| uniform vec3 inv_matrix_m0; |
| uniform vec3 inv_matrix_m1; |
| uniform vec3 inv_matrix_m2; |
| |
| uniform vec2 ellipse_offset; |
| |
| // 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; |
| |
| vec3 hcoords = mat * vec3(gl_FragCoord.xy + ellipse_offset, 1); |
| float inv_w = 1.0 / hcoords.z; |
| vec2 st = hcoords.xy * inv_w; |
| |
| vec4 xy = vec4(mat[0].xy, mat[1].xy); |
| vec2 h = vec2(mat[0].z, mat[1].z); |
| |
| vec4 dstdxy = (xy.xzyw - h.xyxy * st.xxyy) * inv_w; |
| |
| //dstdxy.x = (mat[0].x - mat[0].z * st.x) * inv_w; // ds/dx |
| //dstdxy.y = (mat[1].x - mat[1].z * st.x) * inv_w; // ds/dy |
| //dstdxy.z = (mat[0].y - mat[0].z * st.y) * inv_w; // dt/dx |
| //dstdxy.w = (mat[1].y - mat[1].z * st.y) * inv_w; // dt/dy |
| |
| vec2 inv_r = gl_TexCoord[0].xy; |
| vec2 n = st * inv_r; |
| float g = 1.0 - dot(n, n); |
| |
| vec2 dgdst = -2.0 * n * inv_r; |
| |
| vec2 grad = vec2(dot(dgdst, dstdxy.xz), |
| dot(dgdst, dstdxy.yw)); |
| |
| return smoothstep(-0.5, 0.5, g * inversesqrt(dot(grad, grad))); |
| } |
| |
| void main() |
| { |
| gl_FragColor = ellipse_aa().xxxx; |
| } |