39 lines
785 B
Plaintext
39 lines
785 B
Plaintext
|
#ifndef _ELLIPSE_
|
||
|
|
#define _ELLIPSE_
|
||
|
|
|
||
|
|
struct Ellipse
|
||
|
|
{
|
||
|
|
vec2 center;
|
||
|
|
vec2 radius;
|
||
|
|
};
|
||
|
|
|
||
|
|
float
|
||
|
|
ellipse_distance (Ellipse r, vec2 p)
|
||
|
|
{
|
||
|
|
vec2 e = r.radius;
|
||
|
|
p = p - r.center;
|
||
|
|
|
||
|
|
if (e.x == e.y)
|
||
|
|
return length (p) - e.x;
|
||
|
|
|
||
|
|
/* from https://www.shadertoy.com/view/tt3yz7 */
|
||
|
|
vec2 pAbs = abs(p);
|
||
|
|
vec2 ei = 1.0 / e;
|
||
|
|
vec2 e2 = e*e;
|
||
|
|
vec2 ve = ei * vec2(e2.x - e2.y, e2.y - e2.x);
|
||
|
|
|
||
|
|
vec2 t = vec2(0.70710678118654752, 0.70710678118654752);
|
||
|
|
for (int i = 0; i < 3; i++) {
|
||
|
|
vec2 v = ve*t*t*t;
|
||
|
|
vec2 u = normalize(pAbs - v) * length(t * e - v);
|
||
|
|
vec2 w = ei * (v + u);
|
||
|
|
t = normalize(clamp(w, 0.0, 1.0));
|
||
|
|
}
|
||
|
|
|
||
|
|
vec2 nearestAbs = t * e;
|
||
|
|
float dist = length(pAbs - nearestAbs);
|
||
|
|
return dot(pAbs, pAbs) < dot(nearestAbs, nearestAbs) ? -dist : dist;
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif
|