08: C: Add input visualization (Netpbm P6)

08/solution.c

@@ -1,10 +1,41 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 
+int vis(const char *outpath, const char *in, size_t w, size_t h, size_t stride) {
+    int fd = open(outpath, O_CREAT | O_RDWR | O_NONBLOCK, 0644);
+    if (fd == -1) return 1;
+
+    char head[128];
+    size_t ps = snprintf(head, 128, "P6\n%lu %lu\n255\n", w, h);
+    if (ps >= 128) return 1;
+    size_t mapsiz = ps + w * h * 3;
+    ftruncate(fd, mapsiz);
+    unsigned char *o = mmap(NULL, mapsiz, PROT_WRITE, MAP_SHARED, fd, 0);
+    if (o == MAP_FAILED) return 1;
+    unsigned char *out = o;
+    strncpy((char*)out, head, ps);
+    out += ps;
+
+    for(size_t y = 0; y < h; y++) {
+        for (size_t x = 0; x < w; x++) {
+            int val = in[stride * y + x] - '0';
+            float v = val * 0.75 / 10.0;
+            unsigned char *b = out + w * y * 3 + x * 3;
+            *b++ = 180 * v / 3;
+            *b++ = 220 * v;
+            *b++ = 150 * v / 1.8;
+        }
+    }
+
+    munmap(o, mapsiz);
+    return close(fd);
+}
+
 int main(int argc, char **argv) {
     if (argc < 2) return 1;
 
@@ -22,6 +53,16 @@ int main(int argc, char **argv) {
     size_t visible = w * 2 + (h - 2) * 2;
     size_t maxscore = 0;
 
+    if (argc > 2) {
+        printf("Writing %s... ", argv[2]);
+        fflush(stdout);
+        if (vis(argv[2], in, w, h, stride)) {
+            perror("");
+            return 1;
+        }
+        printf("Done!\n");
+    }
+
 #pragma omp parallel for reduction(+:visible) reduction(max:maxscore) schedule(runtime)
     for (size_t y = 1; y < h - 1; y++) {
         for (size_t x = 1; x < w - 1; x++) {