diff options
Diffstat (limited to 'Documentation/userspace-api/media/v4l/vidioc-g-fbuf.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-g-fbuf.rst | 362 |
1 files changed, 362 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-fbuf.rst b/Documentation/userspace-api/media/v4l/vidioc-g-fbuf.rst new file mode 100644 index 000000000000..0124444419ae --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-g-fbuf.rst @@ -0,0 +1,362 @@ +.. Permission is granted to copy, distribute and/or modify this +.. document under the terms of the GNU Free Documentation License, +.. Version 1.1 or any later version published by the Free Software +.. Foundation, with no Invariant Sections, no Front-Cover Texts +.. and no Back-Cover Texts. A copy of the license is included at +.. Documentation/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +.. _VIDIOC_G_FBUF: + +********************************** +ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF +********************************** + +Name +==== + +VIDIOC_G_FBUF - VIDIOC_S_FBUF - Get or set frame buffer overlay parameters + + +Synopsis +======== + +.. c:function:: int ioctl( int fd, VIDIOC_G_FBUF, struct v4l2_framebuffer *argp ) + :name: VIDIOC_G_FBUF + +.. c:function:: int ioctl( int fd, VIDIOC_S_FBUF, const struct v4l2_framebuffer *argp ) + :name: VIDIOC_S_FBUF + + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <func-open>`. + +``argp`` + Pointer to struct :c:type:`v4l2_framebuffer`. + + +Description +=========== + +Applications can use the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` and :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctl +to get and set the framebuffer parameters for a +:ref:`Video Overlay <overlay>` or :ref:`Video Output Overlay <osd>` +(OSD). The type of overlay is implied by the device type (capture or +output device) and can be determined with the +:ref:`VIDIOC_QUERYCAP` ioctl. One ``/dev/videoN`` +device must not support both kinds of overlay. + +The V4L2 API distinguishes destructive and non-destructive overlays. A +destructive overlay copies captured video images into the video memory +of a graphics card. A non-destructive overlay blends video images into a +VGA signal or graphics into a video signal. *Video Output Overlays* are +always non-destructive. + +To get the current parameters applications call the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` +ioctl with a pointer to a struct :c:type:`v4l2_framebuffer` +structure. The driver fills all fields of the structure or returns an +EINVAL error code when overlays are not supported. + +To set the parameters for a *Video Output Overlay*, applications must +initialize the ``flags`` field of a struct +:c:type:`v4l2_framebuffer`. Since the framebuffer is +implemented on the TV card all other parameters are determined by the +driver. When an application calls :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` with a pointer to +this structure, the driver prepares for the overlay and returns the +framebuffer parameters as :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` does, or it returns an error +code. + +To set the parameters for a *non-destructive Video Overlay*, +applications must initialize the ``flags`` field, the ``fmt`` +substructure, and call :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>`. Again the driver prepares for +the overlay and returns the framebuffer parameters as :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` +does, or it returns an error code. + +For a *destructive Video Overlay* applications must additionally provide +a ``base`` address. Setting up a DMA to a random memory location can +jeopardize the system security, its stability or even damage the +hardware, therefore only the superuser can set the parameters for a +destructive video overlay. + + +.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}| + +.. c:type:: v4l2_framebuffer + +.. cssclass:: longtable + +.. flat-table:: struct v4l2_framebuffer + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 1 2 + + * - __u32 + - ``capability`` + - + - Overlay capability flags set by the driver, see + :ref:`framebuffer-cap`. + * - __u32 + - ``flags`` + - + - Overlay control flags set by application and driver, see + :ref:`framebuffer-flags` + * - void * + - ``base`` + - + - Physical base address of the framebuffer, that is the address of + the pixel in the top left corner of the framebuffer. [#f1]_ + * - + - + - + - This field is irrelevant to *non-destructive Video Overlays*. For + *destructive Video Overlays* applications must provide a base + address. The driver may accept only base addresses which are a + multiple of two, four or eight