; in-class examples
; CS 131 - Week 2, Lecture 1

(require 2htdp/universe)
(require 2htdp/image)

; introducing a new type today: the scene type
;    *   it is a special kind of image
;    *   the image and universe teachpacks support
;        this type (it has operations for it)

; how can I get a scene instance?
; I can use the operation:
; empty-scene: number number -> scene
; purpose: expects a width and a height in pixels
;    and produces an empty scene with those dimensions

(empty-scene 300 200)

; remember how, last Friday, we gave an identifier a
;    name using the define operation?
; we will OFTEN do that, in programs;
;    These are often called NAMED CONSTANTS,
;    and a common style is to write named constants in
;    all uppercase;
;    STARTING WITH WEEK 2 LAB/Homework 2,
;    YOU should use all-uppercase for your named constants,
;    too; [that's a COURSE STYLE STANDARD]

; it is VERY common to use named constants for the width and
;    height of a scene:

(define WIDTH 400)
(define HEIGHT 200)
(empty-scene WIDTH HEIGHT)

(define WIDGET-MAX 13)

; place-image: image number number scene -> scene
; purpose: expects an image, the desired x and y coordinates
;    (in that order, and in pixels),
;    and a scene, and produces a new scene with that image
;    centered at (x,y) within the given scene (and trimmmed
;    to fit in the scene)

(define BACKDROP (empty-scene WIDTH HEIGHT))

(place-image (circle 30 "solid" "blue")
             50
             50
             BACKDROP)

; do you want several images in a scene?
;    well, the result of place-image is a scene;
;    so, have a scene created by a place-image expression as 
;    the last expression in a place-image expression!

(place-image
   (rectangle 20 60 "solid" "green")
   50
   50 
   (place-image (circle 30 "solid" "blue")
                50
                50
                BACKDROP))

;*******************
; bonus after-class examples:
; ...and the above is a scene, so it could itself be the
;    4th expression to ANOTHER place-image call...
;    (and so on, and so on...)

(place-image
   (star 50 "solid" "purple")
   100 
   100
   (place-image
      (rectangle 20 60 "solid" "green")
      50
      50 
      (place-image (circle 30 "solid" "blue")
                   50
                   50
                   BACKDROP))) ; see? 3 parentheses here...

; but as a class member mentioned, you could give names to
;    these scenes to simplify this...

(define CIRCLE-SCENE 
        (place-image (circle 30 "solid" "blue")
                     50
                     50
                     BACKDROP))

(define STRIPED-BALL-SCENE
        (place-image
            (rectangle 20 60 "solid" "green")
            50
            50 
            CIRCLE-SCENE))

(define STRIPED-BALL-STAR-SCENE
        (place-image
            (star 50 "solid" "purple")
            100 
            100
            STRIPED-BALL-SCENE))

STRIPED-BALL-STAR-SCENE

; end of bonus after-class examples
;******************

(place-image
   (rectangle 20 60 "solid" "green")
   50
   50 
   BACKDROP)

(place-image (circle 30 "solid" "red")
             0 HEIGHT
             (empty-scene WIDTH HEIGHT))

; OUR FIRST FUNCTION... (user-defined function)
; consider the math function f(x) = 3x
; here's what it looks like in Racket
;   (and we'll discuss function syntax further on Thursday)

; defining a function -- this says, define a function with
;    the name f and a single parameter variable named x,
;    which will produce is 3 times that parameter's value
;    when it is called/used

(define (f x)
  (* 3 x)
)

; these are function applications -- applying, or using,
;    or calling, that function;

(f 3)
(f 100)
(f (+ 5 5))