[Qgis-developer] Patch for screen updates during long rendering operations

[Tom Elwertowski]

Hi Marco,

The WMS resize optimization doesn't work on a Mac. When I resize a WMS 
layer, the image is repeatedly fetched and the window slowly grows by 
one pixel increments. The problem doesn't happen on Ubuntu. When I 
resize the same layer there, the intermediate redraws are skipped.

One improvement is that newer redraws no longer interrupt the draw in 
progress so the screen corruption during resizing is gone.

I will look for the cause of the extra redraws sometime in the next few 
days.

Another difference is that if I maximize the window on a Mac with 
incremental update enabled, the window resize does not happen until 
after the redraw. First the map view grows and the maximized map is 
incrementally rendered while the full view is not visible. Only at the 
end does the window expand and the map becomes fully visible without 
additional redrawing. On Ubuntu, it works more as expected. The window 
expands first and then the map is incrementally rendered into the 
enlarged and fully visible view.

Tom