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diff --git a/Documentation/DocBook/media/v4l/selection-api.xml b/Documentation/DocBook/media/v4l/selection-api.xml deleted file mode 100644 index 28cbded766c9..000000000000 --- a/Documentation/DocBook/media/v4l/selection-api.xml +++ /dev/null @@ -1,324 +0,0 @@ -<section id="selection-api"> - - <title>Experimental API for cropping, composing and scaling</title> - - <note> - <title>Experimental</title> - - <para>This is an <link linkend="experimental">experimental</link> -interface and may change in the future.</para> - </note> - - <section> - <title>Introduction</title> - -<para>Some video capture devices can sample a subsection of a picture and -shrink or enlarge it to an image of arbitrary size. Next, the devices can -insert the image into larger one. Some video output devices can crop part of an -input image, scale it up or down and insert it at an arbitrary scan line and -horizontal offset into a video signal. We call these abilities cropping, -scaling and composing.</para> - -<para>On a video <emphasis>capture</emphasis> device the source is a video -signal, and the cropping target determine the area actually sampled. The sink -is an image stored in a memory buffer. The composing area specifies which part -of the buffer is actually written to by the hardware. </para> - -<para>On a video <emphasis>output</emphasis> device the source is an image in a -memory buffer, and the cropping target is a part of an image to be shown on a -display. The sink is the display or the graphics screen. The application may -select the part of display where the image should be displayed. The size and -position of such a window is controlled by the compose target.</para> - -<para>Rectangles for all cropping and composing targets are defined even if the -device does supports neither cropping nor composing. Their size and position -will be fixed in such a case. If the device does not support scaling then the -cropping and composing rectangles have the same size.</para> - - </section> - - <section> - <title>Selection targets</title> - - <para> - <figure id="sel-targets-capture"> - <title>Cropping and composing targets</title> - <mediaobject> - <imageobject> - <imagedata fileref="selection.png" format="PNG" /> - </imageobject> - <textobject> - <phrase>Targets used by a cropping, composing and scaling - process</phrase> - </textobject> - </mediaobject> - </figure> - </para> - - <para>See <xref linkend="v4l2-selection-targets" /> for more - information.</para> - </section> - - <section> - - <title>Configuration</title> - -<para>Applications can use the <link linkend="vidioc-g-selection">selection -API</link> to select an area in a video signal or a buffer, and to query for -default settings and hardware limits.</para> - -<para>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 <link -linkend="v4l2-selection-flags"> constraint flags </link>.</para> - - <section> - - <title>Configuration of video capture</title> - -<para>See figure <xref linkend="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.</para> - -<para>The range of coordinates of the top left corner, width and height of -areas that can be sampled is given by the <constant>V4L2_SEL_TGT_CROP_BOUNDS</constant> -target. It is recommended for the driver developers to put the -top/left corner at position <constant>(0,0)</constant>. The rectangle's -coordinates are expressed in pixels.</para> - -<para>The top left corner, width and height of the source rectangle, that is -the area actually sampled, is given by the <constant>V4L2_SEL_TGT_CROP</constant> -target. It uses the same coordinate system as <constant>V4L2_SEL_TGT_CROP_BOUNDS</constant>. -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.</para> - -<para>Each capture device has a default source rectangle, given by the -<constant>V4L2_SEL_TGT_CROP_DEFAULT</constant> target. This rectangle shall -over 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.</para> - -<para>The composing targets refer to a memory buffer. The limits of composing -coordinates are obtained using <constant>V4L2_SEL_TGT_COMPOSE_BOUNDS</constant>. -All coordinates are expressed in pixels. The rectangle's top/left -corner must be located at position <constant>(0,0)</constant>. The width and -height are equal to the image size set by <constant>VIDIOC_S_FMT</constant>. -</para> - -<para>The part of a buffer into which the image is inserted by the hardware is -controlled by the <constant>V4L2_SEL_TGT_COMPOSE</constant> 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 -<link linkend="v4l2-selection-flags"> constraint flags</link>.</para> - -<para>For capture devices the default composing rectangle is queried using -<constant>V4L2_SEL_TGT_COMPOSE_DEFAULT</constant>. It is usually equal to the -bounding rectangle.</para> - -<para>The part of a buffer that is modified by the hardware is given by -<constant>V4L2_SEL_TGT_COMPOSE_PADDED</constant>. It contains all pixels -defined using <constant>V4L2_SEL_TGT_COMPOSE</constant> plus all -padding data modified by hardware during insertion process. All pixels outside -this rectangle <emphasis>must not</emphasis> 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.