Add utility to load P6 images

src/pam.c

@@ -1,4 +1,8 @@
 #include "pam.h"
+#include "img.h"
+#include "mem_arena.h"
+#include <stddef.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -28,3 +32,57 @@ void write_p7_image(u64 width, u64 height, u8 *buf, const char *outfile) {
 
   fclose(fp);
 }
+
+Image *load_p6_image(Arena *arena, const char *filename) {
+  Image *output = NULL;
+
+  if (!arena || !filename) {
+    goto RETURN_VALUE;
+  }
+
+  FILE *fp = fopen(filename, "rb");
+  if (!fp) {
+    goto RETURN_VALUE;
+  }
+
+  char type[4] = {0};
+  fread(type, 3, 1, fp);
+  if (strncmp(type, "P6\n", 4) != 0) {
+    goto CLOSE_FILE;
+  }
+
+  u64 w, h;
+  fscanf(fp, "%lu %lu\n", &w, &h);
+
+  u64 max;
+  fscanf(fp, "%lu\n", &max);
+  if (max > UINT8_MAX) {
+    goto CLOSE_FILE;
+  }
+
+  output = wapp_mem_arena_alloc(arena, sizeof(Image));
+  if (!output) {
+    goto CLOSE_FILE;
+  }
+
+  output->width = w;
+  output->height = h;
+  if (!init_buffer(arena, output)) {
+    goto CLOSE_FILE;
+  }
+
+  Colour colour = {0};
+  for (u64 y = 0; y < h; ++y) {
+    for (u64 x = 0; x < w; ++x) {
+      fread(&colour, 3, 1, fp);
+      colour.a = 255;
+      set_pixel(output, x, y, &colour);
+    }
+  }
+
+CLOSE_FILE:
+  fclose(fp);
+
+RETURN_VALUE:
+  return output;
+}

src/pam.h

@@ -2,7 +2,9 @@
 #define PAM_H
 
 #include "aliases.h"
+#include "img.h"
 
 void write_p7_image(u64 width, u64 height, u8 *buf, const char *outfile);
+Image *load_p6_image(Arena *arena, const char *filename);
 
 #endif // PAM_H