add SkEmptyShader, and return it from CreateBitmapShader if the bitmap is empty

(i.e. has no pixels at all)



git-svn-id: http://skia.googlecode.com/svn/trunk@1792 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 48 insertions, 0 deletions

diff --git a/include/core/SkEmptyShader.h b/include/core/SkEmptyShader.h
new file mode 100644
index 0000000000..1c40d0b1e0
--- /dev/null
+++ b/include/core/SkEmptyShader.h
@@ -0,0 +1,48 @@
+/*
+    Copyright 2011 Google Inc.
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+ */
+
+
+#ifndef SkEmptyShader_DEFINED
+#define SkEmptyShader_DEFINED
+
+#include "SkShader.h"
+
+/**
+ *  \class SkEmptyShader
+ *  A Shader that always draws nothing.
+ */
+class SK_API SkEmptyShader : public SkShader {
+public:
+    SkEmptyShader();
+
+    virtual uint32_t getFlags();
+    virtual uint8_t getSpan16Alpha() const;
+    virtual bool setContext(const SkBitmap& device, const SkPaint& paint,
+                            const SkMatrix& matrix);
+    virtual void shadeSpan(int x, int y, SkPMColor span[], int count);
+    virtual void shadeSpan16(int x, int y, uint16_t span[], int count);
+    virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count);
+
+protected:
+    SkEmptyShader(SkFlattenableReadBuffer&);
+    virtual Factory getFactory();
+    virtual void flatten(SkFlattenableWriteBuffer&);
+
+private:
+    typedef SkShader INHERITED;
+};
+
+#endif