sam
107 lines
2.5 KiB
GLSL
107 lines
2.5 KiB
GLSL
// SPDX-FileCopyrightText: 2024 Erin Catto
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// SPDX-License-Identifier: MIT
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#version 330
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in vec2 f_position;
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in vec2 f_points[8];
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flat in int f_count;
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in float f_radius;
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in vec4 f_color;
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in float f_thickness;
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out vec4 fragColor;
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// https://en.wikipedia.org/wiki/Alpha_compositing
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vec4 blend_colors(vec4 front, vec4 back)
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{
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vec3 cSrc = front.rgb;
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float alphaSrc = front.a;
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vec3 cDst = back.rgb;
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float alphaDst = back.a;
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vec3 cOut = cSrc * alphaSrc + cDst * alphaDst * (1.0 - alphaSrc);
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float alphaOut = alphaSrc + alphaDst * (1.0 - alphaSrc);
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// remove alpha from rgb
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cOut = cOut / alphaOut;
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return vec4(cOut, alphaOut);
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}
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float cross2d(in vec2 v1, in vec2 v2)
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{
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return v1.x * v2.y - v1.y * v2.x;
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}
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// Signed distance function for convex polygon
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float sdConvexPolygon(in vec2 p, in vec2[8] v, in int count)
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{
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// Initial squared distance
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float d = dot(p - v[0], p - v[0]);
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// Consider query point inside to start
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float side = -1.0;
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int j = count - 1;
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for (int i = 0; i < count; ++i)
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{
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// Distance to a polygon edge
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vec2 e = v[i] - v[j];
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vec2 w = p - v[j];
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float we = dot(w, e);
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vec2 b = w - e * clamp(we / dot(e, e), 0.0, 1.0);
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float bb = dot(b, b);
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// Track smallest distance
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if (bb < d)
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{
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d = bb;
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}
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// If the query point is outside any edge then it is outside the entire polygon.
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// This depends on the CCW winding order of points.
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float s = cross2d(w, e);
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if (s >= 0.0)
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{
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side = 1.0;
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}
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j = i;
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}
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return side * sqrt(d);
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}
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void main()
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{
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vec4 borderColor = f_color;
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vec4 fillColor = 0.6f * borderColor;
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float dw = sdConvexPolygon(f_position, f_points, f_count);
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float d = abs(dw - f_radius);
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// roll the fill alpha down at the border
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vec4 back = vec4(fillColor.rgb, fillColor.a * smoothstep(f_radius + f_thickness, f_radius, dw));
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// roll the border alpha down from 1 to 0 across the border thickness
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vec4 front = vec4(borderColor.rgb, smoothstep(f_thickness, 0.0f, d));
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fragColor = blend_colors(front, back);
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// todo debugging
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// float resy = 3.0f / f_thickness;
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// if (resy < 539.9f)
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// {
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// fragColor = vec4(1, 0, 0, 1);
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// }
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// else if (resy > 540.1f)
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// {
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// fragColor = vec4(0, 1, 0, 1);
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// }
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// else
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// {
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// fragColor = vec4(0, 0, 1, 1);
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// }
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}
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