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