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diff --git a/Documentation/userspace-api/media/v4l/control.rst b/Documentation/userspace-api/media/v4l/control.rst new file mode 100644 index 000000000..4463fce69 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/control.rst @@ -0,0 +1,517 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _control: + +************* +User Controls +************* + +Devices typically have a number of user-settable controls such as +brightness, saturation and so on, which would be presented to the user +on a graphical user interface. But, different devices will have +different controls available, and furthermore, the range of possible +values, and the default value will vary from device to device. The +control ioctls provide the information and a mechanism to create a nice +user interface for these controls that will work correctly with any +device. + +All controls are accessed using an ID value. V4L2 defines several IDs +for specific purposes. Drivers can also implement their own custom +controls using ``V4L2_CID_PRIVATE_BASE`` [#f1]_ and higher values. The +pre-defined control IDs have the prefix ``V4L2_CID_``, and are listed in +:ref:`control-id`. The ID is used when querying the attributes of a +control, and when getting or setting the current value. + +Generally applications should present controls to the user without +assumptions about their purpose. Each control comes with a name string +the user is supposed to understand. When the purpose is non-intuitive +the driver writer should provide a user manual, a user interface plug-in +or a driver specific panel application. Predefined IDs were introduced +to change a few controls programmatically, for example to mute a device +during a channel switch. + +Drivers may enumerate different controls after switching the current +video input or output, tuner or modulator, or audio input or output. +Different in the sense of other bounds, another default and current +value, step size or other menu items. A control with a certain *custom* +ID can also change name and type. + +If a control is not applicable to the current configuration of the +device (for example, it doesn't apply to the current video input) +drivers set the ``V4L2_CTRL_FLAG_INACTIVE`` flag. + +Control values are stored globally, they do not change when switching +except to stay within the reported bounds. They also do not change e. g. +when the device is opened or closed, when the tuner radio frequency is +changed or generally never without application request. + +V4L2 specifies an event mechanism to notify applications when controls +change value (see +:ref:`VIDIOC_SUBSCRIBE_EVENT`, event +``V4L2_EVENT_CTRL``), panel applications might want to make use of that +in order to always reflect the correct control value. + +All controls use machine endianness. + + +.. _control-id: + +Control IDs +=========== + +``V4L2_CID_BASE`` + First predefined ID, equal to ``V4L2_CID_BRIGHTNESS``. + +``V4L2_CID_USER_BASE`` + Synonym of ``V4L2_CID_BASE``. + +``V4L2_CID_BRIGHTNESS`` ``(integer)`` + Picture brightness, or more precisely, the black level. + +``V4L2_CID_CONTRAST`` ``(integer)`` + Picture contrast or luma gain. + +``V4L2_CID_SATURATION`` ``(integer)`` + Picture color saturation or chroma gain. + +``V4L2_CID_HUE`` ``(integer)`` + Hue or color balance. + +``V4L2_CID_AUDIO_VOLUME`` ``(integer)`` + Overall audio volume. Note some drivers also provide an OSS or ALSA + mixer interface. + +``V4L2_CID_AUDIO_BALANCE`` ``(integer)`` + Audio