1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
|
// Copyright (c) 2009 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_CONVOLVER_H_
#define SKIA_EXT_CONVOLVER_H_
#include <vector>
// avoid confusion with Mac OS X's math library (Carbon)
#if defined(__APPLE__)
#undef FloatToFixed
#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:
// The number of bits that fixed point values are shifted by.
enum { kShiftBits = 14 };
typedef short Fixed;
ConvolutionFilter1D() : 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];
}
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,
unsigned char* output);
} // namespace skia
#endif // SKIA_EXT_CONVOLVER_H_
|
