Empty picture shaders should draw nothing.

BUG=skia:

Review URL: https://codereview.chromium.org/1142053004

3 files changed, 28 insertions, 12 deletions

diff --git a/src/core/SkPictureShader.cpp b/src/core/SkPictureShader.cpp
index c1c4755058..cb508d476b 100644
--- a/src/core/SkPictureShader.cpp
+++ b/src/core/SkPictureShader.cpp
@@ -114,10 +114,10 @@ SkPictureShader::~SkPictureShader() {
     fPicture->unref();
 }
 
-SkPictureShader* SkPictureShader::Create(const SkPicture* picture, TileMode tmx, TileMode tmy,
+SkShader* SkPictureShader::Create(const SkPicture* picture, TileMode tmx, TileMode tmy,
                                          const SkMatrix* localMatrix, const SkRect* tile) {
     if (!picture || picture->cullRect().isEmpty() || (tile && tile->isEmpty())) {
-        return NULL;
+        return SkShader::CreateEmptyShader();
     }
     return SkNEW_ARGS(SkPictureShader, (picture, tmx, tmy, localMatrix, tile));
 }
@@ -185,7 +185,7 @@ SkShader* SkPictureShader::refBitmapShader(const SkMatrix& matrix, const SkMatri
 
     SkISize tileSize = scaledSize.toRound();
     if (tileSize.isEmpty()) {
-        return NULL;
+        return SkShader::CreateEmptyShader();
     }
 
     // The actual scale, compensating for rounding & clamping.
@@ -204,7 +204,7 @@ SkShader* SkPictureShader::refBitmapShader(const SkMatrix& matrix, const SkMatri
         SkBitmap bm;
         bm.setInfo(SkImageInfo::MakeN32Premul(tileSize));
         if (!cache_try_alloc_pixels(&bm)) {
-            return NULL;
+            return SkShader::CreateEmptyShader();
         }
         bm.eraseColor(SK_ColorTRANSPARENT);
 
diff --git a/src/core/SkPictureShader.h b/src/core/SkPictureShader.h
index 3fa27b5a65..98b6d5f77d 100644
--- a/src/core/SkPictureShader.h
+++ b/src/core/SkPictureShader.h
@@ -21,7 +21,7 @@ class SkPicture;
  */
 class SkPictureShader : public SkShader {
 public:
-    static SkPictureShader* Create(const SkPicture*, TileMode, TileMode, const SkMatrix*,
+    static SkShader* Create(const SkPicture*, TileMode, TileMode, const SkMatrix*,
                                    const SkRect*);
     virtual ~SkPictureShader();
 
diff --git a/tests/PictureShaderTest.cpp b/tests/PictureShaderTest.cpp
index 8d933db600..113f4f86ee 100644
--- a/tests/PictureShaderTest.cpp
+++ b/tests/PictureShaderTest.cpp
@@ -5,22 +5,38 @@
  * found in the LICENSE file.
  */
 
+#include "SkCanvas.h"
 #include "SkPicture.h"
 #include "SkPictureRecorder.h"
 #include "SkShader.h"
 #include "Test.h"
 
 // Test that attempting to create a picture shader with a NULL picture or
-// empty picture returns NULL.
+// empty picture returns a shader that draws nothing.
 DEF_TEST(PictureShader_empty, reporter) {
-    SkShader* shader = SkShader::CreatePictureShader(NULL,
-            SkShader::kClamp_TileMode, SkShader::kClamp_TileMode, NULL, NULL);
-    REPORTER_ASSERT(reporter, NULL == shader);
+    SkPaint paint;
+
+    SkBitmap bitmap;
+    bitmap.allocN32Pixels(1,1);
+
+    SkCanvas canvas(bitmap);
+    canvas.clear(SK_ColorGREEN);
+
+    SkShader* shader = SkShader::CreatePictureShader(
+            NULL, SkShader::kClamp_TileMode, SkShader::kClamp_TileMode, NULL, NULL);
+    paint.setShader(shader)->unref();
+
+    canvas.drawRect(SkRect::MakeWH(1,1), paint);
+    REPORTER_ASSERT(reporter, *bitmap.getAddr32(0,0) == SK_ColorGREEN);
+
 
     SkPictureRecorder factory;
     factory.beginRecording(0, 0, NULL, 0);
     SkAutoTUnref<SkPicture> picture(factory.endRecording());
-    shader = SkShader::CreatePictureShader(picture.get(),
-            SkShader::kClamp_TileMode, SkShader::kClamp_TileMode, NULL, NULL);
-    REPORTER_ASSERT(reporter, NULL == shader);
+    shader = SkShader::CreatePictureShader(
+            picture.get(), SkShader::kClamp_TileMode, SkShader::kClamp_TileMode, NULL, NULL);
+    paint.setShader(shader)->unref();
+
+    canvas.drawRect(SkRect::MakeWH(1,1), paint);
+    REPORTER_ASSERT(reporter, *bitmap.getAddr32(0,0) == SK_ColorGREEN);
 }