vidioc-g-fbuf.rst (13399B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_G_FBUF: 5 6********************************** 7ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF 8********************************** 9 10Name 11==== 12 13VIDIOC_G_FBUF - VIDIOC_S_FBUF - Get or set frame buffer overlay parameters 14 15Synopsis 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 26Arguments 27========= 28 29``fd`` 30 File descriptor returned by :c:func:`open()`. 31 32``argp`` 33 Pointer to struct :c:type:`v4l2_framebuffer`. 34 35Description 36=========== 37 38Applications can use the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` and :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctl 39to 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 42output device) and can be determined with the 43:ref:`VIDIOC_QUERYCAP` ioctl. One ``/dev/videoN`` 44device must not support both kinds of overlay. 45 46The V4L2 API distinguishes destructive and non-destructive overlays. A 47destructive overlay copies captured video images into the video memory 48of a graphics card. A non-destructive overlay blends video images into a 49VGA signal or graphics into a video signal. *Video Output Overlays* are 50always non-destructive. 51 52To get the current parameters applications call the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` 53ioctl with a pointer to a struct :c:type:`v4l2_framebuffer` 54structure. The driver fills all fields of the structure or returns an 55EINVAL error code when overlays are not supported. 56 57To set the parameters for a *Video Output Overlay*, applications must 58initialize the ``flags`` field of a struct 59:c:type:`v4l2_framebuffer`. Since the framebuffer is 60implemented on the TV card all other parameters are determined by the 61driver. When an application calls :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` with a pointer to 62this structure, the driver prepares for the overlay and returns the 63framebuffer parameters as :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` does, or it returns an error 64code. 65 66To set the parameters for a *non-destructive Video Overlay*, 67applications must initialize the ``flags`` field, the ``fmt`` 68substructure, and call :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>`. Again the driver prepares for 69the overlay and returns the framebuffer parameters as :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` 70does, or it returns an error code. 71 72For a *destructive Video Overlay* applications must additionally provide 73a ``base`` address. Setting up a DMA to a random memory location can 74jeopardize the system security, its stability or even damage the 75hardware, therefore only the superuser can set the parameters for a 76destructive video overlay. 77 78.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{6.6cm}| 79 80.. c:type:: v4l2_framebuffer 81 82.. cssclass:: longtable 83 84.. flat-table:: struct v4l2_framebuffer 85 :header-rows: 0 86 :stub-columns: 0 87 :widths: 1 1 1 2 88 89 * - __u32 90 - ``capability`` 91 - 92 - Overlay capability flags set by the driver, see 93 :ref:`framebuffer-cap`. 94 * - __u32 95 - ``flags`` 96 - 97 - Overlay control flags set by application and driver, see 98 :ref:`framebuffer-flags` 99 * - void * 100 - ``base`` 101 - 102 - Physical base address of the framebuffer, that is the address of 103 the pixel in the top left corner of the framebuffer. [#f1]_ 104 * - 105 - 106 - 107 - This field is irrelevant to *non-destructive Video Overlays*. For 108 *destructive Video Overlays* applications must provide a base 109 address. The driver may accept only base addresses which are a 110 multiple of two, four or eight bytes. For *Video Output Overlays* 111 the driver must return a valid base address, so applications can 112 find the corresponding Linux framebuffer device (see 113 :ref:`osd`). 114 * - struct 115 - ``fmt`` 116 - 117 - Layout of the frame buffer. 118 * - 119 - __u32 120 - ``width`` 121 - Width of the frame buffer in pixels. 122 * - 123 - __u32 124 - ``height`` 125 - Height of the frame buffer in pixels. 126 * - 127 - __u32 128 - ``pixelformat`` 129 - The pixel format of the framebuffer. 130 * - 131 - 132 - 133 - For *non-destructive Video Overlays* this field only defines a 134 format for the struct :c:type:`v4l2_window` 135 ``chromakey`` field. 136 * - 137 - 138 - 139 - For *destructive Video Overlays* applications must initialize this 140 field. For *Video Output Overlays* the driver must return a valid 141 format. 