Routines
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AAB0: 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 02. That is only done while the displacement of the rope (Rope_Displacement_Pixels) is not more than the length of the rope divided by 08 with a maximum of 08.
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 AAB0 CALL ReadControls Read the controls.
AAB3 LD HL,$AAA2 Point at the velocity of the end of the rope (Rope_Velocity).
AAB6 EX AF,AF' Keep the controls in AF'.
AAB7 LD A,($AAA4) Fetch the displacement of the end of the rope.
AABA AND A Jump to Update_Rope_Check_Displacement if the displacement is positive.
AABB JP P,Update_Rope_Check_Displacement
AABE NEG Make the displacement positive.
Update_Rope_Check_Displacement AAC0 LD B,A Keep the displacement in B.
AAC1 LD A,($AAA6) Fetch the high byte of the length of the rope.
AAC4 RRA Rotate bit 0 of the high byte into the carry.
AAC5 LD A,($AAA5) Fetch the low byte of the length of the rope.
AAC8 RRA Divide the length by 08 to work out how far the rope may be pushed.
AAC9 RRA
AACA RRA
AACB AND %00111111 Keep only six bits.
AACD CP $08 Jump to Update_Rope_Check_Limit if the limit is less than 08.
AACF JR C,Update_Rope_Check_Limit
AAD1 LD A,$08 Limit the push to 08.
Update_Rope_Check_Limit AAD3 CP B Jump to Skip_Rope_Push if the displacement is larger than the limit, as the rope cannot be pushed any further.
AAD4 JR C,Skip_Rope_Push
Use the left and right controls to push the end of the rope.
AAD6 EX AF,AF' Fetch the controls again from AF'.
AAD7 BIT 0,A Push the rope to the right if the right control is used (bit 0 of the controls is clear).
AAD9 CALL Z,Push_Rope_Right
AADC BIT 1,A Push the rope to the left if the left control is used (bit 1 of the controls is clear).
AADE CALL Z,Push_Rope_Left
This entry point is used by the routine at Skip_Rope_Push.
Use the down and up controls to change the length of the rope.
Update_Rope_Fetch_Length AAE1 LD HL,($AAA5) Fetch the length of the rope.
AAE4 BIT 2,A Lower the rope if the down control is used (bit 2 of the controls is clear).
AAE6 CALL Z,Lower_Rope
AAE9 BIT 3,A Raise the rope if the up control is used (bit 3 of the controls is clear).
AAEB CALL Z,Raise_Rope
AAEE CALL Move_Rope Move the rope (see Move_Rope).
AAF1 JP Position_Rope_End Jump to Position_Rope_End to work out the position of the end of the rope.
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