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65196: Retrieve screen address of co-ordinates
Used by the routines at DO_SHADE, DO_SHADE_1 and DO_SHADE_4.
Input
B y co-ordinate
C x co-ordinate
Output
HL screen address of pixel
Z set if the given pixel is not already set
65196 PUSH BC Store X and Y co-ordinate
65197 CALL 8874 'Pixel address' routine
65200 LD (64215),A Store x co-ordinate % 8
65203 LD BC,64786 BC=pixel conversion table
65206 ADD A,C Offset is 'pixel in byte'
65207 LD C,A BC=entry in pixel conversion table
65208 LD A,(BC) A=pixel converted to byte
65209 POP BC Retrieve X and Y co-ordinate
65210 AND (HL) Is that pixel set?
65211 RET
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