From 6477319da461ad78a120a3c777228eaa8194c9f8 Mon Sep 17 00:00:00 2001
From: rodri <rgl@antares-labs.eu>
Date: Mon, 29 Jun 2020 18:28:02 +0000
Subject: bring flat triangle rasterization back, with some goodies for future
 shading work. add uv coordinates to the vertex.

---
 camera.c   |  2 +-
 graphics.h | 14 ++++++++++++
 mkfile     |  1 +
 triangle.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 88 insertions(+), 1 deletion(-)
 create mode 100644 triangle.c

diff --git a/camera.c b/camera.c
index ca567c8..1d67868 100644
--- a/camera.c
+++ b/camera.c
@@ -15,7 +15,7 @@ verifycfg(Camera *c)
 {
 	assert(c->viewport != nil);
 	if(c->ptype == Ppersp)
-		assert(c->fov > 0 && c->fov < 360);
+		assert(c->fov > 0 && c->fov < 360*DEG);
 	assert(c->clip.n > 0 && c->clip.n < c->clip.f);
 }
 
diff --git a/graphics.h b/graphics.h
index 44f213d..8e63b67 100644
--- a/graphics.h
+++ b/graphics.h
@@ -8,6 +8,7 @@ typedef struct Vertex Vertex;
 typedef struct Framebuffer Framebuffer;
 typedef struct Viewport Viewport;
 typedef struct Camera Camera;
+typedef struct Triangle Triangle;
 
 struct Color
 {
@@ -19,6 +20,7 @@ struct Vertex
 	Point3 p;	/* position */
 	Point3 n;	/* surface normal */
 	Color c;	/* shading color */
+	Point2 uv;	/* texture coordinate */
 };
 
 struct Framebuffer
@@ -47,6 +49,11 @@ struct Camera
 	Projection ptype;
 };
 
+struct Triangle
+{
+	Point p0, p1, p2;
+};
+
 /* Camera */
 void configcamera(Camera*, Image*, double, double, double, Projection);
 void placecamera(Camera*, Point3, Point3, Point3);
@@ -64,5 +71,12 @@ Point toviewport(Camera*, Point3);
 Point2 fromviewport(Camera*, Point);
 void perspective(Matrix3, double, double, double, double);
 void orthographic(Matrix3, double, double, double, double, double, double);
+/* temporary debug helpers */
 void line3(Camera*, Point3, Point3, int, int, Image*);
 Point string3(Camera*, Point3, Image*, Font*, char*);
+
+/* triangle */
+Triangle Trian(int, int, int, int, int, int);
+Triangle Trianpt(Point, Point, Point);
+void triangle(Image*, Triangle, int, Image*, Point);
+void filltriangle(Image*, Triangle, Image*, Point);
diff --git a/mkfile b/mkfile
index e3defa5..7911d47 100644
--- a/mkfile
+++ b/mkfile
@@ -4,6 +4,7 @@ LIB=libgraphics.a$O
 OFILES=\
 	camera.$O\
 	render.$O\
+	triangle.$O\
 
 HFILES=graphics.h ../libgeometry/geometry.h
 
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;
+}
-- 
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