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********
Examples
********
(A video capture device is assumed; change
``V4L2_BUF_TYPE_VIDEO_CAPTURE`` for other devices; change target to
``V4L2_SEL_TGT_COMPOSE_*`` family to configure composing area)
Example: Resetting the cropping parameters
==========================================
.. code-block:: c
struct v4l2_selection sel = {
.type = V4L2_BUF_TYPE_VIDEO_CAPTURE,
.target = V4L2_SEL_TGT_CROP_DEFAULT,
};
ret = ioctl(fd, VIDIOC_G_SELECTION, &sel);
if (ret)
exit(-1);
sel.target = V4L2_SEL_TGT_CROP;
ret = ioctl(fd, VIDIOC_S_SELECTION, &sel);
if (ret)
exit(-1);
Setting a composing area on output of size of *at most* half of limit
placed at a center of a display.
Example: Simple downscaling
===========================
.. code-block:: c
struct v4l2_selection sel = {
.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
.target = V4L2_SEL_TGT_COMPOSE_BOUNDS,
};
struct v4l2_rect r;
ret = ioctl(fd, VIDIOC_G_SELECTION, &sel);
if (ret)
exit(-1);
/* setting smaller compose rectangle */
r.width = sel.r.width / 2;
r.height = sel.r.height / 2;
r.left = sel.r.width / 4;
r.top = sel.r.height / 4;
sel.r = r;
sel.target = V4L2_SEL_TGT_COMPOSE;
sel.flags = V4L2_SEL_FLAG_LE;
ret = ioctl(fd, VIDIOC_S_SELECTION, &sel);
if (ret)
exit(-1);
A video output device is assumed; change ``V4L2_BUF_TYPE_VIDEO_OUTPUT``
for other devices
Example: Querying for scaling factors
=====================================
.. code-block:: c
struct v4l2_selection compose = {
.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
.target = V4L2_SEL_TGT_COMPOSE,
};
struct v4l2_selection crop = {
.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
.target = V4L2_SEL_TGT_CROP,
};
double hscale, vscale;
ret = ioctl(fd, VIDIOC_G_SELECTION, &compose);
if (ret)
exit(-1);
ret = ioctl(fd, VIDIOC_G_SELECTION, &crop);
if (ret)
exit(-1);
/* computing scaling factors */
hscale = (double)compose.r.width / crop.r.width;
vscale = (double)compose.r.height / crop.r.height;
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