WebGL: Free temporary GPU resources held by inactive or hidden WebGL.

Source/platform/graphics/gpu/DrawingBuffer.cpp

Index: Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/Source/platform/graphics/gpu/DrawingBuffer.cpp b/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 8927cd7eb2ea07757d87929eff452128fe81650e..79f385846f069e6d94c61171a002bcd29dae9d30 100644
--- a/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -147,6 +147,7 @@ DrawingBuffer::DrawingBuffer(PassOwnPtr<blink::WebGraphicsContext3D> context,
     , m_sampleCount(0)
     , m_packAlignment(4)
     , m_destructionInProgress(false)
+    , m_isHidden(false)
     , m_contextEvictionManager(contextEvictionManager)
 {
     // Used by browser tests to detect the use of a DrawingBuffer.
@@ -184,6 +185,25 @@ void DrawingBuffer::markLayerComposited()
     m_layerComposited = true;
 }
 
+
+void DrawingBuffer::setIsHidden(bool hidden)

[Ken Russell (switch to Gerrit), 2014/04/28 20:51:45]

What happens when the DrawingBuffer is un-hidden? Will the page redraw
correctly? Is there a test verifying this case?

[dshwang, 2014/04/29 16:07:04]

When un-hidden, DrawingBuffer recreate mailbox for compositor in
prepareMailbox().

That's good concern. I'll make a layout test. It would be pixel test after
hidden and unhidden.

+{
+    ASSERT(!m_destructionInProgress);
+    bool newHiddenValue = hidden || m_destructionInProgress;
+    if (m_isHidden == newHiddenValue)
+        return;
+
+    m_isHidden = newHiddenValue;
+    if (m_isHidden)
+        freeRecycledMailboxes();

[Justin Novosad, 2014/04/28 15:21:42]

This is a good start. Eventually we should experiment with freeing even more.
Perhaps even evict the entire context and restore it when the pages becomes
visible again.

[Ken Russell (switch to Gerrit), 2014/04/28 20:51:45]

zmo@ is actively working on deciding when to evict WebGL contexts, and which
contexts to evict. Let's not collide or duplicate work in this area.

[dshwang, 2014/04/29 16:07:04]

IMO, it's not overlapped with evicting contexts. This CL just removes temporary
mailboxs (= textures), when page is hidden. zmo@, wdyt? 

+}
+
+void DrawingBuffer::freeRecycledMailboxes()
+{
+    while (!m_recycledMailboxQueue.isEmpty())
+        deleteMailbox(m_recycledMailboxQueue.takeLast());
+}
+
 blink::WebGraphicsContext3D* DrawingBuffer::context()
 {
     return m_context.get();
@@ -191,7 +211,7 @@ blink::WebGraphicsContext3D* DrawingBuffer::context()
 
 bool DrawingBuffer::prepareMailbox(blink::WebExternalTextureMailbox* outMailbox, blink::WebExternalBitmap* bitmap)
 {
-    if (!m_contentsChanged)
+    if (!m_contentsChanged || m_isHidden)
         return false;
 
     if (m_destructionInProgress) {
@@ -274,8 +294,8 @@ bool DrawingBuffer::prepareMailbox(blink::WebExternalTextureMailbox* outMailbox,
 
 void DrawingBuffer::mailboxReleased(const blink::WebExternalTextureMailbox& mailbox)
 {
-    if (m_destructionInProgress) {
-        mailboxReleasedWhileDestructionInProgress(mailbox);
+    if (m_destructionInProgress || m_isHidden) {
+        mailboxReleasedWithoutRecycling(mailbox);
         return;
     }
 
@@ -292,7 +312,7 @@ void DrawingBuffer::mailboxReleased(const blink::WebExternalTextureMailbox& mail
     ASSERT_NOT_REACHED();
 }
 
-void DrawingBuffer::mailboxReleasedWhileDestructionInProgress(const blink::WebExternalTextureMailbox& mailbox)
+void DrawingBuffer::mailboxReleasedWithoutRecycling(const blink::WebExternalTextureMailbox& mailbox)
 {
     ASSERT(m_textureMailboxes.size());
     m_context->makeContextCurrent();