Parameters for OS_swis in oslib/os.h library

[David J. Ruck]

On 04/02/2016 20:15, Chris Dewhurst wrote:
> Hi all,
>
> I am not much more than a beginner at the C language which may explain
> why I'm stuck on the following. Hope one of you can help.
>
> The StrongHelp for os_screen_mode (for example) says:
>
>     Declaration: extern void os_set_mode ( void );
>
>     Description: VDU command to change display mode - must be followed
> by 'mode' - prefer OS_ScreenMode

That's the old BBC Micro style way of changing the screen mode by 
sending bytes the VDU stream e.g. MODE 7 is VDU 22,7. In OS Lib the 
os_set_mode is the 22.

> So the start of my C program looks like:
>
>     #include "oslib/os.h
>     extern void osscreenmode_select ( void );

That's a completely different mechanism based on the SWI OS_ScreenMode 
and a mode description block, which you need to be able to select modern 
high resolution, high colour modes.

> My question is how do you "follow" the os_set_mode call with a 'mode'
> number? For instance, to change to Mode 7 where does the 7 go?

Mode 7 isn't supported on modern hardware. If you want an emulation, see 
my !GraphTask program which gives you BBC style graphics in a 
multi-tasking window.

https://armclub.org.uk/free/

> Incidentally when StrongHelp says "prefer OS_ScreenMode" there appears
> to be no reference to OS_ScreenMode, at least it isn't listed in the
> StrongHelp.

You need a more recent help file, or get yourself PRM5a.

Cheers
---David
-- 
Email: druck at druck.org.uk
Phone: +44-(0)7974 108301