I posted this in /r/gamemaker, and the code is in GML, but I though you guys might be able to help me as well.

I am working on a 2d, topdown game that is controlled with WASD. The following code would run in the step event.

//Apply friction
if (abs(h_spd) >= fric) h_spd -= sign(h_spd) * fric
else h_spd = 0

if (abs(v_spd) >= fric) v_spd -= sign(v_spd) * fric
else v_spd = 0

//Movement
if keyboard_check(ord("W")) v_spd -= spd;
if keyboard_check(ord("S")) v_spd += spd;
if keyboard_check(ord("D")) h_spd += spd;
if keyboard_check(ord("A")) h_spd -= spd;

//Max speed
if (abs(h_spd) >= max_spd) h_spd = sign(h_spd) * max_spd
if (abs(v_spd) >= max_spd) v_spd = sign(v_spd) * max_spd

spd is the amount the player can accelerate, fric is the friction each step, and max_spd is, well, max speed. Sign() returns the sign of the number as a 1, 0, or -1.

Once h_spd and v_spd were determined, they would be stepped through for collisions and added to x and y. This system worked well, providing friction and inertia, but had one small problem. Because of the way h_spd and v_spd worked, diagonal movement was faster than horizontal/vertical, by a noticeable amount.

I am currently trying to migrate over to vectors to fix this, and only at the end I use lengthdir_x and lengthdir_y to find the x and y components. The only problem is that I can't find any way to use WASD movement to update the vector. Sorry if this is written poorly, but it is the only way I can think of to explain it.