Mail Archives: djgpp/1999/11/23/10:05:10
Eli Zaretskii writes:
> If your BIOS supports text output in the graphics
> mode you are using, it will work.
Yup. But in my experience only about 50% of VESA implementations have
that support, so it is a bad thing to rely on.
> One way of telling if the particular mode is supported by the BIOS is
> to call the DJGPP functions ScreenRows() and ScreenCols() and compare
> their results with the number of text rows and columns for the
> graphics mode you switched into (which you need to know in advance).
I think it would be more robust to read this directly from the VESA
driver: this can be found in the mode information structure, where
the ModeAttributes field will have bit 2 set if TTY output is available.
As a quick test, run the Allegro "vesainfo -v" program, and see whether
it prints "tty" as part of the ModeAttributes value for the resolution
you are interested in.
Shawn Hargreaves.
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