Drawing Generally and Concisely

a) Define a procedure that corresponds to the following documentation. Include this documentation along with your definition of the procedure.

;;; Procedure:
;;;   shadow
;;; Parameters:
;;;   drawing, a drawing
;;; Purpose:
;;;   Create a shadow for drawing.
;;; Produces:
;;;   my-shadow, a drawing
;;; Preconditions:
;;;   No additional.
;;; Postconditions:
;;;   my-shadow is the same size and shape as drawing.
;;;   my-shadow is colored grey.
;;;   my-shadow is shifted up by 3 units and left by 6 units
;;;     relative to the position of drawing.

Here are some examples of applying this procedure.

(shadow red-eye)

(shadow (drawing-hshift blue-i 10))

b) Define a procedure (pair-with-shadow drawing) that groups a drawing together with its shadow. The shadow should appear behind. For example,

(pair-with-shadow (drawing-hshift (drawing-vshift red-eye 20) 20))

(pair-with-shadow (drawing-hshift (drawing-vshift blue-i 20) 20))

Using the drawings-as-values model, write a program to draw a checkerboard: that is, an 8x8 grid of squares in alternating black and red colors. Your code should take advantage of the many similar elements in this figure.

Recall that the drawings-as-values model includes procedures such as drawing-scale, drawing-hshift, drawing-recolor, and drawing-group.

You have already written several programs to create interesting pictures using the GIMP tools. For example, you wrote programs to make a smiley face and a house for the lab on scripting the GIMP tools. You also wrote a program to create a picture of your own design in homework 2. Recall that the GIMP tools procedures include context-set-fgcolor!, image-select-ellipse!, image-fill-selection!, and so on.

Take one of these three programs: your program to create a smiley face, your program to create a house, or your program from homework 2. Copy and paste it into the body of a new procedure, like so:

(define your-proc-name
  (lambda (image width height)
     ; Your code for making a picture with GIMP tools goes here
     ))

Delete the line of code that defines a new image. You should not define a new image inside the procedure, because the image is one of the parameters. You may need to change the procedure definition so that the parameter name for the image matches the name of the image in your code.

Try calling your procedure. If you originally made a 200x200 image, you would call your new procedure as follows:

> (define canvas (image-new 200 200))
> (image-show canvas)
1
> (your-proc-name canvas 200 200)

You should see your picture of a smiley face, or whatever, appear in the image.

But what if you wanted to make a picture that was some other size, and not 200x200? That is where the width and height parameters come in.

Modify your code, still using the GIMP tools procedures, so that the numbers in your code are related to the width and height parameters. For example, if your original program selected a 100x50 ellipse in a 200x200 image, you would modify the call to image-select-ellipse! to instead select an ellipse with the dimensions (* 0.5 width) by (* 0.25 height).

You may alter your original instructions to make them simpler, for example, changing the size and location of elements or removing elements altogether.

Your procedure may take other parameters if you wish, but this is not required. If you add extra parameters, please provide informal documentation explaining how we should use your procedure.

For example, we defined a procedure called sams-smiley! that generalizes the original smiley face from the lab on scripting the GIMP tools. Here are some examples of using sams-smiley! to make a smiley face in a 200 x 200 image.

(define canvas (image-new 200 200))
(image-show canvas)
(sams-smiley! canvas 200 200)

(define another-canvas (image-new 200 200))
(image-show another-canvas)
(sams-smiley! another-canvas 100 150)