切换到更高的分辨率

Question

Recently, I started developing an operating system in NASM and C. I have already made a boot loader, kernel, filesystem, etc. So far I used the VGA text mode directly in order to write to the address 0x000B8000 . So, I decided to switch to video mode instead of text mode. I chose maximal display resolution 320x200 , but then I realised that there are three problems. Firstly, there are only 256 different colors. Secondly, the resolution is too small. Thirdly, writing to the address 0x000A0000 is too slow. I tried to do some animations, but it is very laggy and sometimes it waits more than one second before the next frame.

I have searched on the internet for some explanations on how to switch to higher resolutions such as 1920x1080 and how to use 256*256*256 colors instead of just 256. Everything I found said that it is very hard to use higher resolutions because you must develop drivers for all the different types of graphics cards and for some cards there are no documentations, so we must use reverse engineering.

I really want to introduce high-resolution graphics to my operating system. Is it really hard or is there any easy method? Any suggestions on how I can solve this?

Answer 1

Nearly every graphics adapter supports VESA framebuffer semantics, you can configure almost every video mode with that. The drawback is that you cannot use vendor specific features (accelerated graphics etc.)

The VESA-Xserver for example works with almost any graphics adapter (but the model specific ones are considerably faster)

See also: https://en.wikipedia.org/wiki/VESA_BIOS_Extensions

Answer 2

You can do high res VESA graphics in assembly and it should be fast enough (in the beginning phase when you are learning and not doing very fancy 3d stuff, especially).

First of all, make sure you are using a good emulator/virtual machine for testing. I was using QEMU and it was way to slow to do any graphics at only 640x480x24bpp. I switched to VirtualBox and though it starts up quite slowly, I have never looked back.

As for the programming part, I encourage you to look at a project called Pure64. You can find it on GitHub. Go to src/init/isa.asm and look at the end of the file - there is some code to do VESA initializations. I am actually using Pure64 to set up a clean 64bit environment and I am doing VESA graphics so I can say that it works fine.

The VESA init consists of two parts - getting mode info and setting the video mode. Once you get the mode info, you get a Video Base Pointer to a region of memory which is continuous and where you can write your pixels without switching banks and doing complicated stuff. At least in 64-bit mode.

The only problem I had with this is that I could not make 32bpp mode working. I can do 24bpp, which is RRGGBB - 3 bytes per pixel (exactly like HTML/CSS color codes). As with everything that comprises of 3 bytes on a binary computer, this makes some things a bit more complex (at least for a beginner). Getting 4 bytes per pixel to work still eludes me. Maybe this is a limitation of VirtualBox or something.

This all means that for basic hi-res graphics there is no need to do a lot of hardware-specific things. If you are on a mildly current hardware, you should do fine.