XFA: Support PNG format in pdfium_test and add image diffing

Lays the groundwork for pixel-diffing tests in pdfium.

This is a port of chromium's tools/image_diff/image_diff_png.cc onto the
top of the fxcodec-provided version of libpng. pdfium_test is modified
to support the new format, and the tools/image_diff.cc image comparison
utility is provided, stripped of its base/ dependencies.

Unfortunately, this can't be back-ported to origin/main, since the
underlying PNG support isn't present inside pdfium.

BUG=https://code.google.com/p/pdfium/issues/detail?id=62
R=thestig@chromium.org

Review URL: https://codereview.chromium.org/870203005

1 files changed, 398 insertions, 0 deletions

diff --git a/samples/image_diff.cc b/samples/image_diff.cc
new file mode 100644
index 0000000000..3f82b66527
--- /dev/null
+++ b/samples/image_diff.cc
@@ -0,0 +1,398 @@
+// Copyright (c) 2011 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.
+
+// This file input format is based loosely on
+// Tools/DumpRenderTree/ImageDiff.m
+
+// The exact format of this tool's output to stdout is important, to match
+// what the run-webkit-tests script expects.
+
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <map>
+#include <string>
+#include <vector>
+
+#include "../third_party/base/logging.h"
+#include "../third_party/base/numerics/safe_conversions.h"
+#include "image_diff_png.h"
+
+#if defined(OS_WIN)
+#include "windows.h"
+#endif
+
+// Return codes used by this utility.
+static const int kStatusSame = 0;
+static const int kStatusDifferent = 1;
+static const int kStatusError = 2;
+
+// Color codes.
+static const uint32_t RGBA_RED = 0x000000ff;
+static const uint32_t RGBA_ALPHA = 0xff000000;
+
+class Image {
+ public:
+  Image() : w_(0), h_(0) {
+  }
+
+  Image(const Image& image)
+      : w_(image.w_),
+        h_(image.h_),
+        data_(image.data_) {
+  }
+
+  bool has_image() const {
+    return w_ > 0 && h_ > 0;
+  }
+
+  int w() const {
+    return w_;
+  }
+
+  int h() const {
+    return h_;
+  }
+
+  const unsigned char* data() const {
+    return &data_.front();
+  }
+
+  // Creates the image from the given filename on disk, and returns true on
+  // success.
+  bool CreateFromFilename(const std::string& path) {
+    FILE* f = fopen(path.c_str(), "rb");
+    if (!f)
+      return false;
+
+    std::vector<unsigned char> compressed;
+    const int buf_size = 1024;
+    unsigned char buf[buf_size];
+    size_t num_read = 0;
+    while ((num_read = fread(buf, 1, buf_size, f)) > 0) {
+      compressed.insert(compressed.end(), buf, buf + num_read);
+    }
+
+    fclose(f);
+
+    if (!image_diff_png::DecodePNG(&compressed[0], compressed.size(),
+                                   &data_, &w_, &h_)) {
+      Clear();
+      return false;
+    }
+    return true;
+  }
+
+  void Clear() {
+    w_ = h_ = 0;
+    data_.clear();
+  }
+
+  // Returns the RGBA value of the pixel at the given location
+  uint32_t pixel_at(int x, int y) const {
+    if (x >= 0 && x < w_ && y >= 0 && y < h_)
+      return *reinterpret_cast<const uint32_t*>(&(data_[(y * w_ + x) * 4]));
+    return 0;
+  }
+
+  void set_pixel_at(int x, int y, uint32_t color) const {
+    if (x >= 0 && x < w_ && y >= 0 && y < h_) {
+      void* addr = &const_cast<unsigned char*>(&data_.front())[(y * w_ + x) * 4];
+      *reinterpret_cast<uint32_t*>(addr) = color;
+    }
+  }
+
+ private:
+  // pixel dimensions of the image
+  int w_, h_;
+
+  std::vector<unsigned char> data_;
+};
+
+float PercentageDifferent(const Image& baseline, const Image& actual) {
+  int w = std::min(baseline.w(), actual.w());
+  int h = std::min(baseline.h(), actual.h());
+
+  // Compute pixels different in the overlap.
+  int pixels_different = 0;
+  for (int y = 0; y < h; y++) {
+    for (int x = 0; x < w; x++) {
+      if (baseline.pixel_at(x, y) != actual.pixel_at(x, y))
+        pixels_different++;
+    }
+  }
+
+  // Count pixels that are a difference in size as also being different.
+  int max_w = std::max(baseline.w(), actual.w());
+  int max_h = std::max(baseline.h(), actual.h());
+  // These pixels are off the right side, not including the lower right corner.
+  pixels_different += (max_w - w) * h;
+  // These pixels are along the bottom, including the lower right corner.
+  pixels_different += (max_h - h) * max_w;
+
+  // Like the WebKit ImageDiff tool, we define percentage different in terms
