I wanna get some old art style (256 color, dithering, etc) in modern OpenGL in an effective way. Maybe using a low resolution (320x240) rendered at a bigger space so that the pixels looks "bigger?" I'd just like to fake this old style on modern GPUs.
To get pixelated look, you can use OpenGL's framebuffer functionality to render to texture (glFramebufferTexture2D etc.), then draw that texture as a rectangle with nearest-neighbour scaling.