JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/pixi.js/4.2.2/pixi.min.js"></script>
<div id="capture_focus" />

CSS

body {
    padding: 0;
    margin: 0;
}

#capture_focus {
  position: absolute;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0);
}

JavaScript

var Degree = Math.PI / 180;
var showDebugOverlays = false;

var Turret = {
    gunAngle: -10 * Degree,
    maxGunAngle: 85 * Degree,
    adaptedGunXOffset: null,

    rotateToTarget: function (target) {
        var delta = Vec.subtract(this.position, target.position);
        var dist = Vec.length(delta);
        var angle = Vec.angle(delta);

        theta = Math.asin(this.adaptedGunXOffset / dist) + this.gunAngle;
        this.rotation = -(angle + theta);

        this.updateGunRay(target);
    },

    setGunAngle: function (angle) {
        var angle = this.clampGunAngle(angle);
        this.gunAngle = angle;
        this.gun.rotation = angle;
        // Account for the fact that the origin of the gun also has an y offset
        // relative to the turret origin
        var extraXOffset = this.gun.position.y * Math.tan(angle);
        var gunXOffset = this.gun.position.x + extraXOffset;
        // This equals "a * cos(δ')" in the angle formula
        this.adaptedGunXOffset = gunXOffset * Math.cos(-angle);

        if (showDebugOverlays) {
            // Show x offsets
            this.removeChild(this.xOffsetOverlay);
            this.removeChild(this.extraXOffsetOverlay);
            this.xOffsetOverlay = addRect(this, 0, 0, this.gun.position.x, 1, 0xf6ff00);
            this.extraXOffsetOverlay = addRect(this, this.gun.position.x, 0, extraXOffset, 1, 0xff00ae);
        }
    },

    rotateGun: function (angleDelta) {
        this.setGunAngle(this.gunAngle + angleDelta);
    },

    updateGunRay: function (target) {
        var delta = this.gun.toLocal(target.position);
        var dist = Vec.length(delta);
        this.gun.removeChild(this.gun.ray);
        this.gun.ray = makeLine(0, 0, 0, -dist);
        this.gun.addChildAt(this.gun.ray, 0);
    },

    clampGunAngle: function (angle) {
        if (angle > this.maxGunAngle) {
            return this.maxGunAngle;
        }
        if (angle < -this.maxGunAngle) {
            return -this.maxGunAngle;
      ...