I think TinyCore should boot into the same screen resolution and color depth independent whether it is booted via MBR or EFI.
As suggested by Juanito I tried:
if loadfont unicode ; then
set gfxmode=1024x768x16
set gfxpayload=keep
set gfxterm_font=unicode
terminal_output gfxterm
fi
menuentry "tc" {
linux /boot/vmlinuz64 loglevel=3 cde vga=791 video=vesafb:ywrap,mtrr=3
initrd /boot/corepure64.gz
}
and then:
if loadfont unicode ; then
set gfxmode=1024x768x16
set gfxpayload=1024x768x16
set gfxterm_font=unicode
terminal_output gfxterm
fi
menuentry "tc" {
linux /boot/vmlinuz64 loglevel=3 cde vga=791 video=vesafb:ywrap,mtrr=3
initrd /boot/corepure64.gz
}
both did not help.
However, if I set gfxpayload without color depth:
if loadfont unicode ; then
set gfxmode=1024x768x16
set gfxpayload=1024x768
set gfxterm_font=unicode
terminal_output gfxterm
fi
The resolution changes to 1024x768 but the color depth is still 32.