Honors-section homework

Use the Intermediate Student Language with lambda for this assignment.

You may use local within existing functions to encapsulate recursion.

You should use "loops" (i.e., abstractions such as map, foldr, filter, etc.) wherever your functions may benefit from them.

---

Missile Defense

Develop Missile Defense. In this game you control an artillery gun centered at the bottom of a 500x500 pixel canvas. Clicking the mouse anywhere on the canvas causes one bullet to be fired from the gun in that direction. The "enemy" is simultaneously firing missiles at you. Unlike bullets, which are always launched under your control from the gun, missiles are launched randomly from invisible silos just above the top of the canvas. There is a silo at every possible horizontal location (i.e. missiles may start out at any in-bounds x coordinate), and each missle has a random direction but always aims downwards (possibly at an angle) so that, unless you shoot it down, it will reach the bottom of the canvas without going out of bounds. Once shot, both missiles and bullets travel in straight lines. A missile is shot down when a bullet collides with it; in that case both the bullet and the missile "explode" (i.e. disappear). Both bullets and missiles are represented as circles, though their radii and color should be different to distinguish them.

The goal of the game is to survive as long as possible. You start out with an initial health count, which is decremented by one each time a missile reaches all the way to the bottom of the canvas. The game is over when your health count reaches zero. You should display the health count on the screen and make the game end when it reaches zero.

Here is an image of the game in play (but yours should show the health count as well):

Data Definitions: Use these data definitions unless you have a good reason for departing (e.g., you want to add extra features like top-score list, animated explosions, smart missiles, etc. -- first see the advice below):

 ;;; A Sprite is a (make-sprite Posn Posn Number String)
 ;;; where
 ;;; - LOC is the sprite's location
 ;;; - VEL is its velocity
 ;;; - SIZE is the radius of the sprite
 ;;; - COLOR is its color.
 ;;; Location, velocity and size are in computer-graphic/pixel coordinates.
 ;;; A sprite represents either an attacker's missile or a defender's
 ;;; anti-missile bullet.

(define-struct sprite (loc vel size color))

 ;;; A LOS (list of sprites) is one of:
 ;;; - empty
 ;;; - (cons Sprite LOS)

 ;;; A world structure is a (make-world LOS LOS Number)
 ;;; - missiles: the missiles attacking the player
 ;;; - bullets: the missiles launched by the player
 ;;; - health: current health of the player -- game-over if health <= 0
(define-struct world (missiles bullets health))

Top-Level Functions: We strongly suggest you use these top-level functions:

;;; move-bullets: World -> World
;;; Move the bullets one time step and remove any that have gone off screen.

;;; move-missiles: World -> World
;;; Move the missiles one time step.

;;; remove-dead-missiles-and-bullets: World -> World
;;; Remove every missile that is touching some bullet and vice versa.

;;; detonate-missiles: World -> World
;;; Remove missiles that landed... and decrement the player's health if any did.

;;; maybe-fire-missle: World -> World
;;; If we haven't maxed out on missiles, launch another one.

Note the shared functionality in some of these. For example, both move-bullets and move-missiles need to advance every Sprite in an LOS. And both move-bullets and detonate-missiles need to cull out-of-bounds Sprites. You should implement helper functions for operations like these so that you don't end up writing the same Sprite processing code in multiple places.

On-Tick Handler: Given those functions, this should be the organization of your on-tick handler:

;;; update-world: World -> World
;;; Step the world one tick.

1. Move the bullets and remove offscreen ones.
2. Move the missiles.
3. Kill any destroyed missiles.
4. Detonate the missiles that landed.
5. Maybe launch another missile.

Some Advice:

• Note that two circles "collide" if the distance between their centers is less than the sum of their radii. Remember, the formula for the distance between two points at coordinates (x0, y0) and (x1, y1) is

  (sqrt (+ (sqr (- x1 x0)) (sqr (- y1 y0))))

• You may implement more features, if you like (e.g., health display, increasing difficulty, fancier graphics, game pausing). However, extra features won't save you from points taken off if your code has bugs or isn't well written. You will not receive 100% credit simply for having code that works. For full credit, your code must work and be well written. So you should put your effort into writing clean, readable, bug-free code.
• As always, we advise you that the Design Recipe will help you get your code written.