stereo balance. Minimum corresponds to all the way left, + maximum to right. + +``V4L2_CID_AUDIO_BASS`` ``(integer)`` + Audio bass adjustment. + +``V4L2_CID_AUDIO_TREBLE`` ``(integer)`` + Audio treble adjustment. + +``V4L2_CID_AUDIO_MUTE`` ``(boolean)`` + Mute audio, i. e. set the volume to zero, however without affecting + ``V4L2_CID_AUDIO_VOLUME``. Like ALSA drivers, V4L2 drivers must mute + at load time to avoid excessive noise. Actually the entire device + should be reset to a low power consumption state. + +``V4L2_CID_AUDIO_LOUDNESS`` ``(boolean)`` + Loudness mode (bass boost). + +``V4L2_CID_BLACK_LEVEL`` ``(integer)`` + Another name for brightness (not a synonym of + ``V4L2_CID_BRIGHTNESS``). This control is deprecated and should not + be used in new drivers and applications. + +``V4L2_CID_AUTO_WHITE_BALANCE`` ``(boolean)`` + Automatic white balance (cameras). + +``V4L2_CID_DO_WHITE_BALANCE`` ``(button)`` + This is an action control. When set (the value is ignored), the + device will do a white balance and then hold the current setting. + Contrast this with the boolean ``V4L2_CID_AUTO_WHITE_BALANCE``, + which, when activated, keeps adjusting the white balance. + +``V4L2_CID_RED_BALANCE`` ``(integer)`` + Red chroma balance. + +``V4L2_CID_BLUE_BALANCE`` ``(integer)`` + Blue chroma balance. + +``V4L2_CID_GAMMA`` ``(integer)`` + Gamma adjust. + +``V4L2_CID_WHITENESS`` ``(integer)`` + Whiteness for grey-scale devices. This is a synonym for + ``V4L2_CID_GAMMA``. This control is deprecated and should not be + used in new drivers and applications. + +``V4L2_CID_EXPOSURE`` ``(integer)`` + Exposure (cameras). [Unit?] + +``V4L2_CID_AUTOGAIN`` ``(boolean)`` + Automatic gain/exposure control. + +``V4L2_CID_GAIN`` ``(integer)`` + Gain control. + + Primarily used to control gain on e.g. TV tuners but also on + webcams. Most devices control only digital gain with this control + but on some this could include analogue gain as well. Devices that + recognise the difference between digital and analogue gain use + controls ``V4L2_CID_DIGITAL_GAIN`` and ``V4L2_CID_ANALOGUE_GAIN``. + +``V4L2_CID_HFLIP`` ``(boolean)`` + Mirror the picture horizontally. + +``V4L2_CID_VFLIP`` ``(boolean)`` + Mirror the picture vertically. + +.. _v4l2-power-line-frequency: + +``V4L2_CID_POWER_LINE_FREQUENCY`` ``(enum)`` + Enables a power line frequency filter to avoid flicker. Possible + values for ``enum v4l2_power_line_frequency`` are: + + ========================================== == + ``V4L2_CID_POWER_LINE_FREQUENCY_DISABLED`` 0 + ``V4L2_CID_POWER_LINE_FREQUENCY_50HZ`` 1 + ``V4L2_CID_POWER_LINE_FREQUENCY_60HZ`` 2 + ``V4L2_CID_POWER_LINE_FREQUENCY_AUTO`` 3 + ========================================== == + +``V4L2_CID_HUE_AUTO`` ``(boolean)`` + Enables automatic hue control by the device. The effect of setting + ``V4L2_CID_HUE`` while automatic hue control is enabled is + undefined, drivers should ignore such request. + +``V4L2_CID_WHITE_BALANCE_TEMPERATURE`` ``(integer)`` + This control specifies the white balance settings as a color + temperature in Kelvin. A driver should have a minimum of 2800 + (incandescent) to 6500 (daylight). For more information about color + temperature see + `Wikipedia <http://en.wikipedia.org/wiki/Color_temperature>`__. + +``V4L2_CID_SHARPNESS`` ``(integer)`` + Adjusts the sharpness filters in a camera. The minimum value + disables the filters, higher values give a sharper picture. + +``V4L2_CID_BACKLIGHT_COMPENSATION`` ``(integer)`` + Adjusts the backlight compensation in a