Marlin Rowley wrote:
> 
>  I'm confused.  I've set up a rectangular region program that will draw 
>  a rectangle and dynamically size it when the user drags the mouse.  
>  This is going to be used for viewing only images within the window.  I 
>  want the pen to be bright red.  And I want it to be that way ALL the 
>  time!  For some reason, when I change the background color of my brush 
>  to something OTHER than black, I get a different color.  Why?

Is it really that confusing?  Notice:


>      def OnMotion(self,event):
>          if event.Dragging() and event.LeftIsDown():
>              # get device context of canvas
>              dc= wx.BufferedDC(wx.ClientDC(self),self.buffer)
>             
>              # Set logical function to XOR for rubberbanding
>              dc.SetLogicalFunction(wx.XOR)

That's the reason.  You are drawing with a red pen, but the logical 
function means that the color of the pen is XOR-ed with the color of the 
background.  When the background is black, the pixel value is 0, and 
anything XORed with 0 is itself.  When the background is not black, 
XORing with red simple inverts the red component in whatever color was 
there before.

This is absolutely normal behavior for rubber banding.  If you really 
want a red rubber band all of the time, then you can't use a simple 
erase-the-old and draw-the-new scheme for drawing the rubber band.  You 
will have to use some kind of double-buffered scheme, by keeping a copy 
of the background in a bitmap.  Then every time the rubber banding 
changes, you'll have to copy the virgin bitmap to the screen, then draw 
the rubber band on top of it.

-- 
Tim Roberts, timr@[...].com
Providenza & Boekelheide, Inc.

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