Improve performance of performance overlay by caching. (flutter#6225)

Cache a SkSurface with previously drawn shapes so that we do not need to draw them again in future frames.

On Nexus 5X test device, old render time for just the overlay was 1.3ms-3.0ms and this version improves to 0.9ms-1.3ms running flutter gallery in profile mode.

flow/instrumentation.cc

@@ -8,6 +8,7 @@
 #include <limits>
 
 #include "third_party/skia/include/core/SkPath.h"
+#include "third_party/skia/include/core/SkSurface.h"
 
 namespace flow {
 
@@ -17,6 +18,8 @@ static const size_t kMaxFrameMarkers = 8;
 Stopwatch::Stopwatch() : start_(fml::TimePoint::Now()), current_sample_(0) {
   const fml::TimeDelta delta = fml::TimeDelta::Zero();
   laps_.resize(kMaxSamples, delta);
+  cache_dirty_ = true;
+  prev_drawn_sample_index_ = 0;
 }
 
 Stopwatch::~Stopwatch() = default;
@@ -60,32 +63,41 @@ fml::TimeDelta Stopwatch::MaxDelta() const {
   return max_delta;
 }
 
-void Stopwatch::Visualize(SkCanvas& canvas, const SkRect& rect) const {
-  SkPaint paint;
+// Initialize the SkSurface for drawing into. Draws the base background and any
+// timing data from before the initial Visualize() call.
+void Stopwatch::InitVisualizeSurface(const SkRect& rect) const {
+  if (!cache_dirty_) {
+    return;
+  }
+  cache_dirty_ = false;
 
-  // Paint the background.
-  paint.setColor(0x99FFFFFF);
-  canvas.drawRect(rect, paint);
+  // TODO(garyq): Use a GPU surface instead of a CPU surface.
+  visualize_cache_surface_ =
+      SkSurface::MakeRasterN32Premul(rect.width(), rect.height());
+
+  SkCanvas* cache_canvas = visualize_cache_surface_->getCanvas();
 
   // Establish the graph position.
-  const SkScalar x = rect.x();
-  const SkScalar y = rect.y();
+  const SkScalar x = 0;
+  const SkScalar y = 0;
   const SkScalar width = rect.width();
   const SkScalar height = rect.height();
-  const SkScalar bottom = y + height;
-  const SkScalar right = x + width;
+
+  SkPaint paint;
+  paint.setColor(0x99FFFFFF);
+  cache_canvas->drawRect(SkRect::MakeXYWH(x, y, width, height), paint);
 
   // Scale the graph to show frame times up to those that are 3 times the frame
   // time.
   const double max_interval = kOneFrameMS * 3.0;
   const double max_unit_interval = UnitFrameInterval(max_interval);
 
-  // Prepare a path for the data.
-  // we start at the height of the last point, so it looks like we wrap around
+  // Draw the old data to initially populate the graph.
+  // Prepare a path for the data. We start at the height of the last point, so
+  // it looks like we wrap around
   SkPath path;
   path.setIsVolatile(true);
-  const double sample_unit_width = (1.0 / kMaxSamples);
-  path.moveTo(x, bottom);
+  path.moveTo(x, height);
   path.lineTo(x, y + height * (1.0 - UnitHeight(laps_[0].ToMillisecondsF(),
                                                 max_unit_interval)));
   double unit_x;
@@ -100,17 +112,61 @@ void Stopwatch::Visualize(SkCanvas& canvas, const SkRect& rect) const {
     path.lineTo(x + width * unit_next_x, sample_y);
   }
   path.lineTo(
-      right,
+      width,
       y + height * (1.0 - UnitHeight(laps_[kMaxSamples - 1].ToMillisecondsF(),
                                      max_unit_interval)));
-  path.lineTo(right, bottom);
+  path.lineTo(width, height);
   path.close();
 
   // Draw the graph.
   paint.setColor(0xAA0000FF);
-  canvas.drawPath(path, paint);
+  cache_canvas->drawPath(path, paint);
+}
+
+void Stopwatch::Visualize(SkCanvas& canvas, const SkRect& rect) const {
+  // Initialize visualize cache if it has not yet been initialized.
+  InitVisualizeSurface(rect);
 
