From bbe2ec049a812155c75da5ecc303bf3793c9cca8 Mon Sep 17 00:00:00 2001
From: John Tsiombikas <nuclear@member.fsf.org>
Date: Sun, 18 Apr 2021 06:28:37 +0300
Subject: [PATCH] curved tunnel

---
 src/gamescr.c  |   11 +++++-----
 tools/tungen.c |   66 ++++++++++++++++++++++++++++++++++++++++----------------
 2 files changed, 54 insertions(+), 23 deletions(-)

diff --git a/src/gamescr.c b/src/gamescr.c
index 70991e8..30ae380 100644
--- a/src/gamescr.c
+++ b/src/gamescr.c
@@ -52,12 +52,13 @@ void gamescr(void)
 __attribute__((noinline, target("arm"), section(".iwram")))
 static void draw_tunnel(void)
 {
-	int i, j, tx, ty, angle, depth, zoffs;
+	int i, j, tx, ty, angle, depth, zoffs, uoffs;
 	uint16_t pptop, ppbot;
 	uint16_t *top, *bot;
 	uint32_t tun, *tunptr;
 
 	zoffs = nframes;
+	uoffs = 0;
 
 	top = vram[backbuf];
 	bot = vram[backbuf] + 159 * 240 / 2;
@@ -71,18 +72,18 @@ static void draw_tunnel(void)
 
 			angle = tun & 0xff;
 			depth = (tun >> 8) & 0xff;
-			tx = ((angle >> 1) + zoffs) & 0x1f;
+			tx = ((angle >> 1) + uoffs) & 0x1f;
 			ty = ((depth >> 1) + zoffs) & 0x1f;
 			pptop = tex[(ty << 5) + tx];
-			tx = ((angle >> 1) - zoffs) & 0x1f;
+			tx = ((angle >> 1) - uoffs) & 0x1f;
 			ppbot = tex[(ty << 5) + tx];
 
 			angle = (tun >> 16) & 0xff;
 			depth = (tun >> 24) & 0xff;
-			tx = ((angle >> 1) + zoffs) & 0x1f;
+			tx = ((angle >> 1) + uoffs) & 0x1f;
 			ty = ((depth >> 1) + zoffs) & 0x1f;
 			pptop |= (uint16_t)tex[(ty << 5) + tx] << 8;
-			tx = ((angle >> 1) - zoffs) & 0x1f;
+			tx = ((angle >> 1) - uoffs) & 0x1f;
 			ppbot |= (uint16_t)tex[(ty << 5) + tx] << 8;
 
 			*top++ = pptop;
diff --git a/tools/tungen.c b/tools/tungen.c
index 8122c95..4148b26 100644
--- a/tools/tungen.c
+++ b/tools/tungen.c
@@ -3,11 +3,16 @@
 #include <stdint.h>
 #include <math.h>
 
+struct vec2 {
+	float x, y;
+};
+
 int main(int argc, char **argv)
 {
-	int i, j, xsz = 240, ysz = 160, texsz = 128;
+	int i, j, imgrad, xsz = 240, ysz = 160, texsz = 128;
 	struct vec2 *tunbuf, *tun;
-	float aspect;
+	float aspect, prev_r;
+	struct vec2 *buf, *ptr;
 
 	for(i=1; i<argc; i++) {
 		if(argv[i][0] == '-') {
@@ -36,6 +41,39 @@ invalopt:	fprintf(stderr, "invalid argument: %s\n", argv[i]);
 		}
 	}
 
+	if(!(buf = malloc(xsz * ysz * sizeof *buf))) {
+		perror("failed to allocate buffer");
+		return 1;
+	}
+	imgrad = sqrt(xsz * xsz + ysz * ysz);
+
+#define UDIV	2048
+#define VDIV	32768
+	prev_r = 0.0f;
+	for(i=0; i<VDIV; i++) {
+		float v = (float)(VDIV - i) / (float)VDIV;
+		float r = 4.0 / v + 16;
+		float z = v * 400.0f;
+
+		/* don't bother drawing rings < 1 pixel apart */
+		if(fabs(r - prev_r) < 0.05) continue;
+
+		for(j=0; j<UDIV; j++) {
+			float u = (float)j / (float)(UDIV - 1);
+			float theta = 2.0f * u * M_PI;
+
+			int x = (int)(cos(theta) * r - z) + xsz / 2;
+			int y = (int)(sin(theta) * r) + ysz / 2;
+
+			if(x >= 0 && x < xsz && y >= 0 && y < ysz) {
+				ptr = buf + y * xsz + x;
+				ptr->x = u;
+				ptr->y = v * 8;
+			}
+		}
+		prev_r = r;
+	}
+
 	FILE *fp = fopen("tun_preview.ppm", "wb");
 	if(fp) {
 		fprintf(fp, "P6\n%d %d\n255\n", xsz, ysz);
@@ -43,32 +81,24 @@ invalopt:	fprintf(stderr, "invalid argument: %s\n", argv[i]);
 
 	aspect = (float)xsz / (float)ysz;
 
-	tun = tunbuf;
+	ptr = buf;
 	for(i=0; i<ysz; i++) {
-		float y = 2.0f * (float)i / (float)(ysz - 1) - 1.0f;
 		for(j=0; j<xsz; j++) {
-			float x = (2.0f * (float)j / (float)(xsz - 1) - 1.0f) * aspect;
-
-			float r = sqrt(x * x + y * y);
-			float theta = atan2(y, x);
+			float u = ptr->x;
+			float v = ptr->y;
+			int r = (int)(u * 8.0 * 255.0f) & 0xff;
+			int b = (int)(v * 8.0 * 255.0f) & 0xff;
 
-			float u = 0.5f * theta / M_PI + 0.5f;
-			float v = 0.8f / r;
+			ptr++;
 
-			/*
-			uint32_t out = ((uint32_t)(u * 65535.0f) & 0xffff) |
-				(((uint32_t)(v * 65535.0f) & 0xffff) << 16);
-			*/
 			uint16_t out = ((uint16_t)(u * 255.0f) & 0xff) |
 				(((uint16_t)(v * 255.0f) & 0xff) << 8);
 			fwrite(&out, sizeof out, 1, stdout);
 
 			if(fp) {
-				int cr = (int)(u * 2048.0f) & 0xff;
-				int cb = (int)(r * 2048.0f) & 0xff;
-				fputc(cr, fp);
+				fputc(r, fp);
 				fputc(0, fp);
-				fputc(cb, fp);
+				fputc(b, fp);
 			}
 		}
 	}
-- 
1.7.10.4