Add fuzzy image matching tool for Linux pixel tests

third_party/fuzzymatch/fuzzymatch.c

Index: third_party/fuzzymatch/fuzzymatch.c
diff --git a/third_party/fuzzymatch/fuzzymatch.c b/third_party/fuzzymatch/fuzzymatch.c
new file mode 100644
index 0000000000000000000000000000000000000000..b1624e0928594c51d485a1d63b88ee0aacb65a09
--- /dev/null
+++ b/third_party/fuzzymatch/fuzzymatch.c
@@ -0,0 +1,98 @@
+// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/* Fuzzy pixel test matching.
+ *
+ * This is designed to compare two layout test images (RGB 800x600) and manage
+ * to ignore the noise caused by the font renderers choosing slightly different
+ * pixels.
+ *
+ *    A             B
+ *    |             |
+ *    |--->delta<---|
+ *           |
+ *           V
+ *          gray
+ *           |
+ *           V
+ *         binary
+ *           |
+ *    |-------------|
+ *    |             |
+ *   1x3           3x1   Morphological openings
+ *    |             |
+ *    |-----OR------|
+ *           |
+ *           V
+ *     count pixels
+ *
+ * The result is that three different pixels in a row (vertically or
+ * horizontally) will cause the match to fail and the binary exits with code 1.
+ * Otherwise the binary exists with code 0.
+ *
+ * This requires leptonica to be installed. On Ubuntu do
+ *   # apt-get install libleptonica libleptonica-dev
+ *
+ * Build with:
+ *   % gcc -o fuzzymatch fuzzymatch.c -llept -ljpeg -ltiff -lpng -lz -lm -Wall -O2
+ */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <leptonica/allheaders.h>
+
+static int
+usage(const char *argv0) {
+  fprintf(stderr, "Usage: %s <input a> <input b>\n", argv0);
+  return 1;
+}
+
+int
+main(int argc, char **argv) {
+  if (argc != 3)
+    return usage(argv[0]);
+
+  PIX *a = pixRead(argv[1]);
+  PIX *b = pixRead(argv[2]);
+
+  if (!a) {
+    fprintf(stderr, "Failed to open %s\n", argv[1]);
+    return 1;
+  }
+
+  if (!b) {
+    fprintf(stderr, "Failed to open %s\n", argv[1]);
+    return 1;
+  }
+
+  if (pixGetWidth(a) != pixGetWidth(b) ||
+      pixGetHeight(a) != pixGetHeight(b)) {
+    fprintf(stderr, "Inputs are difference sizes\n");
+    return 1;
+  }
+
+  PIX *delta = pixAbsDifference(a, b);
+  pixInvert(delta, delta);
+  pixDestroy(&a);
+  pixDestroy(&b);
+
+  PIX *deltagray = pixConvertRGBToGray(delta, 0, 0, 0);
+  pixDestroy(&delta);
+
+  PIX *deltabinary = pixThresholdToBinary(deltagray, 254);
+
+  PIX *hopened = pixOpenBrick(NULL, deltabinary, 3, 1);
+  PIX *vopened = pixOpenBrick(NULL, deltabinary, 1, 3);
+  pixDestroy(&deltabinary);
+
+  PIX *opened = pixOr(NULL, hopened, vopened);
+  pixDestroy(&hopened);
+  pixDestroy(&vopened);
+
+  l_int32 count;
+  pixCountPixels(opened, &count, NULL);
+  fprintf(stderr, "%d\n", count);
+
+  return count;
+}