mrjbom wrote:
1. What's it? Is it VESA or SVGA or something else? What is the name of this mechanism?
Linear frame buffer. GRUB uses the firmware to configure the LFB, so it might use VBE or UGA or GOP depending on what's available.
mrjbom wrote:
2. What draws this graphic? Video card or processor?
The processor puts pixels into the buffer. The video card puts the buffer on the screen.
mrjbom wrote:
3. How universal is this method? On what systems will it work and on what not?
GRUB can set up a LFB on pretty much any PC GRUB can run on. On very old computers, the LFB won't be very nice, but it will be linear and it will be a frame buffer.
On any PC from the past 20 years, GRUB will be able to set up at least 800x600 with at least 15 bits per pixel (though firmware limitations may prevent you from getting exactly the mode you request).
mrjbom wrote:
4. I want to write a system of rendering 3D scenes, polygons, cubes. Something like OpenGL. Is this a good way to display graphics? Or should I choose something more powerful?
If you want to offload any of the 3D rendering work to the graphics card, you'll need to write a driver for it. Different graphics cards will require different drivers.