How Can I Write to Framebuffer Without Using Graphics APIs?

If you're looking for something really low-level, consider managing your framebuffer entirely in software and then exposing it over a network protocol like VNC or RDP. This method is used in some robust emulators, like QEMU. It's really flexible and cross-platform since you can handle pixel display with a separate client program. All you'll need is to work with the socket API, which is quite uniform across major operating systems.

If you’re going the route of building your own OS, you'll need to access the GPU directly. That means dealing with port I/O to get the framebuffer address or configuring it if needed. This process can vary a bit depending on the GPU model. A great start would be to check out the source code for open source GPU drivers that don't use the VESA BIOS. That way, you can see how they handle framebuffer access.

You can absolutely do this! Just keep in mind that there’s usually some OS abstraction in between you and your screen—like an OS API and a device driver. You’ll probably need a window handle and an understanding of the video buffer structure that the OS uses. If you’re aiming for cross-platform compatibility, libraries like SDL, SFML, or Qt can provide a window buffer abstraction for you. Don't stress about it feeling like cheating; the real fun will come from implementing your geometry, rasterizer, and blit operations. So go for it!