This patch proposes a RFC design to handle blending of various framebuffers with different color spaces, using the DRM color properties.
Signed-off-by: Shashank Sharma shashank.sharma@intel.com --- drivers/gpu/drm/rfc-design-blending.txt | 52 +++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) create mode 100644 drivers/gpu/drm/rfc-design-blending.txt
diff --git a/drivers/gpu/drm/rfc-design-blending.txt b/drivers/gpu/drm/rfc-design-blending.txt new file mode 100644 index 0000000..55d96e9 --- /dev/null +++ b/drivers/gpu/drm/rfc-design-blending.txt @@ -0,0 +1,52 @@ +Hi all, + +I wanted to send this design in a separate thread, but then I realized we can use this thread itself as many of the +stakeholders are already active here. + +As you all know, we will be dealing with the complex situations of blending of two(or more) different buffers +in the pipeline, which are in different format and different color space. +(PS: This ascii block design is best visible in a widescreen monitor, or in HTML page) + +===================================================================================================================================================== + + property 1 = CSC property 2 = Degamma property 3 = Gamut property 4 = palette + +------------------+ +-------------------+ +------------------+ +-------------------+ RGB REC 2020 buffer +YUV |color space | |Linearizion | |Gamut mapping | |Non-Linearizion +-------------------+ +REC709--> |conversion +------->+(Degamma) +----->+(REC709->REC2020) +-------+(Gamma) | | + |(YUV->RGB) | | | | | | | +------v---------------+ + +------------------+ +-------------------+ +------------------+ +-------------------+ | | + | | + | Blending unit | + | |------> blended output +RGB REC 2020 buffer (Bypass everything) | | + +---------------------------------------------------------------------------------------------------------------------> | | + | | + +----------------------+ +===================================================================================================================================================== + +This is a design proposal of a blending pipeline, using a sequence of plane level DRM properties. +The description of the block is: +- Input buffers are two different streams for example + - YCBCR buffer in REC709 colorspace + - RGB buffer in BT2020 colorspace +- Aim is to make bending accurate by providing similar input to the blending unit (same in format as well as color space). +- Every block here represents a plane level DRM property, with specific task to do. + - first block is CSC property, which is for conversion from YCBCR->RGB only (This doesnt do gamut mapping) + - second block is the property which will linearize the input, a degamma kind of property + - third block is a Gamut mapping proprty, which will do a gamut conversion (ex 709->2020) + - forth block is a Non-Linearizion block, which will apply back the curve (like Gamma) required + - The output of this pipeline is a RGB buffer in REC2020 color space + - Any driver can map its HW's plane level color correction capabilities to these properties. + - Once blending is done, driver can apply any post blending CRTC level color property, to: + - Change output type (ex. changing RGB->YUV using CRTC level CSC property) + - Apply a curve on the blended output (using CRTC level gamma/LUT property) + +- Important points: + - The sequence of the properties has to be fixed (almost in this order), considering the linear data requirement of Gamut mapping + - The color space of blending needs to be decided in the userspace, by UI manager, with some policies like (examples): + - If any of the buffer is REC2020, all buffers should be converted into 2020, before blending. + - Always blend in Higher/Wider color space. + - Always blend in RGB. + +- Opens: + - Is there a need to communicate HW's capabilities to UI manager/userspace ?