Routines
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24283: Command 3: Fill Attribute Buffer With Single Colour
Used by the routine at PopulateRoomBuffer.
Command 3: fill the attribute buffer with a single colour, then parse an overlay map to apply per-cell colour changes. The overlay uses a simple encoding:
  • 18 + count: skip N attribute cells
  • 27 + count + colour: repeat a colour N times
  • 36: end of attribute data
  • Any other value: set a single attribute cell directly
Input
DE Tile counter
HL Pointer to the room data
Command03_FillAttributes 24283 INC HL Increment the room data pointer by one.
24284 LD C,(HL) Fetch the base fill colour into C.
Fill 704 attribute cells at RoomAttributeBuffer with the base colour.
24285 LD IX,55296 IX=RoomAttributeBuffer.
24289 LD DE,704 DE=0704.
FillAttributes_Loop 24292 LD (IX+0),C Write C to *IX+0.
24295 INC IX Increment IX by one.
24297 DEC DE Decrease DE by one.
24298 LD A,E Jump back to FillAttributes_Loop until DE is zero.
24299 OR D
24300 JR NZ,FillAttributes_Loop
Now parse the attribute overlay data to apply per-cell changes on top of the base fill colour.
FillAttributes_Overlay 24302 INC HL Increment HL by one.
24303 LD DE,705 DE=0705.
24306 LD IX,55296 IX=RoomAttributeBuffer.
FillAttributes_Overlay_Loop 24310 LD A,(HL) A=*HL.
24311 CP 18 Jump to FillAttributes_Skip if A is 18 (skip command).
24313 JR Z,FillAttributes_Skip
24315 CP 27 Jump to FillAttributes_Repeat if A is 27 (repeat command).
24317 JR Z,FillAttributes_Repeat
24319 CP 36 Jump to Room_Attributes_End if A is 36 (end of attribute data).
24321 JR Z,Room_Attributes_End
Otherwise, write this byte directly as a single attribute value.
24323 LD C,(HL) C=*HL.
24324 LD (IX+0),C Write C to *IX+0.
24327 DEC DE Decrease DE by one.
24328 INC IX Increment IX by one.
24330 LD A,E Jump to PopulateRoomBuffer_Error if DE is zero.
24331 OR D
24332 JP Z,PopulateRoomBuffer_Error
24335 INC HL Increment HL by one.
24336 JR FillAttributes_Overlay_Loop Jump to FillAttributes_Overlay_Loop.
Attribute overlay command 18: skip over a number of attribute cells.
The following byte gives the skip count.
FillAttributes_Skip 24338 INC HL Increment HL by one.
24339 LD B,(HL) Fetch the skip count into B.
FillAttributes_Skip_Loop 24340 INC IX Increment IX by one.
24342 DEC DE Decrease DE by one.
24343 LD A,E Jump to PopulateRoomBuffer_Error if DE is zero.
24344 OR D
24345 JP Z,PopulateRoomBuffer_Error
24348 DJNZ FillAttributes_Skip_Loop Decrease the skip counter by one and loop back to FillAttributes_Skip_Loop until done.
24350 INC HL Increment HL by one.
24351 JR FillAttributes_Overlay_Loop Jump to FillAttributes_Overlay_Loop.
Attribute overlay command 27: repeat a colour value a number of times. The following two bytes give the repeat count and colour value.
FillAttributes_Repeat 24353 INC HL Increment HL by one.
24354 LD B,(HL) Fetch the repeat count into B.
24355 INC HL Increment HL by one.
24356 LD C,(HL) Fetch the colour value into C.
24357 INC HL Increment HL past the colour value byte.
FillAttributes_Repeat_Loop 24358 LD (IX+0),C Write C to *IX+0.
24361 INC IX Increment IX by one.
24363 DEC DE Decrease DE by one.
24364 LD A,E Jump to PopulateRoomBuffer_Error if DE is zero.
24365 OR D
24366 JP Z,PopulateRoomBuffer_Error
24369 DJNZ FillAttributes_Repeat_Loop Decrease the repeat counter by one and loop back to FillAttributes_Repeat_Loop until done.
24371 JR FillAttributes_Overlay_Loop Jump to FillAttributes_Overlay_Loop.
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