Re: [PyOpenGL-Users] extremely large screen capture]

[stephan) <mai...@sh...>]

Hi Rich,
As I understand it there are generally 3 approaches to this:
[]mesa off screen rendering
[]glReadPixels
[]pbuffers

glReadPixels seems to be the simplest and has the advantage of being
hardware accelarated but is also restricted to whatever max resolution
the opengl implemntation supports. This calls for tiled rendering as it
is described here:
http://www.mesa3d.org/brianp/TR.html

I did not have time yet to translate this code to python...should be
fairly easy though. It comes down to calling glViewport for each tile
and then patching the parts together with PIL.

If you go for the challenge (on a rainy sunday afternoon with a
delicious cup of darjeeling maybe) please be so kind and post the code
on this list.


stephan)


PS:
http://www.mesa3d.org/osmesa.html
http://www.mesa3d.org/pbuffers.html




Rich Drewes wrote:
> Hello,
> 
> I want to save a very large pyopengl scene to a snapshot file.  The 
> resolution I am trying for is 3200x2400.
> 
> The following code fragment, using PIL, works up to 1600x1200:
> 
> import Image
> ox, oy, width, height = glGetIntegerv(GL_VIEWPORT)
> print width, height, ox, oy
> glPixelStorei(GL_PACK_ALIGNMENT, 1)
> data = glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE)
> image = Image.fromstring("RGB", (width, height), data)
> image = image.transpose(Image.FLIP_TOP_BOTTOM)
> image.save("snap.png", "PNG")
> 
> However if I try to create my initial window at 3200x2400, like this:
> 
> glutInitWindowSize(3200, 2400)
> 
> two things happen.  First, the actual window that is created onscreen is
> only about 1600x1200 (minus a bit for window borders).  When I move around
> my 3D scene, it looks like OpenGL thinks that the scene really is larger
> than what the window is showing me (which is great) but I am only seeing
> part of it.  When I try to do the screen capture with the code above, the
> width and height reported by glGetIntegerv(GL_VIEWPORT) are 3200 and 2400.  
> That looks promising.  However, when I examine the resulting snap.png
> image, it only contains what appears to be the lower quadrant of my
> scene--the portion that was actually visible on screen.
> 
> Is there any simple way to capture an image larger than 1600x1200?  What
> is the resolution-limiting factor in my current approach?
> 
> Would I have to create 4 viewports of 1600x1200, each one showing part of
> the scene (with a different projection matrix but same model transform?)
> and same each as a separate image and then paste them together myself?  
> Does anyone have any suggestions for doing this seamlessly?
> 
> Thanks,
> Rich
> 
> 
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