bytes. For *Video Output Overlays* + the driver must return a valid base address, so applications can + find the corresponding Linux framebuffer device (see + :ref:`osd`). + * - struct + - ``fmt`` + - + - Layout of the frame buffer. + * - + - __u32 + - ``width`` + - Width of the frame buffer in pixels. + * - + - __u32 + - ``height`` + - Height of the frame buffer in pixels. + * - + - __u32 + - ``pixelformat`` + - The pixel format of the framebuffer. + * - + - + - + - For *non-destructive Video Overlays* this field only defines a + format for the struct :c:type:`v4l2_window` + ``chromakey`` field. + * - + - + - + - For *destructive Video Overlays* applications must initialize this + field. For *Video Output Overlays* the driver must return a valid + format. + * - + - + - + - Usually this is an RGB format (for example + :ref:`V4L2_PIX_FMT_RGB565 <V4L2-PIX-FMT-RGB565>`) but YUV + formats (only packed YUV formats when chroma keying is used, not + including ``V4L2_PIX_FMT_YUYV`` and ``V4L2_PIX_FMT_UYVY``) and the + ``V4L2_PIX_FMT_PAL8`` format are also permitted. The behavior of + the driver when an application requests a compressed format is + undefined. See :ref:`pixfmt` for information on pixel formats. + * - + - enum :c:type:`v4l2_field` + - ``field`` + - Drivers and applications shall ignore this field. If applicable, + the field order is selected with the + :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, using the ``field`` + field of struct :c:type:`v4l2_window`. + * - + - __u32 + - ``bytesperline`` + - Distance in bytes between the leftmost pixels in two adjacent + lines. + * - :cspan:`3` + + This field is irrelevant to *non-destructive Video Overlays*. + + For *destructive Video Overlays* both applications and drivers can + set this field to request padding bytes at the end of each line. + Drivers however may ignore the requested value, returning + ``width`` times bytes-per-pixel or a larger value required by the + hardware. That implies applications can just set this field to + zero to get a reasonable default. + + For *Video Output Overlays* the driver must return a valid value. + + Video hardware may access padding bytes, therefore they must + reside in accessible memory. Consider for example the case where + padding bytes after the last line of an image cross a system page + boundary. Capture devices may write padding bytes, the value is + undefined. Output devices ignore the contents of padding bytes. + + When the image format is planar the ``bytesperline`` value applies + to the first plane and is divided by the same factor as the + ``width`` field for the other planes. For example the Cb and Cr + planes of a YUV 4:2:0 image have half as many padding bytes + following each line as the Y plane. To avoid ambiguities drivers + must return a ``bytesperline`` value rounded up to a multiple of + the scale factor. + * - + - __u32 + - ``sizeimage`` + - This field is irrelevant to *non-destructive Video Overlays*. For + *destructive Video Overlays* applications must initialize this + field. For *Video Output Overlays* the driver must return a valid + format. + + Together with ``base`` it defines the framebuffer memory + accessible by the driver. + * - + - enum :c:type:`v4l2_colorspace` + - ``colorspace`` + - This information supplements the ``pixelformat`` and must be set + by the driver, see :ref:`colorspaces`. + * - + - __u32 + - ``priv`` + - Reserved. Drivers and applications must set this field to zero. + + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| + +.. _framebuffer-cap: + +.. flat-table:: Frame Buffer Capability Flags + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_FBUF_CAP_EXTERNOVERLAY`` + - 0x0001 + - The device is capable of non-destructive overlays. When the driver + clears this flag, only destructive overlays are supported. There + are no drivers yet which support both destructive and + non-destructive overlays. Video Output Overlays are in practice + always non-destructive. + * - ``V4L2_FBUF_CAP_CHROMAKEY`` + - 0x0002 + - The device supports clipping by chroma-keying the images. That is, + image pixels replace pixels in the VGA or video signal only where + the latter assume a certain color. Chroma-keying makes no sense + for destructive overlays. + * - ``V4L2_FBUF_CAP_LIST_CLIPPING`` + - 0x0004 + - The device supports clipping using a list of clip rectangles. + * - ``V4L2_FBUF_CAP_BITMAP_CLIPPING`` + - 0x0008 + - The device supports clipping using a bit mask. + * - ``V4L2_FBUF_CAP_LOCAL_ALPHA`` + - 0x0010 + - The device supports clipping/blending using the alpha channel of + the framebuffer or VGA signal. Alpha blending makes no sense for + destructive