Production quality fast image up/downsampler

src/core/SkBitmapScaler.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+ 
+#ifndef SkBitmapScaler_DEFINED
+#define SkBitmapScaler_DEFINED
+
+#include "SkBitmap.h"
+#include "SkConvolver.h"
+ 
+/** \class SkBitmapScaler
+
+    Provides the interface for high quality image resampling.
+ */
+    
+class SK_API SkBitmapScaler {
+public:    
+    enum ResizeMethod {
+        // Quality Methods
+        //
+        // Those enumeration values express a desired quality/speed tradeoff.
+        // They are translated into an algorithm-specific method that depends
+        // on the capabilities (CPU, GPU) of the underlying platform.
+        // It is possible for all three methods to be mapped to the same
+        // algorithm on a given platform.
+        
+        // Good quality resizing. Fastest resizing with acceptable visual quality.
+        // This is typically intended for use during interactive layouts
+        // where slower platforms may want to trade image quality for large
+        // increase in resizing performance.
+        //
+        // For example the resizing implementation may devolve to linear
+        // filtering if this enables GPU acceleration to be used.
+        //
+        // Note that the underlying resizing method may be determined
+        // on the fly based on the parameters for a given resize call.
+        // For example an implementation using a GPU-based linear filter
+        // in the common case may still use a higher-quality software-based
+        // filter in cases where using the GPU would actually be slower - due
+        // to too much latency - or impossible - due to image format or size
+        // constraints.
+        RESIZE_GOOD,
+
+        // Medium quality resizing. Close to high quality resizing (better
+        // than linear interpolation) with potentially some quality being
+        // traded-off for additional speed compared to RESIZE_BEST.
+        //
+        // This is intended, for example, for generation of large thumbnails
+        // (hundreds of pixels in each dimension) from large sources, where
+        // a linear filter would produce too many artifacts but where
+        // a RESIZE_HIGH might be too costly time-wise.
+        RESIZE_BETTER,
+
+        // High quality resizing. The algorithm is picked to favor image quality.
+        RESIZE_BEST,
+        
+        //
+        // Algorithm-specific enumerations
+        //
+        
+        // Box filter. This is a weighted average of all of the pixels touching
+        // the destination pixel. For enlargement, this is nearest neighbor.
+        //
+        // You probably don't want this, it is here for testing since it is easy to
+        // compute. Use RESIZE_LANCZOS3 instead.
+        RESIZE_BOX,
+        RESIZE_TRIANGLE,
+        RESIZE_LANCZOS3,
+        RESIZE_HAMMING,
+        RESIZE_MITCHELL,
+        
+        // enum aliases for first and last methods by algorithm or by quality.
+        RESIZE_FIRST_QUALITY_METHOD = RESIZE_GOOD,
+        RESIZE_LAST_QUALITY_METHOD = RESIZE_BEST,
+        RESIZE_FIRST_ALGORITHM_METHOD = RESIZE_BOX,
+        RESIZE_LAST_ALGORITHM_METHOD = RESIZE_MITCHELL,
+    };
+    
+    // Resizes the given source bitmap using the specified resize method, so that
+    // the entire image is (dest_size) big. The dest_subset is the rectangle in
+    // this destination image that should actually be returned.
+    //
+    // The output image will be (dest_subset.width(), dest_subset.height()). This
+    // will save work if you do not need the entire bitmap.
+    //
+    // The destination subset must be smaller than the destination image.
+    static SkBitmap Resize(const SkBitmap& source,
+                           ResizeMethod method,
+                           int dest_width, int dest_height,
+                           const SkIRect& dest_subset,
+                           SkConvolutionProcs *convolveProcs = NULL,
+                           SkBitmap::Allocator* allocator = NULL);
+
+    // Alternate version for resizing and returning the entire bitmap rather than
+    // a subset.
+    static SkBitmap Resize(const SkBitmap& source,
+                           ResizeMethod method,
+                           int dest_width, int dest_height,
+                           SkConvolutionProcs *convolveProcs = NULL,
+                           SkBitmap::Allocator* allocator = NULL);
+};
+
+#endif