Routines
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47325: Calculate Attribute Address
Used by the routines at 42624, ScoreLabelFlash, MenuWriteText, PrintStringColour, 47908 and DrawRoom.
Input
HL Pixel address co-ordinates
Output
HL Attribute buffer address
Converts a given pixel address to the associated attribute buffer address.
AttributeAddress 47325 PUSH BC Stash BC on the stack.
47326 LD A,L Horizontal co-ordinate.
47327 RRCA Divide by 8.
47328 RRCA
47329 RRCA
47330 AND %00011111 Keep only bits 0-4 (0-31 / minimum-maximum horizontal screen values).
47332 LD L,A Store this back in L.
47333 LD A,H Vertical co-ordinate.
47334 RLCA Multiply by 4.
47335 RLCA
47336 LD C,A Store this in C temporarily.
47337 AND %11100000 Keep only bits 5-7.
47339 OR L Set the bits from L.
47340 LD L,A L=A.
47341 LD A,C Fetch the stored value from C.
47342 AND %00000011 Keep only bits 0-1.
47344 OR %01011000 Set MSB of the attribute buffer 88. This ensures our value is >= 22528.
47346 LD H,A Store this back in H.
47347 POP BC Restore BC from the stack.
47348 RET Return.
View the equivalent code in;
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