Routines
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DB89: Choose Direction
Used by the routine at UpdatePlayerLegs.
Works out the direction that the player is facing from the controls, which is held in bits 6 and 7 of the direction and timer of the player (0 is up the screen, 1 is right, 2 is down and 3 is left). A turn takes a few frames, which are counted in the lowest bits of the timer.
With the keyboard or when the option for directional control is not set, the controls for left and right turn the player. When it is set, the player turns towards the direction that the controls give, one quarter at a time, and moves when it faces that way.
Input
E Controls
IX Player
Output
E Controls, with bit 2 set only if the player is to move forward
Jump to SetFacingFlags while a turn is still counting.
ChooseDirection DB89 LD A,(IX+$06) Fetch the direction and the time left in a turn.
DB8C AND %00000111 Keep the time left in a turn.
DB8E JR Z,ChooseDirection_Controls Jump to ChooseDirection_Controls if the player is not turning.
Count down the turn counter, and set the sprite of the player.
DB90 DEC (IX+$06) Count down the time.
DB93 JR SetFacingFlags Jump to SetFacingFlags.
Use the keyboard unless a joystick is set to give a direction.
ChooseDirection_Controls DB95 LD HL,$BBB0 Point HL at GameOptions.
DB98 LD A,(HL) Fetch GameOptions.
DB99 AND %00000110 Keep the bits for the controls.
DB9B JR Z,ChooseDirection_Relative Jump to ChooseDirection_Relative if the controls are the keyboard.
DB9D BIT 3,(HL) Jump to ChooseDirection_Relative if the option for directional control is not set.
DB9F JR Z,ChooseDirection_Relative
Swap the controls for left and right, and up and down, if the view is rotated.
DBA1 LD A,($BBBA) Fetch ViewRotatedFlag.
DBA4 AND %00000001 Keep the lowest bit.
DBA6 CALL NZ,SwapControls Call SwapControls if the view is rotated.
Turn towards the direction that is pressed.
DBA9 BIT 0,E Jump to ChooseDirection_Right if the control for left is used.
DBAB JR NZ,ChooseDirection_Right
DBAD BIT 2,E Jump to ChooseDirection_Up if the control for up is used.
DBAF JR NZ,ChooseDirection_Up
The controls are not for up.
ChooseDirection_Right DBB1 BIT 1,E Jump to ChooseDirection_WantRight if the control for right is used.
DBB3 JR NZ,ChooseDirection_WantRight
DBB5 BIT 4,E Jump to ChooseDirection_WantDown if the control for down is used.
DBB7 JR NZ,ChooseDirection_WantDown
DBB9 BIT 0,E Jump to ChooseDirection_WantLeft if the control for left is used.
DBBB JR NZ,ChooseDirection_WantLeft
Clear the control for up, and return.
DBBD RES 2,E Clear bit 2 of the controls.
DBBF RET Return.
The controls are for up.
ChooseDirection_Up DBC0 LD A,(IX+$06) Fetch the direction of the player.
How far is the heading from the direction that is wanted?
ChooseDirection_Turn DBC3 AND %11000000 Keep only the heading.
DBC5 RES 2,E Clear bit 2 of the controls.
DBC7 JR Z,ChooseDirection_Forward Jump to ChooseDirection_Forward if the player already faces that way.
DBC9 CP $40 Jump to ChooseDirection_TurnBack if the player has to turn back by a quarter.
DBCB JR Z,ChooseDirection_TurnBack
DBCD CP $C0 Jump to ChooseDirection_TurnOn if the player has to turn on by a quarter.
DBCF JR Z,ChooseDirection_TurnOn
Choose which way to turn from the random seed, as the player has to turn right round.
DBD1 LD A,($BBAA) Fetch the random seed.
DBD4 CP $80 Jump to ChooseDirection_TurnOn if it is less than 80.
DBD6 JR C,ChooseDirection_TurnOn
Turn back a quarter.
ChooseDirection_TurnBack DBD8 LD A,(IX+$06) Fetch the direction of the player.
DBDB SUB $40 Take a quarter turn off it.
DBDD JR ChooseDirection_Counter Jump to ChooseDirection_Counter.
Turn on a quarter.
ChooseDirection_TurnOn DBDF LD A,(IX+$06) Fetch the direction of the player.
DBE2 ADD A,$40 Add a quarter turn to it.
DBE4 JR ChooseDirection_Counter Jump to ChooseDirection_Counter.
The controls are for right.
ChooseDirection_WantRight DBE6 LD A,(IX+$06) Fetch the direction of the player.
DBE9 SUB $40 Take a quarter turn off it.
DBEB JR ChooseDirection_Turn Jump to ChooseDirection_Turn.
The controls are for down.
ChooseDirection_WantDown DBED LD A,(IX+$06) Fetch the direction of the player.
DBF0 SUB $80 Take two quarter turns off it.
DBF2 JR ChooseDirection_Turn Jump to ChooseDirection_Turn.
The controls are for left.
ChooseDirection_WantLeft DBF4 LD A,(IX+$06) Fetch the direction of the player.
DBF7 SUB $C0 Take three quarter turns off it.
DBF9 JR ChooseDirection_Turn Jump to ChooseDirection_Turn.
The player faces the way that was asked.
ChooseDirection_Forward DBFB SET 2,E Set the control for moving forward, and return.
DBFD RET
Left and right turn the player a quarter.
ChooseDirection_Relative DBFE LD A,(IX+$06) Fetch the direction of the player.
Turn the player back by a quarter if the control for left is used.
DC01 BIT 0,E Jump to ChooseDirection_RelativeRight if left is not pressed.
DC03 JR Z,ChooseDirection_RelativeRight
DC05 SUB $40 Take a quarter turn off the heading.
DC07 OR %00000001 Start a turn.
Right turns the player the other way.
ChooseDirection_RelativeRight DC09 BIT 1,E Jump to ChooseDirection_Set if right is not pressed.
DC0B JR Z,ChooseDirection_Set
DC0D ADD A,$40 Add a quarter turn to the heading.
Start a turn and store the heading.
ChooseDirection_Counter DC0F OR %00000001 Start a turn.
ChooseDirection_Set DC11 LD (IX+$06),A Set the direction of the player.
Continue on to SetFacingFlags.
View the equivalent code in;
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