From 336b5505f09dcbc6115d125e7ffdb41da13cb32e Mon Sep 17 00:00:00 2001
From: Sam Nystrom <sam@samnystrom.dev>
Date: Wed, 14 Feb 2024 14:00:33 +0000
Subject: Read STL from stdin instead of mmapping it

This is more portable and ensures that all triangles are aligned in memory.
---
 pineapple.c | 52 ++++++++++++++++++++++++++++------------------------
 1 file changed, 28 insertions(+), 24 deletions(-)

(limited to 'pineapple.c')

diff --git a/pineapple.c b/pineapple.c
index 870fd4c..5137534 100644
--- a/pineapple.c
+++ b/pineapple.c
@@ -2,20 +2,17 @@
 
 #include <endian.h>
 #include <errno.h>
-#include <fcntl.h>
 #include <getopt.h>
 #include <math.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/mman.h>
-#include <sys/stat.h>
-#include <unistd.h>
 
 #define PI 3.14159265358979323846
 
-#define die(code, msg) do { fprintf(stderr, "pineapple: %s\n", msg); exit(code); } while (0);
+#define die(code, msg) do { fprintf(stderr, "pineapple: %s\n", msg); exit(code); } while (0)
+#define diesys(code, msg) do { fprintf(stderr, "pineapple: %s: %s\n", msg, strerror(errno)); exit(code); } while (0)
 
 #define USAGE "pineapple [-v] [-w width] [-h height] [-f | -a]"
 #define dieusage() die(100, "usage: " USAGE)
@@ -24,9 +21,14 @@
 
 typedef struct { float x, y, z; } vec3;
 
-struct __attribute__((__packed__)) triangle {
-	vec3 normal;
-	vec3 vertices[3];
+struct triangle {
+	vec3 n;
+	vec3 a, b, c;
+};
+
+struct __attribute__((__packed__)) triangle_raw {
+	vec3 n;
+	vec3 a, b, c;
 	uint16_t _attr_count; /* unused */
 };
 
@@ -76,9 +78,9 @@ vnorm(vec3 v)
 float
 ray_triangle_intersect(vec3 P, vec3 d, struct triangle tri)
 {
-	vec3 n = tri.normal, A = tri.vertices[0], B = tri.vertices[1], C = tri.vertices[2];
 	d = vnorm(d);
-	n = vnorm(n);
+	vec3 n = vnorm(tri.n);
+	vec3 A = tri.a, B = tri.b, C = tri.c;
 	if (dot(n, d) == 0.0) return NAN;
 	float t = (dot(n, A) - dot(n, P)) / dot(n, d);
 	vec3 Q = vadd(P, smul(d, t));
@@ -111,20 +113,22 @@ main(int argc, char *argv[])
 	argv += optind; argc -= optind;
 	if (argc > 0) dieusage();
 
-	const char *stl;
-	{
-		int stl_fd = open("pineapple.stl", O_RDONLY);
-		if (stl_fd < 0) die(111, "fatal: unable to open pineapple.stl");
-		struct stat stl_stat;
-		if (fstat(stl_fd, &stl_stat) < 0) die(111, "fatal: unable to stat pineapple.stl");
-		stl = mmap(NULL, stl_stat.st_size, PROT_READ, MAP_PRIVATE, stl_fd, 0);
-		close(stl_fd);
-		if (!stl) die(111, "fatal: unable to mmap pineapple.stl");
+	char header[80];
+	if (fread(header, 1, 80, stdin) < 80)
+		diesys(111, "fatal: unable to read STL header from stdin");
+	uint32_t len;
+	if (fread(&len, 4, 1, stdin) < 1)
+		diesys(111, "fatal: unable to read STL length from stdin");
+	len = le32toh(len);
+	struct triangle *triangles = calloc(len, sizeof(struct triangle));
+	if (!triangles) diesys(111, "fatal: unable to allocate enough memory for STL facets");
+	struct triangle_raw raw;
+	for (size_t i = 0; i < len; ++i) {
+		if (fread(&raw, sizeof(raw), 1, stdin) < 1)
+			diesys(111, "fatal: unable to read STL facets");
+		triangles[i] = (struct triangle){ .n = raw.n, .a = raw.a, .b = raw.b, .c = raw.c };
 	}
-	stl += 80;
-	uint32_t len = le32toh(*(uint32_t *)stl);
-	stl += 4;
-	const struct triangle *triangles = (const struct triangle *)stl;
+	if (verbosity >= 1) fprintf(stderr, "finished reading STL: %d facets\n", len);
 
 	vec3 camera_pos = { -70.0, 60.0, 60.0 };
 	float camera_phi = PI * 0.8;
@@ -154,7 +158,7 @@ main(int argc, char *argv[])
 				float d = ray_triangle_intersect(camera_pos, dir, triangles[i]);
 				if (d != NAN && fabs(d) < fabs(shortest)) {
 					shortest = d;
-					shortest_norm = triangles[i].normal;
+					shortest_norm = triangles[i].n;
 				}
 			}
 
-- 
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