2x zoom (pixelated)

OpenGL OpenGL: Basic Coding
1

So what do I do to make things 2x zoom? I’m using openGL and SDL.

2

I think a little more detail is needed than just “…2x zoom”.
Can you describe your sceanero and what you are trying to do?

3

By 2x pixellated zoom, I assume you mean you want a framebuffer that looks something like this:

 1  1  51 51  25  25
 1  1  51 51  25  25 
16 16  89 89  75  75
16 16  89 89  75  75

There are a number of ways. One being to render to a half-res corner of the window. Copy that off to a texture with glCopyTexImage2D, then render that back to the framebuffer at 2X size with a textured QUAD, with texture filtering set to GL_NEAREST.

Yet another way: render half-res to an off-screen texture via framebuffer object (FBO), then blit it to the window via glBlitFramebuffer, scaling to full res and with a filter arg of GL_NEAREST.