ColourTrans mode identification (changes)

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ColourTrans mode identification

Several ColourTrans SWIs allow the user to specify a source/destination mode/palette using a pair of registers (typically R0 & R1) and a flag bit (e.g. bit 0 of R5 in ColourTrans_GenerateTable). This set of values can either describe a screen mode (with either a specific palette, the current palette, or a default palette), or a sprite (with the sprite’s palette). To allow ColourTrans to correctly determine whether your are passing a mode or a sprite, adhere to one of the following argument patterns:

For describing a mode

• R0 (mode/sprite area pointer) should indicate the mode. This can be either:
  • A Mode Specifier (i.e. a mode number, Sprite Mode Word, or a pointer to a Mode Selector Block)
  • -1 to use the current mode
• R1 (palette/sprite pointer) should contain:
  • -1 to use the current palette (Only use if current mode matches the BPP of the indicated mode)
  • 0 to use the default palette for the mode
  • Else a pointer to a palette
• The ‘pointer to sprite’ flag should be clear

If a palette pointer is used, the palette is expected to be 2, 4, 16 or 256 words long for 1bpp, 2bpp, 4bpp or 8bpp respectively. This means that a full 256 entries are expected for old-style 64 colour modes. Palette entries should be in standard &BBGGRR00 format.

For describing a sprite by name

• R0 (mode/sprite area pointer) should be a pointer to the sprite area
• R1 (palette/sprite pointer) should be a pointer to the sprite name
• The ‘pointer to sprite’ flag should be clear

For describing a sprite by pointer

• R0 (mode/sprite area pointer) should either by a pointer to the sprite area, or the special values &8000 or 256. The special values should be used in situations where it is unknown which sprite area the sprite belongs to.
• R1 (palette/sprite pointer) should be a pointer to the sprite
• The ‘pointer to sprite’ flag should be set.

See also

• ColourTrans_GenerateTable
• ColourTrans_SelectTable
• ColourTrans_SelectGCOLTable
• ColourTrans_ReadPalette