From 76cb841cb886eef6b3bee341a2266c76578724ad Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 03:02:30 +0200 Subject: Adding upstream version 4.19.249. Signed-off-by: Daniel Baumann --- .../media/uapi/v4l/selection-api-examples.rst | 84 ++++++++++++++++++++++ 1 file changed, 84 insertions(+) create mode 100644 Documentation/media/uapi/v4l/selection-api-examples.rst (limited to 'Documentation/media/uapi/v4l/selection-api-examples.rst') diff --git a/Documentation/media/uapi/v4l/selection-api-examples.rst b/Documentation/media/uapi/v4l/selection-api-examples.rst new file mode 100644 index 000000000..67e0e9aed --- /dev/null +++ b/Documentation/media/uapi/v4l/selection-api-examples.rst @@ -0,0 +1,84 @@ +.. -*- coding: utf-8; mode: rst -*- + +******** +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; -- cgit v1.2.3