Screen space clipping and backface culling.

2 files changed, 147 insertions, 41 deletions

diff --git a/render.c b/render.c
index e0061fa..e225bb6 100644
--- a/render.c
+++ b/render.c
@@ -149,14 +149,19 @@ Colour col_mul(Colour a, Colour b) {
 
 void ren_begin(Renderer* r, Colour* t, int* d, int w, int h) {
 	r->t = t;
-	r->w = w;
-	r->h = h;
+	r->vp[2] = w;
+	r->vp[3] = h;
 	r->d = d;
 	r->clip.x = 0;
 	r->clip.y = 0;
 	r->clip.w = w;
 	r->clip.h = h;
+	r->vp[0] = 0;
+	r->vp[1] = 0;
+	r->vp[2] = w;
+	r->vp[3] = h;
 	r->asp = (w << fbits) / h;
+	r->n = 8;
 }
 
 void ren_end(Renderer* r) {
@@ -165,21 +170,21 @@ void ren_end(Renderer* r) {
 
 void ren_clear(Renderer* r) {
 	Colour* d = r->t, b = { 0 };
-	int i = 0, e = r->w * r->h;
+	int i = 0, e = r->vp[2] * r->vp[3];
 	for (i = 0; i < e; i++, d++)
 		*d = b;
 }
 
 void ren_clearc(Renderer* r, Colour c) {
 	Colour* d = r->t;
-	int i = 0, e = r->w * r->h;
+	int i = 0, e = r->vp[2] * r->vp[3];
 	for (i = 0; i < e; i++, d++)
 		*d = c;
 }
 
 void ren_cleard(Renderer* r, int depth) {
 	int* d = r->d;
-	int i = 0, e = r->w * r->h;
+	int i = 0, e = r->vp[2] * r->vp[3];
 	for (i = 0; i < e; i++, d++)
 		*d = depth;
 }
@@ -191,9 +196,9 @@ void ren_clip(Renderer* r, const Rect* c) {
 void ren_point(Renderer* r, Colour c, int x, int y) {
 	if (x < 0) return;
 	if (y < 0) return;
-	if (x >= r->w) return;
-	if (y >= r->h) return;
-	r->t[x + y * r->w] = c;
+	if (x >= r->vp[2]) return;
+	if (y >= r->vp[3]) return;
+	r->t[x + y * r->vp[2]] = c;
 }
 
 #define imp_ren_char(chw, chh, fw, data) \
@@ -207,8 +212,8 @@ void ren_point(Renderer* r, Colour c, int x, int y) {
 	rect_clips(&re, &sub, &r->clip); \
 	ex = re.x + re.w; \
 	ey = re.y + re.h; \
-	dst = r->t + (re.x + re.y * r->w); \
-	s = r->w - re.w; \
+	dst = r->t + (re.x + re.y * r->vp[2]); \
+	s = r->vp[2] - re.w; \
 	for (j = re.y, l = sub.y; j < ey; j++, l++) { \
 		for (i = re.x, k = sub.x; i < ex; i++, k++) { \
 			int si = k + l * fw; \
@@ -296,6 +301,16 @@ int tri_hand(
 		(v2[0] - v0[0]) * (v1[1] - v0[1]) > 0;
 }
 
+int tri_winding(
+	const int* v0,
+	const int* v1,
+	const int* v2
+) {
+	return
+		(v1[1] - v0[1]) * (v2[0] - v1[0]) -
+		(v1[0] - v0[0]) * (v2[1] - v1[1]);
+}
+
 Colour sample_tex(
 	const Bitmap* t,
 	int u,
@@ -370,10 +385,13 @@ void ren_tri(
 #define ic 6
 #define ec 8
 	int ha, i;
+	const int fcx = r->clip.x + r->clip.w;
+	const int fcy = r->clip.y + r->clip.h;
 	int v0[ec], v1[ec], v2[ec];
 	Line ne, fe; /* near and far edges */
 	Line ni[ic], fi[ic]; /* near and far interpolants */
 	Line xi[ic]; /* scanline interpolant */
+	if (tri_winding(iv0, iv1, iv2) > 0) return;
 	vec_cpy(v0, iv0, ec);
 	vec_cpy(v1, iv1, ec);
 	vec_cpy(v2, iv2, ec);
@@ -415,30 +433,36 @@ void ren_tri(
 			);
 		}
 	}
+	if (v0[1] > fcy) return;
+	if (v1[1] > fcy) v1[1] = fcy;
 #define scanline\
-		int x;\
-		for (i = 0; i < ic; i++)\
-			init_lerp(\
-				&xi[i],\
-				ni[i].x, fi[i].x,\
-				ne.x, fe.x\
-			);\
-		for (x = ne.x; x < fe.x; x++) {\
-			Colour col;\
-			col.r = (xi[3].x * 255) >> fbits;\
-			col.g = (xi[4].x * 255) >> fbits;\
-			col.b = (xi[5].x * 255) >> fbits;\
-			col.a = 0xff;\
-			if (xi[0].x < r->d[x + fe.y * r->w]) { \
-				r->t[x + fe.y * r->w] =	col_mul(\
-					sample_tex(tex, xi[1].x, xi[2].x),\
-					col\
-				);\
-				r->d[x + fe.y * r->w] = xi[0].x; \
-			} \
+		int x, ex = mini(fe.x, fcx);\
+		if (fe.y >= r->clip.y) { \
 			for (i = 0; i < ic; i++)\
-				while (xi[i].y != x)\
-					step_line(&xi[i]);\
+				init_lerp(\
+					&xi[i],\
+					ni[i].x, fi[i].x,\
+					ne.x, fe.x\
+				);\
+			for (x = ne.x; x < ex; x++) {\
+				Colour col;\
+				if (x >= r->clip.x) { \
+					col.r = (xi[3].x * 255) >> fbits;\
+					col.g = (xi[4].x * 255) >> fbits;\
+					col.b = (xi[5].x * 255) >> fbits;\
+					col.a = 0xff;\
+					if (xi[0].x < r->d[x + fe.y * r->vp[2]]) { \
+						r->t[x + fe.y * r->vp[2]] =	col_mul(\
+							sample_tex(tex, xi[1].x, xi[2].x),\
+							col\
+						);\
+						r->d[x + fe.y * r->vp[2]] = xi[0].x; \
+					} \
+				} \
+				for (i = 0; i < ic; i++)\
+					while (xi[i].y != x)\
+						step_line(&xi[i]);\
+			}\
 		}\
 		step_line(&fe);\
 		for (i = 0; i < ic; i++)\
@@ -469,6 +493,7 @@ void ren_tri(
 				v1[1],     v2[1]
 			);
 	}
+	if (v2[1] > fcy) v2[1] = fcy;
 	while (fe.y < v2[1]) {
 		scanline
 	}
@@ -477,6 +502,67 @@ void ren_tri(
 #undef ec
 }
 
