Bug 1207355 (Part 1) - Stop requesting decodes in nsDocument. r=tn

b2g/app/b2g.js

@@ -343,7 +343,6 @@ pref("image.mem.surfacecache.max_size_kb", 131072);  // 128MB
 pref("image.mem.surfacecache.size_factor", 8);  // 1/8 of main memory
 pref("image.mem.surfacecache.discard_factor", 2);  // Discard 1/2 of the surface cache at a time.
 pref("image.mem.surfacecache.min_expiration_ms", 86400000); // 24h, we rely on the out of memory hook
-pref("image.onload.decode.limit", 24); /* don't decode more than 24 images eagerly */
 
 // XXX this isn't a good check for "are touch events supported", but
 // we don't really have a better one at the moment.

dom/base/nsDocument.cpp

@@ -2117,9 +2117,6 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsDocument)
   tmp->mInUnlinkOrDeletion = false;
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
-static bool sPrefsInitialized = false;
-static uint32_t sOnloadDecodeLimit = 0;
-
 nsresult
 nsDocument::Init()
 {
@@ -2127,11 +2124,6 @@ nsDocument::Init()
     return NS_ERROR_ALREADY_INITIALIZED;
   }
 
-  if (!sPrefsInitialized) {
-    sPrefsInitialized = true;
-    Preferences::AddUintVarCache(&sOnloadDecodeLimit, "image.onload.decode.limit", 0);
-  }
-
   // Force initialization.
   nsINode::nsSlots* slots = Slots();
 
@@ -10522,12 +10514,8 @@ nsDocument::AddImage(imgIRequest* aImage)
 
   // If this is the first insertion and we're locking images, lock this image
   // too.
-  if (oldCount == 0) {
-    if (mLockingImages)
-      rv = aImage->LockImage();
-    if (NS_SUCCEEDED(rv) && (!sOnloadDecodeLimit ||
-                             mImageTracker.Count() < sOnloadDecodeLimit))
-      rv = aImage->StartDecoding();
+  if (oldCount == 0 && mLockingImages) {
+    rv = aImage->LockImage();
   }
 
   // If this is the first insertion and we're animating images, request
@@ -10658,7 +10646,6 @@ PLDHashOperator LockEnumerator(imgIRequest* aKey,
                                void*    userArg)
 {
   aKey->LockImage();
-  aKey->RequestDecode();
   return PL_DHASH_NEXT;
 }
 

layout/base/nsPresShell.cpp

@@ -168,6 +168,7 @@
 #include "mozilla/Telemetry.h"
 #include "nsCanvasFrame.h"
 #include "nsIImageLoadingContent.h"
+#include "nsImageFrame.h"
 #include "nsIScreen.h"
 #include "nsIScreenManager.h"
 #include "nsPlaceholderFrame.h"
@@ -10701,7 +10702,23 @@ nsresult
 PresShell::UpdateImageLockingState()
 {
   // We're locked if we're both thawed and active.
-  return mDocument->SetImageLockingState(!mFrozen && mIsActive);
+  bool locked = !mFrozen && mIsActive;
+
+  nsresult rv = mDocument->SetImageLockingState(locked);
+
+  if (locked) {
+    // Request decodes for visible images; we want to start decoding as
+    // quickly as possible when we get foregrounded to minimize flashing.
+    for (auto iter = mVisibleImages.Iter(); !iter.Done(); iter.Next()) {
+      nsCOMPtr<nsIContent> content = do_QueryInterface(iter.Get()->GetKey());
+      nsImageFrame* imageFrame = do_QueryFrame(content->GetPrimaryFrame());
+      if (imageFrame) {
+        imageFrame->MaybeDecodeForPredictedSize();
+      }
+    }
+  }
+
+  return rv;
 }
 
 PresShell*

layout/generic/nsImageFrame.h

@@ -230,6 +230,7 @@ protected:
 protected:
   friend class nsImageListener;
   friend class nsImageLoadingContent;
+  friend class PresShell;
 
   nsresult OnSizeAvailable(imgIRequest* aRequest, imgIContainer* aImage);
   nsresult OnFrameUpdate(imgIRequest* aRequest, const nsIntRect* aRect);

modules/libpref/init/all.js

@@ -4152,9 +4152,6 @@ pref("image.multithreaded_decoding.limit", -1);
 // cache.
 pref("canvas.image.cache.limit", 0);
 
-// How many images to eagerly decode on a given page. 0 means "no limit".
-pref("image.onload.decode.limit", 0);
-
 // WebGL prefs
 #ifdef ANDROID
 // Disable MSAA on mobile.