Routines
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27922: Update Player Car
Used by the routine at HandlerPlayer.
Called once a frame for the player's car. Adds to the miles travelled, handles the accelerator and the brake, then moves the car, steers it and uses up fuel.
Address Meaning
PlayerMapPosition_Fraction X position of the car (3 bytes, the top two are in map units)
PlayerMapPositionY_Fraction Y position of the car (3 bytes, the top two are in map units)
Player_Direction Direction of the car (1024 is a full turn)
Add the speed to the odometer.
UpdatePlayerCar 27922 LD C,0 Set the miles carry to 0.
27924 LD A,(24077) Fetch the speed of the car (Speed).
27927 RLA Rotate the top bit of A into C.
27928 RL C
27930 RLA Rotate the top bit of A into C again (this multiplies the speed by 4).
27931 RL C
27933 LD HL,24112 Point HL at the fraction of a mile (Miles_Fraction).
27936 ADD A,(HL) Add the scaled speed to the fraction of a mile.
27937 LD (HL),A Write the fraction of a mile back.
27938 LD A,C Fetch the carry from the speed.
27939 LD B,3 Set the byte counter to 3 (the miles are stored in three bytes).
Working backwards, add onto the odometer.
CalcMiles 27941 DEC HL Move back to the previous byte of the miles.
27942 ADC A,(HL) Add the carry to the byte of the miles.
27943 DAA Convert the result to BCD.
27944 LD (HL),A Write the byte of the miles back.
27945 LD A,0 Clear the carry value, keeping the carry flag.
27947 DJNZ CalcMiles Decrease the byte counter by one and loop back to CalcMiles until all three bytes of the miles have been done.
Award some points every time the middle byte of the miles changes.
27949 LD A,(24180) Fetch the middle byte of the miles as it was last time (MilesCheckpoint) and keep it in L.
27952 LD L,A
27953 LD A,(24110) Fetch the middle byte of the miles (24110).
27956 CP L Jump to UpdatePlayerCar_CheckFuel if the middle byte of the miles has not changed.
27957 JR Z,UpdatePlayerCar_CheckFuel
27959 LD (24180),A Store the new middle byte of the miles in MilesCheckpoint.
27962 LD BC,16 Set the points to add, 0016.
27965 CALL AddPointsToScore Add the points to the score using AddPointsToScore.
UpdatePlayerCar_CheckFuel 27968 LD HL,(24069) HL=PlayerMapPosition (the value is not used).
Check fuel.
27971 LD A,(24075) Fetch the fuel level (Fuel_MSB).
See Infinite Fuel.
27974 AND A Jump to UpdatePlayerCar_CheckTemperature if there is still some fuel.
27975 JR NZ,UpdatePlayerCar_CheckTemperature
Handle being out of fuel (or too hot): slow down gradually, but allow the car to be driven again when it is slow enough.
UpdatePlayerCar_NoFuel 27977 LD A,(24077) Fetch the speed of the car (Speed).
27980 CP 51 Jump to UpdatePlayerCar_Accelerate if the speed is below 51 so the car can be driven again.
27982 JR C,UpdatePlayerCar_Accelerate
27984 DEC A Slow the car down by one.
27985 LD (24077),A Write the speed back to Speed.
27988 JR UpdatePlayerCar_Brake Jump to UpdatePlayerCar_Brake.
Check the temperature.
UpdatePlayerCar_CheckTemperature 27990 LD A,(24076) Fetch the temperature (Temperature).
See Infinite Temperature.
27993 CP 160 Jump to UpdatePlayerCar_NoFuel if the temperature is 160 or more.
27995 JR NC,UpdatePlayerCar_NoFuel
Check the accelerator.
UpdatePlayerCar_Accelerate 27997 CALL ReadInputAccelerate Check if the accelerator is pressed using ReadInputAccelerate.
28000 BIT 3,A Jump to HandlerCanAccelerate if the accelerator is pressed.
28002 JR Z,HandlerCanAccelerate
Check the brake.
UpdatePlayerCar_Brake 28004 CALL ReadInputBrake Check if the brake is pressed using ReadInputBrake.
28007 BIT 2,A Jump to HandlerAccelerate_Gauge if the brake is not pressed.
28009 JR NZ,HandlerAccelerate_Gauge
28011 LD A,(24077) Fetch the speed of the car (Speed).
28014 SUB 16 Subtract 16 from the speed.
28016 JR NC,HandlerAccelerate Jump to HandlerAccelerate if the speed did not go below zero.
28018 XOR A Set the speed to 0.
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