SkScaledCodec class

include/codec/SkScaledCodec.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef SkScaledCodec_DEFINED
+#define SkScaledCodec_DEFINED
+
+#include "SkCodec.h"
+#include "SkScanlineDecoder.h"
+
+class SkScanlineDecoder;
+class SkStream;
+
+/**
+ * This class implements scaling, by sampling scanlines in the y direction.
+ * x-wise sampling is implemented in the swizzler, when getScanlines() is called.
+ */
+class SkScaledCodec : public SkCodec {
+public:
+    static SkCodec* NewFromStream(SkStream*);
+    static SkCodec* NewFromData(SkData*);
+
+    virtual ~SkScaledCodec();
+
+    /**
+     * returns a sample size based on the input src and dst dimensions
+     * can only down sample, so dstDimension must be <= than srcDimension
+     */
+    static int GetSampleSize(int srcDimension, int dstDimension) {
+        SkASSERT(dstDimension <= srcDimension);
+        return srcDimension / dstDimension;
+    }
+
+    /**
+     * returns whether a destination's dimensions are supported for down sampling
+     */
+    static bool DimensionsSupportedForSampling(const SkImageInfo& srcInfo, 
+                                               const SkImageInfo& dstInfo) {
+        // heights must be equal as no native y sampling is supported
+        if (dstInfo.height() != srcInfo.height()) {
+            return false;
+        }
+        // only support down sampling, dstWidth cannot be larger that srcWidth
+        if(dstInfo.width() > srcInfo.width()) {
+            return false;
+        }
+        return true;   
+    }
+
+protected:
+    /**
+     * Recommend a set of destination dimensions given a requested scale
+     */
+    SkISize onGetScaledDimensions(float desiredScale) const override;
+
+    Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*)
+            override;
+    SkEncodedFormat onGetEncodedFormat() const override {
+        return fScanlineDecoder->getEncodedFormat();
+    }
+
+    bool onReallyHasAlpha() const override {
+        return fScanlineDecoder->reallyHasAlpha();
+    }
+
+private:
+    SkAutoTDelete<SkScanlineDecoder> fScanlineDecoder;
+
+    explicit SkScaledCodec(SkScanlineDecoder*);
+
+    typedef SkCodec INHERITED;
+};
+#endif // SkScaledCodec_DEFINED