EH> Jasen Betts (3:640/350) schreef aan Eef Hartman op 19-Feb-99 om 19:23:

 JB> No it doesn't because the VGA doesn't work that way, it uses a 
 JB> bitplane scheme where each bit of addresses space addresses a single
 JB> pixel an allows writing to upto 4 bits of video ram....

 EH> That is another mode and I was not writing a "Programming the VGA" manual.
 EH> But then too you never can write/move all of the screen 
 EH> at once, because then too you run out of the 64 KB address space.

No. If you're using virtual screen like in Windows, it actually uses your Video
Ram to store each pixels and there is a command to move it all at once called
"vertical smooth scrolling". Windows '98 and advanced drivers for '95 uses it!
VERY good Pinball games also use it as well as Marble Madness.

 EH> I don't even think you can do "more then one pixel at a 
 EH> time" in this mode, as you're moving "more then one 
 EH> bit" to a bit address. But I'm not really an expert, so 
 EH> I might be wrong.

You can do a dma transfer either by using FILL command, by using the XMS
Transfer command to copy from CONV to CONV or by using the MOVE command.
If you use Turbo Pascal, then MOVE is the fastest, if you're using Borland
Pascal then using the XMS DMA Transfer assembly code is the fastest.
(BP uses all available XMS for your programs.. well it's a option!)

 EH> A third mode a lot of Svga cards have is to map ALL of 
 EH> the video memory into hi address space (above 16 MB, 
 EH> mostly, although some use the 15 to 16 M space). In 32-
 EH> mode (no 64 KB segments) you CAN then address of the 
 EH> video memory at the same time.

Old games uses the 15M-16M space but with the new computers with 128MB ram,
setting the BIOS to 15-16M state will cause it to report 64MB ram left..

In 16bit mode in BP, you can use the HEAP to also be able to write to the video
memory all at once without the 64K thing. But programming to fo that is a
little bit more complex..

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