1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_G_FBUF:
5
6 **********************************
7 ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF
8 **********************************
9
10 Name
11 ====
12
13 VIDIOC_G_FBUF - VIDIOC_S_FBUF - Get or set frame buffer overlay parameters
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_G_FBUF
19
20 ``int ioctl(int fd, VIDIOC_G_FBUF, struct v4l2_framebuffer *argp)``
21
22 .. c:macro:: VIDIOC_S_FBUF
23
24 ``int ioctl(int fd, VIDIOC_S_FBUF, const struct v4l2_framebuffer *argp)``
25
26 Arguments
27 =========
28
29 ``fd``
30 File descriptor returned by :c:func:`open()`.
31
32 ``argp``
33 Pointer to struct :c:type:`v4l2_framebuffer`.
34
35 Description
36 ===========
37
38 Applications can use the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` and :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctl
39 to get and set the framebuffer parameters for a
40 :ref:`Video Overlay <overlay>` or :ref:`Video Output Overlay <osd>`
41 (OSD). The type of overlay is implied by the device type (capture or
42 output device) and can be determined with the
43 :ref:`VIDIOC_QUERYCAP` ioctl. One ``/dev/videoN``
44 device must not support both kinds of overlay.
45
46 The V4L2 API distinguishes destructive and non-destructive overlays. A
47 destructive overlay copies captured video images into the video memory
48 of a graphics card. A non-destructive overlay blends video images into a
49 VGA signal or graphics into a video signal. *Video Output Overlays* are
50 always non-destructive.
51
52 Destructive overlay support has been removed: with modern GPUs and CPUs
53 this is no longer needed, and it was always a very dangerous feature.
54
55 To get the current parameters applications call the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`
56 ioctl with a pointer to a struct :c:type:`v4l2_framebuffer`
57 structure. The driver fills all fields of the structure or returns an
58 EINVAL error code when overlays are not supported.
59
60 To set the parameters for a *Video Output Overlay*, applications must
61 initialize the ``flags`` field of a struct
62 :c:type:`v4l2_framebuffer`. Since the framebuffer is
63 implemented on the TV card all other parameters are determined by the
64 driver. When an application calls :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` with a pointer to
65 this structure, the driver prepares for the overlay and returns the
66 framebuffer parameters as :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` does, or it returns an error
67 code.
68
69 To set the parameters for a *Video Capture Overlay*
70 applications must initialize the ``flags`` field, the ``fmt``
71 substructure, and call :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>`. Again the driver prepares for
72 the overlay and returns the framebuffer parameters as :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`
73 does, or it returns an error code.
74
75 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{6.6cm}|
76
77 .. c:type:: v4l2_framebuffer
78
79 .. cssclass:: longtable
80
81 .. flat-table:: struct v4l2_framebuffer
82 :header-rows: 0
83 :stub-columns: 0
84 :widths: 1 1 1 2
85
86 * - __u32
87 - ``capability``
88 -
89 - Overlay capability flags set by the driver, see
90 :ref:`framebuffer-cap`.
91 * - __u32
92 - ``flags``
93 -
94 - Overlay control flags set by application and driver, see
95 :ref:`framebuffer-flags`
96 * - void *
97 - ``base``
98 -
99 - Physical base address of the framebuffer, that is the address of
100 the pixel in the top left corner of the framebuffer.
101 For :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` this field is no longer supported
102 and the kernel will always set this to NULL.
103 For *Video Output Overlays*
104 the driver will return a valid base address, so applications can
105 find the corresponding Linux framebuffer device (see
106 :ref:`osd`). For *Video Capture Overlays* this field will always be
107 NULL.
108 * - struct
109 - ``fmt``
110 -
111 - Layout of the frame buffer.
112 * -
113 - __u32
114 - ``width``
115 - Width of the frame buffer in pixels.
116 * -
117 - __u32
118 - ``height``
119 - Height of the frame buffer in pixels.
120 * -
121 - __u32
122 - ``pixelformat``
123 - The pixel format of the framebuffer.
124 * -
125 -
126 -
127 - For *non-destructive Video Overlays* this field only defines a
128 format for the struct :c:type:`v4l2_window`
129 ``chromakey`` field.
130 * -
131 -
132 -
133 - For *Video Output Overlays* the driver must return a valid
134 format.