+  // of the size of the 'actual' bitmap.
+  float total_pixels = static_cast<float>(actual.w()) *
+                       static_cast<float>(actual.h());
+  if (total_pixels == 0) {
+    // When the bitmap is empty, they are 100% different.
+    return 100.0f;
+  }
+  return 100.0f * pixels_different / total_pixels;
+}
+
+// FIXME: Replace with unordered_map when available.
+typedef std::map<uint32_t, int32_t> RgbaToCountMap;
+
+float HistogramPercentageDifferent(const Image& baseline, const Image& actual) {
+  // TODO(johnme): Consider using a joint histogram instead, as described in
+  // "Comparing Images Using Joint Histograms" by Pass & Zabih
+  // http://www.cs.cornell.edu/~rdz/papers/pz-jms99.pdf
+
+  int w = std::min(baseline.w(), actual.w());
+  int h = std::min(baseline.h(), actual.h());
+
+  // Count occurences of each RGBA pixel value of baseline in the overlap.
+  RgbaToCountMap baseline_histogram;
+  for (int y = 0; y < h; y++) {
+    for (int x = 0; x < w; x++) {
+      // hash_map operator[] inserts a 0 (default constructor) if key not found.
+      baseline_histogram[baseline.pixel_at(x, y)]++;
+    }
+  }
+
+  // Compute pixels different in the histogram of the overlap.
+  int pixels_different = 0;
+  for (int y = 0; y < h; y++) {
+    for (int x = 0; x < w; x++) {
+      uint32_t actual_rgba = actual.pixel_at(x, y);
+      RgbaToCountMap::iterator it = baseline_histogram.find(actual_rgba);
+      if (it != baseline_histogram.end() && it->second > 0)
+        it->second--;
+      else
+        pixels_different++;
+    }
+  }
+
+  // Count pixels that are a difference in size as also being different.
+  int max_w = std::max(baseline.w(), actual.w());
+  int max_h = std::max(baseline.h(), actual.h());
+  // These pixels are off the right side, not including the lower right corner.
+  pixels_different += (max_w - w) * h;
+  // These pixels are along the bottom, including the lower right corner.
+  pixels_different += (max_h - h) * max_w;
+
+  // Like the WebKit ImageDiff tool, we define percentage different in terms
+  // of the size of the 'actual' bitmap.
+  float total_pixels = static_cast<float>(actual.w()) *
+                       static_cast<float>(actual.h());
+  if (total_pixels == 0) {
+    // When the bitmap is empty, they are 100% different.
+    return 100.0f;
+  }
+  return 100.0f * pixels_different / total_pixels;
+}
+
+void PrintHelp() {
+  fprintf(stderr,
+    "Usage:\n"
+    "  image_diff [--histogram] <compare file> <reference file>\n"
+    "    Compares two files on disk, returning 0 when they are the same;\n"
+    "    passing \"--histogram\" additionally calculates a diff of the\n"
+    "    RGBA value histograms (which is resistant to shifts in layout)\n"
+    "  image_diff --diff <compare file> <reference file> <output file>\n"
+    "    Compares two files on disk, outputs an image that visualizes the\n"
+    "    difference to <output file>\n");
+}
+
+int CompareImages(const std::string& file1,
+                  const std::string& file2,
+                  bool compare_histograms) {
+  Image actual_image;
+  Image baseline_image;
+
+  if (!actual_image.CreateFromFilename(file1)) {
+    fprintf(stderr, "image_diff: Unable to open file \"%s\"\n", file1.c_str());
+    return kStatusError;
+  }
+  if (!baseline_image.CreateFromFilename(file2)) {
+    fprintf(stderr, "image_diff: Unable to open file \"%s\"\n", file2.c_str());
+    return kStatusError;
+  }
+
+  if (compare_histograms) {
+    float percent = HistogramPercentageDifferent(actual_image, baseline_image);
+    const char* passed = percent > 0.0 ? "failed" : "passed";
+    printf("histogram diff: %01.2f%% %s\n", percent, passed);
+  }
+
+  const char* diff_name = compare_histograms ? "exact diff" : "diff";
+  float percent = PercentageDifferent(actual_image, baseline_image);
+  const char* passed = percent > 0.0 ? "failed" : "passed";
+  printf("%s: %01.2f%% %s\n", diff_name, percent, passed);
+  if (percent > 0.0) {
+    // failure: The WebKit version also writes the difference image to
+    // stdout, which seems excessive for our needs.
+    return kStatusDifferent;
+  }
+  // success
+  return kStatusSame;
+
+/* Untested mode that acts like WebKit's image comparator. I wrote this but
+   decided it's too complicated. We may use it in the future if it looks useful
+
+  char buffer[2048];
