[Mesa-dev] 10-bit fbconfigs break most video players using VAAPI+GLX

[Michel Dänzer]

On 2019-02-05 11:30 p.m., Marek Olšák wrote:
> Hi,
> 
> Video players request fbconfigs with these attributes:
> GLX_RED_SIZE = 8
> GLX_GREEN_SIZE = 8
> GLX_BLUE_SIZE = 8
> GLX_ALPHA_SIZE = 0
> 
> Note that the values specify MINIMUM required component sizes, not exact
> sizes. 10-10-10-2 satisfies the requirement and therefore glXChooseFBConfig
> returns it first. Then video players choose the first config.
> 
> There are many video players that have this issue. I guess they copied the
> same code from each other.
> 
> If we expose 10-bit or 16-bit formats, a lot of software will be broken.
> Any ideas how to get out of this rabbit hole?
> 
> My suggestion is to change the behavior of glXChooseFBConfig to return
> 8-8-8 or 8-8-8-8 first if they satisfy the attributes and ignore the spec.

Deliberately violating the spec and diverging from other GL(X)
implementations sounds like a bad idea to me.

We should help getting broken code fixed by identifying it and making
suggestions.


For code using glXChooseFBConfig, unless I'm missing something, a
water-tight way to get a config which exactly matches a specific format
is to specify all of GLX_RED/GREEN/BLUE/ALPHA_SIZE corresponding to each
component's size, and GLX_BUFFER_SIZE corresponding to the sum of all
sizes. The former and the latter have opposing sort orders, so only a
single combination of R/G/B/A sizes should match all five of them.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer