VGA display, color for foreground and background for each character on screen

jasiek

Hey,

I've been going through the code for VGA_HiRes_Text and noticed that color configuration can be set for each row, rather than each character location.

What is this design decision dictated by?

I'm looking for a way to set the background and foreground color for each character.

Thanks,
J

zx81vga

Hi,

@jasiek

i think i can help you.

See attached ZIP-File

Greetings from Nuremberg, Germany

Werner

http://propeller.ws-nbg.de

zx81vga

Hi,

Sorry i forgot the ZIP-File

Greetings from Nuremberg, Germany

Werner

http://propeller.ws-nbg.de

jasiek

Thanks!

I'm still curious as to why this decision was made. Pragmatism or hardware constraints?

Mike Green

Hardware constraints. It takes extra video buffer space to hold the color information plus a color lookup table. The additional information in the video buffer and its decoding (to get 24 bits per pixel) really slows down the video generator code requiring either lower resolution or the use of more cogs to process more in parallel There's also only 32K for the video buffer (and code). If the buffer gets too big, you won't have much of a program to do any work other than drive the display

jasiek

Thanks!

Tubular

Kuroneko posted a series of VGA drivers that do per-cell color, including at quite high text resolutions, eg

http://forums.parallax.com/discussion/136666/fyi-vga-50xh-single-cog-per-cell-colour-despair-and-hope-release

potatohead

Yes, and those are pretty great. He found the hand off point where waitvid will pick up the pixel and color data. Linus actually stumbled on this way early on too. "look ma, no hands!"

That eliminates an entire instruction from the video loop, time for color and or resolution.



But, those drivers do need the 80Mhz clock. Others are clock variable. Just worth knowing, and I'm not making a negative statement.