Fixing laggy chrome on a multitude of accelerated canvases

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

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
index e04ea2b304f96f0bc3e3c80e013ff43918bbac47..ad845e0c00c16bc9e2ec85307c9b8a5251c6ba6e 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
@@ -69,31 +69,45 @@ using namespace HTMLNames;
 namespace {
 
 // These values come from the WhatWG spec.
-const int DefaultWidth = 300;
-const int DefaultHeight = 150;
+const int kDefaultWidth = 300;

[Justin Novosad, 2015/12/02 16:33:33]

The k prefix is a skia thing. In Blink use CapitalizedCamelCase.

[danakj, 2015/12/02 18:23:40]

It's also a chromium thing, I didn't know blink has a diff rule currently.

[danakj, 2015/12/02 18:31:09]

FWIW I only see a blink-specific rule for enums: "Enum members should use
InterCaps with an initial capital letter. [names-enum-members]"

I guess another thing to converge on though.

+const int kDefaultHeight = 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
+const int kMaxCanvasArea = 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.
+const int kMaxSkiaDim = 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 6000000 = 1000 * 500 * 3 * 4 bytes, where 3 is the bufferCount in
+// updateExternallyAllocatedMemory() and 4 means four bytes per pixel per buffer.
+#if !OS(ANDROID)
+const int kMaxTotalExternallyAllocatedMemory = 6000000 * 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 kMaxTotalExternallyAllocatedMemory = 6000000 * 40;
+#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;
+const int kUndefinedQualityValue = -1.0;
 
 // Default image mime type for toDataURL and toBlob functions
-const char DefaultMimeType[] = "image/png";
+const char kDefaultMimeType[] = "image/png";
 
 bool canCreateImageBuffer(const IntSize& size)
 {
     if (size.isEmpty())
         return false;
-    if (size.width() * size.height() > MaxCanvasArea)
+    if (size.width() * size.height() > kMaxCanvasArea)
         return false;
-    if (size.width() > MaxSkiaDim || size.height() > MaxSkiaDim)
+    if (size.width() > kMaxSkiaDim || size.height() > kMaxSkiaDim)
         return false;
     return true;
 }
@@ -111,7 +125,7 @@ PassRefPtr<Image> createTransparentImage(const IntSize& size)
 inline HTMLCanvasElement::HTMLCanvasElement(Document& document)
     : HTMLElement(canvasTag, document)
     , DocumentVisibilityObserver(document)
-    , m_size(DefaultWidth, DefaultHeight)
+    , m_size(kDefaultWidth, kDefaultHeight)
     , m_ignoreReset(false)
     , m_externallyAllocatedMemory(0)
     , m_originClean(true)
@@ -124,9 +138,13 @@ inline HTMLCanvasElement::HTMLCanvasElement(Document& document)
 
 DEFINE_NODE_FACTORY(HTMLCanvasElement)
 
+intptr_t HTMLCanvasElement::s_totalMemoryForAcceleratedCanvases = 0;
+
 HTMLCanvasElement::~HTMLCanvasElement()
 {
     v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(-m_externallyAllocatedMemory);
+    if (m_imageBuffer && m_imageBuffer->isAccelerated())
+        updateTotalMemoryForAcceleratedCanvases(-m_externallyAllocatedMemory);
 #if !ENABLE(OILPAN)
     // Ensure these go away before the ImageBuffer.
     m_context.clear();
@@ -347,11 +365,11 @@ void HTMLCanvasElement::reset()
 
     int w = getAttribute(widthAttr).toInt(&ok);
     if (!ok || w < 0)
-        w = DefaultWidth;
+        w = kDefaultWidth;
 
     int h = getAttribute(heightAttr).toInt(&ok);
     if (!ok || h < 0)
-        h = DefaultHeight;
+        h = kDefaultHeight;
 
     if (m_context && m_context->is2d())
         m_context->reset();
@@ -451,14 +469,14 @@ String HTMLCanvasElement::toEncodingMimeType(const String& mimeType)
 
