From kde-devel  Wed May 31 14:26:00 2006
From: Jason Harris <kstars () 30doradus ! org>
Date: Wed, 31 May 2006 14:26:00 +0000
To: kde-devel
Subject: Re: Fwd: Re: seeking QGraphicsView wisdom
Message-Id: <200605310726.00183.kstars () 30doradus ! org>
X-MARC-Message: https://marc.info/?l=kde-devel&m=114908721105433

On Wednesday 31 May 2006 07:04, Andreas Aardal Hanssen wrote:
> On Wednesday 31 May 2006 15:45, Jason Harris wrote:
> > As long as the shapes are small compared to the radius of the sphere, you
> > can trivially use the local tangent plane to draw these shapes in the
>
> QPolygonF QGraphicsView::mapToScene(const QRect &rect) const
>
> How much sense does this make for a scene that operates in
> spherical coordinates?
>
It makes perfect sense.  So this function will map an input QRect (in the 
spherical coordinate system) to a QPolygonF in screen coordinates, right?  
That's easy.  Pseudocode for the override would look something like:

QPolygonF SphericalView::mapToScene( const QRect &rect ) 
{
    QPolygonF result;

    //The edges need to be composed of short 
    //line-segments to account for their curvature
    //SphericalView assumes that the input coordinates are in degrees.
    //line segments 1 degree long are sufficiently short.

    //Start at the bottom left corner, go around the perimeter 
    //counter-clockwise
    int x = rect.left();
    int y = rect.bottom();
    int s = 1
    while ( x < rect.right() )
        result << toScreen( x++, y );
    while ( y < rect.top() )    
        result << toScreen( x, y++ );
    while ( x > rect.left() )
        result << toScreen( x--, y );
    while ( y > rect.bottom() )    
        result << toScreen( x, y-- );

    return result;
}

Voila!

Jason

-- 
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