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

[Jason Harris]

Hi James,

On Sunday 02 September 2007 09:51:44 am James Bowlin wrote:
> > More information on this: it does not lock up if antialiased drawing
> > is off.  
>
> H'mm.  This is even more strange.  

I diffed the contents of drawLinesFloat() and drawLinesInt(), thee are the 
only substantial differences:

<      psky.drawLine( oLast, oThis );
>      psky.drawLine( oLast.x(), oLast.y(), oThis.x(), oThis.y() );

<      psky.drawLine( oLast, oMid );
>      psky.drawLine( oLast.x(), oLast.y(), oMid.x(), oMid.y() );

<      psky.drawLine( oMid, oThis );
>      psky.drawLine( oMid.x(), oMid.y(), oThis.x(), oThis.y() );

(drawLinesFloat() actually uses toScreenI() and doClipI(), so the float 
versions of those functions can't be the bottleneck).

I really don't think the difference between antialiased and aliased drawing 
can explain the lock-up I'm seeing.  So, on a whim, I modified 
NoPrecessIndex::draw() so that it always calls drawLinesInt():

    if ( skyMesh()->isZoomedIn() ) {
        if ( Options::useAntialias() )
            //DEBUG
            //drawLinesFloat( kstars, psky, scale );
            drawLinesInt( kstars, psky, scale );
        else
            drawLinesInt( kstars, psky, scale );
    }

*Even with this change*, KStars will lock up if all of the following are true
+ high zoom level
+ Coordinate grid is active in toolbar
+ antialiased checkbox checked

So the bottleneck seems to have nothing to do with the actual draw routine, 
since it is now calling drawLinesInt() no matter what useAntialias() is set 
to.   It's possible that I am missing some logic that would cause 
drawLinesFloat() to be called despite the above change, but I can actually 
confirm that the coordinate grid does not call drawLinesFloat(), because I 
have a debug line in drawLinesFloat() that is only triggered if the "this" 
pointer is the coordinate grid.

My current guess is that the problem is in the update routines, not the 
drawing.  Perhaps antialiasing triggers different code for the updates?

Jason