-  // Draw horizontal markers.
+  SkCanvas* cache_canvas = visualize_cache_surface_->getCanvas();
+  SkPaint paint;
+
+  // Establish the graph position.
+  const SkScalar x = 0;
+  const SkScalar y = 0;
+  const SkScalar width = rect.width();
+  const SkScalar height = rect.height();
+
+  // Scale the graph to show frame times up to those that are 3 times the frame
+  // time.
+  const double max_interval = kOneFrameMS * 3.0;
+  const double max_unit_interval = UnitFrameInterval(max_interval);
+
+  const double sample_unit_width = (1.0 / kMaxSamples);
+
+  // Draw vertical replacement bar to erase old/stale pixels.
+  paint.setColor(0x99FFFFFF);
+  paint.setStyle(SkPaint::Style::kFill_Style);
+  paint.setBlendMode(SkBlendMode::kSrc);
+  double sample_x =
+      x + width * (static_cast<double>(prev_drawn_sample_index_) / kMaxSamples);
+  const auto eraser_rect = SkRect::MakeLTRB(
+      sample_x, y, sample_x + width * sample_unit_width, height);
+  cache_canvas->drawRect(eraser_rect, paint);
+
+  // Draws blue timing bar for new data.
+  paint.setColor(0xAA0000FF);
+  paint.setBlendMode(SkBlendMode::kSrcOver);
+  const auto bar_rect = SkRect::MakeLTRB(
+      sample_x,
+      y + height * (1.0 -
+                    UnitHeight(laps_[current_sample_ == 0 ? kMaxSamples - 1
+                                                          : current_sample_ - 1]
+                                   .ToMillisecondsF(),
+                               max_unit_interval)),
+      sample_x + width * sample_unit_width, height);
+  cache_canvas->drawRect(bar_rect, paint);
+
+  // Draw horizontal frame markers.
   paint.setStrokeWidth(0);  // hairline
   paint.setStyle(SkPaint::Style::kStroke_Style);
   paint.setColor(0xCC000000);
@@ -129,27 +185,32 @@ void Stopwatch::Visualize(SkCanvas& canvas, const SkRect& rect) const {
       const double frame_height =
           height * (1.0 - (UnitFrameInterval((frame_index + 1) * kOneFrameMS) /
                            max_unit_interval));
-      canvas.drawLine(x, y + frame_height, right, y + frame_height, paint);
+      cache_canvas->drawLine(x, y + frame_height, width, y + frame_height,
+                             paint);
     }
   }
 
   // Paint the vertical marker for the current frame.
   // We paint it over the current frame, not after it, because when we
   // paint this we don't yet have all the times for the current frame.
   paint.setStyle(SkPaint::Style::kFill_Style);
+  paint.setBlendMode(SkBlendMode::kSrcOver);
   if (UnitFrameInterval(LastLap().ToMillisecondsF()) > 1.0) {
     // budget exceeded
     paint.setColor(SK_ColorRED);
   } else {
     // within budget
     paint.setColor(SK_ColorGREEN);
   }
-  double sample_x =
-      x + width * (static_cast<double>(current_sample_) / kMaxSamples);
-
+  sample_x = x + width * (static_cast<double>(current_sample_) / kMaxSamples);
   const auto marker_rect = SkRect::MakeLTRB(
-      sample_x, y, sample_x + width * sample_unit_width, bottom);
-  canvas.drawRect(marker_rect, paint);
+      sample_x, y, sample_x + width * sample_unit_width, height);
+  cache_canvas->drawRect(marker_rect, paint);
+  prev_drawn_sample_index_ = current_sample_;
+
+  // Draw the cached surface onto the output canvas.
+  paint.reset();
+  visualize_cache_surface_->draw(&canvas, rect.x(), rect.y(), &paint);
 }
 
 CounterValues::CounterValues() : current_sample_(kMaxSamples - 1) {

flow/instrumentation.h

@@ -28,6 +28,8 @@ class Stopwatch {
 
   fml::TimeDelta MaxDelta() const;
 
+  void InitVisualizeSurface(const SkRect& rect) const;
+
   void Visualize(SkCanvas& canvas, const SkRect& rect) const;
 
   void Start();
@@ -40,6 +42,11 @@ class Stopwatch {
   fml::TimePoint start_;
   std::vector<fml::TimeDelta> laps_;
   size_t current_sample_;
+  // Mutable data cache for performance optimization of the graphs. Prevents
+  // expensive redrawing of old data.
+  mutable bool cache_dirty_;
+  mutable sk_sp<SkSurface> visualize_cache_surface_;
+  mutable size_t prev_drawn_sample_index_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(Stopwatch);
 };