Re: [Linaro-mm-sig] [RFC] New dma_buf -> EGLImage EGL extension

Hey,

Bit late reply, hopefully not too late.

Op 30-08-12 16:00, Tom Cooksey schreef:

Hi All,

Over the last few months I've been working on & off with a few people from Linaro on a new EGL extension. The extension allows constructing an EGLImage from a (set of) dma_buf file descriptors, including support for multi-plane YUV. I envisage the primary use-case of this extension to be importing video frames from v4l2 into the EGL/GLES graphics driver to texture from. Originally the intent was to develop this as a Khronos-ratified extension. However, this is a little too platform-specific to be an officially sanctioned Khronos extension. It also goes against the general "EGLStream" direction the EGL working group is going in. As such, the general feeling was to make this an EXT "multi-vendor" extension with no official stamp of approval from Khronos. As this is no-longer intended to be a Khronos extension, I've re-written it to be a lot more Linux & dma_buf specific. It also allows me to circulate the extension more widely (I.e. To those outside Khronos membership).

ARM are implementing this extension for at least our Mali-T6xx driver and likely earlier drivers too. I am sending this e-mail to solicit feedback, both from other vendors who might implement this extension (Mesa3D?) and from potential users of the extension. However, any feedback is welcome. Please find the extension text as it currently stands below. There several open issues which I've proposed solutions for, but I'm not really happy with those proposals and hoped others could chip-in with better ideas. There are likely other issues I've not thought about which also need to be added and addressed.

Once there's a general consensus or if no-one's interested, I'll update the spec, move it out of Draft status and get it added to the Khronos registry, which includes assigning values for the new symbols.

Cheers,

Tom

---------8<---------

Name

EXT_image_dma_buf_import

Name Strings

EGL_EXT_image_dma_buf_import

Contributors

Jesse Barker
Rob Clark
Tom Cooksey

Contacts

Jesse Barker (jesse 'dot' barker 'at' linaro 'dot' org)
Tom Cooksey (tom 'dot' cooksey 'at' arm 'dot' com)

Status

DRAFT

Version

Version 3, August 16, 2012

Number

EGL Extension ???

Dependencies

EGL 1.2 is required.

EGL_KHR_image_base is required.

The EGL implementation must be running on a Linux kernel supporting the
dma_buf buffer sharing mechanism.

This extension is written against the wording of the EGL 1.2

Specification.

Overview

This extension allows creating an EGLImage from a Linux dma_buf file
descriptor or multiple file descriptors in the case of multi-plane YUV
images.

New Types

None

New Procedures and Functions

None

New Tokens

Accepted by the <target> parameter of eglCreateImageKHR:

    EGL_LINUX_DMA_BUF_EXT

Accepted as an attribute in the <attrib_list> parameter of
eglCreateImageKHR:

    EGL_LINUX_DRM_FOURCC_EXT
    EGL_DMA_BUF_PLANE0_FD_EXT
    EGL_DMA_BUF_PLANE0_OFFSET_EXT
    EGL_DMA_BUF_PLANE0_PITCH_EXT
    EGL_DMA_BUF_PLANE1_FD_EXT
    EGL_DMA_BUF_PLANE1_OFFSET_EXT
    EGL_DMA_BUF_PLANE1_PITCH_EXT
    EGL_DMA_BUF_PLANE2_FD_EXT
    EGL_DMA_BUF_PLANE2_OFFSET_EXT
    EGL_DMA_BUF_PLANE2_PITCH_EXT

You might want to add PLANE3 just in case someone wants to import a AYUV image.

Additions to Chapter 2 of the EGL 1.2 Specification (EGL Operation)

Add to section 2.5.1 "EGLImage Specification" (as defined by the
EGL_KHR_image_base specification), in the description of
eglCreateImageKHR:

"Values accepted for <target> are listed in Table aaa, below.

+-------------------------+--------------------------------------------+ | <target> | Notes | +-------------------------+--------------------------------------------+ | EGL_LINUX_DMA_BUF_EXT | Used for EGLImages imported from Linux | | | dma_buf file descriptors | +-------------------------+--------------------------------------------+ Table aaa. Legal values for eglCreateImageKHR <target> parameter

...

If <target> is EGL_LINUX_DMA_BUF_EXT, <dpy> must be a valid display,

<ctx> must be EGL_NO_CONTEXT, and <buffer> must be NULL, cast into the type EGLClientBuffer. The details of the image is specified by the attributes passed into eglCreateImageKHR. Required attributes and their values are as follows:

    * EGL_WIDTH & EGL_HEIGHT: The logical dimensions of the buffer in

pixels

    * EGL_LINUX_DRM_FOURCC_EXT: The pixel format of the buffer, as

specified by drm_fourcc.h and used as the pixel_format parameter of the drm_mode_fb_cmd2 ioctl.

    * EGL_DMA_BUF_PLANE0_FD_EXT: The dma_buf file descriptor of plane 0

of the image.

    * EGL_DMA_BUF_PLANE0_OFFSET_EXT: The offset from the start of the
      dma_buf of the first sample in plane 0, in bytes.

* EGL_DMA_BUF_PLANE0_PITCH_EXT: The number of bytes between the start of subsequent rows of samples in plane 0. May have special meaning for non-linear formats.

For images in an RGB color-space or those using a single-plane YUV

format, only the first plane's file descriptor, offset & pitch should be specified. For semi-planar YUV formats, the chroma samples are stored in plane 1 and for fully planar formats, U-samples are stored in plane 1 and V-samples are stored in plane 2. Planes 1 & 2 are specified by the following attributes, which have the same meanings as defined above for plane 0:

Nitpick, Y'CbCr not YUV.

How do you want to deal with the case where Y' and CbCr are different hardware buffers? Could some support for 2d arrays be added in case Y' and CbCr are separated into top/bottom fields? How are semi-planar/planar formats handled that have a different width/height for Y' and CbCr? (YUV420)

~Maarten