[Qgis-developer] Clipping symbols

Magnus Homann magnus at homann.se
Tue Jan 8 16:44:20 EST 2008

In the rendering branch I'm trying to fix clipping of hard symbols 
(#705). Much of the confusion comes from the fact the pointSize does not 
determine a rectangular boundigbox, but instead specifies an area.

So, for a hard marker with pointSize=10, the area should be the same 
between circel, rectangle, diamond and triangle, with the circle as the 
determining symbol.

The interesting thing happens when you specifiy a diamond fitting into a 
10x10 box, and with the same areas as a circle with radius=5. Not so 
easy withou clipping!

And then there is the line width... :-)

Can we all agree that instead a symbol with pointSize=10 should render a 
circle with radius=5, a rectangel with side=10, a diamond with 
*diagonal*=10 and a triangle with base and height=10. They will then all 
have different areas.

The numbers above are including line width, so there will be no exact 
area scale.

(Hmm, I got a deja vu writing this. Tim, did we discuss this a couple of 
years back? Creepy...)


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