Revert "Revert of https://codereview.chromium.org/110593003/"

include/core/SkPixelRef.h

Index: include/core/SkPixelRef.h
diff --git a/include/core/SkPixelRef.h b/include/core/SkPixelRef.h
index e611dc0ef8b852a5ee0e79e74b2fb9316c9f69e7..a332b76a5dab84f4c2c0e8df5adb50ad2ed0414f 100644
--- a/include/core/SkPixelRef.h
+++ b/include/core/SkPixelRef.h
@@ -14,8 +14,11 @@
 #include "SkRefCnt.h"
 #include "SkString.h"
 #include "SkFlattenable.h"
+#include "SkImageInfo.h"
 #include "SkTDArray.h"
 
+//#define SK_SUPPORT_LEGACY_ONLOCKPIXELS
+
 #ifdef SK_DEBUG
     /**
      *  Defining SK_IGNORE_PIXELREF_SETPRELOCKED will force all pixelref
@@ -60,23 +63,48 @@ public:
     /** Return the pixel memory returned from lockPixels, or null if the
         lockCount is 0.
     */
-    void* pixels() const { return fPixels; }
+    void* pixels() const { return fRec.fPixels; }
 
     /** Return the current colorTable (if any) if pixels are locked, or null.
     */
-    SkColorTable* colorTable() const { return fColorTable; }
+    SkColorTable* colorTable() const { return fRec.fColorTable; }
 
     /**
+     *  To access the actual pixels of a pixelref, it must be "locked".
+     *  Calling lockPixels returns a LockRec struct (on success).
+     */
+    struct LockRec {
+        void*           fPixels;
+        SkColorTable*   fColorTable;
+        size_t          fRowBytes;
+        
+        void zero() { sk_bzero(this, sizeof(*this)); }
+
+        bool isZero() const {
+            return NULL == fPixels && NULL == fColorTable && 0 == fRowBytes;
+        }
+    };
+    
+    /**
      *  Returns true if the lockcount > 0
      */
     bool isLocked() const { return fLockCount > 0; }
 
     SkDEBUGCODE(int getLockCount() const { return fLockCount; })
 
-    /** Call to access the pixel memory, which is returned. Balance with a call
-        to unlockPixels().
-    */
-    void lockPixels();
+    /**
+     *  Call to access the pixel memory. Return true on success. Balance this
+     *  with a call to unlockPixels().
+     */
+    bool lockPixels();
+
+    /**
+     *  Call to access the pixel memory. On success, return true and fill out
+     *  the specified rec. On failure, return false and ignore the rec parameter.
+     *  Balance this with a call to unlockPixels().
+     */
+    bool lockPixels(LockRec* rec);
+
     /** Call to balanace a previous call to lockPixels(). Returns the pixels
         (or null) after the unlock. NOTE: lock calls can be nested, but the
         matching number of unlock calls must be made in order to free the
@@ -233,18 +261,27 @@ public:
     void addGenIDChangeListener(GenIDChangeListener* listener);
 
 protected:
-    /** Called when the lockCount goes from 0 to 1. The caller will have already
-        acquire a mutex for thread safety, so this method need not do that.
-    */
-    virtual void* onLockPixels(SkColorTable**) = 0;
+#ifdef SK_SUPPORT_LEGACY_ONLOCKPIXELS
+    virtual void* onLockPixels(SkColorTable**);
+    virtual bool onNewLockPixels(LockRec*);
+#else
+    /**
+     *  On success, returns true and fills out the LockRec for the pixels. On
+     *  failure returns false and ignores the LockRec parameter.
+     *
+     *  The caller will have already acquired a mutex for thread safety, so this
+     *  method need not do that.
+     */
+    virtual bool onNewLockPixels(LockRec*) = 0;
+#endif
 
     /**
-     *  Called when the lock count goes from 1 to 0. The caller will have
-     *  already acquire a mutex for thread safety, so this method need not do
-     *  that.
+     *  Balancing the previous successful call to onNewLockPixels. The locked
+     *  pixel address will no longer be referenced, so the subclass is free to
+     *  move or discard that memory.
      *
-     *  If the previous call to onLockPixels failed (i.e. returned NULL), then
-     *  the onUnlockPixels will NOT be called.
+     *  The caller will have already acquired a mutex for thread safety, so this
+     *  method need not do that.
      */
     virtual void onUnlockPixels() = 0;
 
@@ -289,15 +326,15 @@ protected:
     // only call from constructor. Flags this to always be locked, removing
     // the need to grab the mutex and call onLockPixels/onUnlockPixels.
     // Performance tweak to avoid those calls (esp. in multi-thread use case).
-    void setPreLocked(void* pixels, SkColorTable* ctable);
+    void setPreLocked(void*, size_t rowBytes, SkColorTable*);
 
 private:
     SkBaseMutex*    fMutex; // must remain in scope for the life of this object
 
     const SkImageInfo fInfo;
 
-    void*           fPixels;
-    SkColorTable*   fColorTable;    // we do not track ownership, subclass does
+    // LockRec is only valid if we're in a locked state (isLocked())
+    LockRec         fRec;
     int             fLockCount;
 
     mutable uint32_t fGenerationID;