[mcclim-devel] incremental redisplay optimization(?)

[Duncan Rose]

On Friday, June 17, 2005, at 12:48  pm, Christophe Rhodes wrote:

> Hi,
>
> The new(ish) code for optimizing incremental redisplay by replaying
> move-overlapping and erase-overlapping records all at once is actually
> a huge pessimization for many disconnected records: I think that
> region-union is a precise operation, so the asymptotic complexity of
> the union operation is O(n^2), and I think the complexity of the
> replay is O(n^3).  Specifically, for my tablature editor, an operation
> which causes most records to be redraw takes 200 seconds with the
> current code, with most time (about 77%) being spent in BANDS-OP.
>
> The attached fixes the performance problem by being a little less
> precise.  Is it right?
>

Disclaimer: I'm not an incremental redisplay expert. Even less wrt the 
McCLIM incremental redisplay code. So I should probably be quiet on 
this ;-)  However...

Won't this potentially cause large parts of the output to be redrawn 
unnecessarily? For example:

+-------------------+
| A                 |   <- output record gets changed
+-------------------+
| B                 |
+-------------------+
| C                 |
+-------------------+
| D                 |
+-------------------+
     ...
+-------------------+
| X                 |   <- output record gets changed
+-------------------+

The bounding rect of the region union of output records A + X includes 
the bounds of the output records B - W (so they'll be redrawn I think).

Obviously this is a worst-case type scenario; I don't know if it's 
worth worrying about, just thought I'd throw it into the mixer.

-Duncan


> <ir.diff>
> Cheers,
>
> Christophe
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