Name: krT82822 Date: 03/03/2000


(3 Mar 2000, eval1127@eng -- see also 4305614)

java version "1.3beta"
java(TM) 2 Runtime Environment, Standard Edition (build 1.3beta-0)
Java(TM) Hotspot Client VM (build 1.3beta-0, mixed mode)


Current RepaintManager policy for combining dirty regions within a single
component by simply taking the union of the rectangles can be very inefficient
in some cases.
In particular if the component is a JTable containing 50 rows and 40 columns and
the cause of dirty region is because the value in a cell has been updated.
Then for example if the cell 0,0 is updated and also the cell 49,39 is updated
at the same time then a requests to paint the rectangle covering cell 0,0 and a
seperate request to paint the rectangle covering cell 49,39 are generated and
combined by the RepaintManager into a dirty region which covers the entire
table!
Thus when the JTable receives the paintImmediately() call, it must repaint all
2000 cells instead of only the 2 cells which actually require it.

In a way this is a general performance issue, if I could repaint the whole 2000
cell Jtable in a small fraction of a second I could afford to ignore the
inefficiency of the RepaintManager algorithm.
However with columns set to 30 pixels wide (default 16 pixel height) under
Windows NT on a Compaq Deskpro EP series 6400 Pentium II 400Mhz it takes about
1.7 seconds for a single repaint of the whole 2000 cell JTable.
(Review ID: 99811)
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