50 lines
1.7 KiB
GLSL
50 lines
1.7 KiB
GLSL
// pathfinder/shaders/gles2/stencil-aaa.fs.glsl
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//
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// Copyright (c) 2018 The Pathfinder Project Developers.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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varying vec3 vUV;
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varying vec3 vXDist;
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void main() {
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// Unpack.
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vec3 uv = vUV;
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vec2 dUVDX = dFdx(uv.xy), dUVDY = dFdy(uv.xy);
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vec3 xDist = vXDist;
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vec2 dXDistDX = dFdx(xDist.xz);
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// Calculate X distances between endpoints (x02, x10, and x21 respectively).
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vec3 vDist = xDist - xDist.zxy;
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// Compute winding number and convexity.
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bool inCurve = insideCurve(uv);
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float openWinding = fastSign(-vDist.x);
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float convex = uv.z != 0.0 ? uv.z : fastSign(vDist.x * dUVDY.y);
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// Compute open rect area.
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vec2 areas = clamp(xDist.xz / dXDistDX, -0.5, 0.5);
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float openRectArea = openWinding * (areas.y - areas.x);
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// Compute closed rect area and winding, if necessary.
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float closedRectArea = 0.0, closedWinding = 0.0;
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if (inCurve && vDist.y * vDist.z < 0.0) {
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closedRectArea = 0.5 - fastSign(vDist.y) * (vDist.x * vDist.y < 0.0 ? areas.y : areas.x);
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closedWinding = fastSign(vDist.y * dUVDY.y);
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}
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// Calculate approximate area of the curve covering this pixel square.
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float curveArea = estimateArea(signedDistanceToCurve(uv.xy, dUVDX, dUVDY, inCurve));
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// Calculate alpha.
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vec2 alpha = vec2(openWinding, closedWinding) * 0.5 + convex * curveArea;
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alpha *= vec2(openRectArea, closedRectArea);
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// Finish up.
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gl_FragColor = vec4(alpha.x + alpha.y);
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}
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