Mode Specifier

OS SWI Calls

» OS_ReadModeVariable

» Mode Specifier

Mode Specifier

A mode specifier is a single-word value used to specify a screen mode. It is handled as follows:

• If it is a number from 0 to 255, it is assumed to be a mode number
• Else if the bottom bit is set, it is assumed to be a Sprite Mode Word (describing a RISC OS 3.5 or RISC OS 5 format sprite)
• Otherwise it is assumed to be a pointer to a Mode Selector Block

Unless otherwise noted, all APIs for dealing with screen modes accept all of the above forms.

Note that some APIs have additional rules, e.g. a mode specifier of -1 may be used to refer to the current screen mode. Remember that these are extensions to the specification and are not understood by all APIs.

Also remember that it is nonsensical to pass in a sprite mode word to some APIs; for example attempting to set the screen mode using a RISC OS 3.5 sprite mode word will fail, as the mode word does not contain any width or height information.

See also

• Screen Modes
• Sprite Mode Word
• Mode Selector Block
• OS_ScreenMode
• OS_ReadModeVariable
• Wimp_SetMode

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