// Copyright (c) 2006-2012 The Chromium Authors. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in
// the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google, Inc. nor the names of its contributors
// may be used to endorse or promote products derived from this
// software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
// COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
// OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
// AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
// OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
#ifndef SKIA_EXT_CONVOLVER_H_
#define SKIA_EXT_CONVOLVER_H_
#include <cmath>
#include <vector>
#include "SkTypes.h"
// avoid confusion with Mac OS X's math library (Carbon)
#if defined(__APPLE__)
#undef FloatToFixed
#undef FixedToFloat
#endif
namespace skia {
// Represents a filter in one dimension. Each output pixel has one entry in this
// object for the filter values contributing to it. You build up the filter
// list by calling AddFilter for each output pixel (in order).
//
// We do 2-dimensional convolution by first convolving each row by one
// ConvolutionFilter1D, then convolving each column by another one.
//
// Entries are stored in fixed point, shifted left by kShiftBits.
class ConvolutionFilter1D {
public:
typedef short Fixed;
// The number of bits that fixed point values are shifted by.
enum { kShiftBits = 14 };
ConvolutionFilter1D();
~ConvolutionFilter1D();
// Convert between floating point and our fixed point representation.
static Fixed FloatToFixed(float f) {
return static_cast<Fixed>(f * (1 << kShiftBits));
}
static unsigned char FixedToChar(Fixed x) {
return static_cast<unsigned char>(x >> kShiftBits);
}
static float FixedToFloat(Fixed x) {
// The cast relies on Fixed being a short, implying that on
// the platforms we care about all (16) bits will fit into
// the mantissa of a (32-bit) float.
//COMPILE_ASSERT(sizeof(Fixed) == 2, fixed_type_should_fit_in_float_mantissa);
float raw = static_cast<float>(x);
return ldexpf(raw, -kShiftBits);
}
// Returns the maximum pixel span of a filter.
int max_filter() const { return max_filter_; }
// Returns the number of filters in this filter. This is the dimension of the
// output image.
int num_values() const { return static_cast<int>(filters_.size()); }
// Appends the given list of scaling values for generating a given output
// pixel. |filter_offset| is the distance from the edge of the image to where
// the scaling factors start. The scaling factors apply to the source pixels
// starting from this position, and going for the next |filter_length| pixels.
//
// You will probably want to make sure your input is normalized (that is,
// all entries in |filter_values| sub to one) to prevent affecting the overall
// brighness of the image.
//
// The filter_length must be > 0.
//
// This version will automatically convert your input to fixed point.
void AddFilter(int filter_offset,
const float* filter_values,
int filter_length);
// Same as the above version, but the input is already fixed point.
void AddFilter(int filter_offset,
const Fixed* filter_values,
int filter_length);
// Retrieves a filter for the given |value_offset|, a position in the output
// image in the direction we're convolving. The offset and length of the
// filter values are put into the corresponding out arguments (see AddFilter
// above for what these mean), and a pointer to the first scaling factor is
// returned. There will be |filter_length| values in this array.
inline const Fixed* FilterForValue(int value_offset,
int* filter_offset,
int* filter_length) const {
const FilterInstance& filter = filters_[value_offset];
*filter_offset = filter.offset;
*filter_length = filter.length;
if (filter.length == 0) {
return NULL;
}
return &filter_values_[filter.data_location];
}
inline void PaddingForSIMD(int padding_count) {
// Padding |padding_count| of more dummy coefficients after the coefficients
// of last filter to prevent SIMD instructions which load 8 or 16 bytes
// together to access invalid memory areas. We are not trying to align the
// coefficients right now due to the opaqueness of <vector> implementation.
// This has to be done after all |AddFilter| calls.
for (int i = 0; i < padding_count; ++i)
filter_values_.push_back(static_cast<Fixed>(0));
}
private:
struct FilterInstance {
// Offset within filter_values for this instance of the filter.
int data_location;
// Distance from the left of the filter to the center. IN PIXELS
int offset;
// Number of values in this filter instance.
int length;
};
// Stores the information for each filter added to this class.
std::vector<FilterInstance> filters_;
// We store all the filter values in this flat list, indexed by
// |FilterInstance.data_location| to avoid the mallocs required for storing
// each one separately.
std::vector<Fixed> filter_values_;
// The maximum size of any filter we've added.
int max_filter_;
};
// Does a two-dimensional convolution on the given source image.
//
// It is assumed the source pixel offsets referenced in the input filters
// reference only valid pixels, so the source image size is not required. Each
// row of the source image starts |source_byte_row_stride| after the previous
// one (this allows you to have rows with some padding at the end).
//
// The result will be put into the given output buffer. The destination image
// size will be xfilter.num_values() * yfilter.num_values() pixels. It will be
// in rows of exactly xfilter.num_values() * 4 bytes.
//
// |source_has_alpha| is a hint that allows us to avoid doing computations on
// the alpha channel if the image is opaque. If you don't know, set this to
// true and it will work properly, but setting this to false will be a few
// percent faster if you know the image is opaque.
//
// The layout in memory is assumed to be 4-bytes per pixel in B-G-R-A order
// (this is ARGB when loaded into 32-bit words on a little-endian machine).
void BGRAConvolve2D(const unsigned char* source_data,
int source_byte_row_stride,
bool source_has_alpha,
const ConvolutionFilter1D& xfilter,
const ConvolutionFilter1D& yfilter,
int output_byte_row_stride,
unsigned char* output);
} // namespace skia
#endif // SKIA_EXT_CONVOLVER_H_