Скачать или смотреть QuickBASIC VGA Mode Y Vertical Scrolling Demo

I used Mike Hawk's VGA Mode Y QuickBASIC code to make a demo showing that VGA can do vertical hardware scrolling in Mode X and Y.


The Video Graphics Array IBM PC standard has several screen modes in its BIOS that have different capabilities. For example, Mode 12h is a 640x480 16-colour planar square-pixel video mode that runs at 60hz (60 frames per second) where the entire screen is composed of 4 different arrays of bits, each one combining to provide 16 colours. Another VGA video mode is Mode 13h, a 320x200 256-colour packed-pixel video mode that runs at 70hz (70 frames per second) where each pixel is taller than it is wide, and is stored as a single byte each, and thus much easier to address in a program than in Mode 12h.


Some programmers were able to have their code write to VGA's registers directly to make Mode X, a 60hz 320x240 256-colour packed-square-pixel video mode that also has 3 pages, allowing to use video memory as a double-buffer where you draw to an invisible page and copy that invisible page to the visible page so that only the final result of each frame can be seen. Unfortunately, the pages are interleaved, so it takes quite a bit of maths to address each page separately.


However, it is also possible to tweak Mode 13h to make Mode Y, which is basically just Mode 13h with 4 (still interleaved) video pages. This combines the benefits of double-buffering with the faster 70hz frame rate. This also allows you to use hardware scrolling, which this QuickBASIC program demonstrates. Since this is done in hardware, it's pretty smooth since the CPU isn't moving 64,000 pixels around.



Mike Hawk's VGA Mode Y QuickBASIC page: https://qbmikehawk.neocities.org/arti...


The full source code to my demo:
https://1034co.neocities.org/hax/mody...


The reason why the video looks jerky is because this demo actually runs at the full 70 frames per second of VGA Mode Y and Mode 13h, which YouTube (as well as most modern monitors) doesn't support.



Video made with DOSBox and Olive Video Editor and FFMPEG.