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timbuk2

OpenGL creating offscreen OpenGL

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timbuk2    122
Hi all, Does anyone know if/ how i can create an OpenGL world offscreen, i.e. without creating a window. I want to set up some kind of rendering engine in the background of my application where i can grab bitmaps from it every now and again but don''t want to see it on the screen. I have possible found two methods, one using P-Buffers, the other to set the PIXELFORMATDESCRIPTOR to draw PFD_DRAW_TO_BITMAP instead of PFD_DRAW_TO_WINDOW. Have any of you had any experience doing what I''m attempting, Hopefully someone can point me in the right direction, many thanx - Tim

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Brother Bob    10344
If performance is not important I strongly reccomend Mesa, or more precisely OSMesa (Off Screen Mesa). If can render directly into your own allocated frame buffer. Like this.

  
GLubyte *frameBuffer = new GLubyte[witdh*height*4];

OSMesaContext OSRC;

OSRC = OSMesaCreateContextExt(OSMESA_RGB, 16, 0, 0, 0);
OSMesaMakeCurrent(OSRC, frameBuffer, GL_UNSIGNED_BYTE, width, height)

// OpenGL code here

glFinish();

OSMesaDestroyContext(OSRC);

After the rendering context is destroyed, frameBuffer contains the image you just rendered.

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timbuk2    122
I would quite like it to be efficient, if anyone else has another method I would like to know. i will definately look into Mesa for the moment, thanx Brother Bob!!

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63616C68h    122
Read about the many subsets of buffers withen the array of the "Frame Buffer." The color buffer itself contains sometimes 4 sub-buffers: right and left ("stereo"), and back and front buffering. And they're meant to do exactly that, buffer. Ever hear of double-buffering? That's using both the front and back buffers and having a buffered frame ready to go. Here are free online books written by the geniuses at SGI who made da shit(OpenGL): Here's an OpenGL reference . But I don't think this is the part of the site that I was referring to. Still will help you. Does anybody know the link to the "Red Book" and the "Blue Book?"

[edited by - 63616C68h on March 8, 2003 10:34:16 AM]

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