FBG – Lightweight C Linux framebuffer graphics with parallelism

Re:FBG – Lightweight C Linux framebuffer graphics with paral... by userbinator on Sunday June 17, 2018 @10:51PM (#17335699)

Without proprietary video card driver both Windows and Linux had troubles even scrolling a window, it was very laggy. Why was unaccelerated VGA (or VESA?) mode so slow, I wonder?

I haven't looked into the details on Linux but on Windows the "default" VESA/VGA mode uses the VGA BIOS, whose code is run in 16-bit VM86 mode:

https://wiki.osdev.org/Virtual_8086_Mode#Usage

http://nuclear.mutantstargoat.com/articles/pcmetal/pcmetal04...

The 16-bit code is not optimised for speed (is your framebuffer more than 64K? It's probably doing bankswitching and only copying 64K at a time), and the video BIOS itself may reside behind a slow serial interface on the GPU[1] --- so executing from it is very slow.

[1] https://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bu...

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Re:FBG – Lightweight C Linux framebuffer graphics with paral... by vsampath on Monday June 18, 2018 @12:42AM (#17336051)

On a modern system (Windows 7+, Linux wth GRUB 2.0 bootloader) all of the drawing is done without the VBIOS; the VBIOS is just used to set up the mode.

The VBIOS is a 16-bit x86 application, but it does not run on these systems in vm86; reason being that mode is not supported in 64-bit long mode.

When the VBIOS does execute, it never does from Flash. SBIOS copies into system memory first.

Source: I’ve worked on VBIOS

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