A Couple of questions on OGL Lineshapes

[Javier Cámara Moreno]

crjjrc escribió:
> On Jul 13, 5:19 am, jcam... at lcc.uma.es (Javier Cámara Moreno) wrote:
>
>   
>> I am developing a little graph editor using python 2.5 and wx 2.8.
>> Whenever I try to add text to a line shape I get a big rectangle on the
>> background which covers the shapes. Is there a way to render the text on
>> a transparent background?
>>     
>
> I think you're probably better of asking these questions in an OpenGL
> forum, like comp.graphics.api.opengl.
>
>   
First of all, thank you very much for your interest, Chris. I didn't 
mean OpenGL, maybe I should have specified the whole name. I was 
referring to the OGL (Object Graphics Library), provided with wx 
(wx.lib.ogl). The problem is specifically located in the LineShape 
class. When I try to add text I always get a background rectangle 
associated to the region of the line shape. I've seen several posts in 
forums describing the same problem (i.e., drawing the text on a 
transparent background) but haven't found any answers. I don't know if 
it is a bug or maybe there is a workaround to make that background 
transparent. Check out the following code snippet:
              
               ...
               line = ogl.LineShape()
               line.AddText('I want this text to be drawn on a 
transparent background')
               line.AddArrow(ogl.ARROW_ARROW,1,8,0.0,'',None,-1)
               line.SetBrush(wx.BLACK_BRUSH)
               line.MakeLineControlPoints(2)
               source.AddLine(line, target)
               self.canvas.AddShape(line)
               ...

 If there is anybody out there experienced with OGL, I'd appreciate very 
much a hint with this. Unfortunately, there isn't much documentation 
about the library, nor code samples to learn from (regarding this 
particular problem) available.

- Javier
> For bitmap or textured fonts, you're going to need to implement some
> blending and masking operations to get what you want, unless your
> images have alpha defined appropriately and you can use the alpha
> test.  Check out nehe.gamedev.net, lesson 20, for how to use masking
> and blending.  Or you can use vector fonts which are drawn using
> geometric primitives to construct each letter.
>
>   
>> The second thing is: If I am drawing a lineshape as an spline, control
>> points are fixed. Is there a way to update the position of this control
>> points when I move the shapes which are connected to the line?
>>     
>
> You provide the control points to build the spline.  Why not just
> provide the new control points to rebuild the spline?
>
> - Chris
>
>
>
>
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