summaryrefslogtreecommitdiffstats
path: root/src/opengl/util/trap_exact_aa.glsl
diff options
context:
space:
mode:
Diffstat (limited to 'src/opengl/util/trap_exact_aa.glsl')
-rw-r--r--src/opengl/util/trap_exact_aa.glsl58
1 files changed, 58 insertions, 0 deletions
diff --git a/src/opengl/util/trap_exact_aa.glsl b/src/opengl/util/trap_exact_aa.glsl
new file mode 100644
index 0000000000..1637f430b5
--- /dev/null
+++ b/src/opengl/util/trap_exact_aa.glsl
@@ -0,0 +1,58 @@
+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;
+}
+