[Mesa-dev] intel, dma-buf import and egl image external

[Eric Anholt]

Chad Versace <chad.versace at linux.intel.com> writes:

> On Mon, Mar 24, 2014 at 09:07:32AM +1000, Dave Airlie wrote:
>> On Sat, Mar 8, 2014 at 12:13 AM, Pohjolainen, Topi
>> <topi.pohjolainen at intel.com> wrote:
>> > On Mon, Mar 03, 2014 at 01:19:48PM +1000, Dave Airlie wrote:
>> >> There is a comment and two checks in the i965 dma-buf importer,
>> >>
>> >> * Images originating via EGL_EXT_image_dma_buf_import can be used only
>> >> * with GL_OES_EGL_image_external only.
>> >>
>> >> however I can't find any reference to this in the spec txt, and
>> >> removing the checks make my test app run fine using TEXTURE_2D.
>> >
>> > You are correct that there is nothing in the spec about this, but it also leaves
>> > it open for the driver to choose on which buffers it allows the external
>> > sampling.
>> > After quite a bit of debate on when/where it would be safe to use dma-buffers,
>> > it was decided that we simply allow dma-buffers for external sampling only -
>> > that extension already restricts the use for single-miplevel and read-only
>> > which is exactly what we wanted.
>> > The same time it wasn't clear what kind of sources we should allow for external
>> > sampling (besides dma), and hence we simply kept things as they were before -
>> > none other. Note that before the introduction of dma-buffers the image external
>> > extension wasn't enabled at all on i965.
>> >
>> 
>> This is a really bad idea, since it means you can't use dma-buf
>> imported things with standard shader programs, if I want to import a
>> dma-buf I shouldn't have to write specific shader programs or use
>> special bindings, unless the spec says so.
>
> Bringing your request to its logical conclusion...
>
>> Either the spec should be more restrictive, or the implementation
>> shouldn't have arbitrary differences from what other implementations
>> could do.
>
> ...leads to disaster.  It's naive to expect each implementation to support
> what other implementations *could*, or even *currently* do.
>
> Are you prepared to impelement support for these horrorshows?
>
> A. Import a YUV EGLImage backed by two dma_bufs (Y in the first, UV in
>    the second) as a GL_TEXTURE_EXTERNAL_OES and transparently handle the
>    YUV->RGB transcode in your shader code generator? Because, iirc, ARM's
>    EGL/GLES2 stack supports that for Chrome.
>
> B. Same idea as A, but support importing the image as a GL_TEXTURE_2D
>    and again transparently handle the YUV->RGB transcode. 
>    Because, for all we know, ARM's stack may support that too.

Ignore YUV for now.  YUV is the thing that image_external is for, with
all of its weird requirements and unspecifiedness and making your images
undefined on import.

What airlied wants (I think) and what I definitely want, is to import
normal ARGB dma_bufs and use them with GL_TEXTURE_2D.  I think we can do
this, and it's just a matter of making some solid tests to make sure
we're not screwing up sibling management, and that the offset/stride/etc
handling all works.
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