The steps involved are the following:
- Render the scene to a high-resolution texture.
- Compute the log-average luminance (on the CPU).
- Render a screen-filling quad to execute the fragment shader for each screen pixel. In the fragment shader, read from the texture created in step 1, apply the tone mapping operator, and send the results to the screen.
To get set up, create a high-res texture (using GL_RGB32F or a similar format) attached to a framebuffer with a depth attachment. Set up your fragment shader with a uniform to select the pass. The vertex shader can simply pass through the position and normal in eye coordinates.
