Routines
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64694: Handler: Train
Used by the routine at RunHandlers.
Handler_Train 64694 LD A,(54277) Return if train spawning is set to be off (*TrainState is equal to 254).
64697 CP 254
64699 RET Z
64700 CP 255 Jump to Handler_Train_Movement if a train is already active (*TrainState is equal to 255).
64702 JR Z,Handler_Train_Movement
Else the counter is a counter, so count it down.
64704 DEC A Decrease *TrainState by one.
64705 LD (54277),A
64708 RET NZ Return if *TrainState is still in progress.
Else the countdown is complete so set the counter/ state to indicate that a train has been spawned and then spawn a train!
64709 LD A,255 Write 255 to *TrainState.
64711 LD (54277),A
Randomly bring the train in from either the left or right hand side of the play area.
64714 CALL RandomNumber Get a random number of either zero or one.
64717 AND %00000001
64719 JR NZ,Handler_SpawnTrainRight Jump to Handler_SpawnTrainRight if the random number is one.
Train moves from left-to-right.
64721 LD A,19 Write 19 to *TrainYPosition.
64723 LD (54279),A
64726 LD A,240 Write 240 to *TrainXPosition.
64728 LD (54278),A
64731 JR Handler_Train_Movement Jump to Handler_Train_Movement.
Bit 7 signifies that this train moves from right-to-left.
Handler_SpawnTrainRight 64733 LD A,147 Write 147 (19 + bit 7 set) to *TrainYPosition.
64735 LD (54279),A
64738 LD A,32 Write 32 to *TrainXPosition.
64740 LD (54278),A
Handler_Train_Movement 64743 LD A,(54279) A=*TrainYPosition.
64746 AND %01000000 Keep only bit 6.
Set the carry flag according to bit 6.
64748 RLCA Rotate A left twice, moving bit 6 to bit 0 and setting the carry flag if bit 0 was set.
64749 RLCA
64750 LD C,A C=A.
Which direction should the train be moving in?
64751 LD A,(54279) Jump to Handler_MoveTrain_RightToLeft if *TrainYPosition is higher than 128 (bit 7 is set).
64754 CP 128
64756 JR NC,Handler_MoveTrain_RightToLeft
Handles moving the train from the left-to-right hand side of the play area.
64758 AND %00111111 Strip off the right-to-left flag.
64760 LD B,A B=train Y position.
64761 LD A,(54278) A=*TrainXPosition.
64764 INC A Increment A by one.
64765 ADD A,C A+=C.
Draw the train.
DrawTrain 64766 LD (54278),A Write A to *TrainXPosition.
64769 LD C,A C=train X position.
64770 LD A,121 A=sprite ID 121.
ID Sprite
121 sprite-121-left
64772 PUSH BC Stash the train position on the stack.
64773 CALL PrintSprite Call PrintSprite.
64776 POP BC Restore the train position from the stack.
Draws the centre sprite of the train three times.
64777 LD A,3 A=3 (counter).
DrawTrain_Loop 64779 PUSH AF Stash the counter on the stack.
64780 INC C Increment the X position by two to draw the next section of the train.
64781 INC C
64782 LD A,123 A=sprite ID 123.
ID Sprite
123 sprite-123-left
64784 PUSH BC Stash the train position on the stack.
64785 CALL PrintSprite Call PrintSprite.
64788 POP BC Restore the train position and counter from the stack.
64789 POP AF
64790 DEC A Decrease the counter held by A by one.
64791 JR NZ,DrawTrain_Loop Jump to DrawTrain_Loop until all centre sprites have been drawn.
Now draw the rear section of the train.
64793 INC C Increment the X position by two to draw the next section of the train.
64794 INC C
64795 LD A,121 A=sprite ID 121.
ID Sprite
121 sprite-121-right
64797 CALL PrintSprite_Mirrored Call PrintSprite_Mirrored.
64800 RET Return.
Handles moving the train from the right-to-left hand side of the play area.
Handler_MoveTrain_RightToLeft 64801 AND %00111111 Strip off the right-to-left flag.
64803 LD B,A B=train Y position.
64804 LD A,(54278) A=*TrainXPosition.
64807 DEC A Decrease A by one.
64808 SUB C A-=C.
64809 JR DrawTrain Jump to DrawTrain.
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