.GetTyreForces TXA \ Set G = X + 2 CLC \ ADC #2 \ So G = 2 for the front tyres and 3 for the rear tyres STA G LDY throttleBrakeState \ If throttleBrakeState = 1 then the throttle is being DEY \ applied, so jump to tyfo1 BEQ tyfo1 \ If we get here then the throttle is not being applied LDY #9 \ Set Y = 8 so the call to Scale16Bit scales zVelocity JSR Scale16Bit \ Scale up |zVelocity| by 2^5, capping the result at the \ maximum possible positive value of &7Fxx, and \ returning the result in (NN MM) LDA zVelocityHi \ Set H = zVelocityHi with the sign flipped EOR #%10000000 STA H LDA wingForce,X \ Set A to wingForce for tyre X CPX #1 \ If X = 1, then we are processing the rear tyres, so BEQ tyfo2 \ jump to tyfo2 to use this value of A in the \ calculation LSR A \ Set A = (A / 2 + wingForce) / 2 CLC \ = (wingForce / 2 + wingForce) / 2 ADC wingForce,X \ = wingForce * 3 / 4 LSR A JMP tyfo2 \ Jump to tyfo2 to use this value of A in the \ calculation .tyfo1 \ If we get here then the throttle is being applied CPX #1 \ If X <> 1, then we are processing the front tyres, so BNE tyfo4 \ jump to tyfo4 to return from the subroutine with the C \ flag set LDA gearNumber \ Set H = gearNumber - 1 SEC SBC #1 STA H LDA engineTorque \ Set A = engineTorque .tyfo2 STA U \ Store the value of A in U to use in the multiplication \ below LDA throttleBrake \ Set A to the amount of throttle or brake being applied JSR Multiply8x8 \ Set (A T) = A * U \ = throttleBrake * U LDY throttleBrakeState \ If throttleBrakeState <> 1 then the throttle is not DEY \ being applied, so jump to tyfo3 BNE tyfo3 LSR A \ The throttle is being applied, so set: ROR T \ \ (A T) = (A T) / 2 .tyfo3 CLC \ Clear the C flag to indicate that we are returning a \ set of calculated values RTS \ Return from the subroutine .tyfo4 SEC \ Set the C flag to indicate that we are not returning \ any calculated values RTS \ Return from the subroutineName: GetTyreForces [Show more] Type: Subroutine Category: Driving model Summary: Calculate the tyre forces due to the throttle or brakes Deep dive: The core driving model SkiddingContext: See this subroutine in context in the source code References: This subroutine is called as follows: * ApplySkidForces calls GetTyreForces * ApplyTyreForces calls GetTyreForces
Calculate the following: * If the throttle is not being applied: * (NN MM) = scaled up |zVelocity| * H = zVelocityHi with the sign flipped * (A T) = throttleBrake * wingForce (rear tyres) = throttleBrake * wingForce * 3 / 4 (front tyres) * C flag clear * If the throttle is being applied: * When we are processing the front tyres: * C flag set * When we are processing the rear tyres: * H = gearNumber - 1 * (A T) = (throttleBrake * engineTorque) / 2 * C flag clear The routine also sets G to 2 or 3 (for the front or rear tyres).
Arguments: X The set of tyres to process: * 0 = front tyres * 1 = rear tyres
Returns: C flag Calculation status: * Set if we are returning a set of calculated values * Clear if we are not returning any values (which happens if the throttle is being applied and we are processing the front tyres) G Set to the correct offset for calling ApplyLimitThrottle or ApplyLimitAndSign: * 2 = zTyreForceNose * 3 = zTyreForceRear H The sign of the force (A T) The force (NN MM) If the throttle is not being applied, a maximum for the force
[X]
Subroutine Multiply8x8 (category: Maths (Arithmetic))
Calculate (A T) = T * U
[X]
Subroutine Scale16Bit (category: Maths (Arithmetic))
Scale up a 16-bit value by 2^5
[X]
Variable engineTorque in workspace Zero page
The power being generated by the engine
[X]
Variable gearNumber in workspace Zero page
The current gear number
[X]
Variable throttleBrake in workspace Zero page
The amount of throttle or brake being applied
[X]
Variable throttleBrakeState in workspace Zero page
Denotes whether the throttle or brake are being applied
[X]
Label tyfo1 is local to this routine
[X]
Label tyfo2 is local to this routine
[X]
Label tyfo3 is local to this routine
[X]
Label tyfo4 is local to this routine
[X]
Variable wingForce (category: Driving model)
The downward force from the front and rear wings
[X]
Variable zVelocityHi (category: Driving model)
High byte of the z-coordinate of the player's velocity vector, from the player's frame of reference