[orx-shader-phrases] Add SDF shader phrases for ellipse and star shapes

orx-shader-phrases/src/commonMain/kotlin/sdf/SDFPhrases.kt

@@ -0,0 +1,61 @@
+package org.openrndr.extra.shaderphrases.sdf
+
+import kotlin.math.PI
+
+const val sdEllipsePhrase = """#ifndef SP_SDELLIPSE
+#define SP_SDELLIPSE
+float sdEllipse( in 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 m2 = m*m; 
+    float n = ab.y*p.y/l;      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 h = acos(q/c3)/3.0;
+        float s = cos(h);
+        float t = sin(h)*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 );
+        co = (ry/sqrt(rm-rx)+2.0*g/rm-m)/2.0;
+    }
+    vec2 r = ab * vec2(co, sqrt(1.0-co*co));
+    return length(r-p) * sign(p.y-r.y);
+}
+#endif
+"""
+
+const val sdStarPhrase = """#ifndef SP_SDSTAR
+#define SP_SDSTAR
+float sdStar( in vec2 p, in float r, in int n, in float sharpness)
+{
+    float m = mix(2.0, float(n), sharpness);
+
+    // next 4 lines can be precomputed for a given shape
+    float an = ${PI}/float(n);
+    float en = ${PI}/m;  // m is between 2 and n
+    vec2  acs = vec2(cos(an),sin(an));
+    vec2  ecs = vec2(cos(en),sin(en)); // ecs=vec2(0,1) for regular polygon
+
+    float bn = mod(atan(p.x,p.y),2.0*an) - an;
+    p = length(p)*vec2(cos(bn),abs(sin(bn)));
+    p -= r*acs;
+    p += ecs*clamp( -dot(p,ecs), 0.0, r*acs.y/ecs.y);
+    return length(p)*sign(p.x);
+}
+#endif
+"""