Add capture snapshot as data to SkWriter32, use it to optimise record->playback.

This is a new way of implementing https://codereview.chromium.org/155863005/
It uses copy on write semantics to return a buffer without copying it, so that record -> playback does not need to copy the buffer.

BUG=skia:2125
R=tomhudson@google.com, mtklein@google.com, reed@google.com, iancottrell@chromium.org

Author: iancottrell@google.com

Review URL: https://codereview.chromium.org/167113003

git-svn-id: http://skia.googlecode.com/svn/trunk@13769 2bbb7eff-a529-9590-31e7-b0007b416f81

2 files changed, 30 insertions, 8 deletions

diff --git a/src/core/SkPicturePlayback.cpp b/src/core/SkPicturePlayback.cpp
index 05c2c4e56b..d61e616c4d 100644
--- a/src/core/SkPicturePlayback.cpp
+++ b/src/core/SkPicturePlayback.cpp
@@ -70,10 +70,12 @@ SkPicturePlayback::SkPicturePlayback(const SkPictureRecord& record, bool deepCop
     record.validate(record.writeStream().bytesWritten(), 0);
     const SkWriter32& writer = record.writeStream();
     init();
+    SkASSERT(!fOpData);
     if (writer.bytesWritten() == 0) {
         fOpData = SkData::NewEmpty();
         return;
     }
+    fOpData = writer.snapshotAsData();
 
     fBoundingHierarchy = record.fBoundingHierarchy;
     fStateTree = record.fStateTree;
@@ -85,14 +87,6 @@ SkPicturePlayback::SkPicturePlayback(const SkPictureRecord& record, bool deepCop
         fBoundingHierarchy->flushDeferredInserts();
     }
 
-    {
-        size_t size = writer.bytesWritten();
-        void* buffer = sk_malloc_throw(size);
-        writer.flatten(buffer);
-        SkASSERT(!fOpData);
-        fOpData = SkData::NewFromMalloc(buffer, size);
-    }
-
     // copy over the refcnt dictionary to our reader
     record.fFlattenableHeap.setupPlaybacks();
 
diff --git a/src/core/SkWriter32.cpp b/src/core/SkWriter32.cpp
index fe33e4a39c..c7bfd92d56 100644
--- a/src/core/SkWriter32.cpp
+++ b/src/core/SkWriter32.cpp
@@ -74,4 +74,32 @@ void SkWriter32::growToAtLeast(size_t size) {
         // we were external, so copy in the data
         memcpy(fData, fExternal, fUsed);
     }
+    // Invalidate the snapshot, we know it is no longer useful.
+    fSnapshot.reset(NULL);
+}
+
+SkData* SkWriter32::snapshotAsData() const {
+    // get a non const version of this, we are only conceptually const
+    SkWriter32& mutable_this = *const_cast<SkWriter32*>(this);
+    // we use size change detection to invalidate the cached data
+    if ((fSnapshot.get() != NULL) && (fSnapshot->size() != fUsed)) {
+        mutable_this.fSnapshot.reset(NULL);
+    }
+    if (fSnapshot.get() == NULL) {
+        uint8_t* buffer = NULL;
+        if ((fExternal != NULL) && (fData == fExternal)) {
+            // We need to copy to an allocated buffer before returning.
+            buffer = (uint8_t*)sk_malloc_throw(fUsed);
+            memcpy(buffer, fData, fUsed);
+        } else {
+            buffer = mutable_this.fInternal.detach();
+            // prepare us to do copy on write, by pretending the data buffer
+            // is external and size limited
+            mutable_this.fData = buffer;
+            mutable_this.fCapacity = fUsed;
+            mutable_this.fExternal = buffer;
+        }
+        mutable_this.fSnapshot.reset(SkData::NewFromMalloc(buffer, fUsed));
+    }
+    return SkRef(fSnapshot.get()); // Take an extra ref for the caller.
 }