ref: 8560a458d2b4ade92ff8354e2a16db3256bead43
dir: /sys/src/libgeometry/triangle.c/
#include <u.h> #include <libc.h> #include <geometry.h> /* 2D */ Point2 centroid(Triangle2 t) { return divpt2(addpt2(t.p0, addpt2(t.p1, t.p2)), 3); } /* * based on the implementation from: * * Dmitry V. Sokolov, “Tiny Renderer: Lesson 2”, * https://github.com/ssloy/tinyrenderer/wiki/Lesson-2:-Triangle-rasterization-and-back-face-culling */ Point3 barycoords(Triangle2 t, Point2 p) { Point2 p0p1 = subpt2(t.p1, t.p0); Point2 p0p2 = subpt2(t.p2, t.p0); Point2 pp0 = subpt2(t.p0, p); Point3 v = crossvec3(Vec3(p0p2.x, p0p1.x, pp0.x), Vec3(p0p2.y, p0p1.y, pp0.y)); /* handle degenerate triangles—i.e. the ones where every point lies on the same line */ if(fabs(v.z) < 1) return Pt3(-1,-1,-1,1); return Pt3(1 - (v.x + v.y)/v.z, v.y/v.z, v.x/v.z, 1); } /* 3D */ Point3 centroid3(Triangle3 t) { return divpt3(addpt3(t.p0, addpt3(t.p1, t.p2)), 3); }