4K & 64K ScreenModes in OS 5

Reminded by Sprow that KinoAmp was a little bit out of date in its screen depth support. I started to add support of 4K screen modes in KinoAmp.

Now, for the front end and for automatic screen mode selection, the problem is how to detect screen depths supported by a system:
- Standard OS_ScreenMode enumeration gives you log2bpp of screen depth, nothing more.
- OS_CheckModeValid doesn’t seem to reject invalid or unsupported NColour,ModeFlags,Log2Bpp combinations passed to mode descriptors.
- OS_ScreenMode12, subreason 3, which is used by Select to list available screen depths is not available on OS 5.

Is there another way for an application to find out available screen depths?

GraphicsV 8 will tell you valid bpp, I don’t think calling it directly is the officially supported way of finding the info though.

The correct way of doing it under RISC OS 5 is to use the OS_ScreenMode enumeration call – the format of the data it returns has been extended to allow the mode flags, Log2BPP and NColour to all be returned (luckily Acorn had the foresight to add a ‘block format’ field to the header). See here for details of block format 1.

OS_CheckModeValid doesn’t seem to reject invalid or unsupported NColour,ModeFlags,Log2Bpp combinations passed to mode descriptors.

That sounds like a bug – what machine & OS version is this, and what’s the mode descriptor you’re passing through?