Add mock capability to PerformanceOverlayLayer (flutter#7537)

So we can do golden test on PerformanceOverlay to avoid regression like
flutter/flutter#26387

ci/licenses_golden/licenses_flutter

@@ -57,6 +57,7 @@ FILE: ../../../flutter/flow/layers/opacity_layer.cc
 FILE: ../../../flutter/flow/layers/opacity_layer.h
 FILE: ../../../flutter/flow/layers/performance_overlay_layer.cc
 FILE: ../../../flutter/flow/layers/performance_overlay_layer.h
+FILE: ../../../flutter/flow/layers/performance_overlay_layer_unittests.cc
 FILE: ../../../flutter/flow/layers/physical_shape_layer.cc
 FILE: ../../../flutter/flow/layers/physical_shape_layer.h
 FILE: ../../../flutter/flow/layers/picture_layer.cc

flow/BUILD.gn

@@ -95,6 +95,7 @@ executable("flow_unittests") {
   sources = [
     "matrix_decomposition_unittests.cc",
     "raster_cache_unittests.cc",
+    "layers/performance_overlay_layer_unittests.cc",
   ]
 
   deps = [

flow/layers/performance_overlay_layer.cc

@@ -15,8 +15,12 @@ namespace {
 void DrawStatisticsText(SkCanvas& canvas,
                         const std::string& string,
                         int x,
-                        int y) {
+                        int y,
+                        const std::string& font_path) {
   SkFont font;
+  if (font_path != "") {
+    font = SkFont(SkTypeface::MakeFromFile(font_path.c_str()));
+  }
   font.setSize(15);
   font.setLinearMetrics(false);
   SkPaint paint;
@@ -33,7 +37,8 @@ void VisualizeStopWatch(SkCanvas& canvas,
                         SkScalar height,
                         bool show_graph,
                         bool show_labels,
-                        const std::string& label_prefix) {
+                        const std::string& label_prefix,
+                        const std::string& font_path) {
   const int label_x = 8;    // distance from x
   const int label_y = -10;  // distance from y+height
 
@@ -51,14 +56,20 @@ void VisualizeStopWatch(SkCanvas& canvas,
     stream << label_prefix << "  "
            << "max " << max_ms_per_frame << " ms/frame, "
            << "avg " << average_ms_per_frame << " ms/frame";
-    DrawStatisticsText(canvas, stream.str(), x + label_x, y + height + label_y);
+    DrawStatisticsText(canvas, stream.str(), x + label_x, y + height + label_y,
+                       font_path);
   }
 }
 
 }  // namespace
 
-PerformanceOverlayLayer::PerformanceOverlayLayer(uint64_t options)
-    : options_(options) {}
+PerformanceOverlayLayer::PerformanceOverlayLayer(uint64_t options,
+                                                 const char* font_path)
+    : options_(options) {
+  if (font_path != nullptr) {
+    font_path_ = font_path;
+  }
+}
 
 void PerformanceOverlayLayer::Paint(PaintContext& context) const {
   const int padding = 8;
@@ -73,15 +84,15 @@ void PerformanceOverlayLayer::Paint(PaintContext& context) const {
   SkScalar height = paint_bounds().height() / 2;
   SkAutoCanvasRestore save(context.leaf_nodes_canvas, true);
 
-  VisualizeStopWatch(*context.leaf_nodes_canvas, context.frame_time, x, y,
-                     width, height - padding,
-                     options_ & kVisualizeRasterizerStatistics,
-                     options_ & kDisplayRasterizerStatistics, "GPU");
+  VisualizeStopWatch(
+      *context.leaf_nodes_canvas, context.frame_time, x, y, width,
+      height - padding, options_ & kVisualizeRasterizerStatistics,
+      options_ & kDisplayRasterizerStatistics, "GPU", font_path_);
 
   VisualizeStopWatch(*context.leaf_nodes_canvas, context.engine_time, x,
                      y + height, width, height - padding,
                      options_ & kVisualizeEngineStatistics,
-                     options_ & kDisplayEngineStatistics, "UI");
+                     options_ & kDisplayEngineStatistics, "UI", font_path_);
 }
 
 }  // namespace flow

flow/layers/performance_overlay_layer.h

@@ -5,6 +5,8 @@
 #ifndef FLUTTER_FLOW_LAYERS_PERFORMANCE_OVERLAY_LAYER_H_
 #define FLUTTER_FLOW_LAYERS_PERFORMANCE_OVERLAY_LAYER_H_
 
+#include <string>
+
 #include "flutter/flow/layers/layer.h"
 #include "flutter/fml/macros.h"
 
