float quad_aa() | |
{ | |
float top = min(gl_FragCoord.y + 0.5, gl_TexCoord[0].x); | |
float bottom = max(gl_FragCoord.y - 0.5, gl_TexCoord[0].y); | |
float area = top - bottom; | |
float left = gl_FragCoord.x - 0.5; | |
float right = gl_FragCoord.x + 0.5; | |
// use line equations to compute intersections of left/right edges with top/bottom of truncated pixel | |
vec4 vecX = gl_TexCoord[1].xxzz * vec2(top, bottom).xyxy + gl_TexCoord[1].yyww; | |
vec2 invA = gl_TexCoord[0].zw; | |
// transform right line to left to be able to use same calculations for both | |
vecX.zw = 2.0 * gl_FragCoord.x - vecX.zw; | |
vec2 topX = vec2(vecX.x, vecX.z); | |
vec2 bottomX = vec2(vecX.y, vecX.w); | |
// transform lines such that top intersection is to the right of bottom intersection | |
vec2 topXTemp = max(topX, bottomX); | |
vec2 bottomXTemp = min(topX, bottomX); | |
// make sure line slope reflects mirrored lines | |
invA = mix(invA, -invA, step(topX, bottomX)); | |
vec2 vecLeftRight = vec2(left, right); | |
// compute the intersections of the lines with the left and right edges of the pixel | |
vec4 intersectY = bottom + (vecLeftRight.xyxy - bottomXTemp.xxyy) * invA.xxyy; | |
vec2 temp = mix(area - 0.5 * (right - bottomXTemp) * (intersectY.yw - bottom), // left < bottom < right < top | |
(0.5 * (topXTemp + bottomXTemp) - left) * area, // left < bottom < top < right | |
step(topXTemp, right.xx)); | |
vec2 excluded = 0.5 * (top - intersectY.xz) * (topXTemp - left); // bottom < left < top < right | |
excluded = mix((top - 0.5 * (intersectY.yw + intersectY.xz)) * (right - left), // bottom < left < right < top | |
excluded, step(topXTemp, right.xx)); | |
excluded = mix(temp, // left < bottom < right (see calculation of temp) | |
excluded, step(bottomXTemp, left.xx)); | |
excluded = mix(vec2(area, area), // right < bottom < top | |
excluded, step(bottomXTemp, right.xx)); | |
excluded *= step(left, topXTemp); | |
return (area - excluded.x - excluded.y) * step(bottom, top); | |
} | |
void main() | |
{ | |
gl_FragColor = quad_aa().xxxx; | |
} | |