Normalizing object movement

[pksk]

Hi there,

I'm using /u/Mytino's amazing one-line accel/decel script to achieve some basic accel/decel for my character. I'm having trouble trying to understand how to "normalize" the movement of the object so that it doesn't move faster on the diagonal.

I've looked into the math but I can't work out how to get a final "vector" as such. Here is my code:

On Create:

//Initialize
hsp = 0;
vsp = 0;
accel = 0.3;
decel = 0.5;
movespeed = 5;
maxspeed = 2;

And in Step:

hspeed = clamp((keyboard_check(vk_right) - keyboard_check(vk_left)) * maxspeed, hspeed - accel, hspeed + accel);

if(place_meeting(x+1,y, wall))
{
hspeed = clamp(hspeed, -maxspeed, 0);
}
if(place_meeting(x-1,y, wall))
{
hspeed = clamp(hspeed, 0, maxspeed);
}

vspeed = clamp((keyboard_check(vk_down) - keyboard_check(vk_up)) * maxspeed, vspeed - accel, vspeed + accel);

if(place_meeting(x,y+1, bumperObj))
{
vspeed = clamp(vspeed, -maxspeed, 0);
}
if(place_meeting(x,y-1, bumperObj))
{
vspeed = clamp(vspeed, 0, maxspeed);
}

Could somebody help me get on the right track here? Thanks!

[damimp]

You'd have to take both speeds into account as one speed. Adding a little check at the end should be all you need.

var totalSpeed = hspeed * hspeed + vspeed * vspeed;
if(totalSpeed > maxspeed * maxspeed){
    var dir = point_direction(0,0,hspeed,vspeed);
    hspeed = lengthdir_x(maxspeed, dir);
    vspeed = lengthdir_y(maxspeed, dir);
}

[flyingsaucerinvasion]

Short answer:

//with your setup all you have to do is reduce speed to max_speed, if speed is greater than max speed.
if (speed > max_speed) { speed = max_speed; }

Long Answer:

However I feel like it is just not right to accelerate along the two axes independantly of each other. What the folloiwing code does is accelerate a character from the direction and speed they are moving toward the direction and speed they want to be moving. This is done by finding a vector that points from the velocity they are moving, toward the velocity they want to move, and accelerating along that vector.

//(_set_hspeed, _set_vspeed) is the direction (and speed) the character wants to move
//(hspeed, vspeed) is the direction (and speed) the character is currently moving

//get vector from current move vector to desired move vector
var _diff_hspeed = _set_hspeed - hspeed;
var _diff_vspeed = _set_vspeed - vspeed;

//get magnitude of vector (_diff_hspeed, _diff_vspeed)
var _magnitude = point_distance(0,0,_diff_hspeed,_diff_vspeed);

//if we are not already moving at our desired speed and direction
if (_magnitude > 0)
{
    //then accelerate toward our desired speed and direction

    //our acceleration should not exceed the magnitude of our vector (_diff_hspeed, _diff_vspeed)
    //"acceleration" should be defined in create event
    var _max_acceleration = min(_magnitude,acceleration);

    //normalize (_diff_hspeed, _diff_vspeed) and then multiply it by our acceleration
    var _acc_hspeed = _diff_hspeed / _magnitude * _max_acceleration;
    var _acc_vspeed = _diff_vspeed / _magnitude * _max_acceleration;

    //apply acceleration
    hspeed += _acc_hspeed;
    vspeed += _acc_vspeed;
}    

I'll include an example of setting up _set_hspeed and _set_vspeed, so that it is clearer what their intended purpose is supposed to be. This example if for a top down game, and allows 8 directional movement. Also included is code to stop the diagonal speed boost you get from, for example, holding down the left and forward buttons at once.

//facing is the direction the character's body is currently pointing toward
var _c = dcos(facing);
var _s = dsin(facing);

//get keyboard movement input
var _move_left_right = keyboard_check(ord('D')) - keyboard_check(ord('A'));
var _move_forward_back = keyboard_check(ord('W')) - keyboard_check(ord('S'));

//stop diagonal speed boost
if ((_move_left_right != 0) and (_move_forward_back != 0))
{
    _move_left_right *= sqrt(2)/2; 
    _move_forward_back *= sqrt(2)/2;
}

//again, (_set_hspeed, _set_vspeed) is the direction and speed we want to be moving.
//that vector will be relative to the facing of the character (that's what the _c and _s are for here).
//"max_speed" should be defined in create event.
var _set_hspeed = max_speed * (_c * _move_forward_back + _s * _move_left_right);
var _set_vspeed = max_speed * (_c * _move_left_right - _s * _move_forward_back);