Experiment: add flag for finish-recording to return null

tests/PictureTest.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBBoxHierarchy.h"
 #include "SkBlurImageFilter.h"
 #include "SkCanvas.h"
@@ skipping 1429 matching lines @@
     }
     REPORTER_ASSERT(r, analyzer.suitableForGpuRasterization());
 
     for (int i = 0; i < 50; ++i) {
         analyzer.analyzeClipPath(concaveClip, SkRegion::kIntersect_Op, true);
     }
     REPORTER_ASSERT(r, !analyzer.suitableForGpuRasterization());
 }
 
 #endif // SK_SUPPORT_GPU
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+static void empty_ops(SkCanvas* canvas) {
+}
+static void clip_ops(SkCanvas* canvas) {
+    canvas->save();
+    canvas->clipRect(SkRect::MakeWH(20, 20));
+    canvas->restore();
+}
+static void matrix_ops(SkCanvas* canvas) {
+    canvas->save();
+    canvas->scale(2, 3);
+    canvas->restore();
+}
+static void matrixclip_ops(SkCanvas* canvas) {
+    canvas->save();
+    canvas->scale(2, 3);
+    canvas->clipRect(SkRect::MakeWH(20, 20));
+    canvas->restore();
+}
+typedef void (*CanvasProc)(SkCanvas*);
+
+DEF_TEST(Picture_RecordEmpty, r) {
+    const SkRect cull = SkRect::MakeWH(100, 100);
+
+    CanvasProc procs[] { empty_ops, clip_ops, matrix_ops, matrixclip_ops };
+
+    for (auto proc : procs) {
+        {
+            SkPictureRecorder rec;
+            proc(rec.beginRecording(cull));
+            sk_sp<SkPicture> pic = rec.finishRecordingAsPicture(0);
+            REPORTER_ASSERT(r, pic.get());

[mtklein, 2016/06/29 19:44:19]

We should also be able to assert pic->approximateOpCount() == 0 here if that
makes things clearer.

[reed1, 2016/07/06 13:55:09]

Done.

+        }
+        {
+            SkPictureRecorder rec;
+            proc(rec.beginRecording(cull));
+            sk_sp<SkPicture> pic = rec.finishRecordingAsPicture(
+                                                 SkPictureRecorder::kReturnNullForEmpty_FinishFlag);
+            REPORTER_ASSERT(r, !pic.get());
+        }
+        {
+            SkPictureRecorder rec;
+            proc(rec.beginRecording(cull));
+            sk_sp<SkDrawable> dr = rec.finishRecordingAsDrawable(0);
+            REPORTER_ASSERT(r, dr.get());
+        }
+        {
+            SkPictureRecorder rec;
+            proc(rec.beginRecording(cull));
+            sk_sp<SkDrawable> dr = rec.finishRecordingAsDrawable(
+                                                 SkPictureRecorder::kReturnNullForEmpty_FinishFlag);
+            REPORTER_ASSERT(r, !dr.get());
+        }
+    }
+}