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// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef SKIA_EXT_RECURSIVE_GAUSSIAN_CONVOLUTION_H_
#define SKIA_EXT_RECURSIVE_GAUSSIAN_CONVOLUTION_H_
#include "skia/ext/convolver.h"
#include "third_party/skia/include/core/SkSize.h"
#include "third_party/skia/include/core/SkTypes.h"
namespace skia {
// RecursiveFilter, paired with SingleChannelRecursiveGaussianX and
// SingleChannelRecursiveGaussianY routines below implement recursive filters as
// described in 'Recursive implementation of the Gaussian filter' (Young, Vliet)
// (1995). Single-letter variable names mirror exactly the usage in the paper to
// ease reading and analysis.
class RecursiveFilter {
public:
enum Order {
FUNCTION,
FIRST_DERIVATIVE,
SECOND_DERIVATIVE
};
static float qFromSigma(float sigma);
static void computeCoefficients(float q, float b[4]);
SK_API RecursiveFilter(float sigma, Order order);
Order order() const { return order_; }
const float* b() const { return b_; }
private:
Order order_;
float q_;
float b_[4];
};
// Applies a gaussian recursive filter given as |filter| to a single channel at
// |input_channel_index| to image given in |source_data| along X axis.
// The output is placed into |output| into channel |output_channel_index|.
SK_API unsigned char SingleChannelRecursiveGaussianX(
const unsigned char* source_data,
int source_byte_row_stride,
int input_channel_index,
int input_channel_count,
const RecursiveFilter& filter,
const SkISize& image_size,
unsigned char* output,
int output_byte_row_stride,
int output_channel_index,
int output_channel_count,
bool absolute_values);
// Applies a gaussian recursive filter along Y axis.
SK_API unsigned char SingleChannelRecursiveGaussianY(
const unsigned char* source_data,
int source_byte_row_stride,
int input_channel_index,
int input_channel_count,
const RecursiveFilter& filter,
const SkISize& image_size,
unsigned char* output,
int output_byte_row_stride,
int output_channel_index,
int output_channel_count,
bool absolute_values);
} // namespace skia
#endif // SKIA_EXT_RECURSIVE_GAUSSIAN_CONVOLUTION_H_
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