skia/ext/image_operations.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef SKIA_EXT_IMAGE_OPERATIONS_H_
   6 #define SKIA_EXT_IMAGE_OPERATIONS_H_
   7
   8 #include "third_party/skia/include/core/SkBitmap.h"
   9 #include "third_party/skia/include/core/SkTypes.h"
  10
  11 struct SkIRect;
  12
  13 namespace skia {
  14
  15 class SK_API ImageOperations {
  16  public:
  17   enum ResizeMethod {
  18     //
  19     // Quality Methods
  20     //
  21     // Those enumeration values express a desired quality/speed tradeoff.
  22     // They are translated into an algorithm-specific method that depends
  23     // on the capabilities (CPU, GPU) of the underlying platform.
  24     // It is possible for all three methods to be mapped to the same
  25     // algorithm on a given platform.
  26
  27     // Good quality resizing. Fastest resizing with acceptable visual quality.
  28     // This is typically intended for use during interactive layouts
  29     // where slower platforms may want to trade image quality for large
  30     // increase in resizing performance.
  31     //
  32     // For example the resizing implementation may devolve to linear
  33     // filtering if this enables GPU acceleration to be used.
  34     //
  35     // Note that the underlying resizing method may be determined
  36     // on the fly based on the parameters for a given resize call.
  37     // For example an implementation using a GPU-based linear filter
  38     // in the common case may still use a higher-quality software-based
  39     // filter in cases where using the GPU would actually be slower - due
  40     // to too much latency - or impossible - due to image format or size
  41     // constraints.
  42     RESIZE_GOOD,
  43
  44     // Medium quality resizing. Close to high quality resizing (better
  45     // than linear interpolation) with potentially some quality being
  46     // traded-off for additional speed compared to RESIZE_BEST.
  47     //
  48     // This is intended, for example, for generation of large thumbnails
  49     // (hundreds of pixels in each dimension) from large sources, where
  50     // a linear filter would produce too many artifacts but where
  51     // a RESIZE_HIGH might be too costly time-wise.
  52     RESIZE_BETTER,
  53
  54     // High quality resizing. The algorithm is picked to favor image quality.
  55     RESIZE_BEST,
  56
  57     //
  58     // Algorithm-specific enumerations
  59     //
  60
  61     // Box filter. This is a weighted average of all of the pixels touching
  62     // the destination pixel. For enlargement, this is nearest neighbor.
  63     //
  64     // You probably don't want this, it is here for testing since it is easy to
  65     // compute. Use RESIZE_LANCZOS3 instead.
  66     RESIZE_BOX,
  67
  68     // 1-cycle Hamming filter. This is tall is the middle and falls off towards
  69     // the window edges but without going to 0. This is about 40% faster than
  70     // a 2-cycle Lanczos.
  71     RESIZE_HAMMING1,
  72
  73     // 2-cycle Lanczos filter. This is tall in the middle, goes negative on
  74     // each side, then returns to zero. Does not provide as good a frequency
  75     // response as a 3-cycle Lanczos but is roughly 30% faster.
  76     RESIZE_LANCZOS2,
  77
  78     // 3-cycle Lanczos filter. This is tall in the middle, goes negative on
  79     // each side, then oscillates 2 more times. It gives nice sharp edges.
  80     RESIZE_LANCZOS3,
  81
  82     // Lanczos filter + subpixel interpolation. If subpixel rendering is not
  83     // appropriate we automatically fall back to Lanczos.
  84     RESIZE_SUBPIXEL,
  85
  86     // enum aliases for first and last methods by algorithm or by quality.
  87     RESIZE_FIRST_QUALITY_METHOD = RESIZE_GOOD,
  88     RESIZE_LAST_QUALITY_METHOD = RESIZE_BEST,
  89     RESIZE_FIRST_ALGORITHM_METHOD = RESIZE_BOX,
  90     RESIZE_LAST_ALGORITHM_METHOD = RESIZE_SUBPIXEL,
  91   };
  92
  93   // Resizes the given source bitmap using the specified resize method, so that
  94   // the entire image is (dest_size) big. The dest_subset is the rectangle in
  95   // this destination image that should actually be returned.
  96   //
  97   // The output image will be (dest_subset.width(), dest_subset.height()). This
  98   // will save work if you do not need the entire bitmap.
  99   //
 100   // The destination subset must be smaller than the destination image.
 101   static SkBitmap Resize(const SkBitmap& source,
 102                          ResizeMethod method,
 103                          int dest_width, int dest_height,
 104                          const SkIRect& dest_subset,
 105                          SkBitmap::Allocator* allocator = NULL);
 106
 107   // Alternate version for resizing and returning the entire bitmap rather than
 108   // a subset.
 109   static SkBitmap Resize(const SkBitmap& source,
 110                          ResizeMethod method,
 111                          int dest_width, int dest_height,
 112                          SkBitmap::Allocator* allocator = NULL);
 113
 114  private:
 115   ImageOperations();  // Class for scoping only.
 116
 117   // Supports all methods except RESIZE_SUBPIXEL.
 118   static SkBitmap ResizeBasic(const SkBitmap& source,
 119                               ResizeMethod method,
 120                               int dest_width, int dest_height,
 121                               const SkIRect& dest_subset,
 122                               SkBitmap::Allocator* allocator = NULL);
 123
 124   // Subpixel renderer.
 125   static SkBitmap ResizeSubpixel(const SkBitmap& source,
 126                                  int dest_width, int dest_height,
 127                                  const SkIRect& dest_subset,
 128                                  SkBitmap::Allocator* allocator = NULL);
 129 };
 130
 131 }  // namespace skia
 132
 133 #endif  // SKIA_EXT_IMAGE_OPERATIONS_H_