How to use GLUT/OpenGL to render to a file?

Question

I have a program which simulates a physical system that changes over time. I want to, at predetermined intervals (say every 10 seconds) output a visualization of the state of the simulation to a file. I want to do it in such a way that it is easy to "turn the visualization off" and not output the visualization at all.

I am looking at OpenGL and GLUT as graphics tools to do the visualization. However the problem seems to be that first of all, it looks like it only outputs to a window and can't output to a file. Second, in order to generate the visualization you have to call GLUTMainLoop and that stops the execution of the main function - the only functions that get called from then on are calls from the GUI. However I do not want this to be a GUI based application - I want it to just be an application that you run from the command line, and it generates a series of images. Is there a way to do this in GLUT/OpenGL? Or is OpenGL the wrong tool for this completely and I should use something else

Answer 1

Not sure OpenGL is the best solution.
But you can always render to an off-screen buffer.

The typical way to write openGL output to a file is to use readPixels to copy the resulting scene pixel-pixel to an image file

Answer 2

You almost certainly don't want GLUT, regardless. Your requirements don't fit what it's intended to do (and even when your requirements do fit its intended purpose, you usually don't want it anyway).

You can use OpenGL. To generate output in a file, you basically set up OpenGL to render to a texture, and then read the resulting texture into main memory and save it to a file. At least on some systems (e.g., Windows), I'm pretty sure you'll still have to create a window and associate the rendering context with the window, though it will probably be fine if the window is always hidden.

Answer 3

You could use SFML http://www.sfml-dev.org/. You can use the image class to save your rendered output.

http://www.sfml-dev.org/documentation/1.6/classsf_1_1Image.htm

To get your rendered output, you can render to a texture or copy your screen.

Rendering to a texture:

• http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=36
• http://zavie.free.fr/opengl/index.html.en#rendertotexture

Copying screen output:

• http://eonstrife.wordpress.com/2007/06/02/taking-a-screenshot-from-an-opengl-application/