Fixing laggy chrome on a multitude of accelerated canvases

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 62 matching lines @@
 const int DefaultHeight = 150;
 
 // Firefox limits width/height to 32767 pixels, but slows down dramatically before it
 // reaches that limit. We limit by area instead, giving us larger maximum dimensions,
 // in exchange for a smaller maximum canvas size.
 const int MaxCanvasArea = 32768 * 8192; // Maximum canvas area in CSS pixels
 
 // In Skia, we will also limit width/height to 32767.
 const int MaxSkiaDim = 32767; // Maximum width/height in CSS pixels.
 
+// We estimate the max limit of GPU allocated memory for canvases before Chrome
+// becomes laggy by setting the total allocated memory for accelerated canvases
+// to be equivalent to memory used by 80 accelerated canvases, each has a size
+// of 1000*500 and 2d context.
+// Each such canvas occupies 4000000 = 1000 * 500 * 2 * 4 bytes, where 2 is the
+// gpuBufferCount in ImageBuffer::updateGPUMemoryUsage() and 4 means four bytes
+// per pixel per buffer.
+#if !OS(ANDROID)
+const int MaxGlobalGPUMemoryUsage = 4000000 * 80;
+#else
+// We estimate that the max limit for android phones is a quarter of that for
+// desktops based on local experimental results on Android One.,
+const int MaxGlobalGPUMemoryUsage = 4000000 * 20;
+#endif
+
 // A default value of quality argument for toDataURL and toBlob
-// It is in an invalid range (outside 0.0 - 1.0) so that it will not be misinterpreted as a user-input value
+// It is in an invalid range (outside 0.0 - 1.0) so that it will not be
+// misinterpreted as a user-input value
 const int UndefinedQualityValue = -1.0;
 
 // Default image mime type for toDataURL and toBlob functions
 const char DefaultMimeType[] = "image/png";
 
 bool canCreateImageBuffer(const IntSize& size)
 {
     if (size.isEmpty())
         return false;
     if (size.width() * size.height() > MaxCanvasArea)
@@ skipping 552 matching lines @@
             return false;
     }
 
     // Do not use acceleration for small canvas.
     if (canvasPixelCount < settings->minimumAccelerated2dCanvasSize())
         return false;
 
     if (!Platform::current()->canAccelerate2dCanvas())
         return false;
 
+    // When GPU allocated memory runs low (due to having created too many
+    // accelerated canvases), the compositor starves and browser becomes laggy.
+    // Thus, we should stop allocating more GPU memory to new canvases created
+    // when the current memory usage exceeds the threshold.
+    if (ImageBuffer::getGlobalGPUMemoryUsage() >= MaxGlobalGPUMemoryUsage)
+        return false;
+
     return true;
 }
 
 class UnacceleratedSurfaceFactory : public RecordingImageBufferFallbackSurfaceFactory {
 public:
     virtual PassOwnPtr<ImageBufferSurface> createSurface(const IntSize& size, OpacityMode opacityMode)
     {
         return adoptPtr(new UnacceleratedImageBufferSurface(size, opacityMode));
     }
 
@@ skipping 324 matching lines @@
     }
     return ImageBitmapSource::fulfillImageBitmap(scriptState, isPaintable() ? ImageBitmap::create(this, IntRect(sx, sy, sw, sh)) : nullptr);
 }
 
 bool HTMLCanvasElement::isOpaque() const
 {
     return m_context && !m_context->hasAlpha();
 }
 
 } // blink