=> R4 = reason code:
1 read palette
2 set palette
3 set first flash state
4 set second flash state
5 set default palette
6 blank screen
7 read palette entries
8 write palette entries
9 set gamma correction tables
Other registers dependent on call
This vector is called whenever the palette is read or written. Set R4 = 0 to claim the call, and prevent RISC OS from performing the default action. It is used to indirect VDU 19, OS_Word 12, OS_ReadPalette, ColourTrans_ReadPalette and ColourTrans_WritePalette. PRM 1-105 suggests that there may be other calls it indirects.
See PRM 1, page 84.
Read Palette
=> R0 = logical colour
R1 = type of colour (16,17,18,24,25)
R4 = 1 (reason code)
<= R2 = 1st flash colour (&BBGGRRxx) - device colour
R3 = 2nd flash colour (&BBGGRRxx) - device colour
R4 = 0 if operation complete
Set Palette
=> R0 = logical colour
R1 = type of colour (16,17,18,24,25)
R2 = 1st flash colour (&BBGGRRxx) - device colour
R3 = 2nd flash colour (&BBGGRRxx) - device colour
R4 = 2 (reason code)
<= R4 = 0 if operation complete
Set Flash state
=> R4 = 3 (set first flash state)
4 (set second flash state)
<= R4 = 0 if operation complete
Set default palette
=> R4 = 5 (reason code)
<= R4 = 0 if operation complete
Blank screen
=> R0 = 0 to unblank, 1 to blank
R4 = 6 (reason code)
This call is used by the ScreenBlanker module to blank and unblank the screen.
Read palette entries
=> R0 = pointer to word aligned list of logical colours (words) or 0
R1 = type and number of colours
bits 0-23 = number of entries to read
bits 24-31 = type of colour (16,17,18,24,25)
R2 = pointer to buffer for first flash colour (&BBGGRRxx)
R3 = pointer to buffer for second flash colour (&BBGGRRxx)
R4 = 7 (reason code)
Write palette entries
=> R0 = pointer to word aligned list of logical colours (words) or 0
R1 = type and number of colours
bits 0-23 = number of entries to read
bits 24-31 = type of colour (16,17,18,24,25)
R2 = pointer to list of device colours
R4 = 8 (reason code)
Set gamma correction
=> R0 = pointer to table for red
R1 = pointer to table for green
R2 = pointer to table for blue
R4 = 9 (reason code)
This call sets the gamma correction tables. Each table is a word aligned array of 256 bytes giving the gamma corrected value when indexed by the normal colour value.
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