Object velocities are calculated with a trigonometric algorithm that standardizes velocity rather than using slope. Misc: Collisions are handled by individual objects by sending properties to a universal collision function in the Util file. Rounded corners for buttons are a staple in today's web but drawing out something mildly complex can become laborious.
However, canvas can be very unforgiving when trying to stylize elements. The basic shapes in use made this implementation feasible. This separation of concerns also allowed for a robust utility file where many functions are shared between the various objects.Ĭanvas: With the exception of background images, gun icons, and sound icons, Earth Defender is drawn entirely on canvas. Each object instantiates a "new Audio()" object, allowing for sound layering. This allows for delegation of drawing and collision logic to the object itself as well as an efficient way to handle sound effects.
JavaScript Structure: Each projectile is an instance of that projectile's class. Tracks items that are rendered but do not affect actual gameplay (score, timer, shields, icons, sound, etc.) Game - handles gameplay, render cycles, and acts as a conduit for object interactions (missiles, collisions, etc.).GameView - entry point, game initialization/ end/ restart, as well as user input difficulty timers.Most of the components are separated into their own classes with the major ones being: Toggle sound on/off by clicking on the speaker iconĮarth Defender was built with vanilla JavaScript and HTML5 Canvas. Toggle music on/off by clicking on the music icon We need you to hold out as long as possible but they're aiming for your shields and you're a sitting duck once your shields are depleted. Take care, incoming missiles will be sent with increasing speed as the aliens adjust their tactics. Use keyboard keys ASDF to toggle weapons (Rocket, Cluster Bomb, Gravity Gun, and Laser, respectively). Intercept these missiles before they hit the ground and reduce your shields!Ĭlick on the screen to shoot at that point. Missiles will appear at the top of the screen with a trajectory toward the ground. Once a game has been initiated, players will have to defend against incoming enemy missiles.
InstructionsĪt the splash screen, players can either start a new game or view current high scores (local high scores only). Godspeed commander, we're counting on you. You command the latest missile defense system known to man and have access to the world's most highly classified weapons - released for use by order of the United Defense Initiation Edict or UnDefInEd for short. The alien attack on earth has commenced and you're our only hope. A turret defense game inspired by Atari's "Missile Command" and built with JavaScript and HTML5 Canvas.
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