camera. The minimum value + disables backlight compensation. + +``V4L2_CID_CHROMA_AGC`` ``(boolean)`` + Chroma automatic gain control. + +``V4L2_CID_CHROMA_GAIN`` ``(integer)`` + Adjusts the Chroma gain control (for use when chroma AGC is + disabled). + +``V4L2_CID_COLOR_KILLER`` ``(boolean)`` + Enable the color killer (i. e. force a black & white image in case + of a weak video signal). + +.. _v4l2-colorfx: + +``V4L2_CID_COLORFX`` ``(enum)`` + Selects a color effect. The following values are defined: + + + +.. tabularcolumns:: |p{5.7cm}|p{11.8cm}| + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 11 24 + + * - ``V4L2_COLORFX_NONE`` + - Color effect is disabled. + * - ``V4L2_COLORFX_ANTIQUE`` + - An aging (old photo) effect. + * - ``V4L2_COLORFX_ART_FREEZE`` + - Frost color effect. + * - ``V4L2_COLORFX_AQUA`` + - Water color, cool tone. + * - ``V4L2_COLORFX_BW`` + - Black and white. + * - ``V4L2_COLORFX_EMBOSS`` + - Emboss, the highlights and shadows replace light/dark boundaries + and low contrast areas are set to a gray background. + * - ``V4L2_COLORFX_GRASS_GREEN`` + - Grass green. + * - ``V4L2_COLORFX_NEGATIVE`` + - Negative. + * - ``V4L2_COLORFX_SEPIA`` + - Sepia tone. + * - ``V4L2_COLORFX_SKETCH`` + - Sketch. + * - ``V4L2_COLORFX_SKIN_WHITEN`` + - Skin whiten. + * - ``V4L2_COLORFX_SKY_BLUE`` + - Sky blue. + * - ``V4L2_COLORFX_SOLARIZATION`` + - Solarization, the image is partially reversed in tone, only color + values above or below a certain threshold are inverted. + * - ``V4L2_COLORFX_SILHOUETTE`` + - Silhouette (outline). + * - ``V4L2_COLORFX_VIVID`` + - Vivid colors. + * - ``V4L2_COLORFX_SET_CBCR`` + - The Cb and Cr chroma components are replaced by fixed coefficients + determined by ``V4L2_CID_COLORFX_CBCR`` control. + * - ``V4L2_COLORFX_SET_RGB`` + - The RGB components are replaced by the fixed RGB components determined + by ``V4L2_CID_COLORFX_RGB`` control. + + +``V4L2_CID_COLORFX_RGB`` ``(integer)`` + Determines the Red, Green, and Blue coefficients for + ``V4L2_COLORFX_SET_RGB`` color effect. + Bits [7:0] of the supplied 32 bit value are interpreted as Blue component, + bits [15:8] as Green component, bits [23:16] as Red component, and + bits [31:24] must be zero. + +``V4L2_CID_COLORFX_CBCR`` ``(integer)`` + Determines the Cb and Cr coefficients for ``V4L2_COLORFX_SET_CBCR`` + color effect. Bits [7:0] of the supplied 32 bit value are + interpreted as Cr component, bits [15:8] as Cb component and bits + [31:16] must be zero. + +``V4L2_CID_AUTOBRIGHTNESS`` ``(boolean)`` + Enable Automatic Brightness. + +``V4L2_CID_ROTATE`` ``(integer)`` + Rotates the image by specified angle. Common angles are 90, 270 and + 180. Rotating the image to 90 and 270 will reverse the height and + width of the display window. It is necessary to set the new height + and width of the picture using the + :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl according to the + rotation angle selected. + +``V4L2_CID_BG_COLOR`` ``(integer)`` + Sets the background color on the current output device. Background + color needs to be specified in the RGB24 format. The supplied 32 bit + value is interpreted as bits 0-7 Red color information, bits 8-15 + Green color information, bits 16-23 Blue color information and bits + 24-31 must be zero. + +``V4L2_CID_ILLUMINATORS_1 V4L2_CID_ILLUMINATORS_2`` ``(boolean)`` + Switch on or off the illuminator 1 or 2 of the device (usually a + microscope). + +``V4L2_CID_MIN_BUFFERS_FOR_CAPTURE`` ``(integer)`` + This is a read-only control that can be read