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Akbar Hashimi

_velocity.y = move_and_slide_with_snap().y question

So in this code i understand that "move_and_slide_with_snap()" returns the 'y' component of a Vector2D and moves the character. My question is in trying to understand the logic of the movement and why it works. Do we return the y component first and then move the character or what is the 'algorithm' of the move and slide function? As it was weird to me that we needed to return the y component of the vector at all.

  • Nathan Lovato replied

    Here's what's happening.

    A function takes some parameters, makes some calculations, and optionally returns a value.

    move_and_slide_with_snap() takes some parameters, starting with a velocity, makes some calculations, moves your characters, and it returns a modified velocity.

    That modified velocity is the remainder of the character's movement after collisions like hitting the floor (can reduce the Y velocity to 0), hitting a wall (can reduce the X velocity to 0), or any other collision.

    The function returns that new velocity, but unless we store it in a variable, the returned value is lost.

    That's why we write _velocity.y = move_and_slide_with_snap().y

    The ".y" makes it so we extract the Y component of the returned velocity vector and assign it to the Y component of our _velocity variable. Now, why do we have this ".y" on either side of the equal sign?

    Well, in this game, the enemies move at a fixed horizontal speed. When they hit a wall, we multiply their horizontal velocity by -1 to change their movement direction. This makes them move like the Goombas in Mario.

    If we applied the returned X velocity from move_and_slide_with_snap(), when the enemies hit a wall, their X velocity would be reduced to 0, and they would stop moving entirely.

    That's why we only override our _velocity.y variable.

    But the important part is that the move_and_slide_with_snap() function calculates and returns a new velocity, and that, depending on your needs, you can save that value, be it entirely or just one vector component.

  • H
    Akbar Hashimi replied

    Thank you so much, this helps me understand it way better than before. Thank you for telling me that when a collision happens (in x or y), it can reduce (x or y) to zero. I needed to know that for it to make sense, thank you so much and I appreciate the work you put in for creating these courses :)