135 * -
136 -
137 -
138 - Usually this is an RGB format (for example
139 :ref:`V4L2_PIX_FMT_RGB565 <V4L2-PIX-FMT-RGB565>`) but YUV
140 formats (only packed YUV formats when chroma keying is used, not
141 including ``V4L2_PIX_FMT_YUYV`` and ``V4L2_PIX_FMT_UYVY``) and the
142 ``V4L2_PIX_FMT_PAL8`` format are also permitted. The behavior of
143 the driver when an application requests a compressed format is
144 undefined. See :ref:`pixfmt` for information on pixel formats.
145 * -
146 - enum :c:type:`v4l2_field`
147 - ``field``
148 - Drivers and applications shall ignore this field. If applicable,
149 the field order is selected with the
150 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, using the ``field``
151 field of struct :c:type:`v4l2_window`.
152 * -
153 - __u32
154 - ``bytesperline``
155 - Distance in bytes between the leftmost pixels in two adjacent
156 lines.
157 * - :cspan:`3`
158
159 This field is irrelevant to *non-destructive Video Overlays*.
160
161 For *Video Output Overlays* the driver must return a valid value.
162
163 Video hardware may access padding bytes, therefore they must
164 reside in accessible memory. Consider for example the case where
165 padding bytes after the last line of an image cross a system page
166 boundary. Capture devices may write padding bytes, the value is
167 undefined. Output devices ignore the contents of padding bytes.
168
169 When the image format is planar the ``bytesperline`` value applies
170 to the first plane and is divided by the same factor as the
171 ``width`` field for the other planes. For example the Cb and Cr
172 planes of a YUV 4:2:0 image have half as many padding bytes
173 following each line as the Y plane. To avoid ambiguities drivers
174 must return a ``bytesperline`` value rounded up to a multiple of
175 the scale factor.
176 * -
177 - __u32
178 - ``sizeimage``
179 - This field is irrelevant to *non-destructive Video Overlays*.
180 For *Video Output Overlays* the driver must return a valid
181 format.
182
183 Together with ``base`` it defines the framebuffer memory
184 accessible by the driver.
185 * -
186 - enum :c:type:`v4l2_colorspace`
187 - ``colorspace``
188 - This information supplements the ``pixelformat`` and must be set
189 by the driver, see :ref:`colorspaces`.
190 * -
191 - __u32
192 - ``priv``
193 - Reserved. Drivers and applications must set this field to zero.
194
195 .. tabularcolumns:: |p{7.4cm}|p{1.6cm}|p{8.3cm}|
196
197 .. _framebuffer-cap:
198
199 .. flat-table:: Frame Buffer Capability Flags
200 :header-rows: 0
201 :stub-columns: 0
202 :widths: 3 1 4
203
204 * - ``V4L2_FBUF_CAP_EXTERNOVERLAY``
205 - 0x0001
206 - The device is capable of non-destructive overlays. When the driver
207 clears this flag, only destructive overlays are supported. There
208 are no drivers yet which support both destructive and
209 non-destructive overlays. Video Output Overlays are in practice
210 always non-destructive.
211 * - ``V4L2_FBUF_CAP_CHROMAKEY``
212 - 0x0002
213 - The device supports clipping by chroma-keying the images. That is,
214 image pixels replace pixels in the VGA or video signal only where
215 the latter assume a certain color. Chroma-keying makes no sense
216 for destructive overlays.
217 * - ``V4L2_FBUF_CAP_LIST_CLIPPING``
218 - 0x0004
219 - The device supports clipping using a list of clip rectangles.
220 Note that this is no longer supported.
221 * - ``V4L2_FBUF_CAP_BITMAP_CLIPPING``
222 - 0x0008
223 - The device supports clipping using a bit mask.
224 Note that this is no longer supported.
225 * - ``V4L2_FBUF_CAP_LOCAL_ALPHA``
226 - 0x0010
227 - The device supports clipping/blending using the alpha channel of
228 the framebuffer or VGA signal. Alpha blending makes no sense for
229 destructive overlays.
230 * - ``V4L2_FBUF_CAP_GLOBAL_ALPHA``
231 - 0x0020
232 - The device supports alpha blending using a global alpha value.
233 Alpha blending makes no sense for destructive overlays.
234 * - ``V4L2_FBUF_CAP_LOCAL_INV_ALPHA``
235 - 0x0040
236 - The device supports clipping/blending using the inverted alpha
237 channel of the framebuffer or VGA signal. Alpha blending makes no
238 sense for destructive overlays.
