Ping On Fri, Apr 11, 2014 at 1:36 AM, Jason Ekstrand <[email protected]> wrote:
> On Fri, Apr 11, 2014 at 2:03 AM, Pekka Paalanen <[email protected]> > wrote: > >> On Thu, 10 Apr 2014 09:42:55 -0500 >> Jason Ekstrand <[email protected]> wrote: >> >> > On Thu, Apr 10, 2014 at 6:37 AM, Pekka Paalanen <[email protected]> >> wrote: >> > >> > > Hi Jason, >> > > >> > > thanks for working on this, it does seem very useful, practically a >> > > mandatory feature to support. >> > > >> > >> > Hi Pekka, >> > Yeah, I've been itching to knock this out for a while. Just finally got >> > around to it. Comments below. >> >> ... >> >> > > On Wed, 2 Apr 2014 09:48:29 -0500 >> > > Jason Ekstrand <[email protected]> wrote: >> > > >> > > > It's worth noting that there is one small backwards-compatability >> issue >> > > > here. Namely, if the client is built against protocol stubs from an >> > > > earlier version of libwayland but links against a library built >> against a >> > > > newer version, then all objects created by the client will report a >> > > version >> > > > of 1. This is because the old api uses >> wl_proxy_marshal_constructor in >> > > > wl_registry_bind so all objects will inherit the protocol version of >> > > > wl_display which is 1. The library the client linked against is >> aware of >> > > > the wl_proxy_version function but has no way of knowing that the >> library >> > > > does not. >> > > >> > > I was about to say that wl_registry_bind() does pass the version to >> > > wl_proxy_marshal_constructor, but that indeed is in the request >> > > arguments and not a mandatory argument. >> > > >> > > But wl_proxy_marshal_constructor() would still have all the >> information >> > > it needs, if we special-case wl_registry.bind inside it. Ugly, but I >> > > guess it'd work for wl_registry. Would that make the >> > > backward-compatibility issue go away? In all other cases you would >> take >> > > the version from the parent wl_proxy, which you always have available >> > > in wl_proxy_marshal_constructor(), and the versioned variant would not >> > > be needed? >> > > >> > >> > Yes, we could do that, and I considered it. However, it would only bump >> > the compatibility issue back to wl_proxy_marshal_constructor. Older >> code >> > that uses wl_proxy_create inside of wl_registry_bind is still in >> trouble. >> > I don't think it's a huge savings to just bump the compatibility issues >> > back to 1.3 rather than 1.4/1.5. In the long run, I don't think it's >> worth >> > the mess that we would create inside wl_proxy_marshal_constructor. >> >> Ok, I didn't even know to think that far back. Makes sense. >> >> > > But I guess it would still be broken on any other request that used >> the >> > > interfaceless format of new_id? >> > > >> > >> > Nope, that's not a problem. The wayland-scanner program doesn't >> actually >> > special case wl_registry_bind but interfaceless new_id's in general. >> > Anything else that specifies a new_id with no interface will hit the >> same >> > code-path and get wl_proxy_marshal_constructor_versioned. >> >> I meant if we special-case wl_registry.bind, then all other requests >> using interfaceless new_ids would still be in trouble. But yes, a moot >> point now. >> >> > > > One possible solution for this is to set the version of wl_display >> to >> > > zero >> > > > and use zero to mean "unversioned". Then, if a library wants to use >> > > > something that's not strictly backwards-compatable, it can check >> for zero >> > > > and use whatever it's non-versioned fallback is. >> > > >> > >> > Thoughts on this? ^^ >> >> Well... if you don't know the version, is there a difference between >> assuming it is 1, and knowning it is unknown and then assuming whatever? >> >> As I see it, the only benefit of knowing when you don't know, is that >> you could then explicitly assume a higher version than 1, and then die >> on a protocol error if you are wrong. I'm not sure if that is better >> than assuming 1 which will always work if the application only accepts >> that. >> > > There is a case where I would do something different on unknown vs. > version == 1. In fact, it's the exact came case that inspired me to > actually sit down and write this. The wl_surface.damage request, from the > perspective of EGL implementations, is completely broken on wl_surface > versions 2 and 3 (trying to fix it for 4). An EGL implementation could > check for unknown, 2, or 3 and just do wl_surface.damage(0, 0, INT32_MAX, > INT32_MAX) in both eglSwapBuffers and eglSwapBuffersWithDamageEXT to work > around this. Then, if the version is 2 or >= 4, they could just damage the > surface correctly. It's kind of a specific example and the only reason why > we care is because we broke stuff at wl_surface version 2 but it's an > example. > > --Jason > > >> It looks like a trade-off between an "unknown method" protocol error / >> events that never come, and the application complaining the server is >> too old, when things go wrong. >> >> I can't say. >> >> >> Thanks, >> pq >> > >
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