1 .. SPDX-License-Identifier: GFDL-1.1-no-invari !! 1 .. Permission is granted to copy, distribute and/or modify this
>> 2 .. document under the terms of the GNU Free Documentation License,
>> 3 .. Version 1.1 or any later version published by the Free Software
>> 4 .. Foundation, with no Invariant Sections, no Front-Cover Texts
>> 5 .. and no Back-Cover Texts. A copy of the license is included at
>> 6 .. Documentation/userspace-api/media/fdl-appendix.rst.
>> 7 ..
>> 8 .. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
2 9
3 ******** 10 ********
4 Examples 11 Examples
5 ******** 12 ********
6 13
7 (A video capture device is assumed; change 14 (A video capture device is assumed; change
8 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` for other devi 15 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` for other devices; change target to
9 ``V4L2_SEL_TGT_COMPOSE_*`` family to configure 16 ``V4L2_SEL_TGT_COMPOSE_*`` family to configure composing area)
10 17
11 Example: Resetting the cropping parameters 18 Example: Resetting the cropping parameters
12 ========================================== 19 ==========================================
13 20
14 .. code-block:: c 21 .. code-block:: c
15 22
16 struct v4l2_selection sel = { 23 struct v4l2_selection sel = {
17 .type = V4L2_BUF_TYPE_VIDEO_CAPTUR 24 .type = V4L2_BUF_TYPE_VIDEO_CAPTURE,
18 .target = V4L2_SEL_TGT_CROP_DEFAUL 25 .target = V4L2_SEL_TGT_CROP_DEFAULT,
19 }; 26 };
20 ret = ioctl(fd, VIDIOC_G_SELECTION, &s 27 ret = ioctl(fd, VIDIOC_G_SELECTION, &sel);
21 if (ret) 28 if (ret)
22 exit(-1); 29 exit(-1);
23 sel.target = V4L2_SEL_TGT_CROP; 30 sel.target = V4L2_SEL_TGT_CROP;
24 ret = ioctl(fd, VIDIOC_S_SELECTION, &s 31 ret = ioctl(fd, VIDIOC_S_SELECTION, &sel);
25 if (ret) 32 if (ret)
26 exit(-1); 33 exit(-1);
27 34
28 Setting a composing area on output of size of 35 Setting a composing area on output of size of *at most* half of limit
29 placed at a center of a display. 36 placed at a center of a display.
30 37
31 Example: Simple downscaling 38 Example: Simple downscaling
32 =========================== 39 ===========================
33 40
34 .. code-block:: c 41 .. code-block:: c
35 42
36 struct v4l2_selection sel = { 43 struct v4l2_selection sel = {
37 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT 44 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
38 .target = V4L2_SEL_TGT_COMPOSE_BOU 45 .target = V4L2_SEL_TGT_COMPOSE_BOUNDS,
39 }; 46 };
40 struct v4l2_rect r; 47 struct v4l2_rect r;
41 48
42 ret = ioctl(fd, VIDIOC_G_SELECTION, &s 49 ret = ioctl(fd, VIDIOC_G_SELECTION, &sel);
43 if (ret) 50 if (ret)
44 exit(-1); 51 exit(-1);
45 /* setting smaller compose rectangle * 52 /* setting smaller compose rectangle */
46 r.width = sel.r.width / 2; 53 r.width = sel.r.width / 2;
47 r.height = sel.r.height / 2; 54 r.height = sel.r.height / 2;
48 r.left = sel.r.width / 4; 55 r.left = sel.r.width / 4;
49 r.top = sel.r.height / 4; 56 r.top = sel.r.height / 4;
50 sel.r = r; 57 sel.r = r;
51 sel.target = V4L2_SEL_TGT_COMPOSE; 58 sel.target = V4L2_SEL_TGT_COMPOSE;
52 sel.flags = V4L2_SEL_FLAG_LE; 59 sel.flags = V4L2_SEL_FLAG_LE;
53 ret = ioctl(fd, VIDIOC_S_SELECTION, &s 60 ret = ioctl(fd, VIDIOC_S_SELECTION, &sel);
54 if (ret) 61 if (ret)
55 exit(-1); 62 exit(-1);
56 63
57 A video output device is assumed; change ``V4L 64 A video output device is assumed; change ``V4L2_BUF_TYPE_VIDEO_OUTPUT``
58 for other devices 65 for other devices
59 66
60 Example: Querying for scaling factors 67 Example: Querying for scaling factors
61 ===================================== 68 =====================================
62 69
63 .. code-block:: c 70 .. code-block:: c
64 71
65 struct v4l2_selection compose = { 72 struct v4l2_selection compose = {
66 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT 73 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
67 .target = V4L2_SEL_TGT_COMPOSE, 74 .target = V4L2_SEL_TGT_COMPOSE,
68 }; 75 };
69 struct v4l2_selection crop = { 76 struct v4l2_selection crop = {
70 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT 77 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
71 .target = V4L2_SEL_TGT_CROP, 78 .target = V4L2_SEL_TGT_CROP,
72 }; 79 };
73 double hscale, vscale; 80 double hscale, vscale;
74 81
75 ret = ioctl(fd, VIDIOC_G_SELECTION, &c 82 ret = ioctl(fd, VIDIOC_G_SELECTION, &compose);
76 if (ret) 83 if (ret)
77 exit(-1); 84 exit(-1);
78 ret = ioctl(fd, VIDIOC_G_SELECTION, &c 85 ret = ioctl(fd, VIDIOC_G_SELECTION, &crop);
79 if (ret) 86 if (ret)
80 exit(-1); 87 exit(-1);
81 88
82 /* computing scaling factors */ 89 /* computing scaling factors */
83 hscale = (double)compose.r.width / cro 90 hscale = (double)compose.r.width / crop.r.width;
84 vscale = (double)compose.r.height / cr 91 vscale = (double)compose.r.height / crop.r.height;
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