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
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
|
/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* Copyright (C) 2020, Raspberry Pi (Trading) Limited
*
* transform.cpp - 2D plane transforms.
*/
#include <libcamera/transform.h>
/**
* \file transform.h
* \brief Enum to represent and manipulate 2D plane transforms
*/
namespace libcamera {
/**
* \enum Transform
* \brief Enum to represent a 2D plane transform
*
* The Transform can take 8 distinct values, representing the usual 2D plane
* transforms listed below. Each of these transforms can be constructed
* out of 3 basic operations, namely a horizontal flip (mirror), a vertical
* flip, and a transposition (about the main diagonal). The transforms are
* encoded such that a single bit indicates the presence of each of the 3
* basic operations:
*
* - bit 0 - presence of a horizontal flip
* - bit 1 - presence of a vertical flip
* - bit 2 - presence of a transposition.
*
* We regard these 3 basic operations as being applied in a specific order:
* first the two flip operations (actually they commute, so the order between
* them is unimportant) and finally any transpose operation.
*
* Functions are provided to manipulate directly the bits within the transform
* encoding, but there are also higher-level functions to invert and compose
* transforms. Transforms are composed according to the usual mathematical
* convention such that the right transform is applied first, and the left
* transform is applied second.
*
* Finally, we have a total of 8 distinct transformations, as follows (a
* couple of them have additional synonyms for convenience). We illustrate each
* with its nominal effect on a rectangle with vertices labelled A, B, C and D.
*
* **Identity**
*
* Identity transform.
~~~
A-B A-B
Input image | | goes to output image | |
C-D C-D
~~~
* Numeric value: 0 (no bits set).
*
* **Rot0**
*
* Synonym for `Identity` (zero degree rotation).
*
* **HFlip**
*
* Horizontal flip.
~~~
A-B B-A
Input image | | goes to output image | |
C-D D-C
~~~
* Numeric value: 1 (horizontal flip bit set only).
*
* **VFlip**
*
* Vertical flip.
~~~
A-B C-D
Input image | | goes to output image | |
C-D A-B
~~~
* Numeric value: 2 (vertical flip bit set only).
*
* **HVFlip**
*
* Horizontal and vertical flip (identical to a 180 degree rotation).
~~~
A-B D-C
Input image | | goes to output image | |
C-D B-A
~~~
* Numeric value: 3 (horizontal and vertical flip bits set).
*
* **Rot180**
*
* Synonym for `HVFlip` (180 degree rotation).
*
* **Transpose**
*
* Transpose (about the main diagonal).
~~~
A-B A-C
Input image | | goes to output image | |
C-D B-D
~~~
* Numeric value: 4 (transpose bit set only).
*
* **Rot270**
*
* Rotation by 270 degrees clockwise (90 degrees anticlockwise).
~~~
A-B B-D
Input image | | goes to output image | |
C-D A-C
~~~
* Numeric value: 5 (transpose and horizontal flip bits set).
*
* **Rot90**
*
* Rotation by 90 degrees clockwise (270 degrees anticlockwise).
~~~
A-B C-A
Input image | | goes to output image | |
C-D D-B
~~~
* Numeric value: 6 (transpose and vertical flip bits set).
*
* **Rot180Transpose**
*
* Rotation by 180 degrees followed by transpose (alternatively, transposition
* about the "opposite diagonal").
~~~
A-B D-B
Input image | | goes to output image | |
C-D C-A
~~~
* Numeric value: 7 (all bits set).
*
* \sa https://en.wikipedia.org/wiki/Examples_of_groups#dihedral_group_of_order_8
*
* The set of 2D plane transforms is also known as the symmetry group of a
* square, described in the link. Note that the group can be generated by
* only 2 elements (the horizontal flip and a 90 degree rotation, for
* example), however, the encoding used here makes the presence of the vertical
* flip explicit.
*/
/**
* \fn operator &(Transform t0, Transform t1)
* \brief Apply bitwise AND operator between the bits in the two transforms
* \param[in] t0 The first transform
* \param[in] t1 The second transform
*/
/**
* \fn operator |(Transform t0, Transform t1)
|
