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Lesson 1: Triangle rasterization and back-face culling—Preparation

--- a/main.c

+++ b/main.c

@@ -103,9 +103,10 @@

 void

 bresenham(Memimage *dst, Point p0, Point p1, Memimage *src)

 {

-	int steep = 0, Δe, e;

+	int steep = 0, Δe, e, Δy;

 	Point p, dp;

+	/* transpose the points */

 	if(abs(p0.x-p1.x) < abs(p0.y-p1.y)){

 		steep = 1;

 		swap(&p0.x, &p0.y);

@@ -121,6 +122,7 @@

 	dp = subpt(p1, p0);

 	Δe = 2*abs(dp.y);

 	e = 0;

+	Δy = p1.y > p0.y? 1: -1;

 	for(p = p0; p.x <= p1.x; p.x++){

 		if(steep) swap(&p.x, &p.y);

@@ -129,7 +131,7 @@

 		e += Δe;

 		if(e > dp.x){

-			p.y += p1.y > p0.y? 1: -1;

+			p.y += Δy;

 			e -= 2*dp.x;

 		}

 	}

@@ -136,6 +138,14 @@

 }

 void

+triangle(Memimage *dst, Point p0, Point p1, Point p2, Memimage *src)

+{

+	bresenham(dst, p0, p1, src);

+	bresenham(dst, p1, p2, src);

+	bresenham(dst, p2, p0, src);

+}

+

+void

 redraw(void)

 {

 	lockdisplay(display);

@@ -211,6 +221,7 @@

 	bresenham(fb, Pt(40,40), Pt(300,300), red);

 	bresenham(fb, Pt(80,80), Pt(100,200), red);

 	bresenham(fb, Pt(80,80), Pt(200,100), red);

+	triangle(fb, Pt(30,10), Pt(45, 45), Pt(5, 100), red);

 	display->locking = 1;

 	unlockdisplay(display);