Line Mid Point

class Example extends Phaser.Scene
{
    create ()
    {
        const graphics = this.add.graphics({ lineStyle: { width: 4, color: 0xaa00aa }, fillStyle: { color: 0x0000aa } });

        const line = new Phaser.Geom.Line(0, 300, 400, 100);

        this.input.on('pointermove', pointer =>
        {

            line.x2 = pointer.x;
            line.y2 = pointer.y;

            redraw();
        });

        redraw();

        function redraw ()
        {
            graphics.clear();

            const midPoint = Phaser.Geom.Line.GetMidPoint(line);

            graphics.strokeLineShape(line);

            graphics.fillPointShape(midPoint, 25);
        }
    }
}

const config = {
    scale: { mode: Phaser.Scale.FIT },
    width: 800,
    height: 600,
    type: Phaser.AUTO,
    parent: 'game-container',
    scene: Example
};

const game = new Phaser.Game(config);