@@ -17,12 +19,14 @@ const int kVisualizeEngineStatistics = 1 << 3;
 
 class PerformanceOverlayLayer : public Layer {
  public:
-  explicit PerformanceOverlayLayer(uint64_t options);
+  explicit PerformanceOverlayLayer(uint64_t options,
+                                   const char* font_path = nullptr);
 
   void Paint(PaintContext& context) const override;
 
  private:
   int options_;
+  std::string font_path_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(PerformanceOverlayLayer);
 };

flow/layers/performance_overlay_layer_unittests.cc

@@ -0,0 +1,90 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/flow/layers/performance_overlay_layer.h"
+#include "flutter/flow/raster_cache.h"
+
+#include "third_party/skia/include/core/SkSurface.h"
+#include "third_party/skia/include/utils/SkBase64.h"
+
+#include "gtest/gtest.h"
+
+// To get the size of kMockedTimes in compile time.
+template <class T, std::size_t N>
+constexpr int size(const T (&array)[N]) noexcept {
+  return N;
+}
+
+constexpr int kMockedTimes[] = {17, 1,  4,  24, 4,  25, 30, 4,  13, 34,
+                                14, 0,  18, 9,  32, 36, 26, 23, 5,  8,
+                                32, 18, 29, 16, 29, 18, 0,  36, 33, 10};
+
+const char* kGoldenFileName =
+    "flutter/testing/resources/performance_overlay_gold.png";
+
+const char* kNewGoldenFileName =
+    "flutter/testing/resources/performance_overlay_gold_new.png";
+
+// Ensure the same font across different operation systems.
+const char* kFontFilePath =
+    "flutter/third_party/txt/third_party/fonts/Roboto-Regular.ttf";
+
+TEST(PerformanceOverlayLayer, Gold) {
+  flow::Stopwatch mock_stopwatch;
+  for (int i = 0; i < size(kMockedTimes); ++i) {
+    mock_stopwatch.SetLapTime(
+        fml::TimeDelta::FromMilliseconds(kMockedTimes[i]));
+  }
+
+  const SkImageInfo image_info = SkImageInfo::MakeN32Premul(1000, 1000);
+  sk_sp<SkSurface> surface = SkSurface::MakeRaster(image_info);
+
+  ASSERT_TRUE(surface != nullptr);
+
+  flow::TextureRegistry unused_texture_registry;
+
+  flow::Layer::PaintContext paintContext = {
+      nullptr,        surface->getCanvas(),    nullptr, mock_stopwatch,
+      mock_stopwatch, unused_texture_registry, nullptr, false};
+
+  flow::PerformanceOverlayLayer layer(flow::kDisplayRasterizerStatistics |
+                                          flow::kVisualizeRasterizerStatistics |
+                                          flow::kDisplayEngineStatistics |
+                                          flow::kVisualizeEngineStatistics,
+                                      kFontFilePath);
+  layer.set_paint_bounds(SkRect::MakeWH(1000, 400));
+  surface->getCanvas()->clear(SK_ColorTRANSPARENT);
+  layer.Paint(paintContext);
+
+  sk_sp<SkImage> snapshot = surface->makeImageSnapshot();
+  sk_sp<SkData> snapshot_data = snapshot->encodeToData();
+
+  sk_sp<SkData> golden_data = SkData::MakeFromFileName(kGoldenFileName);
+  EXPECT_TRUE(golden_data != nullptr)
+      << "Golden file not found: " << kGoldenFileName << ".\n"
+      << "Please make sure that the unit test is run from the right directory "
+      << "(e.g., flutter/engine/src)";
+
+  const bool golden_data_matches = golden_data->equals(snapshot_data.get());
+  if (!golden_data_matches) {
+    SkFILEWStream wstream(kNewGoldenFileName);
+    wstream.write(snapshot_data->data(), snapshot_data->size());
+    wstream.flush();
+
+    size_t b64_size =
+        SkBase64::Encode(snapshot_data->data(), snapshot_data->size(), nullptr);
+    char* b64_data = new char[b64_size];
+    SkBase64::Encode(snapshot_data->data(), snapshot_data->size(), b64_data);
+
+    EXPECT_TRUE(golden_data_matches)
+        << "Golden file mismatch. Please check "
+        << "the difference between " << kGoldenFileName << " and "
+        << kNewGoldenFileName << ", and  replace the former "
+        << "with the latter if the difference looks good.\n\n"
+        << "See also the base64 encoded " << kNewGoldenFileName << ":\n"
+        << b64_data;
+
+    delete[] b64_data;
+  }
+}