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diff --git a/Documentation/media/uapi/v4l/dev-osd.rst b/Documentation/media/uapi/v4l/dev-osd.rst deleted file mode 100644 index d3ad67da6386..000000000000 --- a/Documentation/media/uapi/v4l/dev-osd.rst +++ /dev/null @@ -1,157 +0,0 @@ -.. 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/media/uapi/fdl-appendix.rst. -.. -.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections - -.. _osd: - -****************************** -Video Output Overlay Interface -****************************** - -**Also known as On-Screen Display (OSD)** - -Some video output devices can overlay a framebuffer image onto the -outgoing video signal. Applications can set up such an overlay using -this interface, which borrows structures and ioctls of the -:ref:`Video Overlay <overlay>` interface. - -The OSD function is accessible through the same character special file -as the :ref:`Video Output <capture>` function. - -.. note:: - - The default function of such a ``/dev/video`` device is video - capturing or output. The OSD function is only available after calling - the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. - - -Querying Capabilities -===================== - -Devices supporting the *Video Output Overlay* interface set the -``V4L2_CAP_VIDEO_OUTPUT_OVERLAY`` flag in the ``capabilities`` field of -struct :c:type:`v4l2_capability` returned by the -:ref:`VIDIOC_QUERYCAP` ioctl. - - -Framebuffer -=========== - -Contrary to the *Video Overlay* interface the framebuffer is normally -implemented on the TV card and not the graphics card. On Linux it is -accessible as a framebuffer device (``/dev/fbN``). Given a V4L2 device, -applications can find the corresponding framebuffer device by calling -the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` ioctl. It returns, amongst -other information, the physical address of the framebuffer in the -``base`` field of struct :c:type:`v4l2_framebuffer`. -The framebuffer device ioctl ``FBIOGET_FSCREENINFO`` returns the same -address in the ``smem_start`` field of struct -struct :c:type:`fb_fix_screeninfo`. The ``FBIOGET_FSCREENINFO`` -ioctl and struct :c:type:`fb_fix_screeninfo` are defined in -the ``linux/fb.h`` header file. - -The width and height of the framebuffer depends on the current video -standard. A V4L2 driver may reject attempts to change the video standard -(or any other ioctl which would imply a framebuffer size change) with an -``EBUSY`` error code until all applications closed the framebuffer device. - -Example: Finding a framebuffer device for OSD ---------------------------------------------- - -.. code-block:: c - - #include <linux/fb.h> - - struct v4l2_framebuffer fbuf; - unsigned int i; - int fb_fd; - - if (-1 == ioctl(fd, VIDIOC_G_FBUF, &fbuf)) { - perror("VIDIOC_G_FBUF"); - exit(EXIT_FAILURE); - } - - for (i = 0; i < 30; i++) { - char dev_name[16]; - struct fb_fix_screeninfo si; - - snprintf(dev_name, sizeof(dev_name), "/dev/fb%u", i); - - fb_fd = open(dev_name, O_RDWR); - if (-1 == fb_fd) { - switch (errno) { - case ENOENT: /* no such file */ - case ENXIO: /* no driver */ - continue; - - default: - perror("open"); - exit(EXIT_FAILURE); - } - } - - if (0 == ioctl(fb_fd, FBIOGET_FSCREENINFO, &si)) { - if (si.smem_start == (unsigned long)fbuf.base) - break; - } else { - /* Apparently not a framebuffer device. */ - } - - close(fb_fd); - fb_fd = -1; - } - - /* fb_fd is the file descriptor of the framebuffer device - for the video output overlay, or -1 if no device was found. */ - - -Overlay Window and Scaling -========================== - -The overlay is controlled by source and target rectangles. The source -rectangle selects a subsection of the framebuffer image to be overlaid, -the target rectangle an area in the outgoing video signal where the -image will appear. Drivers may or may not support scaling, and arbitrary -sizes and positions of these rectangles. Further drivers may support any -(or none) of the clipping/blending methods defined for the -:ref:`Video Overlay <overlay>` interface. - -A struct :c:type:`v4l2_window` defines the size of the -source rectangle, its position in the framebuffer and the -clipping/blending method to be used for the overlay. To get the current -parameters applications set the ``type`` field of a struct -:c:type:`v4l2_format` to -``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` and call the -:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl. The driver fills the -struct :c:type:`v4l2_window` substructure named ``win``. It is not -possible to retrieve a previously programmed clipping list or bitmap. - -To program the source rectangle applications set the ``type`` field of a -struct :c:type:`v4l2_format` to -``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY``, initialize the ``win`` -substructure and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. -The driver adjusts the parameters against hardware limits and returns -the actual parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`, -the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl can be used to learn -about driver capabilities without actually changing driver state. Unlike -:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` this also works after the overlay has been enabled. - -A struct :c:type:`v4l2_crop` defines the size and position -of the target rectangle. The scaling factor of the overlay is implied by -the width and height given in struct :c:type:`v4l2_window` -and struct :c:type:`v4l2_crop`. The cropping API applies to -*Video Output* and *Video Output Overlay* devices in the same way as to -*Video Capture* and *Video Overlay* devices, merely reversing the -direction of the data flow. For more information see :ref:`crop`. - - -Enabling Overlay -================ - -There is no V4L2 ioctl to enable or disable the overlay, however the -framebuffer interface of the driver may support the ``FBIOBLANK`` ioctl. |