Routines
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9995: Look up a sprite's bitmap and work out where it goes
Used by the routines at BLIT_SPRITE, BLIT_SPRITE_MIRRORED, DRAW_TURNED_RIGHT, DRAW_FLIP_ANTIDIAGONAL, DRAW_UPSIDE_DOWN, BLIT_SPRITE_FLIPPED, DRAW_FLIP_DIAGONAL and DRAW_TURNED_LEFT.
Sprite numbers are 1-based, so the number is decremented before being doubled into the table of addresses at FURNITURE_SPRITES. The first two bytes of the data are its size, and the pointer is left just past them.
Input
C Sprite number
DE On exit, the first row of bitmap data
B On exit, width in bytes
C On exit, height in rows
HL On exit, where the top-left corner lands in the display file
FETCH_SPRITE 9995 LD HL,FURNITURE_SPRITES The table of sprite addresses.
9998 DEC C Numbered from 1, two bytes each.
9999 LD B,$00
999B SLA C
999D RL B
999F ADD HL,BC
99A0 LD A,(HL) The address of the bitmap itself.
99A1 INC HL
99A2 LD H,(HL)
99A3 LD L,A
99A4 EX DE,HL
99A5 CALL PIXEL_TO_SCREEN Turn the pixel coordinates into a display file address.
99A8 LD A,(DE) Width then height, and step past them to the first row.
99A9 LD B,A
99AA INC DE
99AB LD A,(DE)
99AC LD C,A
99AD INC DE
99AE RET
Watched live, the sizes coming back are 4 by 24 for the characters and 6 by 5 or 6 by 6 for smaller pieces -- so width really is in bytes, eight pixels at a time.
FURNITURE_SPRITES is not a table of its own. It is the 161st entry of SPRITE_TABLE, and this routine does the same arithmetic SPRITE_ADDRESS does, so asking it for sprite 1 fetches entry 161. The base is what says which family of sprites is wanted. An earlier reading of this routine took the 39 entries between FURNITURE_SPRITES and FURNITURE_COLOURS for the whole table and concluded it held the knight, the wizard and seven frames of the serf; that was an accident of where the next base happens to fall.
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