28 lines
1.2 KiB
Plaintext
28 lines
1.2 KiB
Plaintext
|
// pathfinder/shaders/fill_area.inc.glsl
|
||
|
//
|
||
|
// Copyright © 2020 The Pathfinder Project Developers.
|
||
|
//
|
||
|
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
|
||
|
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
|
||
|
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
|
||
|
// option. This file may not be copied, modified, or distributed
|
||
|
// except according to those terms.
|
||
|
|
||
|
vec4 computeCoverage(vec2 from, vec2 to, sampler2D areaLUT) {
|
||
|
// Determine winding, and sort into a consistent order so we only need to find one root below.
|
||
|
vec2 left = from.x < to.x ? from : to, right = from.x < to.x ? to : from;
|
||
|
|
||
|
// Shoot a vertical ray toward the curve.
|
||
|
vec2 window = clamp(vec2(from.x, to.x), -0.5, 0.5);
|
||
|
float offset = mix(window.x, window.y, 0.5) - left.x;
|
||
|
float t = offset / (right.x - left.x);
|
||
|
|
||
|
// Compute position and derivative to form a line approximation.
|
||
|
float y = mix(left.y, right.y, t);
|
||
|
float d = (right.y - left.y) / (right.x - left.x);
|
||
|
|
||
|
// Look up area under that line, and scale horizontally to the window size.
|
||
|
float dX = window.x - window.y;
|
||
|
return texture(areaLUT, vec2(y + 8.0, abs(d * dX)) / 16.0) * dX;
|
||
|
}
|