg/dt * dt/dx
// dg/dy = dg/ds * ds/dy + dg/dt * dt/dy

float ellipse_aa()
{
    mat3 mat;

    mat[0] = inv_matrix_m0;
    mat[1] = inv_matrix_m1;
    mat[2] = inv_matrix_m2;