Add Camera, Action !

Add Camera, Action !

Required

Add a Camera Object to move game view according to a target position in the game play area. the target must be an Entity.

• add a smooth effect between target and the Camera move.

figure 8.1 - What is a Camera in a game ?

Here are:

• the play area at (0,0) with a size of 500 x 400,
• a player Entity at (p.x,p.y) with a size of 16x16,
• the Camera object is targeting the player entity with a specific tween factor used to add some elasticity and delay in the tracking operation.

Implementation proposal

The Camera object will drive the rendering view port to follow a GameObject target, with a certain delay fixed by the tween factor value.

The Camera object

The Camera class will inherit from Entity and introduce 3 new attributes:

figure 8.2 - Camera and Scene, how to interact with ?

Some java code :

public static class Camera extends Entity {
    private Entity target;
    private double tween;
    private Rectangle2D viewport;
}

All the mechanics is hidden in the update method:

In short the position of the camera is shortly delayed one based on the target position. This delay is computed upon the tween factor that is set between 0.0 to 1.0.

CameraPos = CameraPos + distance (CameraPos,TargetPos) * tween * dt

where

• CameraPos is the current camera position,
• TargetPos is the position of the tracked target,
• tween is the delay factor,
• dt is the elapsed time since previous call.

The corresponding simplified code :

public static class Camera extends Entity {
    //...
    public void update(long dt) {
        this.position.x += Math
                .ceil((target.position.x + (target.w * 0.5) - ((viewport.getWidth()) * 0.5) - this.position.x)
                        * tween * Math.min(dt, 10));
        this.position.y += Math
                .ceil((target.position.y + (target.h * 0.5) - ((viewport.getHeight()) * 0.5) - this.position.y)
                        * tween * Math.min(dt, 10));

        this.viewport.setRect(this.position.x, this.position.y, this.viewport.getWidth(),
                this.viewport.getHeight());
    }
}

Usage

TODO