mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-10-26 11:45:37 +00:00
70 lines
1.8 KiB
GLSL
70 lines
1.8 KiB
GLSL
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
#ifdef WR_FRAGMENT_SHADER
|
|
|
|
//
|
|
// Signed distance to an ellipse.
|
|
// Taken from http://www.iquilezles.org/www/articles/ellipsedist/ellipsedist.htm
|
|
// Note that this fails for exact circles.
|
|
//
|
|
float sdEllipse( vec2 p, in vec2 ab ) {
|
|
p = abs( p ); if( p.x > p.y ){ p=p.yx; ab=ab.yx; }
|
|
float l = ab.y*ab.y - ab.x*ab.x;
|
|
|
|
float m = ab.x*p.x/l;
|
|
float n = ab.y*p.y/l;
|
|
float m2 = m*m;
|
|
float n2 = n*n;
|
|
|
|
float c = (m2 + n2 - 1.0)/3.0;
|
|
float c3 = c*c*c;
|
|
|
|
float q = c3 + m2*n2*2.0;
|
|
float d = c3 + m2*n2;
|
|
float g = m + m*n2;
|
|
|
|
float co;
|
|
|
|
if( d<0.0 )
|
|
{
|
|
float p = acos(q/c3)/3.0;
|
|
float s = cos(p);
|
|
float t = sin(p)*sqrt(3.0);
|
|
float rx = sqrt( -c*(s + t + 2.0) + m2 );
|
|
float ry = sqrt( -c*(s - t + 2.0) + m2 );
|
|
co = ( ry + sign(l)*rx + abs(g)/(rx*ry) - m)/2.0;
|
|
}
|
|
else
|
|
{
|
|
float h = 2.0*m*n*sqrt( d );
|
|
float s = sign(q+h)*pow( abs(q+h), 1.0/3.0 );
|
|
float u = sign(q-h)*pow( abs(q-h), 1.0/3.0 );
|
|
float rx = -s - u - c*4.0 + 2.0*m2;
|
|
float ry = (s - u)*sqrt(3.0);
|
|
float rm = sqrt( rx*rx + ry*ry );
|
|
float p = ry/sqrt(rm-rx);
|
|
co = (p + 2.0*g/rm - m)/2.0;
|
|
}
|
|
|
|
float si = sqrt( 1.0 - co*co );
|
|
|
|
vec2 r = vec2( ab.x*co, ab.y*si );
|
|
|
|
return length(r - p ) * sign(p.y-r.y);
|
|
}
|
|
|
|
float distance_to_ellipse(vec2 p, vec2 radii) {
|
|
// sdEllipse fails on exact circles, so handle equal
|
|
// radii here. The branch coherency should make this
|
|
// a performance win for the circle case too.
|
|
if (radii.x == radii.y) {
|
|
return length(p) - radii.x;
|
|
} else {
|
|
return sdEllipse(p, radii);
|
|
}
|
|
}
|
|
|
|
#endif
|