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1be21a33d9
We can use this to properly compute distance in scaled situations. We also now compute coverage with (imperfect) antialiasing.
39 lines
785 B
GLSL
39 lines
785 B
GLSL
#ifndef _ELLIPSE_
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#define _ELLIPSE_
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struct Ellipse
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{
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vec2 center;
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vec2 radius;
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};
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float
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ellipse_distance (Ellipse r, vec2 p)
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{
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vec2 e = r.radius;
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p = p - r.center;
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if (e.x == e.y)
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return length (p) - e.x;
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/* from https://www.shadertoy.com/view/tt3yz7 */
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vec2 pAbs = abs(p);
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vec2 ei = 1.0 / e;
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vec2 e2 = e*e;
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vec2 ve = ei * vec2(e2.x - e2.y, e2.y - e2.x);
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vec2 t = vec2(0.70710678118654752, 0.70710678118654752);
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for (int i = 0; i < 3; i++) {
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vec2 v = ve*t*t*t;
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vec2 u = normalize(pAbs - v) * length(t * e - v);
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vec2 w = ei * (v + u);
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t = normalize(clamp(w, 0.0, 1.0));
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}
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vec2 nearestAbs = t * e;
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float dist = length(pAbs - nearestAbs);
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return dot(pAbs, pAbs) < dot(nearestAbs, nearestAbs) ? -dist : dist;
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}
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#endif
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