[PyOpenGL-Users] Drawing a bitmap at "native" resolution

[Christopher B. <Chr...@no...>]

Hi folks,

Anyone know of a performant way to draw a bitmap at its "native" 
resolution -- i.e. one pixel in the bitmap is one pixel on screen, 
regardless of zoom level, etc. I think I've heard this referred to as 
"billboard" view, but that may be a term specific to one visualization 
lib (VTK, maybe)?

Anyway, the task at hand is using bitmaps fonts as textures to do simple 
text labels, lot of them, in a scientific visualization app.

For each data point ( up to 100s of thousands ) we need a little text 
label. But we want the text to not change size as the user zooms in or out.

Our current solution is something like this:

Each label is a texture (actually, I think a piece of a big texture).

When rendering, we calculate where the corners of the label should be in 
world coordinates, so that it scales to one pixel per pixel. This does 
produce the desired result.

The problem with this is that with each draw call, those coordinates 
need to be re-calculated. This can be pretty slow, particularly in 
python. We've got numpy doing it now, but that requires some pretty big 
arrays of coordinates to be kept around, which take up memory, and is 
still a bit pokey.

Is there any way to do this directly in OpenGL?

Or, if not, it seems that we may be able to use a shader to do that 
coordinate calculation -- should that be doable? I have no idea where to 
even start with that.

(this a 2D app, but I think the principle is the same either way)

Any suggestions would be appreciated.

-Chris







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Christopher Barker, Ph.D.
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Chr...@no...