1 files changed, 72 insertions, 0 deletions
diff --git a/triangle.c b/triangle.c
new file mode 100644
index 0000000..843ff6a
--- /dev/null
+++ b/triangle.c
@@ -0,0 +1,72 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+#include <geometry.h>
+#include <graphics.h>
+
+/*
+ * comparison of a point p with an edge [e0 e1]
+ * p to the right: +
+ * p to the left: -
+ * p on the edge: 0
+ */
+static int
+edgeptcmp(Point e0, Point e1, Point p)
+{
+	Point3 e0p, e01, r;
+
+	p = subpt(p, e0);
+	e1 = subpt(e1, e0);
+	e0p = Vec3(p.x,p.y,0);
+	e01 = Vec3(e1.x,e1.y,0);
+	r = crossvec3(e0p, e01);
+
+	/* clamp to avoid overflow */
+	return fclamp(r.z, -1, 1); /* e0.x*e1.y - e0.y*e1.x */
+}
+
+Triangle
+Trian(int x0, int y0, int x1, int y1, int x2, int y2)
+{
+	return (Triangle){Pt(x0, y0), Pt(x1, y1), Pt(x2, y2)};
+}
+
+Triangle
+Trianpt(Point p0, Point p1, Point p2)
+{
+	return (Triangle){p0, p1, p2};
+};
+
+void
+triangle(Image *dst, Triangle t, int thick, Image *src, Point sp)
+{
+	Point pl[4];
+
+	pl[0] = t.p0;
+	pl[1] = t.p1;
+	pl[2] = t.p2;
+	pl[3] = pl[0];
+
+	poly(dst, pl, nelem(pl), 0, 0, thick, src, sp);
+}
+
+void
+filltriangle(Image *dst, Triangle t, Image *src, Point sp)
+{
+	Point pl[3];
+
+	pl[0] = t.p0;
+	pl[1] = t.p1;
+	pl[2] = t.p2;
+
+	fillpoly(dst, pl, nelem(pl), 0, src, sp);
+}
+
+int
+ptintriangle(Point p, Triangle t)
+{
+	/* counter-clockwise check */
+	return edgeptcmp(t.p0, t.p2, p) <= 0 &&
+		edgeptcmp(t.p2, t.p1, p) <= 0 &&
+		edgeptcmp(t.p1, t.p0, p) <= 0;
+}