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

[Justin Novosad, 2015/12/08 22:15:27]

There is no hard rule for this in Blink, but we generally respect 80col for
multi-line comments

+// 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 MaxTotalGPUMemoryUsage = 4000000 * 80;
+#else
+// We estimate that the max limit for android phones is half of that for desktops based on local
+// experimental results on Android One; though a very slight lagginess on Android One is still expected,
+// other Android devices should work fine.
+const int MaxTotalGPUMemoryUsage = 4000000 * 40;

[Justin Novosad, 2015/12/08 22:15:27]

This limit feels excessive

+#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
 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())
@@ skipping 514 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

[Justin Novosad, 2015/12/08 22:15:27]

wrapping

+    // new canvases created when the current memory usage exceeds the threshold.
+    if (ImageBuffer::getTotalGPUMemoryUsage() >= MaxTotalGPUMemoryUsage)
+        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 128 matching lines @@
             // The number of internal GPU buffers vary between one (stable
             // non-displayed state) and three (triple-buffered animations).
             // Adding 2 is a pessimistic but relevant estimate.
             // Note: These buffers might be allocated in GPU memory.
             bufferCount += 2;
         }
     }
     if (m_copiedImage)
         bufferCount++;
 
-    // Four bytes per pixel per buffer.

[Justin Novosad, 2015/12/08 22:15:27]

Why remove this comment?

     Checked<intptr_t, RecordOverflow> checkedExternallyAllocatedMemory = 4 * bufferCount;
     if (is3D())
         checkedExternallyAllocatedMemory += m_context->externallyAllocatedBytesPerPixel();
 
     checkedExternallyAllocatedMemory *= width();
     checkedExternallyAllocatedMemory *= height();
     intptr_t externallyAllocatedMemory;
     if (checkedExternallyAllocatedMemory.safeGet(externallyAllocatedMemory) == CheckedState::DidOverflow)
         externallyAllocatedMemory = std::numeric_limits<intptr_t>::max();
 
@@ skipping 174 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