Re: Redisplay problems?

[Eli Zaretskii]

> From: Stefan Monnier <address@hidden>
> Cc: address@hidden,  address@hidden,  address@hidden,  address@hidden,  
> address@hidden
> Date: Fri, 21 Mar 2014 15:39:17 -0400
> 
> >> > If so, you have no other way but marking such frames "garbaged" when
> >> > they are deiconified.
> >> I highly doubt it.
> > How else can you redisplay a frame whose current glyph matrices fell
> > behind, while the frame was iconified?
> 
> While the frame is iconified, glyph matrices are not updated, so if some
> part of the frame is modified during this time, its `redisplay' bit will
> be set (and stay set), so after it gets deiconified, redisplay will know
> that the glyph matrices need to be updated.

Once again, redisplaying a set of windows needs (a) to compute their
desired matrices, and (b) compare them against the current matrices,
and deliver the differences to the glass.  The 'redisplay' flag takes
care of (a), but if there are no current matrices we can trust,
there's no way to perform (b).  Setting the frame's garbaged flag
tells Emacs that the current matrices are unreliable, and then it
bypasses the matrix comparison in (b), and simply redraws every screen
line in every window of the frame.