----- Original Message ----- > On Mit, 2013-01-30 at 08:35 -0800, Jose Fonseca wrote: > > > > ----- Original Message ----- > > > On Mit, 2013-01-30 at 06:12 -0800, Jose Fonseca wrote: > > > > > > > > ----- Original Message ----- > > > > > On Mon, 2013-01-28 at 06:56 -0500, Adam Jackson wrote: > > > > > > I've been looking at untangling the pixel format code for > > > > > > big-endian. > > > > > > My current theory is that blindly byte-swapping values is > > > > > > just > > > > > > wrong. > > > > > > > > > > Certainly. :) I think you're discovering that this hasn't > > > > > really > > > > > been > > > > > thought through beyond what's necessary for things to work > > > > > with > > > > > little > > > > > endian CPU and GPU. Any code there is for dealing with big > > > > > endian > > > > > CPUs > > > > > has been bolted on as an afterthought. > > > > > > > > My memory is a bit fuzzy, but I thought that we decided that > > > > gallium > > > > formats were always defined in terms of little-endian, which is > > > > why > > > > all need to be byte-swapped. The state tracker was the one > > > > responsible > > > > to translate endian-neutral API formats into the non-neutral > > > > gallium > > > > ones. > > > > > > I know that was the suggested solution when this was discussed > > > previously, but I'm still not really convinced that cuts it. Just > > > for > > > one example, last time in > > > 864e97f3-352a-4fdb-9bb7-6d41a1969...@zimbra-prod-mbox-2.vmware.com > > > you > > > seemed to agree it doesn't make sense for vertex elements. > > > > I couldn't find it by id, but I think you mean: > > > > http://lists.freedesktop.org/archives/mesa-dev/2011-April/007109.html > > > > Yes, that's right. (I did say my memory was fuzzy :) > > Yeah, that's what I was referring to. > > > > > For another example (which I suspect is more relevant for this > > > thread), > > > wouldn't it be nice if the software rendering drivers could > > > directly > > > represent the window system renderbuffer format as a Gallium > > > format > > > in > > > all cases? > > > > I'm missing your point, could you give an example of where that's > > currently not possible? > > E.g. an XImage of depth 16, where the pixels are generally packed in > big > endian if the X server runs on a big endian machine. It's impossible > to > represent that with PIPE_FORMAT_*5*6*5_UNORM packed in little endian.
I see. Is this something that could be worked around? > > > I can't help feeling it would be better to treat endianness > > > explicitly > > > rather than implicitly in the format description, so drivers and > > > state > > > trackers could choose to use little/big/native/foreign endian > > > formats > > > as > > > appropriate for the hardware and APIs they're dealing with. > > > > What you mean by explicitly vs implicitly? Do you mean r5g6b5_be, > > r5g6b5_le, r32g32b32a32_unorm_le, r32g32b32a32_unorm_be, etc? > > Yeah, something like that, with the byte order only applying within > each > component for array formats. I don't oppose that. But it does seem a lot of work. How would hardware drivers handle this? Specially those that have a single LE/BE bit to choose? (BTW, I do believe we should unify Mesa format handling and Gallium's u_format module into a shared external helper library for formats before we venture into that though as the effort of doing that would pretty much double. I think it is also worth considering the other extreme: all formats are expected to be LE on LE platforms, BE on BE platforms. Is this feasible, or are there APIs that need (i.e, require) to handle both LE/BE formats? (Or hardware only capable of LE formats?) If not, would it be feasible to byte-swap at state tracker level? In short, in order to support BE platforms properly, there will be some pain regardless the approach we take. I really don't feel strongly about any approach -- just want a level of pain we (ie. the whole community) can sustain. Because if the "right thing" is onerous and few care I suspect this will quickly rot or never get completed. Jose _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