142 * - 143 - 144 - 145 - Usually this is an RGB format (for example 146 :ref:`V4L2_PIX_FMT_RGB565 <V4L2-PIX-FMT-RGB565>`) but YUV 147 formats (only packed YUV formats when chroma keying is used, not 148 including ``V4L2_PIX_FMT_YUYV`` and ``V4L2_PIX_FMT_UYVY``) and the 149 ``V4L2_PIX_FMT_PAL8`` format are also permitted. The behavior of 150 the driver when an application requests a compressed format is 151 undefined. See :ref:`pixfmt` for information on pixel formats. 152 * - 153 - enum :c:type:`v4l2_field` 154 - ``field`` 155 - Drivers and applications shall ignore this field. If applicable, 156 the field order is selected with the 157 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, using the ``field`` 158 field of struct :c:type:`v4l2_window`. 159 * - 160 - __u32 161 - ``bytesperline`` 162 - Distance in bytes between the leftmost pixels in two adjacent 163 lines. 164 * - :cspan:`3` 165 166 This field is irrelevant to *non-destructive Video Overlays*. 167 168 For *destructive Video Overlays* both applications and drivers can 169 set this field to request padding bytes at the end of each line. 170 Drivers however may ignore the requested value, returning 171 ``width`` times bytes-per-pixel or a larger value required by the 172 hardware. That implies applications can just set this field to 173 zero to get a reasonable default. 174 175 For *Video Output Overlays* the driver must return a valid value. 176 177 Video hardware may access padding bytes, therefore they must 178 reside in accessible memory. Consider for example the case where 179 padding bytes after the last line of an image cross a system page 180 boundary. Capture devices may write padding bytes, the value is 181 undefined. Output devices ignore the contents of padding bytes. 182 183 When the image format is planar the ``bytesperline`` value applies 184 to the first plane and is divided by the same factor as the 185 ``width`` field for the other planes. For example the Cb and Cr 186 planes of a YUV 4:2:0 image have half as many padding bytes 187 following each line as the Y plane. To avoid ambiguities drivers 188 must return a ``bytesperline`` value rounded up to a multiple of 189 the scale factor. 190 * - 191 - __u32 192 - ``sizeimage`` 193 - This field is irrelevant to *non-destructive Video Overlays*. For 194 *destructive Video Overlays* applications must initialize this 195 field. For *Video Output Overlays* the driver must return a valid 196 format. 197 198 Together with ``base`` it defines the framebuffer memory 199 accessible by the driver. 200 * - 201 - enum :c:type:`v4l2_colorspace` 202 - ``colorspace`` 203 - This information supplements the ``pixelformat`` and must be set 204 by the driver, see :ref:`colorspaces`. 205 * - 206 - __u32 207 - ``priv`` 208 - Reserved. Drivers and applications must set this field to zero. 209 210.. tabularcolumns:: |p{7.4cm}|p{1.6cm}|p{8.3cm}| 211 212.. _framebuffer-cap: 213 214.. flat-table:: Frame Buffer Capability Flags 215 :header-rows: 0 216 :stub-columns: 0 217 :widths: 3 1 4 218 219 * - ``V4L2_FBUF_CAP_EXTERNOVERLAY`` 220 - 0x0001 221 - The device is capable of non-destructive overlays. When the driver 222 clears this flag, only destructive overlays are supported. There 223 are no drivers yet which support both destructive and 224 non-destructive overlays. Video Output Overlays are in practice 225 always non-destructive. 226 * - ``V4L2_FBUF_CAP_CHROMAKEY`` 227 - 0x0002 228 - The device supports clipping by chroma-keying the images. That is, 229 image pixels replace pixels in the VGA or video signal only where 230 the latter assume a certain color. Chroma-keying makes no sense 231 for destructive overlays. 232 * - ``V4L2_FBUF_CAP_LIST_CLIPPING`` 233 - 0x0004 234 - The device supports clipping using a list of clip rectangles. 235 * - ``V4L2_FBUF_CAP_BITMAP_CLIPPING`` 236 - 0x0008 237 - The device supports clipping using a bit mask. 238 * - ``V4L2_FBUF_CAP_LOCAL_ALPHA`` 239 - 0x0010 240 - The device supports clipping/blending using the alpha channel of 241 the framebuffer or VGA signal. Alpha blending makes no sense for 242 destructive overlays. 243 * - ``V4L2_FBUF_CAP_GLOBAL_ALPHA`` 244 - 0x0020 245 - The device supports alpha blending using a global alpha value. 246 Alpha blending makes no sense for destructive overlays. 247 * - ``V4L2_FBUF_CAP_LOCAL_INV_ALPHA`` 248 - 0x0040 249 - The device supports clipping/blending using the inverted alpha 250 channel of the framebuffer or VGA signal. Alpha blending makes no 251 sense for destructive overlays. 252 * - ``V4L2_FBUF_CAP_SRC_CHROMAKEY`` 253 - 0x0080 254 - The device supports Source Chroma-keying. Video pixels with the 255 chroma-key colors are replaced by framebuffer pixels, which is 256 exactly opposite of ``V4L2_FBUF_CAP_CHROMAKEY`` 257 258.. tabularcolumns:: |p{7.4cm}|p{1.6cm}|p{8.3cm}| 259 260.. _framebuffer-flags: 261 262.. cssclass:: longtable 263 264.. flat-table:: Frame Buffer Flags 265 :header-rows: 0 266 :stub-columns: 0 267 :widths: 3 1 4 268 269 * - ``V4L2_FBUF_FLAG_PRIMARY`` 270 - 0x0001 271 - The framebuffer is the primary graphics surface. In other words, 272 the overlay is destructive. This flag is typically set by any 273 driver that doesn't have the ``V4L2_FBUF_CAP_EXTERNOVERLAY`` 274 capability and it is cleared otherwise. 275 * - ``V4L2_FBUF_FLAG_OVERLAY`` 276 - 0x0002 277 - If this flag is set for a video capture device, then the driver 278 will set the initial overlay size to cover the full framebuffer 279 size, otherwise the existing overlay size (as set by 280 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`) will be used. Only one 281 video capture driver (bttv) supports this flag. The use of this 282 flag for capture devices is deprecated. There is no way to detect 283 which drivers support this flag, so the only reliable method of 284 setting the overlay size is through 285 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`. If this flag is set for a 286 video output device, then the video output overlay window is 287 relative to the top-left corner of the framebuffer and restricted 288 to the size of the framebuffer. If it is cleared, then the video 289 output overlay window is relative to the video output display. 290 * - ``V4L2_FBUF_FLAG_CHROMAKEY`` 291 - 0x0004 292 - Use chroma-keying. The chroma-key color is determined by the 293 ``chromakey`` field of struct :c:type:`v4l2_window` 294 and negotiated with the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` 295 ioctl, see :ref:`overlay` and :ref:`osd`. 296 * - :cspan:`2` There are no flags to enable clipping using a list of 297 clip rectangles or a bitmap. These methods are negotiated with the 298 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay` 299 and :ref:`osd`. 300 * - ``V4L2_FBUF_FLAG_LOCAL_ALPHA`` 301 - 0x0008 302 - Use the alpha channel of the framebuffer to clip or blend 303 framebuffer pixels with video images. The blend function is: 304 output = framebuffer pixel * alpha + video pixel * (1 - alpha). 305 The actual alpha depth depends on the framebuffer pixel format. 306 * - ``V4L2_FBUF_FLAG_GLOBAL_ALPHA`` 307 - 0x0010 308 - Use a global alpha value to blend the framebuffer with video 309 images. The blend function is: output = (framebuffer pixel * alpha 310 + video pixel * (255 - alpha)) / 255. The alpha value is 311 determined by the ``global_alpha`` field of struct 312 :c:type:`v4l2_window` and negotiated with the 313 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay` 314 and :ref:`osd`. 315 * - ``V4L2_FBUF_FLAG_LOCAL_INV_ALPHA`` 316 - 0x0020 317 - Like ``V4L2_FBUF_FLAG_LOCAL_ALPHA``, use the alpha channel of the 318 framebuffer to clip or blend framebuffer pixels with video images, 319 but with an inverted alpha value. The blend function is: output = 320 framebuffer pixel * (1 - alpha) + video pixel * alpha. The actual 321 alpha depth depends on the framebuffer pixel format. 322 * - ``V4L2_FBUF_FLAG_SRC_CHROMAKEY`` 323 - 0x0040 324 - Use source chroma-keying. The source chroma-key color is 325 determined by the ``chromakey`` field of struct 326 :c:type:`v4l2_window` and negotiated with the 327 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, see :ref:`overlay` 328 and :ref:`osd`. Both chroma-keying are mutual exclusive to each 329 other, so same ``chromakey`` field of struct 330 :c:type:`v4l2_window` is being used. 331 332Return Value 333============ 334 335On success 0 is returned, on error -1 and the ``errno`` variable is set 336appropriately. The generic error codes are described at the 337:ref:`Generic Error Codes <gen-errors>` chapter. 338 339EPERM 340 :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` can only be called by a privileged user to 341 negotiate the parameters for a destructive overlay. 342 343EINVAL 344 The :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` parameters are unsuitable. 345 346.. [#f1] 347 A physical base address may not suit all platforms. GK notes in 348 theory we should pass something like PCI device + memory region + 349 offset instead. If you encounter problems please discuss on the 350 linux-media mailing list: 351 `https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__.