media: docs: selection: rename files to something meaningful

These files have an automatically-generated numbering. Rename them
with a name that suggests their meaning.

Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

1 files changed, 84 insertions, 0 deletions

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 000000000000..67e0e9aed9e8
--- /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;