Routines
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B165: Set Speed Towards Player
Used by the routines at HandleChasingDome and HandleHomingSparkle.
Sets the speed of an object along the x and y axes so that it heads towards the player.
Input
B Speed along the y axis
C Speed along the x axis
IX The address of the object
Head towards the player along each axis.
SetSpeedTowardsPlayer B165 LD HL,$5B89 Point HL at 5B89.
B168 LD A,(IX+$01) Fetch the x position of the object.
B16B SUB (HL) Subtract the player's x position.
B16C INC HL Move on to the y position.
B16D LD A,C Fetch the speed along the x axis.
B16E JP M,SetSpeedTowardsPlayer_SetX Jump to SetSpeedTowardsPlayer_SetX if the object is west of the player.
B171 NEG Make the speed negative.
SetSpeedTowardsPlayer_SetX B173 LD (IX+$09),A Set the speed along the x axis.
B176 LD A,(IX+$02) Fetch the y position of the object.
B179 SUB (HL) Subtract the player's y position.
B17A INC HL Move on.
B17B LD A,B Fetch the speed along the y axis.
B17C JP M,SetSpeedTowardsPlayer_SetY Jump to SetSpeedTowardsPlayer_SetY if the object is south of the player.
B17F NEG Make the speed negative.
SetSpeedTowardsPlayer_SetY B181 LD (IX+$0A),A Set the speed along the y axis.
B184 RET Return.
View the equivalent code in;
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