239 * - ``V4L2_FBUF_CAP_SRC_CHROMAKEY``
240 - 0x0080
241 - The device supports Source Chroma-keying. Video pixels with the
242 chroma-key colors are replaced by framebuffer pixels, which is
243 exactly opposite of ``V4L2_FBUF_CAP_CHROMAKEY``
244
245 .. tabularcolumns:: |p{7.4cm}|p{1.6cm}|p{8.3cm}|
246
247 .. _framebuffer-flags:
248
249 .. cssclass:: longtable
250
251 .. flat-table:: Frame Buffer Flags
252 :header-rows: 0
253 :stub-columns: 0
254 :widths: 3 1 4
255
256 * - ``V4L2_FBUF_FLAG_PRIMARY``
257 - 0x0001
258 - The framebuffer is the primary graphics surface. In other words,
259 the overlay is destructive. This flag is typically set by any
260 driver that doesn't have the ``V4L2_FBUF_CAP_EXTERNOVERLAY``
261 capability and it is cleared otherwise.
262 * - ``V4L2_FBUF_FLAG_OVERLAY``
263 - 0x0002
264 - If this flag is set for a video capture device, then the driver
265 will set the initial overlay size to cover the full framebuffer
266 size, otherwise the existing overlay size (as set by
267 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`) will be used. Only one
268 video capture driver (bttv) supports this flag. The use of this
269 flag for capture devices is deprecated. There is no way to detect
270 which drivers support this flag, so the only reliable method of
271 setting the overlay size is through
272 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`. If this flag is set for a
273 video output device, then the video output overlay window is
274 relative to the top-left corner of the framebuffer and restricted
275 to the size of the framebuffer. If it is cleared, then the video
276 output overlay window is relative to the video output display.
277 * - ``V4L2_FBUF_FLAG_CHROMAKEY``
278 - 0x0004
279 - Use chroma-keying. The chroma-key color is determined by the
280 ``chromakey`` field of struct :c:type:`v4l2_window`
281 and negotiated with the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
282 ioctl, see :ref:`overlay` and :ref:`osd`.
283 * - :cspan:`2` There are no flags to enable clipping using a list of
284 clip rectangles or a bitmap. These methods are negotiated with the
285 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay`
286 and :ref:`osd`.
287 * - ``V4L2_FBUF_FLAG_LOCAL_ALPHA``
288 - 0x0008
289 - Use the alpha channel of the framebuffer to clip or blend
290 framebuffer pixels with video images. The blend function is:
291 output = framebuffer pixel * alpha + video pixel * (1 - alpha).
292 The actual alpha depth depends on the framebuffer pixel format.
293 * - ``V4L2_FBUF_FLAG_GLOBAL_ALPHA``
294 - 0x0010
295 - Use a global alpha value to blend the framebuffer with video
296 images. The blend function is: output = (framebuffer pixel * alpha
297 + video pixel * (255 - alpha)) / 255. The alpha value is
298 determined by the ``global_alpha`` field of struct
299 :c:type:`v4l2_window` and negotiated with the
300 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay`
301 and :ref:`osd`.
302 * - ``V4L2_FBUF_FLAG_LOCAL_INV_ALPHA``
303 - 0x0020
304 - Like ``V4L2_FBUF_FLAG_LOCAL_ALPHA``, use the alpha channel of the
305 framebuffer to clip or blend framebuffer pixels with video images,
306 but with an inverted alpha value. The blend function is: output =
307 framebuffer pixel * (1 - alpha) + video pixel * alpha. The actual
308 alpha depth depends on the framebuffer pixel format.
309 * - ``V4L2_FBUF_FLAG_SRC_CHROMAKEY``
310 - 0x0040
311 - Use source chroma-keying. The source chroma-key color is
312 determined by the ``chromakey`` field of struct
313 :c:type:`v4l2_window` and negotiated with the
314 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay`
315 and :ref:`osd`. Both chroma-keying are mutual exclusive to each
316 other, so same ``chromakey`` field of struct
317 :c:type:`v4l2_window` is being used.
318
319 Return Value
320 ============
321
322 On success 0 is returned, on error -1 and the ``errno`` variable is set
323 appropriately. The generic error codes are described at the
324 :ref:`Generic Error Codes <gen-errors>` chapter.
325
326 EPERM
327 :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` can only be called by a privileged user to
328 negotiate the parameters for a destructive overlay.
329
330 EINVAL
331 The :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` parameters are unsuitable.
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