+  while (fgets(buffer, sizeof(buffer), stdin)) {
+
+    if (strncmp("Content-length: ", buffer, 16) == 0) {
+      char* context;
+      strtok_s(buffer, " ", &context);
+      int image_size = strtol(strtok_s(NULL, " ", &context), NULL, 10);
+
+      bool success = false;
+      if (image_size > 0 && actual_image.has_image() == 0) {
+        if (!actual_image.CreateFromStdin(image_size)) {
+          fputs("Error, input image can't be decoded.\n", stderr);
+          return 1;
+        }
+      } else if (image_size > 0 && baseline_image.has_image() == 0) {
+        if (!baseline_image.CreateFromStdin(image_size)) {
+          fputs("Error, baseline image can't be decoded.\n", stderr);
+          return 1;
+        }
+      } else {
+        fputs("Error, image size must be specified.\n", stderr);
+        return 1;
+      }
+    }
+
+    if (actual_image.has_image() && baseline_image.has_image()) {
+      float percent = PercentageDifferent(actual_image, baseline_image);
+      if (percent > 0.0) {
+        // failure: The WebKit version also writes the difference image to
+        // stdout, which seems excessive for our needs.
+        printf("diff: %01.2f%% failed\n", percent);
+      } else {
+        // success
+        printf("diff: %01.2f%% passed\n", percent);
+      }
+      actual_image.Clear();
+      baseline_image.Clear();
+    }
+
+    fflush(stdout);
+  }
+*/
+}
+
+bool CreateImageDiff(const Image& image1, const Image& image2, Image* out) {
+  int w = std::min(image1.w(), image2.w());
+  int h = std::min(image1.h(), image2.h());
+  *out = Image(image1);
+  bool same = (image1.w() == image2.w()) && (image1.h() == image2.h());
+
+  // TODO(estade): do something with the extra pixels if the image sizes
+  // are different.
+  for (int y = 0; y < h; y++) {
+    for (int x = 0; x < w; x++) {
+      uint32_t base_pixel = image1.pixel_at(x, y);
+      if (base_pixel != image2.pixel_at(x, y)) {
+        // Set differing pixels red.
+        out->set_pixel_at(x, y, RGBA_RED | RGBA_ALPHA);
+        same = false;
+      } else {
+        // Set same pixels as faded.
+        uint32_t alpha = base_pixel & RGBA_ALPHA;
+        uint32_t new_pixel = base_pixel - ((alpha / 2) & RGBA_ALPHA);
+        out->set_pixel_at(x, y, new_pixel);
+      }
+    }
+  }
+
+  return same;
+}
+
+int DiffImages(const std::string& file1,
+               const std::string& file2,
+               const std::string& out_file) {
+  Image actual_image;
+  Image baseline_image;
+
+  if (!actual_image.CreateFromFilename(file1)) {
+    fprintf(stderr, "image_diff: Unable to open file \"%s\"\n", file1.c_str());
+    return kStatusError;
+  }
+  if (!baseline_image.CreateFromFilename(file2)) {
+    fprintf(stderr, "image_diff: Unable to open file \"%s\"\n", file2.c_str());
+    return kStatusError;
+  }
+
+  Image diff_image;
+  bool same = CreateImageDiff(baseline_image, actual_image, &diff_image);
+  if (same)
+    return kStatusSame;
+
+  std::vector<unsigned char> png_encoding;
+  image_diff_png::EncodeRGBAPNG(
+      diff_image.data(), diff_image.w(), diff_image.h(),
+      diff_image.w() * 4, &png_encoding);
+
+  FILE *f = fopen(out_file.c_str(), "wb");
+  if (!f)
+    return kStatusError;
+
+  size_t size = png_encoding.size();
+  char *ptr = reinterpret_cast<char*>(&png_encoding.front());
+  if (fwrite(ptr, 1, size, f) != size)
+    return kStatusError;
+
+  return kStatusDifferent;
+}
+
+int main(int argc, const char* argv[]) {
+  bool histograms = false;
+  bool produce_diff_image = false;
+  std::string filename1;
+  std::string filename2;
+  std::string diff_filename;
+
+  int i;
+  for (i = 1; i < argc; ++i) {
+    const char* arg = argv[i];
+    if (strstr(arg, "--") != arg)
+      break;
+    if (strcmp(arg, "--histogram") == 0) {
+      histograms = true;
+    } else if (strcmp(arg, "--diff") == 0) {
+      produce_diff_image = true;
+    }
+  }
+  if (i < argc) {
+    filename1 = argv[i];
+    ++i;
+  }
+  if (i < argc) {
+    filename2 = argv[i];
+    ++i;
+  }
+  if (i < argc) {
+    diff_filename = argv[i];
+    ++i;
+  }
+
+  if (produce_diff_image) {
+    if (!diff_filename.empty()) {
+      return DiffImages(filename1, filename2, diff_filename);
+    }
+  } else if (!filename2.empty()) {
+    return CompareImages(filename1, filename2, histograms);
+  }
+
+  PrintHelp();
+  return kStatusError;
+}