Experiment: add flag for finish-recording to return null

src/core/SkPictureRecorder.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBigPicture.h"
 #include "SkData.h"
 #include "SkDrawable.h"
@@ skipping 33 matching lines @@
         : SkRecorder::Record_DrawPictureMode;
     fRecorder->reset(fRecord.get(), cullRect, dpm, &fMiniRecorder);
     fActivelyRecording = true;
     return this->getRecordingCanvas();
 }
 
 SkCanvas* SkPictureRecorder::getRecordingCanvas() {
     return fActivelyRecording ? fRecorder.get() : nullptr;
 }
 
-sk_sp<SkPicture> SkPictureRecorder::finishRecordingAsPicture() {
+sk_sp<SkPicture> SkPictureRecorder::finishRecordingAsPicture(uint32_t finishFlags) {
     fActivelyRecording = false;
     fRecorder->restoreToCount(1);  // If we were missing any restores, add them now.
 
     if (fRecord->count() == 0) {
+        if (finishFlags & kReturnNullForEmpty_FinishFlag) {
+            return nullptr;
+        }
         return fMiniRecorder.detachAsPicture(fCullRect);
     }
 
     // TODO: delay as much of this work until just before first playback?
     SkRecordOptimize(fRecord);
 
+    if (fRecord->count() == 0) {
+        if (finishFlags & kReturnNullForEmpty_FinishFlag) {
+            return nullptr;
+        }
+    }
+
     SkAutoTUnref<SkLayerInfo> saveLayerData;
 
     if (fBBH && (fFlags & kComputeSaveLayerInfo_RecordFlag)) {
         saveLayerData.reset(new SkLayerInfo);
     }
 
     SkDrawableList* drawableList = fRecorder->getDrawableList();
     SkBigPicture::SnapshotArray* pictList =
         drawableList ? drawableList->newDrawableSnapshot() : nullptr;
 
@@ skipping 15 matching lines @@
     }
 
     size_t subPictureBytes = fRecorder->approxBytesUsedBySubPictures();
     for (int i = 0; pictList && i < pictList->count(); i++) {
         subPictureBytes += SkPictureUtils::ApproximateBytesUsed(pictList->begin()[i]);
     }
     return sk_make_sp<SkBigPicture>(fCullRect, fRecord.release(), pictList, fBBH.release(),
                             saveLayerData.release(), subPictureBytes);
 }
 
-sk_sp<SkPicture> SkPictureRecorder::finishRecordingAsPictureWithCull(const SkRect& cullRect) {
+sk_sp<SkPicture> SkPictureRecorder::finishRecordingAsPictureWithCull(const SkRect& cullRect,
+                                                                     uint32_t finishFlags) {
     fCullRect = cullRect;
-    return this->finishRecordingAsPicture();
+    return this->finishRecordingAsPicture(finishFlags);
 }
 
 
 void SkPictureRecorder::partialReplay(SkCanvas* canvas) const {
     if (nullptr == canvas) {
         return;
     }
 
     int drawableCount = 0;
     SkDrawable* const* drawables = nullptr;
     SkDrawableList* drawableList = fRecorder->getDrawableList();
     if (drawableList) {
         drawableCount = drawableList->count();
         drawables = drawableList->begin();
     }
     SkRecordDraw(*fRecord, canvas, nullptr, drawables, drawableCount, nullptr/*bbh*/, nullptr/*callback*/);
 }
 
-sk_sp<SkDrawable> SkPictureRecorder::finishRecordingAsDrawable() {
+sk_sp<SkDrawable> SkPictureRecorder::finishRecordingAsDrawable(uint32_t finishFlags) {
     fActivelyRecording = false;
     fRecorder->flushMiniRecorder();
     fRecorder->restoreToCount(1);  // If we were missing any restores, add them now.
 
-    // TODO: delay as much of this work until just before first playback?
     SkRecordOptimize(fRecord);
 
+    if (fRecord->count() == 0) {
+        if (finishFlags & kReturnNullForEmpty_FinishFlag) {
+            return nullptr;
+        }
+    }
+
     if (fBBH.get()) {
         SkAutoTMalloc<SkRect> bounds(fRecord->count());
         SkRecordFillBounds(fCullRect, *fRecord, bounds);
         fBBH->insert(bounds, fRecord->count());
     }
 
     sk_sp<SkDrawable> drawable =
            sk_make_sp<SkRecordedDrawable>(fRecord, fBBH, fRecorder->detachDrawableList(), fCullRect,
                                    SkToBool(fFlags & kComputeSaveLayerInfo_RecordFlag));
 
     // release our refs now, so only the drawable will be the owner.
     fRecord.reset(nullptr);
     fBBH.reset(nullptr);
 
     return drawable;
 }