Due: &shapes-due; Summary: In this assignment, you will develop procedures that allow us to use files to store information about simple shapes and to reproduce those shapes from the stored information. Purposes: To give you more experience with files. To help you think about yet more representations of images. Expected Time: Two to three hours. Collaboration: We encourage you to work in groups of size three. You may, however, work alone or work in a group of size two or size four. You may discuss this assignment with anyone, provided you credit such discussions when you submit the assignment. Submitting: Email your answer to &grader-email;. The title of your email should have the form &shapes-subject; and should contain your answers to all parts of the assignment. Scheme code should be in the body of the message. Warning: So that this assignment is a learning experience for everyone, we may spend class time publicly critiquing your work.

As you've just seen in the exam, it can be useful to describe images as a sequence of simple drawing objects, such as circles and squares. There are many ways that we can represent such objects. In Scheme, one of the most natural techniques is to use a list. However, it can be difficult to make those lists persist between invocations of Scheme. We might also want to provide a slightly more human-readable approach to representing these objects. Here's one such technique: We use a file to store the drawing objects in an image. Each line of the file represents one object. A line begins with the name of the object, such as "filled ellipse", "empty circle", "line", or "filled square". The remaining values on the line depend on the kind of object. An empty ellipse, which is stroked, is followed by the color, the brush, the left edge, the top edge, the width, and the height of the ellipse. A filled ellipse, which is filled, is followed by the color, the left edge, the top edge, the width, and the height of the ellipse. An empty circle, which is stroked, is followed by the color, the brush, the left edge, the top edge, and the diameter of the circle. A filled circle, which is filled, is followed by the color, the left edge, the right edge, and the diameter of the circle. An empty rectangle, which is stroked, is followed by the color, the brush, the left edge, the top edge, the width, and the height of the rectangle. A filled rectangle, which is filled, is followed by the color, the left edge, the top edge, the width, and the height of the rectangle. An empty square, which is stroked, is followed by the color, the brush, the left edge, the top edge, and the side length of the square. A filled square, which is filled, is followed by the color, the left edge, the top edge, and the side length of the box. A line is followed by the color, the brush, the starting column, the starting row, the ending column, and the ending row of the line. For example, here's a simple drawing: "empty ellipse" "red" "Circle (03)" 10 10 80 40 "filled square" "rich blue" 30 30 80 "line" "green" "Circle Fuzzy (11)" 0 90 100 20 The first goal is to read these values from a file and draw them. Here's a start. You can find the helper procedures at the end of this assignment.

a. Right now, image-read-object! reads the color to use and the brush to use but then ignores both. Update the procedure so that it sets the brush and color before drawing. b. Right now, image-read-object! only does about half of the desired shapes. Extend it to do the other shapes. c. Write a procedure, (image.load-objects! image filename), that reads and renders every object in the named file. d. Write procedures that let us write each kind of object from Scheme. For example,

We will evaluate your assignment primarily on its correctness: Does it correctly read and write these kinds of values. However, since this program can be written with very repetitious code, we will also look to ways to avoid repetition. (You'll note that the sample code avoids some repetition by doing only one selection for related object. However, it also repeats some code. Can you do better?)

You are likely to find the following procedures useful.