webpdec.h: single-file WebP decoder

libwebp 1.6.0's decode + demux path (lossy VP8, lossless VP8L, VP8X container, ALPH alpha, and the WebPDemux/WebPAnimDecoder animation API) amalgamated into one stb-style header, built as portable C99 with all SIMD, threads and host file I/O disabled. amalgamate.py regenerates webpdec.h from a pinned, auto-cloned libwebp checkout; tests/run.sh checks decode output bit-exactly against reference libwebp. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-14 03:28:11 +00:00
commit 4da9a48d7c
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+/* test harness: decode a .webp to RGBA, report, dump a PPM for eyeballing */
+#include <stdio.h>
+#include <stdlib.h>
+
+#define WEBPDEC_IMPLEMENTATION
+#include "webpdec.h"
+
+int main(int argc, char **argv) {
+  if (argc < 2) { fprintf(stderr, "usage: %s file.webp [out.ppm]\n", argv[0]); return 2; }
+  FILE *f = fopen(argv[1], "rb");
+  if (!f) { perror("open"); return 1; }
+  fseek(f, 0, SEEK_END); long n = ftell(f); fseek(f, 0, SEEK_SET);
+  unsigned char *buf = malloc(n);
+  if (fread(buf, 1, n, f) != (size_t)n) { perror("read"); return 1; }
+  fclose(f);
+
+  int w = 0, h = 0;
+  if (!WebPGetInfo(buf, n, &w, &h)) { fprintf(stderr, "not a webp / bad header\n"); return 1; }
+  printf("WebPGetInfo: %dx%d\n", w, h);
+
+  uint8_t *rgba = WebPDecodeRGBA(buf, n, &w, &h);
+  if (!rgba) { fprintf(stderr, "decode FAILED\n"); return 1; }
+  printf("decoded: %dx%d, RGBA (R,G,B,A top-to-bottom)\n", w, h);
+
+  /* sample a few pixels */
+  long center = ((long)h/2 * w + w/2) * 4;
+  printf("center px RGBA = %d %d %d %d\n",
+         rgba[center], rgba[center+1], rgba[center+2], rgba[center+3]);
+
+  /* checksum + alpha presence */
+  unsigned long sum = 0; int has_alpha = 0;
+  for (long i = 0; i < (long)w*h; i++) {
+    sum += rgba[i*4] + rgba[i*4+1] + rgba[i*4+2];
+    if (rgba[i*4+3] != 255) has_alpha = 1;
+  }
+  printf("rgb checksum=%lu  non-opaque-alpha=%s\n", sum, has_alpha ? "yes" : "no");
+
+  if (argc >= 3) {  /* .raw => raw RGBA dump; else opaque PPM */
+    const char *p = argv[2];
+    size_t L = 0; while (p[L]) L++;
+    FILE *o = fopen(argv[2], "wb");
+    if (L >= 4 && p[L-4]=='.' && p[L-3]=='r' && p[L-2]=='a' && p[L-1]=='w') {
+      fwrite(rgba, 4, (size_t)w*h, o);
+    } else {
+      fprintf(o, "P6\n%d %d\n255\n", w, h);
+      for (long i = 0; i < (long)w*h; i++) fwrite(&rgba[i*4], 1, 3, o);
+    }
+    fclose(o);
+    printf("wrote %s\n", argv[2]);
+  }
+  WebPFree(rgba);
+  free(buf);
+  return 0;
+}