Routines
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43696: Update Rope
Used by the routines at Handle_Sabreman_On_Rope and Handle_Sabreman_Falling.
Reads the controls and updates the rope that Sabreman hangs from.
The left and right controls (bits 0 and 1 of the controls, which are clear when the control is used) push the end of the rope by changing the velocity in Rope_Velocity by 2. That is only done while the displacement of the rope (Rope_Displacement_Pixels) is not more than the length of the rope divided by 8 with a maximum of 8.
The down and up controls (bits 2 and 3) make the rope longer, which lowers Sabreman, and shorter, which raises him. Then Move_Rope moves the rope and Position_Rope_End works out where its end is.
Input
IX Object record of Sabreman
Read the controls and find out whether the rope may be pushed.
Update_Rope 43696 CALL ReadControls Read the controls.
43699 LD HL,43682 Point at the velocity of the end of the rope (Rope_Velocity).
43702 EX AF,AF' Keep the controls in AF'.
43703 LD A,(43684) Fetch the displacement of the end of the rope.
43706 AND A Jump to Update_Rope_Check_Displacement if the displacement is positive.
43707 JP P,Update_Rope_Check_Displacement
43710 NEG Make the displacement positive.
Update_Rope_Check_Displacement 43712 LD B,A Keep the displacement in B.
43713 LD A,(43686) Fetch the high byte of the length of the rope.
43716 RRA Rotate bit 0 of the high byte into the carry.
43717 LD A,(43685) Fetch the low byte of the length of the rope.
43720 RRA Divide the length by 8 to work out how far the rope may be pushed.
43721 RRA
43722 RRA
43723 AND %00111111 Keep only six bits.
43725 CP 8 Jump to Update_Rope_Check_Limit if the limit is less than 8.
43727 JR C,Update_Rope_Check_Limit
43729 LD A,8 Limit the push to 8.
Update_Rope_Check_Limit 43731 CP B Jump to Skip_Rope_Push if the displacement is larger than the limit, as the rope cannot be pushed any further.
43732 JR C,Skip_Rope_Push
Use the left and right controls to push the end of the rope.
43734 EX AF,AF' Fetch the controls again from AF'.
43735 BIT 0,A Push the rope to the right if the right control is used (bit 0 of the controls is clear).
43737 CALL Z,Push_Rope_Right
43740 BIT 1,A Push the rope to the left if the left control is used (bit 1 of the controls is clear).
43742 CALL Z,Push_Rope_Left
This entry point is used by the routine at Skip_Rope_Push.
Use the down and up controls to change the length of the rope.
Update_Rope_Fetch_Length 43745 LD HL,(43685) Fetch the length of the rope.
43748 BIT 2,A Lower the rope if the down control is used (bit 2 of the controls is clear).
43750 CALL Z,Lower_Rope
43753 BIT 3,A Raise the rope if the up control is used (bit 3 of the controls is clear).
43755 CALL Z,Raise_Rope
43758 CALL Move_Rope Move the rope (see Move_Rope).
43761 JP Position_Rope_End Jump to Position_Rope_End to work out the position of the end of the rope.
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