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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/userspace-api/media/v4l/selection-api-configuration.rst | |
parent | Initial commit. (diff) | |
download | linux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.tar.xz linux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/userspace-api/media/v4l/selection-api-configuration.rst')
-rw-r--r-- | Documentation/userspace-api/media/v4l/selection-api-configuration.rst | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/selection-api-configuration.rst b/Documentation/userspace-api/media/v4l/selection-api-configuration.rst new file mode 100644 index 000000000..37617eda2 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/selection-api-configuration.rst @@ -0,0 +1,137 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +************* +Configuration +************* + +Applications can use the :ref:`selection API <VIDIOC_G_SELECTION>` to +select an area in a video signal or a buffer, and to query for default +settings and hardware limits. + +Video hardware can have various cropping, composing and scaling +limitations. It may only scale up or down, support only discrete scaling +factors, or have different scaling abilities in the horizontal and +vertical directions. Also it may not support scaling at all. At the same +time the cropping/composing rectangles may have to be aligned, and both +the source and the sink may have arbitrary upper and lower size limits. +Therefore, as usual, drivers are expected to adjust the requested +parameters and return the actual values selected. An application can +control the rounding behaviour using +:ref:`constraint flags <v4l2-selection-flags>`. + + +Configuration of video capture +============================== + +See figure :ref:`sel-targets-capture` for examples of the selection +targets available for a video capture device. It is recommended to +configure the cropping targets before to the composing targets. + +The range of coordinates of the top left corner, width and height of +areas that can be sampled is given by the ``V4L2_SEL_TGT_CROP_BOUNDS`` +target. It is recommended for the driver developers to put the top/left +corner at position ``(0,0)``. The rectangle's coordinates are expressed +in pixels. + +The top left corner, width and height of the source rectangle, that is +the area actually sampled, is given by the ``V4L2_SEL_TGT_CROP`` target. +It uses the same coordinate system as ``V4L2_SEL_TGT_CROP_BOUNDS``. The +active cropping area must lie completely inside the capture boundaries. +The driver may further adjust the requested size and/or position +according to hardware limitations. + +Each capture device has a default source rectangle, given by the +``V4L2_SEL_TGT_CROP_DEFAULT`` target. This rectangle shall cover what the +driver writer considers the complete picture. Drivers shall set the +active crop rectangle to the default when the driver is first loaded, +but not later. + +The composing targets refer to a memory buffer. The limits of composing +coordinates are obtained using ``V4L2_SEL_TGT_COMPOSE_BOUNDS``. All +coordinates are expressed in pixels. The rectangle's top/left corner +must be located at position ``(0,0)``. The width and height are equal to +the image size set by :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`. + +The part of a buffer into which the image is inserted by the hardware is +controlled by the ``V4L2_SEL_TGT_COMPOSE`` target. The rectangle's +coordinates are also expressed in the same coordinate system as the +bounds rectangle. The composing rectangle must lie completely inside +bounds rectangle. The driver must adjust the composing rectangle to fit +to the bounding limits. Moreover, the driver can perform other +adjustments according to hardware limitations. The application can +control rounding behaviour using +:ref:`constraint flags <v4l2-selection-flags>`. + +For capture devices the default composing rectangle is queried using +``V4L2_SEL_TGT_COMPOSE_DEFAULT``. It is usually equal to the bounding +rectangle. + +The part of a buffer that is modified by the hardware is given by +``V4L2_SEL_TGT_COMPOSE_PADDED``. It contains all pixels defined using +``V4L2_SEL_TGT_COMPOSE`` plus all padding data modified by hardware +during insertion process. All pixels outside this rectangle *must not* +be changed by the hardware. The content of pixels that lie inside the +padded area but outside active area is undefined. The application can +use the padded and active rectangles to detect where the rubbish pixels +are located and remove them if needed. + + +Configuration of video output +============================= + +For output devices targets and ioctls are used similarly to the video +capture case. The *composing* rectangle refers to the insertion of an +image into a video signal. The cropping rectangles refer to a memory +buffer. It is recommended to configure the composing targets before to +the cropping targets. + +The cropping targets refer to the memory buffer that contains an image +to be inserted into a video signal or graphical screen. The limits of +cropping coordinates are obtained using ``V4L2_SEL_TGT_CROP_BOUNDS``. +All coordinates are expressed in pixels. The top/left corner is always +point ``(0,0)``. The width and height is equal to the image size +specified using :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. + +The top left corner, width and height of the source rectangle, that is +the area from which image date are processed by the hardware, is given +by the ``V4L2_SEL_TGT_CROP``. Its coordinates are expressed in in the +same coordinate system as the bounds rectangle. The active cropping area +must lie completely inside the crop boundaries and the driver may +further adjust the requested size and/or position according to hardware +limitations. + +For output devices the default cropping rectangle is queried using +``V4L2_SEL_TGT_CROP_DEFAULT``. It is usually equal to the bounding +rectangle. + +The part of a video signal or graphics display where the image is +inserted by the hardware is controlled by ``V4L2_SEL_TGT_COMPOSE`` +target. The rectangle's coordinates are expressed in pixels. The +composing rectangle must lie completely inside the bounds rectangle. The +driver must adjust the area to fit to the bounding limits. Moreover, the +driver can perform other adjustments according to hardware limitations. + +The device has a default composing rectangle, given by the +``V4L2_SEL_TGT_COMPOSE_DEFAULT`` target. This rectangle shall cover what +the driver writer considers the complete picture. It is recommended for +the driver developers to put the top/left corner at position ``(0,0)``. +Drivers shall set the active composing rectangle to the default one when +the driver is first loaded. + +The devices may introduce additional content to video signal other than +an image from memory buffers. It includes borders around an image. +However, such a padded area is driver-dependent feature not covered by +this document. Driver developers are encouraged to keep padded rectangle +equal to active one. The padded target is accessed by the +``V4L2_SEL_TGT_COMPOSE_PADDED`` identifier. It must contain all pixels +from the ``V4L2_SEL_TGT_COMPOSE`` target. + + +Scaling control +=============== + +An application can detect if scaling is performed by comparing the width +and the height of rectangles obtained using ``V4L2_SEL_TGT_CROP`` and +``V4L2_SEL_TGT_COMPOSE`` targets. If these are not equal then the +scaling is applied. The application can compute the scaling ratios using +these values. |