The image resampling code has been transplanted from Chrome; it's incredibly fast.
We've tested this CL plumbed into Chrome and done benchmarking with excellent results.
This CL can land independent of any Chrome changes; it's completely internal to skia.
BUG=
R=reed@google.com
Review URL: https://codereview.chromium.org/19335002
git-svn-id: http://skia.googlecode.com/svn/trunk@10206 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/core/SkBitmapScaler.h b/src/core/SkBitmapScaler.h
new file mode 100644
index 0000000..5682cc5
--- /dev/null
+++ b/src/core/SkBitmapScaler.h
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+/*
+ * 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