On Tue, Jan 09, 2018 at 02:53:22PM +0100, Maxime Ripard wrote: > On Tue, Jan 09, 2018 at 01:32:41PM +0100, Daniel Vetter wrote: > > On Tue, Jan 09, 2018 at 11:56:25AM +0100, Maxime Ripard wrote: > > > Some drivers duplicate the logic to create a property to store a per-plane > > > alpha. > > > > > > Let's create a helper in order to move that to the core. > > > > > > Cc: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> > > > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > > > Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> > > > > Do we have userspace for this? > > Wayland seems to be on its way to implement this, with ChromeOS using > it: > https://lists.freedesktop.org/archives/wayland-devel/2017-August/034741.html > > and more specifically: > https://chromium.googlesource.com/chromium/src/+/master/third_party/wayland-protocols/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml#118 Yay, would be good to include these links in the patch description. Really happy we're having a real standard now used by multiple people. > > Is encoding a fixed 0-255 range really the best idea? > > I don't really know, is there hardware or formats where there is more > than 255? Or did you mean less than that? 30bit I'd assume wants more alpha. In the past we've done some fixed-point stuff (e.g. for LUT), using the 0.0-1.0 float range. Using that for the blend equation docs is also what I recommend (and that we map from 0-255 to 0.0-1.0 logically). Ofc the hw might not do any of that ... I think 0.16 fixed point, stored in a u16 is probably best. That's what we're doing for gamma tables already, and that way drivers can simply throw away the lower bits. > > I know other drivers have skimped on the rules here a bit ... But at least > > internally (i.e. within the drm_plane_state) we probably should restrict > > ourselves to u8. And this needs real docs (i.e. the full blend equation > > drivers are supposed to implement). > > You mean straight vs premultiplied? Maybe we should implement this as > an additional property in read only depending on how the hardware > behaves? No need for an additional property right now, but definitely document whether you mean straight or pre-multiplied. Just writing down the blend equation is probably best. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
