Optimize ScreenResources::{enabled_crtcs, crtc}

[Erk-]

ScreenResources::enabled_crtcs: This method would cause a unnecessary allocation through ScreenResources::crtcs.

ScreenResources::crtc: This would call Crtc::from_xid on all XId's this would cause a massive amount of spam in the Xorg log files. This will now only instantiate the Crtc that is asked for.

[Rintse]

Good changes, avoiding the collect() step from crtcs() in enabled_crts() is very much desired.

Your change to crtc() has made me think though:
Why is this function even a method of ScreenResources?
I think it originally must have been to mirror the call signature of libxrandr's XRRGetCrtcInfo(), which is provided a ScreenResources and an XID to obtain the Crtc info.

Perhaps it would be nice to check whether the XID requested is actually part of the ScreenResources instance we call crtc() on.

Your thoughts?

[Erk-]

Perhaps it would be nice to check whether the XID requested is actually part of the ScreenResources instance we call crtc() on.

I have added that.

Why is this function even a method of ScreenResources?

Yeah I thought the same, though I attempted to not introduce any breaking changes in this pr, though it could be something to look into in the future.

[Rintse]

Sorry this issue has turned out to reveal a major oversight.

I looked into the libxrandr source and found the source of the confusion here.
There is a field of XRRScreenResources that is used in XRRGetCrtcInfo(): the timestamp.

This crate therefore should also make sure that this timestamp is properly passed to the XRRGetCrtcInfo() call.
The way to do this is not throw away the raw pointer ptr in the screenresources handle and pass it into the GetCrtcInfo call, rather than allocating a new handle like I do now.

Perhaps it is best if I fix this first, and then we continue with this PR.