Routines
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D848: Attribute address of a pixel position
Used by the routines at text_attr_addr and show_carried_slot.
HL is kept.
Input
H the pixel y, counted up from the bottom of the screen
L the pixel x
DE on exit, the attribute address
calc_attrib_addr D848 PUSH HL
D849 LD A,H H = (255 - y) / 8: the character row counted from the top, plus 8
D84A CPL
D84B LD H,A
D84C SRL H
D84E SRL H
D850 SRL H
D852 SRL H three more shifts across H and L: row * 32 + x / 8
D854 RR L
D856 SRL H
D858 RR L
D85A SRL H
D85C RR L
D85E LD DE,$5700 $5700 is the attribute file less those 8 rows
D861 ADD HL,DE
D862 EX DE,HL
D863 POP HL
D864 RET
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