Hello everyone, This patch-set introduces new ioctls to V4L2 API. The new method for configuration of cropping and composition is presented. There is some confusion in understanding of a cropping in current version of V4L2. For CAPTURE devices cropping refers to choosing only a part of input data stream and processing it and storing it in a memory buffer. The buffer is fully filled by data. It is not possible to choose only a part of a buffer for being updated by hardware. In case of OUTPUT devices, the whole content of a buffer is passed by hardware to output display. Cropping means selecting only a part of an output display/signal. It is not possible to choose only a part for a memory buffer to be processed. The overmentioned flaws in cropping API were discussed in post: http://article.gmane.org/gmane.linux.drivers.video-input-infrastructure/28945 A solution was proposed during brainstorming session in Warsaw. 1. Data structures. The structure v4l2_crop used by current API lacks any place for further extensions. Therefore new structure is proposed. struct v4l2_selection { u32 type; struct v4l2_rect r; u32 flags; u32 reserved[10]; }; Where, type - type of buffer queue: V4L2_BUF_TYPE_VIDEO_CAPTURE, V4L2_BUF_TYPE_VIDEO_OUTPUT, etc. r - selection rectangle flags - control over coordinates adjustments reserved - place for further extensions, adjust struct size to 64 bytes At first, the distinction between cropping and composing was stated. The cropping operation means choosing only part of input data bounding it by a cropping rectangle. All other data must be discarded. On the other hand, composing means pasting processed data into rectangular part of data sink. The sink may be output device, user buffer, etc. 2. Crop/Compose ioctl. Four new ioctls would be added to V4L2. Name VIDIOC_S_EXTCROP - set cropping rectangle on an input of a device Synopsis int ioctl(fd, VIDIOC_S_EXTCROP, struct v4l2_selection *s) Description: The ioctl is used to configure: - for input devices, a part of input data that is processed in hardware - for output devices, a part of a data buffer to be passed to hardware Drivers may adjust a cropping area. The adjustment can be controlled by v4l2_selection::flags. Please refer to Hints section. - an adjusted crop rectangle is returned in v4l2_selection::r Return value On success 0 is returned, on error -1 and the errno variable is set appropriately: ERANGE - failed to find a rectangle that satisfy all constraints EINVAL - incorrect buffer type, cropping not supported ----------------------------------------------------------------- Name VIDIOC_G_EXTCROP - get cropping rectangle on an input of a device Synopsis int ioctl(fd, VIDIOC_G_EXTCROP, struct v4l2_selection *s) Description: The ioctl is used to query: - for input devices, a part of input data that is processed in hardware - for output devices, a part of data buffer to be passed to hardware Return value On success 0 is returned, on error -1 and the errno variable is set appropriately: EINVAL - incorrect buffer type, cropping not supported ----------------------------------------------------------------- Name VIDIOC_S_COMPOSE - set destination rectangle on an output of a device Synopsis int ioctl(fd, VIDIOC_S_COMPOSE, struct v4l2_selection *s) Description: The ioctl is used to configure: - for input devices, a part of a data buffer that is filled by hardware - for output devices, a area on output device where image is inserted Drivers may adjust a composing area. The adjustment can be controlled by v4l2_selection::flags. Please refer to Hints section. - an adjusted composing rectangle is returned in v4l2_selection::r Return value On success 0 is returned, on error -1 and the errno variable is set appropriately: ERANGE - failed to find a rectangle that satisfy all constraints EINVAL - incorrect buffer type, composing not supported ----------------------------------------------------------------- Name VIDIOC_G_COMPOSE - get destination rectangle on an output of a device Synopsis int ioctl(fd, VIDIOC_G_COMPOSE, struct v4l2_selection *s) Description: The ioctl is used to query: - for input devices, a part of a data buffer that is filled by hardware - for output devices, a area on output device where image is inserted Return value On success 0 is returned, on error -1 and the errno variable is set appropriately: EINVAL - incorrect buffer type, composing not supported 3. Hints The v4l2_selection::flags field is used to give a driver a hint about coordinate adjustments. Below one can find the proposition of adjustment flags. The syntax is V4L2_SEL_{name}_{LE/GE}, where {name} refer to a field in struct v4l2_rect. The LE is abbreviation from "lesser or equal". It prevents the driver form increasing a parameter. In similar fashion GE means "greater or equal" and it disallows decreasing. Combining LE and GE flags prevents the driver from any adjustments of parameters. In such a manner, setting flags field to zero would give a driver a free hand in coordinate adjustment. #define V4L2_SEL_WIDTH_GE 0x00000001 #define V4L2_SEL_WIDTH_LE 0x00000002 #define V4L2_SEL_HEIGHT_GE 0x00000004 #define V4L2_SEL_HEIGHT_LE 0x00000008 #define V4L2_SEL_LEFT_GE 0x00000010 #define V4L2_SEL_LEFT_LE 0x00000020 #define V4L2_SEL_TOP_GE 0x00000040 #define V4L2_SEL_TOP_LE 0x00000080 #define V4L2_SEL_WIDTH_FIXED 0x00000003 #define V4L2_SEL_HEIGHT_FIXED 0x0000000c #define V4L2_SEL_LEFT_FIXED 0x00000030 #define V4L2_SEL_TOP_FIXED 0x000000c0 #define V4L2_SEL_FIXED 0x000000ff The hint flags may be useful in a following scenario. There is a sensor with a face detection functionality. An application receives information about a position of a face on sensor array. Assume that the camera pipeline is capable of an image scaling. The application is capable of obtaining a location of a face using V4L2 controls. The task it to grab only part of image that contains a face, and store it to a framebuffer at a fixed window. Therefore following constrains have to be satisfied: - the rectangle that contains a face must lay inside cropping area - hardware is allowed only to access area inside window on the framebuffer Both constraints could be satisfied with two ioctl calls. - VIDIOC_EXTCROP with flags field equal to V4L2_SEL_TOP_FIXED | V4L2_SEL_LEFT_FIXED | V4L2_SEL_WIDTH_GE | V4L2_SEL_HEIGHT_GE. - VIDIOC_COMPOSE with flags field equal to V4L2_SEL_TOP_FIXED | V4L2_SEL_LEFT_FIXED | V4L2_SEL_WIDTH_LE | V4L2_SEL_HEIGHT_LE Feel free to add a new flag if necessary. 4. Possible improvements and extensions. - combine composing and cropping ioctl into a single ioctl - add subpixel resolution * hardware is often capable of subpixel processing. The ioctl triple S_EXTCROP, S_SCALE, S_COMPOSE can be converted to S_EXTCROP and S_COMPOSE pair if a subpixel resolution is supported What it your opinion about proposed solutions? Looking for a reply, Best regards, Tomasz Stanislawski Tomasz Stanislawski (2): v4l: add support for extended crop/compose API v4l: simulate old crop API using extcrop/compose drivers/media/video/v4l2-compat-ioctl32.c | 4 + drivers/media/video/v4l2-ioctl.c | 102 +++++++++++++++++++++++++++-- include/linux/videodev2.h | 30 +++++++++ include/media/v4l2-ioctl.h | 8 ++ 4 files changed, 137 insertions(+), 7 deletions(-) -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