by the application and + used as a hint to determine the number of CAPTURE buffers to pass to + REQBUFS. The value is the minimum number of CAPTURE buffers that is + necessary for hardware to work. + +``V4L2_CID_MIN_BUFFERS_FOR_OUTPUT`` ``(integer)`` + This is a read-only control that can be read by the application and + used as a hint to determine the number of OUTPUT buffers to pass to + REQBUFS. The value is the minimum number of OUTPUT buffers that is + necessary for hardware to work. + +.. _v4l2-alpha-component: + +``V4L2_CID_ALPHA_COMPONENT`` ``(integer)`` + Sets the alpha color component. When a capture device (or capture + queue of a mem-to-mem device) produces a frame format that includes + an alpha component (e.g. + :ref:`packed RGB image formats <pixfmt-rgb>`) and the alpha value + is not defined by the device or the mem-to-mem input data this + control lets you select the alpha component value of all pixels. + When an output device (or output queue of a mem-to-mem device) + consumes a frame format that doesn't include an alpha component and + the device supports alpha channel processing this control lets you + set the alpha component value of all pixels for further processing + in the device. + +``V4L2_CID_LASTP1`` + End of the predefined control IDs (currently + ``V4L2_CID_ALPHA_COMPONENT`` + 1). + +``V4L2_CID_PRIVATE_BASE`` + ID of the first custom (driver specific) control. Applications + depending on particular custom controls should check the driver name + and version, see :ref:`querycap`. + +Applications can enumerate the available controls with the +:ref:`VIDIOC_QUERYCTRL` and +:ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>` ioctls, get and set a +control value with the :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` and +:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctls. Drivers must implement +``VIDIOC_QUERYCTRL``, ``VIDIOC_G_CTRL`` and ``VIDIOC_S_CTRL`` when the +device has one or more controls, ``VIDIOC_QUERYMENU`` when it has one or +more menu type controls. + + +.. _enum_all_controls: + +Example: Enumerating all controls +================================= + +.. code-block:: c + + struct v4l2_queryctrl queryctrl; + struct v4l2_querymenu querymenu; + + static void enumerate_menu(__u32 id) + { + printf(" Menu items:\\n"); + + memset(&querymenu, 0, sizeof(querymenu)); + querymenu.id = id; + + for (querymenu.index = queryctrl.minimum; + querymenu.index <= queryctrl.maximum; + querymenu.index++) { + if (0 == ioctl(fd, VIDIOC_QUERYMENU, &querymenu)) { + printf(" %s\\n", querymenu.name); + } + } + } + + memset(&queryctrl, 0, sizeof(queryctrl)); + + queryctrl.id = V4L2_CTRL_FLAG_NEXT_CTRL; + while (0 == ioctl(fd, VIDIOC_QUERYCTRL, &queryctrl)) { + if (!(queryctrl.flags & V4L2_CTRL_FLAG_DISABLED)) { + printf("Control %s\\n", queryctrl.name); + + if (queryctrl.type == V4L2_CTRL_TYPE_MENU) + enumerate_menu(queryctrl.id); + } + + queryctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL; + } + if (errno != EINVAL) { + perror("VIDIOC_QUERYCTRL"); + exit(EXIT_FAILURE); + } + +Example: Enumerating all controls including compound controls +============================================================= + +.. code-block:: c + + struct v4l2_query_ext_ctrl query_ext_ctrl; + + memset(&query_ext_ctrl, 0, sizeof(query_ext_ctrl)); + + query_ext_ctrl.id = V4L2_CTRL_FLAG_NEXT_CTRL | V4L2_CTRL_FLAG_NEXT_COMPOUND; + while (0 == ioctl(fd, VIDIOC_QUERY_EXT_CTRL, &query_ext_ctrl)) { + if (!