skia/ext/recursive_gaussian_convolution.h

   1 // Copyright (c) 2013 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_RECURSIVE_GAUSSIAN_CONVOLUTION_H_
   6 #define SKIA_EXT_RECURSIVE_GAUSSIAN_CONVOLUTION_H_
   7
   8 #include "skia/ext/convolver.h"
   9 #include "third_party/skia/include/core/SkSize.h"
  10 #include "third_party/skia/include/core/SkTypes.h"
  11
  12 namespace skia {
  13
  14 // RecursiveFilter, paired with SingleChannelRecursiveGaussianX and
  15 // SingleChannelRecursiveGaussianY routines below implement recursive filters as
  16 // described in 'Recursive implementation of the Gaussian filter' (Young, Vliet)
  17 // (1995). Single-letter variable names mirror exactly the usage in the paper to
  18 // ease reading and analysis.
  19 class RecursiveFilter {
  20  public:
  21   enum Order {
  22     FUNCTION,
  23     FIRST_DERIVATIVE,
  24     SECOND_DERIVATIVE
  25   };
  26
  27   static float qFromSigma(float sigma);
  28   static void computeCoefficients(float q, float b[4]);
  29   SK_API RecursiveFilter(float sigma, Order order);
  30
  31   Order order() const { return order_; }
  32   const float* b() const { return b_; }
  33
  34  private:
  35   Order order_;
  36   float q_;
  37   float b_[4];
  38 };
  39
  40 // Applies a gaussian recursive filter given as |filter| to a single channel at
  41 // |input_channel_index| to image given in |source_data| along X axis.
  42 // The output is placed into |output| into channel |output_channel_index|.
  43 SK_API unsigned char SingleChannelRecursiveGaussianX(
  44     const unsigned char* source_data,
  45     int source_byte_row_stride,
  46     int input_channel_index,
  47     int input_channel_count,
  48     const RecursiveFilter& filter,
  49     const SkISize& image_size,
  50     unsigned char* output,
  51     int output_byte_row_stride,
  52     int output_channel_index,
  53     int output_channel_count,
  54     bool absolute_values);
  55
  56 // Applies a gaussian recursive filter along Y axis.
  57 SK_API unsigned char  SingleChannelRecursiveGaussianY(
  58     const unsigned char* source_data,
  59     int source_byte_row_stride,
  60     int input_channel_index,
  61     int input_channel_count,
  62     const RecursiveFilter& filter,
  63     const SkISize& image_size,
  64     unsigned char* output,
  65     int output_byte_row_stride,
  66     int output_channel_index,
  67     int output_channel_count,
  68     bool absolute_values);
  69 }  // namespace skia
  70
  71 #endif  // SKIA_EXT_RECURSIVE_GAUSSIAN_CONVOLUTION_H_