在libgdx Java中基于手臂旋转的射击对象

Question

I am trying to shoot an object(a spell) depending on the rotation of the players arm. The spell is supposed to come out of the hand and shoot towards where the mouse cicked(the arm rotates and points to where the mouse is). This is how the arm rotates in game.

    public boolean mouseMoved(int screenX, int screenY) {
    tmp.x = screenX;
    tmp.y = screenY;
    tmp.z = 0;
    cam.unproject(tmp);
    rot = MathUtils.radiansToDegrees * MathUtils.atan2((float)tmp.y - (float)player.getArmSprite().getY() - player.getArmSprite().getHeight(),
            tmp.x -player.getArmSprite().getX() - player.getArmSprite().getWidth());
    if (rot < 0) rot += 360;

    //Last right or left means if hes looking left or right
    if(player.lastRight)
        player.setObjectRotation(rot + 80);
     if(player.lastLeft)
        player.setObjectRotation(-rot - 80);

And this is how the spell is supposed to shoot based off rotation

    //destination is a vector of where on screen the mouse was clicked
    if(position.y < destination.y){
        position.y += vel.y * Gdx.graphics.getDeltaTime();
    }
    if(position.x < destination.x){
        position.x += vel.x * Gdx.graphics.getDeltaTime();
    }

However this is very wonky and never really reacts the way it supposed to with a few exceptions. It fires from the hand and then if the y axis is equal it completely evens out and goes till it reaches the x position, I want it to fire from the hand to the position clicks perfectly straight from point a to point b, this is clearly a rotation problem that I just can't seem to figure out how to tackle.

Here is an image of what is happening

Example image

The red indicates where I clicked, as you can see it reached the x pos first and now is traveling to the y when it should have reached the x and y pos of where I clicked first

Any help with this problem is extremely appreciated!

Answer 1

I'm pretty bad at radians and tangents but luckily we have vectors.

Since you have the rot ation in degrees of the arm. I advice to use Vectors to use for any Vector related math now.

//A vector pointing up
Vector2 direction = new Vector2(0, 1);

//Let's rotate that by the rotation of the arm
direction.rotate(rot);

Now direction is the direction the arm is pointing. If your rot ation is calculated where up = 0 . So you might need to rotate it 180, 90 or -90 degrees. Or in the case you did something silly any degrees.

Your spell should have a Vector too for it's position. Set that to the hand or wherever you want to start from. Now all you need to do is scale that direction since it's currently has a length of 1. If you want to move 5 units each frame you can do direction.scl(5) now it is of length 5. But technically speaking it's no direction anymore now everybody calls it velocity so let's do.

//when you need to fire
float speed = 5;
Vector2 velocity = direction.cpy().scl(speed);

//update
position.add(velocity);
draw(fireballImage, position.x, position.y);

I copied direction first, otherwise it would also be scaled. Then I just added the velocity to the position and draw using that Vector.

And to show Vectors are awesome you should see this awesome badlogic vs mouse program I created. https://github.com/madmenyo/FollowMouse there are just a view lines of my own code. It just takes a little bit of vector knowledge and it's very readable.