     // FIXME: Make isSupportedImageMIMETypeForEncoding threadsafe (to allow this method to be used on a worker thread).
     if (mimeType.isNull() || !MIMETypeRegistry::isSupportedImageMIMETypeForEncoding(lowercaseMimeType))
-        lowercaseMimeType = DefaultMimeType;
+        lowercaseMimeType = kDefaultMimeType;
 
     return lowercaseMimeType;
 }
 
 const AtomicString HTMLCanvasElement::imageSourceURL() const
 {
-    return AtomicString(toDataURLInternal(DefaultMimeType, 0, FrontBuffer));
+    return AtomicString(toDataURLInternal(kDefaultMimeType, 0, FrontBuffer));
 }
 
 void HTMLCanvasElement::prepareSurfaceForPaintingIfNeeded() const
@@ -521,7 +539,7 @@ String HTMLCanvasElement::toDataURL(const String& mimeType, const ScriptValue& q
         exceptionState.throwSecurityError("Tainted canvases may not be exported.");
         return String();
     }
-    double quality = UndefinedQualityValue;
+    double quality = kUndefinedQualityValue;
     if (!qualityArgument.isEmpty()) {
         v8::Local<v8::Value> v8Value = qualityArgument.v8Value();
         if (v8Value->IsNumber()) {
@@ -544,7 +562,7 @@ void HTMLCanvasElement::toBlob(FileCallback* callback, const String& mimeType, c
         return;
     }
 
-    double quality = UndefinedQualityValue;
+    double quality = kUndefinedQualityValue;
     if (!qualityArgument.isEmpty()) {
         v8::Local<v8::Value> v8Value = qualityArgument.v8Value();
         if (v8Value->IsNumber()) {
@@ -561,7 +579,7 @@ void HTMLCanvasElement::toBlob(FileCallback* callback, const String& mimeType, c
     RefPtr<DOMUint8ClampedArray> imageDataRef(imageData->data());
 
     RefPtr<CanvasAsyncBlobCreator> asyncCreatorRef = CanvasAsyncBlobCreator::create(imageDataRef.release(), encodingMimeType, imageData->size(), callback);
-    if (Platform::current()->isThreadedCompositingEnabled() && (encodingMimeType == DefaultMimeType)) {
+    if (Platform::current()->isThreadedCompositingEnabled() && (encodingMimeType == kDefaultMimeType)) {
         asyncCreatorRef->scheduleAsyncBlobCreation(true);
     } else {
         asyncCreatorRef->scheduleAsyncBlobCreation(false, quality);
@@ -616,6 +634,12 @@ bool HTMLCanvasElement::shouldAccelerate(const IntSize& size) const
     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 (s_totalMemoryForAcceleratedCanvases >= kMaxTotalExternallyAllocatedMemory)

[Justin Novosad, 2015/12/02 16:33:34]

Constant should be named in a way that reflects the fact that is is about GPU
memeory, and not externally allocated.  The notion of "externally allocated" is
a V8 concept that has nothing to do with this.

+        return false;
+
     return true;
 }
 
@@ -776,8 +800,25 @@ void HTMLCanvasElement::updateExternallyAllocatedMemory() const
         externallyAllocatedMemory = std::numeric_limits<intptr_t>::max();
 
     // Subtracting two intptr_t that are known to be positive will never underflow.
-    v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(externallyAllocatedMemory - m_externallyAllocatedMemory);
+    intptr_t diffFromCurrAllocatedMemory = externallyAllocatedMemory - m_externallyAllocatedMemory;
+    v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(diffFromCurrAllocatedMemory);
     m_externallyAllocatedMemory = externallyAllocatedMemory;
+
+    if (m_imageBuffer && m_imageBuffer->isAccelerated())
+        updateTotalMemoryForAcceleratedCanvases(diffFromCurrAllocatedMemory);

[Justin Novosad, 2015/12/02 16:33:34]

This is wrong. You need to track gpu allocated memory independently of
externally allocated memory otherwise your total will drift when you have a
canvas that switches between accelerated and non-accelerated (for example when
it is resized).

+}
+
+void HTMLCanvasElement::updateTotalMemoryForAcceleratedCanvases(intptr_t diffFromCurrAllocatedMemory)
+{
+    ASSERT(isMainThread());
+
+    Checked<intptr_t, RecordOverflow> checkedExternallyAllocatedMemory = s_totalMemoryForAcceleratedCanvases;

[Justin Novosad, 2015/12/02 16:33:33]

Don't use the term "ExternallyAllocated" here, it is confusing.

+    checkedExternallyAllocatedMemory += diffFromCurrAllocatedMemory;
+    intptr_t externallyAllocatedMemory;
+    if (checkedExternallyAllocatedMemory.safeGet(externallyAllocatedMemory) == CheckedState::DidOverflow)
+        externallyAllocatedMemory = std::numeric_limits<intptr_t>::max();
+
+    s_totalMemoryForAcceleratedCanvases = externallyAllocatedMemory;
 }
 
 SkCanvas* HTMLCanvasElement::drawingCanvas() const