Routines
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6124: Calculate fuel gauge sprite offset
Computes a sprite data offset for the fuel gauge display using the formula: offset = (7 - B) * 8 + D. The result is patched into the operand of the following RLC instruction via self-modifying code.
Input
B Fuel gauge row (0-7, top to bottom)
D Sub-row pixel offset within the gauge row
Output
B Rotated fuel gauge row (used by caller for next iteration)
calculate_fuel_gauge_offset 6124 LD A,$07 Calculate offset = (7 - B) * 8 + D and patch into next instruction.
6126 PUSH DE
6127 SUB B
6128 SLA A
612A SLA A
612C SLA A
612E POP DE
612F ADD A,D
6130 LD ($6134),A
6133 RLC B Rotate B left through carry.
6135 RET
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