[wxPython-users] select object by box in PseudoDC

[Christopher Barker]

Martin Landa wrote:
> maybe a silly question, but anyway. I am trying to select ids of
> objects in PseudoDC by box (rectangle bounding box). Is there any way
> how to do it? I am trying to use FindObjects() or
> FindObjectsByBBox()...

wx.DCs don't have any thing like this. It's up to you to keep track of 
what you've drawn. I suppose PseudoDC could add this feature, but as 
you've noticed, it doesn't appear to.

There are a number of ways of doing it. in wx.lib.floatcanvas, I set it 
up so that an extra bitmap is kept in memory in which you draw the 
objects you want to find, each in a different color. checking the color 
of pixel tells you which object is hit. This creates some overhead when 
drawing, but is lightning fast when doing the hit-testing. However, this 
approach doesn't allow you to find multiple overlapping objects.

It wouldn't be that hard to just store the Bounding Boxes of all your 
objects and search that list. If you have a LOT, and need to search 
fast, you might need a spatial index (quad tree, B-tree, etc).

wx.GraphicsContext has methods for checking the bounding box of objects. 
It might be nice to make a PseudoDC that uses that -- for better drawing 
as well.

Good luck!

-Chris



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