Consider separating pixel resolution from framebuffer resolution

This might be useful if people want to write post-processing anti-aliasing filters, or have an effect produce an output that is higher resolution than the input pixel texture.

The issue names no files, tests, or entry points. Start by locating where pixel and framebuffer dimensions are represented and used in the rendering path, then define how separate input and output resolutions should behave and verify the result with a focused example or test.

Written by the indexing model from the issue text.