Help wanted on SIMPLE task

[Seth Manley]

>From some of my old wxWin 1.6x based code:

wxClientDC dc(this);
[...]
dc.SetLogicalFunction(wxINVERT);

-Seth
http://www.xmlworkbench.com



>From: Bengt Nilsson <bengt.nilsson11 at spray.se>
>Reply-To: wx-users at lists.wxwidgets.org
>To: wx-users at lists.wxwidgets.org
>Subject: Re: Help wanted on SIMPLE task
>Date: Sun, 4 Mar 2007 14:44:15 +0100
>
>Thanks for the extensive suggestions.
>I will try the inverted line first.
>However, I cannot find anything about "inverted" in the wx docs.
>How do I set it?
>
>4 mar 2007 kl. 14.34 skrev Stephan Rose:
>
>>On Sunday 04 March 2007 14:05, Bengt Nilsson wrote:
>>>Hi!
>>>
>>>I am very new to wx programming and I need help on a simple task.
>>>
>>>How do I make a simple selection dragbox (using e.g. OnMouseEvent )
>>>in a graphics window without destroying what's in it?
>>>
>>>I have the "Cross-Platform GUI Programming whith wxWidgets" book, and
>>>I think I have seen the source listing for the method there, but I
>>>just can't seem to find int.
>>>I have gone thru it several times and failed.
>>>
>>>I do not want to paint anything in the graphics window, I just want
>>>to make a flickering frame over the content to select an area to get
>>>input to a zooming in function.
>>>
>>>Extremely standard, apparently too simple to be demonstrated in
>>>wxWidgets samples, since I cannot find it there.
>>
>>There are multiple ways you can do this.
>>
>>First way is to draw all your stuff in your window to a backbuffer.  Then 
>>when
>>you go draw your selection box, first copy your backbuffer to your  
>>graphics
>>window and then draw your selection box.
>>
>>This way you always have a copy of your original data without the  
>>selection
>>box in it.
>>
>>That is the way I'd recommend it.
>>
>>The other way is to use inverted lines to draw your selection box.  Using 
>>that
>>method you do not need a backbuffer. An inverted line basically  draws 
>>itself
>>by inverting pixels instead of drawing itself in a set color.
>>
>>If you invert the pixel again, it goes back to its previous color.
>>
>>So basically it works like this:
>>
>>- Draw box with inverted line
>>- Mouse move
>>- Draw box *again* with inverted line on previous coordinates
>>- Draw new box now with inverted lines on new coordinates
>>
>>You basically draw the box twice each mouse move. Once to erase the  old 
>>box,
>>then again to draw the new box.
>>
>>This was a very popular technique in the DOS and early windows days  as it
>>requires very little CPU resources to implement.
>>
>>Drawback though is that it is easy to screw up. If your coordinates  get 
>>out of
>>sync for any reason you will end up with pixels that stay inverted  until 
>>you
>>redraw your entire view.
>>
>>Another way, this is how I do it, is to use hardware accelerated  drawing 
>>and
>>simply draw the entire view every frame. That requires OpenGL  though. I 
>>can
>>draw over 20,000 objects in less than 10ms on this system here so I  can
>>afford to redraw the entire view every frame. =)
>>
>>
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>
>
>
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