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

--- a/main.c

+++ b/main.c

@@ -16,8 +16,9 @@

 Channel *drawc;

 void resized(void);

+uvlong nanosec(void);

-void*

+void *

 emalloc(ulong n)

 {

 	void *p;

@@ -29,7 +30,7 @@

 	return p;

 }

-void*

+void *

 erealloc(void *p, ulong n)

 {

 	void *np;

@@ -47,7 +48,7 @@

 	return np;

 }

-Image*

+Image *

 eallocimage(Display *d, Rectangle r, ulong chan, int repl, ulong col)

 {

 	Image *i;

@@ -58,7 +59,7 @@

 	return i;

 }

-Memimage*

+Memimage *

 eallocmemimage(Rectangle r, ulong chan)

 {

 	Memimage *i;

@@ -70,7 +71,19 @@

 	return i;

 }

-Memimage*

+int

+min(int a, int b)

+{

+	return a < b? a: b;

+}

+

+int

+max(int a, int b)

+{

+	return a > b? a: b;

+}

+

+Memimage *

 rgb(ulong c)

 {

 	Memimage *i;

@@ -87,10 +100,12 @@

 {

 	Rectangle r;

-	r.min = addpt(dst->r.min, p);

-	r.max = addpt(r.min, Pt(1,1));

+	if(dst == nil || src == nil)

+		return;

-	memimagedraw(dst, r, src, ZP, nil, ZP, SoverD);

+	r = rectaddpt(Rect(0,0,1,1), p);

+

+	memimagedraw(dst, rectaddpt(r, dst->r.min), src, ZP, nil, ZP, SoverD);

 }

 void

@@ -183,16 +198,54 @@

 	dp₁₂ = subpt(t[2], t[1]);

 	m₁₂ = (double)dp₁₂.x/dp₁₂.y;

-	fprint(2, "%P %P %P\n", t[0], t[1], t[2]);

-	fprint(2, "m₀₂ %g m₀₁ %g m₁₂ %g\n", m₀₂, m₀₁, m₁₂);

-

+	/* first half */

 	for(y = t[0].y; y <= t[1].y; y++)

 		bresenham(dst, Pt(t[0].x + (y-t[0].y)*m₀₂,y), Pt(t[0].x + (y-t[0].y)*m₀₁,y), src);

+	/* second half */

 	for(; y <= t[2].y; y++)

 		bresenham(dst, Pt(t[0].x + (y-t[0].y)*m₀₂,y), Pt(t[1].x + (y-t[1].y)*m₁₂,y), src);

 }

 void

+shade(Memimage *dst, Memimage *(*shader)(Point))

+{

+	Point p;

+	Memimage *c;

+

+	p = ZP;

+	for(; p.y < Dy(dst->r); p.y++)

+		for(p.x = 0; p.x < Dx(dst->r); p.x++)

+			if((c = shader(p)) != nil)

+				pixel(dst, p, c);

+}

+

+Memimage *

+triangleshader(Point p)

+{

+	Triangle2 t;

+	Rectangle bbox;

+	Point3 bc;

+

+	t.p0 = Pt2(240,200,1);

+	t.p1 = Pt2(400,40,1);

+	t.p2 = Pt2(240,40,1);

+

+	bbox = Rect(

+		min(min(t.p0.x, t.p1.x), t.p2.x),

+		min(min(t.p0.y, t.p1.y), t.p2.y),

+		max(max(t.p0.x, t.p1.x), t.p2.x),

+		max(max(t.p0.y, t.p1.y), t.p2.y)

+	);

+	if(!ptinrect(p, bbox))

+		return nil;

+

+	bc = barycoords(t, Pt2(p.x,p.y,1));

+	if(bc.x < 0 || bc.y < 0 || bc.z < 0)

+		return nil;

+	return red;

+}

+

+void

 redraw(void)

 {

 	lockdisplay(display);

@@ -244,6 +297,7 @@

 	Mousectl *mc;

 	Keyboardctl *kc;

 	Rune r;

+	uvlong t0, t1;

 	GEOMfmtinstall();

 	ARGBEGIN{

@@ -267,9 +321,11 @@

 	red = rgb(DRed);

 	green = rgb(DGreen);

 	blue = rgb(DBlue);

+

 	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);

+

 	filltriangle(fb, Pt(30,10), Pt(45, 45), Pt(5, 100), blue);

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

 	filltriangle(fb, Pt(300,120), Pt(200,350), Pt(50, 210), blue);

@@ -276,6 +332,11 @@

 	triangle(fb, Pt(300,120), Pt(200,350), Pt(50, 210), red);

 	filltriangle(fb, Pt(400,230), Pt(450,180), Pt(150, 320), blue);

 	triangle(fb, Pt(400,230), Pt(450,180), Pt(150, 320), red);

+

+	t0 = nanosec();

+	shade(fb, triangleshader);

+	t1 = nanosec();

+	fprint(2, "shader took %lludns\n", t1-t0);

 	drawc = chancreate(sizeof(void*), 1);

--- a/mkfile

+++ b/mkfile

@@ -4,5 +4,6 @@

 TARG=tinyrend

 OFILES=\

 	main.$O\

+	nanosec.$O\

 </sys/src/cmd/mkone