overlays. + * - ``V4L2_FBUF_CAP_GLOBAL_ALPHA`` + - 0x0020 + - The device supports alpha blending using a global alpha value. + Alpha blending makes no sense for destructive overlays. + * - ``V4L2_FBUF_CAP_LOCAL_INV_ALPHA`` + - 0x0040 + - The device supports clipping/blending using the inverted alpha + channel of the framebuffer or VGA signal. Alpha blending makes no + sense for destructive overlays. + * - ``V4L2_FBUF_CAP_SRC_CHROMAKEY`` + - 0x0080 + - The device supports Source Chroma-keying. Video pixels with the + chroma-key colors are replaced by framebuffer pixels, which is + exactly opposite of ``V4L2_FBUF_CAP_CHROMAKEY`` + + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| + +.. _framebuffer-flags: + +.. cssclass:: longtable + +.. flat-table:: Frame Buffer Flags + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_FBUF_FLAG_PRIMARY`` + - 0x0001 + - The framebuffer is the primary graphics surface. In other words, + the overlay is destructive. This flag is typically set by any + driver that doesn't have the ``V4L2_FBUF_CAP_EXTERNOVERLAY`` + capability and it is cleared otherwise. + * - ``V4L2_FBUF_FLAG_OVERLAY`` + - 0x0002 + - If this flag is set for a video capture device, then the driver + will set the initial overlay size to cover the full framebuffer + size, otherwise the existing overlay size (as set by + :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`) will be used. Only one + video capture driver (bttv) supports this flag. The use of this + flag for capture devices is deprecated. There is no way to detect + which drivers support this flag, so the only reliable method of + setting the overlay size is through + :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`. If this flag is set for a + video output device, then the video output overlay window is + relative to the top-left corner of the framebuffer and restricted + to the size of the framebuffer. If it is cleared, then the video + output overlay window is relative to the video output display. + * - ``V4L2_FBUF_FLAG_CHROMAKEY`` + - 0x0004 + - Use chroma-keying. The chroma-key color is determined by the + ``chromakey`` field of struct :c:type:`v4l2_window` + and negotiated with the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` + ioctl, see :ref:`overlay` and :ref:`osd`. + * - :cspan:`2` There are no flags to enable clipping using a list of + clip rectangles or a bitmap. These methods are negotiated with the + :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay` + and :ref:`osd`. + * - ``V4L2_FBUF_FLAG_LOCAL_ALPHA`` + - 0x0008 + - Use the alpha channel of the framebuffer to clip or blend + framebuffer pixels with video images. The blend function is: + output = framebuffer pixel * alpha + video pixel * (1 - alpha). + The actual alpha depth depends on the framebuffer pixel format. + * - ``V4L2_FBUF_FLAG_GLOBAL_ALPHA`` + - 0x0010 + - Use a global alpha value to blend the framebuffer with video + images. The blend function is: output = (framebuffer pixel * alpha + + video pixel * (255 - alpha)) / 255. The alpha value is + determined by the ``global_alpha`` field of struct + :c:type:`v4l2_window` and negotiated with the + :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay` + and :ref:`osd`. + * - ``V4L2_FBUF_FLAG_LOCAL_INV_ALPHA`` + - 0x0020 + - Like ``V4L2_FBUF_FLAG_LOCAL_ALPHA``, use the alpha channel of the + framebuffer to clip or blend framebuffer pixels with video images, + but with an inverted alpha value. The blend function is: output = + framebuffer pixel * (1 - alpha) + video pixel * alpha. The actual + alpha depth depends on the framebuffer pixel format. + * - ``V4L2_FBUF_FLAG_SRC_CHROMAKEY`` + - 0x0040 + - Use source chroma-keying. The source chroma-key color is + determined by the ``chromakey`` field of struct + :c:type:`v4l2_window` and negotiated with the + :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay` + and :ref:`osd`. Both chroma-keying are mutual exclusive to each + other, so same ``chromakey`` field of struct + :c:type:`v4l2_window` is being used. + + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. + +EPERM + :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` can only be called by a privileged user to + negotiate the parameters for a destructive overlay. + +EINVAL + The :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` parameters are unsuitable. + +.. [#f1] + A physical base address may not suit all platforms. GK notes in + theory we should pass something like PCI device + memory region + + offset instead. If you encounter problems please discuss on the + linux-media mailing list: + `https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__. |