</para> - - </section> - - <section> - - <title>Configuration of video output</title> - -<para>For output devices targets and ioctls are used similarly to the video -capture case. The <emphasis>composing</emphasis> 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.</para> - -<para>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 <constant>V4L2_SEL_TGT_CROP_BOUNDS</constant>. -All coordinates are expressed in pixels. The top/left corner is always point -<constant>(0,0)</constant>. The width and height is equal to the image size -specified using <constant>VIDIOC_S_FMT</constant> ioctl.</para> - -<para>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 -<constant>V4L2_SEL_TGT_CROP</constant>. 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.</para> - -<para>For output devices the default cropping rectangle is queried using -<constant>V4L2_SEL_TGT_CROP_DEFAULT</constant>. It is usually equal to the -bounding rectangle.</para> - -<para>The part of a video signal or graphics display where the image is -inserted by the hardware is controlled by <constant>V4L2_SEL_TGT_COMPOSE</constant> -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.</para> - -<para>The device has a default composing rectangle, given by the -<constant>V4L2_SEL_TGT_COMPOSE_DEFAULT</constant> 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 <constant>(0,0)</constant>. -Drivers shall set the active composing rectangle to the default -one when the driver is first loaded.</para> - -<para>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 <constant>V4L2_SEL_TGT_COMPOSE_PADDED</constant> -identifier. It must contain all pixels from the <constant>V4L2_SEL_TGT_COMPOSE</constant> -target.</para> - - </section> - - <section> - - <title>Scaling control</title> - -<para>An application can detect if scaling is performed by comparing the width -and the height of rectangles obtained using <constant>V4L2_SEL_TGT_CROP</constant> -and <constant>V4L2_SEL_TGT_COMPOSE</constant> targets. If -these are not equal then the scaling is applied. The application can compute -the scaling ratios using these values.</para> - - </section> - - </section> - - <section> - - <title>Comparison with old cropping API</title> - -<para>The selection API was introduced to cope with deficiencies of previous -<link linkend="crop"> API</link>, that was designed to control simple capture -devices. Later the cropping API was adopted by video output drivers. The ioctls -are used to select a part of the display were the video signal is inserted. It -should be considered as an API abuse because the described operation is -actually the composing. The selection API makes a clear distinction between -composing and cropping operations by setting the appropriate targets. The V4L2 -API lacks any support for composing to and cropping from an image inside a -memory buffer. The application could configure a capture device to fill only a -part of an image by abusing V4L2 API. Cropping a smaller image from a larger -one is achieved by setting the field -&v4l2-pix-format;<structfield>::bytesperline</structfield>. Introducing an image offsets -could be done by modifying field &v4l2-buffer;<structfield>::m_userptr</structfield> -before calling <constant>VIDIOC_QBUF</constant>. Those -operations should be avoided because they are not portable (endianness), and do -not work for macroblock and Bayer formats and mmap buffers. The selection API -deals with configuration of buffer cropping/composing in a clear, intuitive and -portable way. Next, with the selection API the concepts of the padded target -and constraints flags are introduced. Finally, &v4l2-crop; and &v4l2-cropcap; -have no reserved fields. Therefore there is no way to extend their functionality. -The new &v4l2-selection; provides a lot of place for future -extensions. Driver developers are encouraged to implement only selection API. -The former cropping API would be simulated using the new one.</para> - - </section> - - <section> - <title>Examples</title> - <example> - <title>Resetting the cropping parameters</title> - - <para>(A video capture device is assumed; change -<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> for other devices; change target to -<constant>V4L2_SEL_TGT_COMPOSE_*</constant> family to configure composing -area)</para> - - <programlisting> - - &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); - - </programlisting> - </example> - - <example> - <title>Simple downscaling</title> - <para>Setting a composing area on output of size of <emphasis> at most -</emphasis> half of limit placed at a center of a display.</para> - <programlisting> - - &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); - - </programlisting> - </example> - - <example> - <title>Querying for scaling factors</title> - <para>A video output device is assumed; change -<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> for other devices</para> - <programlisting> - - &v4l2-selection; compose = { - .type = V4L2_BUF_TYPE_VIDEO_OUTPUT, - .target = V4L2_SEL_TGT_COMPOSE, - }; - &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; - - </programlisting> - </example> - - </section> - -</section> |