+#define max_clip 6
+
+void ren_tri3(
+	Renderer* r,
+	const int* iv0,
+	const int* iv1,
+	const int* iv2,
+	const Bitmap* tex
+) {
+#define ec 8
+#define ec2 (ec * 2)
+	int tri[ec2 * 3];
+	int tc = 1, i;
+	vec_cpy(&tri[0],  iv0, ec);
+	vec_cpy(&tri[8],  iv1, ec);
+	vec_cpy(&tri[16], iv2, ec);
+	for (i = 0; i < tc; i++) {
+		int ti = i * ec, j;
+		for (j = 0; j < 3; j++) {
+			int vi = ti + j * ec;
+			persp(&tri[vi], r->asp);
+			ndc2clip(r->vp, &tri[vi]);
+		}
+		if (!tri_os(r, &tri[0], &tri[8], &tri[16]))
+			continue;
+		ren_tri(
+			r,
+			&tri[ti],
+			&tri[ti + 8],
+			&tri[ti + 16],
+			tex
+		);
+	}
+#undef ec
+#undef ec2
+}
+
+int tri_os(
+	const Renderer* r,
+	const int* v0,
+	const int* v1,
+	const int* v2
+) {
+	return
+		point_os(r, v0[0], v0[1]) ||
+		point_os(r, v1[0], v1[1]) ||
+		point_os(r, v2[0], v2[1]);
+}
+
+int point_os(
+	const Renderer* r,
+	int x,
+	int y
+) {
+	return
+		x >= r->vp[0] &&
+		y >= r->vp[1] &&
+		x <  r->vp[2] &&
+		y <  r->vp[3];
+}
+
 void ren_mesh(
 	Renderer* r,
 	const Mesh* m,
@@ -485,19 +571,19 @@ void ren_mesh(
 	int vc = m->vc;
 	int tri[8 * 3];
 	int n[4];
-	int i, asp = r->asp;
+	int i;
 	for (i = 0; i < vc; i += 3) {
 		int j;
 		for (j = 0; j < 3; j++) {
 			Mesh_Vert v = m->verts[i + j];
 			int* wv = &tri[j * 8];
-			wv[0] = m->p[v.p * 3 + 0];
-			wv[1] = m->p[v.p * 3 + 1];
-			wv[2] = m->p[v.p * 3 + 2];
+			vec_cpy(wv, &m->p[v.p * 3], 3);
 			wv[3] = f1;
 			mtx_apply(mtx_peek(), wv);
-			persp(wv, asp);
-			ndc2clip((int*)&r->clip, wv);
+		}
+		for (j = 0; j < 3; j++) {
+			Mesh_Vert v = m->verts[i + j];
+			int* wv = &tri[j * 8];
 			n[0] = m->n[v.n * 3 + 0];
 			n[1] = m->n[v.n * 3 + 1];
 			n[2] = m->n[v.n * 3 + 2];
@@ -521,7 +607,7 @@ void ren_mesh(
 				wv[7] = l;
 			}
 		}
-		ren_tri(r, &tri[0], &tri[8], &tri[16], tex);
+		ren_tri3(r, &tri[0], &tri[8], &tri[16], tex);
 	}
 }
 
diff --git a/render.h b/render.h
index 3c8938f..e51478f 100644
--- a/render.h
+++ b/render.h
@@ -37,10 +37,23 @@ typedef struct Mesh {
 typedef struct {
 	Colour* t;
 	int* d;
-	int w, h, asp;
+	int asp, n;
+	int vp[4];
 	Rect clip;
 } Renderer;
 
+int tri_os(
+	const Renderer* r,
+	const int* v0,
+	const int* v1,
+	const int* v2
+);
+int point_os(
+	const Renderer* r,
+	int x,
+	int y
+);
+
 void ren_begin(Renderer* r, Colour* t, int* d, int w, int h);
 void ren_end(Renderer* r);
 void ren_clear(Renderer* r);
@@ -86,7 +99,14 @@ void ren_tri(
 	const int* v1,
 	const int* v2,
 	const Bitmap* tex
-);
+); /* Unsafe for 3D. Clips against the r->clip */
+void ren_tri3(
+	Renderer* r,
+	const int* v0,
+	const int* v1,
+	const int* v2,
+	const Bitmap* tex
+); /* Does perspective calculation and clips against the near. */
 void ren_mesh(
 	Renderer* r,
 	const Mesh* mesh,