Hey, I just learned how to use VGA mode (sooo SIMPLE!) and now I'm moving on up to VBE3 VESA mode, and I'm trying to print a whole mess of colors to the screen by incrementing the color value each time I go to a new pixel. Now, I can use the loop counter register CX for only WORD values, but the whole screen in even 640 x 480 mode goes beyond the 1 WORD limit (640 * 480 = 307200 decimal, 04B000 in hexadecimal). So after I tried that, I then tried creating my own DOUBLE WORD variable, and in the loop incremented it's value and compared it's value to the full amount of pixels on the screen. All that happens when I do that is that the screen just comes up black. If someone could help me here, I'd be very appreciative. Heres the code:



Thanks for your time!

-Rhyno

Also, I have another issue, if I try to go any higher than mode 101h (640 x 480 with 256 colors), it compiles okay but when I run it, my monitor puts up a message "Out of scan range" then below that "14.8kHz/154Hz".

i've programmed some demos a few years ago - http://asembler.republika.pl/bin/progsy.zip (comments and labels in polish - demos for directx, vesa banked and linear modes - from 320x200x8 to 640x480x24).

there are two vesa modes - banked and linear.

in 16- bit you can use only banked mode. why it's named banked? screen is divided into 64 kb parts called banks. you must switch to apropriate bank before drawing anything on screen.

in 32- bit (protected mode - you can use dpmi, pmodew, wdosx or other pmode servers) you can use linear framebuffer. but it uses paging to map video memory to system memory. it's much faster and imo it's easier to use.

i recommend you linear mode, but if you will be using banked mode don't forget about bank switching. afair it done like that:

I'll be doing this as a test for an OS GUI most likely, but how does accessing the linear framebuffer work? Is that what I'm doing in that program by accessing video memory directly?

in both modes you accesses video memory directly. the only difference is that in banked mode you can use only 16- bit addressing, while in linear mode you can use 32- bit addressing and you don't need to switch between banks (which is slow on moder gfx cards).

example of filling screen with color.

16- bit banked mode:


32- bit linear mode:

Thanks again, Donkey! I think I get it now... But I'm wondering, with my source code up there, how can I write to all of the screen the way I'm going? Or is it impossible because the loop counter and BX are both only limited to one word each?

This probably should have gone in the OS Construction area...

What I did is enable gate A20 and setup VESA mode with linear buffer bit set in 16 bit real mode, then switch to protected mode, this allows you to load the 32 bit video address pointer and use ecx to loop your drawing algorithm.

Enabling A20 means it uses linear buffer, as I learnt recently . Using protected mode you can also use larger screen resolutions easily (if you want).

HTH

Ah, I see! Thanks!