47 lines
1.7 KiB
GLSL
47 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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precision mediump float;
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uniform sampler2D uAreaLUT;
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varying vec2 vFrom;
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varying vec2 vCtrl;
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varying vec2 vTo;
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void main() {
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// Unpack.
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vec2 from = vFrom, ctrl = vCtrl, to = vTo;
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// Determine winding, and sort into a consistent order so we only need to find one root below.
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vec2 v0 = ctrl - from, v1 = to - ctrl;
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// Shoot a vertical ray toward the curve.
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vec2 window = clamp(vec2(from.x, to.x), -0.5, 0.5);
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//float offset = mix(window.x, window.y, 0.5) - left.x;
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//float t = offset / (v0.x + sqrt(v1.x * offset - v0.x * (offset - v0.x)));
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float t = 0.5;
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float x = mix(mix(from.x, ctrl.x, t), mix(ctrl.x, to.x, t), t);
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float dX = 2.0 * mix(v0.x, v1.x, t);
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t -= x / dX;
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x = mix(mix(from.x, ctrl.x, t), mix(ctrl.x, to.x, t), t);
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dX = 2.0 * mix(v0.x, v1.x, t);
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t -= x / dX;
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// Compute position and derivative to form a line approximation.
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float y = mix(mix(from.y, ctrl.y, t), mix(ctrl.y, to.y, t), t);
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//float dYDX = mix(v0.y, v1.y, t) / mix(v0.x, v1.x, t);
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float dYDX = dFdx(y);
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// Look up area under that line, and scale horizontally to the window size.
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dX = (gl_FrontFacing ? 1.0 : -1.0) * (window.x - window.y);
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gl_FragColor = vec4(texture2D(uAreaLUT, vec2(y + 8.0, abs(dYDX * dX)) / 16.0).r * dX);
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}
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