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// Copyright (c) 2006-2008 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.
#include <vector>
// avoid confusion with Mac OS X's math library (Carbon)
#if defined(__APPLE__)
#undef FloatToFixed
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 convolusion by first convolving each row by one
// ConvolusionFilter1D, then convolving each column by another one.
// Entries are stored in fixed point, shifted left by kShiftBits.
class ConvolusionFilter1D {
// The number of bits that fixed point values are shifted by.
enum { kShiftBits = 14 };
typedef short Fixed;
ConvolusionFilter1D() : max_filter_(0) {
// 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);
// 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;
return &filter_values_[filter.data_location];
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 convolusion 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 ConvolusionFilter1D& xfilter,
const ConvolusionFilter1D& yfilter,
unsigned char* output);
} // namespace skia