(query_ext_ctrl.flags & V4L2_CTRL_FLAG_DISABLED)) { + printf("Control %s\\n", query_ext_ctrl.name); + + if (query_ext_ctrl.type == V4L2_CTRL_TYPE_MENU) + enumerate_menu(query_ext_ctrl.id); + } + + query_ext_ctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL | V4L2_CTRL_FLAG_NEXT_COMPOUND; + } + if (errno != EINVAL) { + perror("VIDIOC_QUERY_EXT_CTRL"); + exit(EXIT_FAILURE); + } + +Example: Enumerating all user controls (old style) +================================================== + +.. code-block:: c + + + memset(&queryctrl, 0, sizeof(queryctrl)); + + for (queryctrl.id = V4L2_CID_BASE; + queryctrl.id < V4L2_CID_LASTP1; + queryctrl.id++) { + if (0 == ioctl(fd, VIDIOC_QUERYCTRL, &queryctrl)) { + if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) + continue; + + printf("Control %s\\n", queryctrl.name); + + if (queryctrl.type == V4L2_CTRL_TYPE_MENU) + enumerate_menu(queryctrl.id); + } else { + if (errno == EINVAL) + continue; + + perror("VIDIOC_QUERYCTRL"); + exit(EXIT_FAILURE); + } + } + + for (queryctrl.id = V4L2_CID_PRIVATE_BASE;; + queryctrl.id++) { + if (0 == ioctl(fd, VIDIOC_QUERYCTRL, &queryctrl)) { + if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) + continue; + + printf("Control %s\\n", queryctrl.name); + + if (queryctrl.type == V4L2_CTRL_TYPE_MENU) + enumerate_menu(queryctrl.id); + } else { + if (errno == EINVAL) + break; + + perror("VIDIOC_QUERYCTRL"); + exit(EXIT_FAILURE); + } + } + + +Example: Changing controls +========================== + +.. code-block:: c + + struct v4l2_queryctrl queryctrl; + struct v4l2_control control; + + memset(&queryctrl, 0, sizeof(queryctrl)); + queryctrl.id = V4L2_CID_BRIGHTNESS; + + if (-1 == ioctl(fd, VIDIOC_QUERYCTRL, &queryctrl)) { + if (errno != EINVAL) { + perror("VIDIOC_QUERYCTRL"); + exit(EXIT_FAILURE); + } else { + printf("V4L2_CID_BRIGHTNESS is not supported\n"); + } + } else if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) { + printf("V4L2_CID_BRIGHTNESS is not supported\n"); + } else { + memset(&control, 0, sizeof (control)); + control.id = V4L2_CID_BRIGHTNESS; + control.value = queryctrl.default_value; + + if (-1 == ioctl(fd, VIDIOC_S_CTRL, &control)) { + perror("VIDIOC_S_CTRL"); + exit(EXIT_FAILURE); + } + } + + memset(&control, 0, sizeof(control)); + control.id = V4L2_CID_CONTRAST; + + if (0 == ioctl(fd, VIDIOC_G_CTRL, &control)) { + control.value += 1; + + /* The driver may clamp the value or return ERANGE, ignored here */ + + if (-1 == ioctl(fd, VIDIOC_S_CTRL, &control) + && errno != ERANGE) { + perror("VIDIOC_S_CTRL"); + exit(EXIT_FAILURE); + } + /* Ignore if V4L2_CID_CONTRAST is unsupported */ + } else if (errno != EINVAL) { + perror("VIDIOC_G_CTRL"); + exit(EXIT_FAILURE); + } + + control.id = V4L2_CID_AUDIO_MUTE; + control.value = 1; /* silence */ + + /* Errors ignored */ + ioctl(fd, VIDIOC_S_CTRL, &control); + +.. [#f1] + The use of ``V4L2_CID_PRIVATE_BASE`` is problematic because different + drivers may use the same ``V4L2_CID_PRIVATE_BASE`` ID for different + controls. This makes it hard to programmatically set such controls + since the meaning of the control with that ID is driver dependent. In + order to resolve this drivers use unique IDs and the + ``V4L2_CID_PRIVATE_BASE`` IDs are mapped to those unique IDs by the + kernel. Consider these ``V4L2_CID_PRIVATE_BASE`` IDs as aliases to + the real IDs. + + Many applications today still use the ``V4L2_CID_PRIVATE_BASE`` IDs + instead of using :ref:`VIDIOC_QUERYCTRL` with + the ``V4L2_CTRL_FLAG_NEXT_CTRL`` flag to enumerate all IDs, so + support for ``V4L2_CID_PRIVATE_BASE`` is still around. |