accelerate( var* speed,var accel,var friction);

Calculates the move distance for a given speed and acceleration. The resistance of a surrounding medium can be given by the friction parameter. This function can be used for actor movement and rotation.

Parameters:

speed current speed in quants per tick. This value is changed by the acceleration.
accel acceleration in quants per square tick.
friction the resistance parameter of the surrounding medium, in the range of 0..1. 0 means no resistance, 1 full resistance.

Returns:

Distance to cover in quants.

Modifies:

speed - current speed vector in quants per tick.

Speed:

Fast

Algorithm:

if (friction == 0) {
   distance = speed*time_step + 0.5*accel*time_step*time_step
   speed = speed + accel*time_step
} else {
   distance = accel*time_step/friction + (speed-accel/friction)*(1-exp(-friction*time_step))/friction
   speed = accel/friction + (speed-accel/friction)*exp(-friction*time_step) 
}

Example: 

var aspeed; // local var to store the current angular speed
// accelerate the camera left-right rotation with cursor keys
vec_add(camera.pan,accelerate(aspeed,5*key_force.x,0.7));

See also:

vec_accelerate, smooth

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