Detection of Amiga RTG Modes

TOPIC

This article explains how third-party apps running in AmigaOS within Amiga Forever can tell the difference between native Amiga screen modes and RTG modes.

DISCUSSION

Within Amiga Forever configurations like "Amiga 4000 Enhanced 3.X", RTG (retargetable graphics) screen modes are used to provide modern display resolutions that can be significantly higher than those of the original Amiga modes. Unlike Amiga modes, RTG screens use "chunky" (rather than "planar") bitmaps, which cannot be accessed by the Amiga custom chips. For these reasons, applications may need to be able to recognize RTG modes if they process bitmaps directly.

Because the set of native Amiga screen modes is well-known, a time-tested mechanism that works in AmigaOS 3.x is:

#include <graphics/modeid.h>

BOOL IsRTGModeID(ULONG modeID)
{
	switch (modeID & MONITOR_ID_MASK)
	{
		case DEFAULT_MONITOR_ID:
		case NTSC_MONITOR_ID:
		case PAL_MONITOR_ID:
		case VGA_MONITOR_ID:
		case A2024_MONITOR_ID:
		case PROTO_MONITOR_ID:
		case EURO72_MONITOR_ID:
		case EURO36_MONITOR_ID:
		case SUPER72_MONITOR_ID:
		case DBLNTSC_MONITOR_ID:
		case DBLPAL_MONITOR_ID:
			return FALSE;
	}
	return TRUE;
}

The above can in most cases be used as a direct replacement for IsCyberModeID(), which requires third-party apps like CyberGraphX or Picasso96.

Related Links

• Troubleshooting Unavailable Amiga Display IDs