Re: mouse-drag-and-drop-region

[Stefan Monnier]

> This model is incomplete.  Emacs first tries to reuse (parts of) the
> current matrix, if that's possible given the information about what
> has changed since the last redisplay cycle.  It only generates a new
> ("desired") glyph matrix if the attempt to reuse the current one
> failed.
> In addition, AFAIR there are situations when only small portions of
> the desired matrix are generated.  When doing this, Emacs must be able
> to decide which parts don't need to be regenerated.

Right.  These are optimizations which would apply identically to the
other model, (where the "current matrix" would be the "desired matrix"
computed last time, rather than the "combined matrix" computed last
time).

> If you are thinking about reviewing the existing optimizations and
> changing them to account for the new model, including adding some new
> optimization methods, then I'm sure it's possible.  But it's a large
> job, and I cannot promise that the result will be acceptable,
> performance-wise, unless very deep changes are done in the control and
> logic flow of the current code.

Indeed.  I'm pretty sure it can be done with good enough performance,
but I do not know how much work it would take.


        Stefan