[Kstars-devel] Problem with coordinate grid at high zoom

[Torsten Rahn]

> The problem really is in the QT QPainter::drawLine() code.
>
> Contrary to my earlier assumptions, it is incredibly slow when it has
> to clip lines to the borders of the window.  By simply increasing the
> point density of the coordinate grid by a factor of 4 I was able to
> reduce/eliminate the problem at the zoom level I was working at but
> (of course) it came back when I increased the zoom level.

Are you sure about this? Maybe it's just related to the drawing done 
differently if it exceeds the memory of the graphics card. Or it's related to 
rasterization time increasing with O(n log(n)).

http://trolltech.com/company/newsroom/events/allevents/devroadshow/presentations/qtrs06-effgraphicsprogramming

Page 30.

Anyways, I clip all QPainter::drawPolygon calls using my own QPainter class in 
Marble (it's called "ClipPainter" there and still has some issues though).

> would be a bit of a mess if we needed to interleave the screen clipping
> with the horizon clipping.  But we only need to do the screen clipping

Well, we also do that in Marble already.

BTW: Do you have any "before"-"after" figures available concerning your 
spatial index introduction in KStars? I'd be interested in introducing a 
spatial index for Marble as well, where/if it makes sense (at least for 
storing location data on the hard disk to save space for the marble 
distribution package). 

Torsten
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 Torsten Rahn

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