640x512x16bpp with VESA ?

Hello,

I have to use a 1280x1024 screen but there are too many pixels
to compute there. I think that a halved resolution would fit
but 1:1.25 ratio modes are very scarce. Practically, I use
the VESA2 framebuffer in ASM with my own bootloader so the
help of an operating system is useless, unless it gives me
correct parameters. Should I dump the registers after X.org
has set this mode ?

I guess that I have to setup 1280x1024x16 then tweak the CRTC
to "double scan" (so i get 1280x512). I have read books 12 years
ago about this but i don't remember the particularities of the X mode :-)
I have to half the clock speed too but it's above my ability now
(i don't have the books anymore). Hint : my graphics chip is based on S3.

My requirement is to conserve the 1:1.25 ratio of the screen
with practically fine values. If you know of other resolutions
that fit, fine, as long as I can set it with a simple asm program.

thanks,
YG (not been here for 8 years or so...)

.

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