Adding Image Crosshairs

[bpseudopod-returns]

I always thought the built-in crosshair for Quakespasm and its forks was kind of janky. So, I put together a proof-of-concept for image-based crosshairs that I've implemented in my fork.

Screencast_20260528_223849.webm

Right now, it upgrades the crosshair cvar to display an image texture for the crosshair when it's set to either 1 or 2, being the options you can currently access through the options menu. I've added appropriate textures to ironwail.pak. The crosshair cvar has a bunch of undocumented features, which are all still intact, and if ironwail.pak isn't present it'll gracefully downgrade to the usual char-based crosshairs.

This is NOT ready for a PR yet, mostly due to scaling issues. The crosshair is affected by scr_pixelaspect, which means that when Options > Interface > Pixels is set to Stretched, the crosshair will be stretched too:

Plus, they're too big in general. Currently the image I'm using for the crosshairs is 32x32, which seems small enough, but I'm not quite sure what's the best method for making sure they're not so huge they cover up the game.

I'm not well-versed in OpenGL, and I haven't gotten too deep into the renderer, so I'm not sure how to fix these problems.

Does anyone have any pointers for potentially fixing the scaling issues? Or any ideas in general for how the crosshairs should look and feel?