SkBitmapScaler.h revision 138ebc3e4061cf533ea2f7f3717239670fdc6e43 
1/*
2 * Copyright 2013 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#ifndef SkBitmapScaler_DEFINED
9#define SkBitmapScaler_DEFINED
10
11#include "SkBitmap.h"
12#include "SkConvolver.h"
13
14/** \class SkBitmapScaler
15
16    Provides the interface for high quality image resampling.
17 */
18
19class SK_API SkBitmapScaler {
20public:
21    enum ResizeMethod {
22        // Quality Methods
23        //
24        // Those enumeration values express a desired quality/speed tradeoff.
25        // They are translated into an algorithm-specific method that depends
26        // on the capabilities (CPU, GPU) of the underlying platform.
27        // It is possible for all three methods to be mapped to the same
28        // algorithm on a given platform.
29
30        // Good quality resizing. Fastest resizing with acceptable visual quality.
31        // This is typically intended for use during interactive layouts
32        // where slower platforms may want to trade image quality for large
33        // increase in resizing performance.
34        //
35        // For example the resizing implementation may devolve to linear
36        // filtering if this enables GPU acceleration to be used.
37        //
38        // Note that the underlying resizing method may be determined
39        // on the fly based on the parameters for a given resize call.
40        // For example an implementation using a GPU-based linear filter
41        // in the common case may still use a higher-quality software-based
42        // filter in cases where using the GPU would actually be slower - due
43        // to too much latency - or impossible - due to image format or size
44        // constraints.
45        RESIZE_GOOD,
46
47        // Medium quality resizing. Close to high quality resizing (better
48        // than linear interpolation) with potentially some quality being
49        // traded-off for additional speed compared to RESIZE_BEST.
50        //
51        // This is intended, for example, for generation of large thumbnails
52        // (hundreds of pixels in each dimension) from large sources, where
53        // a linear filter would produce too many artifacts but where
54        // a RESIZE_HIGH might be too costly time-wise.
55        RESIZE_BETTER,
56
57        // High quality resizing. The algorithm is picked to favor image quality.
58        RESIZE_BEST,
59
60        //
61        // Algorithm-specific enumerations
62        //
63
64        // Box filter. This is a weighted average of all of the pixels touching
65        // the destination pixel. For enlargement, this is nearest neighbor.
66        //
67        // You probably don't want this, it is here for testing since it is easy to
68        // compute. Use RESIZE_LANCZOS3 instead.
69        RESIZE_BOX,
70        RESIZE_TRIANGLE,
71        RESIZE_LANCZOS3,
72        RESIZE_HAMMING,
73        RESIZE_MITCHELL,
74
75        // enum aliases for first and last methods by algorithm or by quality.
76        RESIZE_FIRST_QUALITY_METHOD = RESIZE_GOOD,
77        RESIZE_LAST_QUALITY_METHOD = RESIZE_BEST,
78        RESIZE_FIRST_ALGORITHM_METHOD = RESIZE_BOX,
79        RESIZE_LAST_ALGORITHM_METHOD = RESIZE_MITCHELL,
80    };
81
82    // Resizes the given source bitmap using the specified resize method, so that
83    // the entire image is (dest_size) big. The dest_subset is the rectangle in
84    // this destination image that should actually be returned.
85    //
86    // The output image will be (dest_subset.width(), dest_subset.height()). This
87    // will save work if you do not need the entire bitmap.
88    //
89    // The destination subset must be smaller than the destination image.
90    static SkBitmap Resize(const SkBitmap& source,
91                           ResizeMethod method,
92                           int dest_width, int dest_height,
93                           const SkIRect& dest_subset,
94                           SkConvolutionProcs *convolveProcs = NULL,
95                           SkBitmap::Allocator* allocator = NULL);
96
97    // Alternate version for resizing and returning the entire bitmap rather than
98    // a subset.
99    static SkBitmap Resize(const SkBitmap& source,
100                           ResizeMethod method,
101                           int dest_width, int dest_height,
102                           SkConvolutionProcs *convolveProcs = NULL,
103                           SkBitmap::Allocator* allocator = NULL);
104};
105
106#endif
107