Mark layers that can use LCD text based on layer transform and opacity.

cc/content_layer.cc

Index: cc/content_layer.cc
diff --git a/cc/content_layer.cc b/cc/content_layer.cc
index b34ce107e0ced197af3d767f4dc3b8c67f74016f..6f70913ca55786077850a146e66de09233ded938 100644
--- a/cc/content_layer.cc
+++ b/cc/content_layer.cc
@@ -4,6 +4,7 @@
 
 #include "cc/content_layer.h"
 
+#include "base/debug/trace_event.h"
 #include "base/metrics/histogram.h"
 #include "base/time.h"
 #include "cc/bitmap_content_layer_updater.h"
@@ -34,6 +35,8 @@ void ContentLayerPainter::paint(SkCanvas* canvas, const gfx::Rect& contentRect,
     HISTOGRAM_CUSTOM_COUNTS("Renderer4.AccelContentPaintMegapixPerSecond", pixelsPerSec / 1000000, 10, 210, 30);
 }
 
+const int ContentLayer::kLCDTextMaxChangeCount = 1;
+
 scoped_refptr<ContentLayer> ContentLayer::create(ContentLayerClient* client)
 {
     return make_scoped_refptr(new ContentLayer(client));
@@ -42,6 +45,7 @@ scoped_refptr<ContentLayer> ContentLayer::create(ContentLayerClient* client)
 ContentLayer::ContentLayer(ContentLayerClient* client)
     : TiledLayer()
     , m_client(client)
+    , m_lcdTextChangeCount(0)
 {
 }
 
@@ -65,6 +69,8 @@ void ContentLayer::setTexturePriorities(const PriorityCalculator& priorityCalc)
 void ContentLayer::update(ResourceUpdateQueue& queue, const OcclusionTracker* occlusion, RenderingStats& stats)
 {
     createUpdaterIfNeeded();
+    syncCanUseLCDText();
+
     TiledLayer::update(queue, occlusion, stats);
     m_needsDisplay = false;
 }
@@ -103,4 +109,40 @@ void ContentLayer::setContentsOpaque(bool opaque)
         m_updater->setOpaque(opaque);
 }
 
+void ContentLayer::syncCanUseLCDText()
+{
+    if (m_canUseLCDText == drawProperties().can_use_lcd_text)
+        return;
+
+    if (!canUseLCDTextWillChange()) {
+        drawProperties().can_use_lcd_text = m_canUseLCDText;

[enne (OOO), 2012/12/12 17:56:52]

Draw properties should only be set during calcDrawProperties. 

Can you just expose m_canUseLCDText to wherever it needs to go to turn on LCD
text rather than going through draw properties? Maybe m_canUseLCDText could be
renamed to m_isUsingLCDText to make that more clear.

[alokp, 2012/12/12 19:03:04]

Not sure if this is what you meant, but I moved m_canUseLCDText to the base
Layer class. The only derived class that cares about LCD text, ContentLayer,
syncs the member variable m_canUseLCDText with that in
DrawProperties::can_use_lcd_text during update.

The other option is make canUseLCDText virtual. The base Layer class will just
return the value in DrawProperties, while ContentLayer will return a different
value.

[enne (OOO), 2012/12/12 19:14:46]

Sorry that I wasn't clear enough.  Here's some more explanation:

The Layer class knows about "can use LCD text".  This is a draw property (not a
layer property), and it is only written to during calcDrawProperties.

The ContentLayer class knows about "is using LCD text" and handles invalidation
and a heuristic about switching too often.  This "is using LCD text" flag (what
you are calling ContentLayer::m_canUseLCDText here and I suggest should be
called something like m_usingLCDText instead) only exists on ContentLayer as a
member (and you'll want an accessor function).

I'm trying to say that this line that I'm commenting on here
("drawProperties().can_use_lcd_text = m_canUseLCDText") breaks the "draw
property" abstraction.  Draw properties should only get set during
calcDrawProperties.  Also, setting it to false seems wrong.  The ContentLayer
*can* use LCD text, it's just choosing not to use it.

If you want to trigger LCD text, you should not do it on Layer::canUseLCDText,
but instead you should modify WebContentLayerImpl::paintContents to get this
flag from ContentLayer::isUsingLCDText instead.

+        return;
+    }
+
+    m_canUseLCDText = drawProperties().can_use_lcd_text;
+    canUseLCDTextDidChange();
+}
+
+bool ContentLayer::canUseLCDTextWillChange() const
+{
+    // Always allow disabling LCD text.
+    if (m_canUseLCDText)
+        return true;
+ 
+    return m_lcdTextChangeCount < kLCDTextMaxChangeCount;
+}
+
+void ContentLayer::canUseLCDTextDidChange()
+{
+    if (m_lcdTextChangeCount > 0) {
+        // Do not record the first time LCD text is enabled because
+        // it does not really cause any invalidation.
+        TRACE_EVENT_INSTANT0("cc", "ContentLayer::canUseLCDTextDidChange");
+    }
+    ++m_lcdTextChangeCount;
+ 
+    // Need to repaint the layer with different text AA setting.
+    setNeedsDisplay();
+}
+
 }  // namespace cc