Homework 3: Simple Drawing Program Part 2

Description

Redesign your simple drawing program so that you can easily add new features. To minimize the effort and maximize code reuse, design your program to take advantage of the object-oriented concepts that you have learned in class.

Object-oriented Design

For this assignment, you will add to the drawing program new features that are similar to the current ones. Apply object-oriented design concepts, such as inheritance and polymorphism, to make it easier to extend your program. Design your class hierarchy and explain your design to yourself or your classmates (but NOT your source code!).

Input Language

A drawing consists of zero or more picture elements, with each element modified by zero or more transformations. The drawing may also have zero or more parameter settings before any picture element. All numbers should be handled in floating-point. The coordinate (0,0) is the origin and is the lower left corner of the drawing. X-coordinate values increase to the right and y-coordinate values increase to the top.

Create picture elements using the commands below.

(line X₀ Y₀ X₁ Y₁): Draw a line with the first endpoint at (X₀, Y₀) and the second endpoint at (X₁, Y₁).
(rect X Y W H): Draw the outline of a rectangle whose lower left corner is at (X,Y), and which has a width of W and height of H. Draw the rectangle counter-clockwise starting from the lower left corner.
(filledrect X Y W H): Same as rect, but fill the rectangle rather than simply drawing its boundary.
(tri X Y R): Draw the outline of an equilateral triangle whose center is at (X, Y) with one of the vertices at (X + R, Y). Draw the triangle counter-clockwise starting from (X + R, Y). This order applies to all the following picture elements.
(filledtri X Y R): Same as tri, but fill the triangle rather than simply drawing its boundary.
(square X Y R): Draw the outline of a square whose center is at (X, Y) with one of the vertices at (X + R, Y).
(filledsquare X Y R): Same as square, but fill the square rather than simply drawing its boundary.
(penta X Y R): Draw the outline of a regular pentagon whose center is at (X, Y) with one of the vertices at (X + R, Y).
(filledpenta X Y R): Same as penta, but fill the pentagon rather than simply drawing its boundary.
(hexa X Y R): Draw the outline of a regular hexagon whose center is at (X, Y) with one of the vertices at (X + R, Y).
(filledhexa X Y R): Same as hexa, but fill the hexagon rather than simply drawing its boundary.
(ngon X Y R N): Draw the outline of a regular N-gon for integer N > 2, whose center is at (X, Y) with one of the vertices at (X + R, Y).
(filledngon X Y R N): Same as ngon, but fill the ngon rather than simply drawing its boundary.

Create transformations using the commands below.

(translate X Y): Translate the following picture element by X units along the x-axis, and Y units along the y-axis.
(rotate X): Rotate the following picture element by X degrees about the origin.
(scale S): Scale the following picture element by a factor of S, where S > 0. If (X ,Y) was a vertice on the picture, then its new coordinate after scaling is (X * S, Y * S).

Create drawing parameters using the commands below.

(color R G B): Set the current color to (R,G,B). The arguments must be numbers between 0 and 1, inclusive. Initially, R = G = B = 0 (i.e. black).
(linewidth W): Set the current line width to W, which must be a non-negative number. This meaning of this width value is as that of PostScript, meaning you can pass this value directly to PostScript commands. The initial value of the line width is 1.

Zero or more whitespaces are allowed between a parenthesis and the start or end of a command, and between commands. At least one character of whitespace is required to separate arguments within a command.

For example, the following would draw a thick blue square, rotated 45 degrees.
(linewidth 5) (color 0 0 1) (rotate 45)(rect 100 100 100 100)

We will test your program with only valid drawing input. In other words, your program need not handle input errors.

PostScript

The output of your program will be a PostScript document. You can view a PostScript file with any PostScript viewer. A popular one is gv available on Linux. A PostScript file has the following form:

%!PS-Adobe-3.1
commands
showpage

The commands of the PostScript language are in postfix notation. The actual PostScript language is free form, meaning operands and operators can be separated by arbitrary whitespace. Your output, however, must mimic the reference program to make your program easier to debug and grade. Each command will start on a newline with operands separated by a single space.

The origin of a PostScript starts at (0,0) in the lower left corner, with x-coordinates increasing to the right and y-coordinates increasing to the top. To draw something, one builds a path, and then strokes it or fills it. The PostScript interpreter maintains a graphics state, which for our purposes consists of

A current point, (x,y) coordinate, which is initially undefined.
A current path.
A current color, a 3-tuple (r,g,b), where each color intensity r,g,b is between 0 and 1 inclusive. (0,0,0) is black and (1,1,1) is white.
A current line thickness, which indicates the thickness of lines drawn when stroking.

You can use the following subset of the PostScript language to construct your PostScript file. In this subset, all operands are decimal numbers (e.g. 0.1, 2.3, 45).

X Y moveto: Set the current point to (X, Y).
X Y lineto: Add a line segment to the current path starting at the current point and going to (X, Y), which becomes the new current point.
stroke: Draw lines with the current line width and color over all the segments in the current path. Clear the current path and undefine the current point.
fill: Fill the interior of the current line path with the current color. Clear the current path and set the current point to undefined.
W setlinewidth: Set the current line width to W. The initial value of the line width is 1.
R G B setrgbcolor: Set the current color to (R, G, B).

To tolerate small errors in floating point computation, the gradebot uses cmpfloat.py (SHA-1: 08ed50ecf4b0356527da25e967b06483876f7f75) to compare the output of your program to that of the reference program. When they are equal, cmpfloat.py outputs nothing.

Hints

Process the input through the following stages:

Tokenzier: reads input, and outputs a sequence of tokens, such as (, ), line, translate, color, etc.
Parser: reads tokens from the tokenizer, and outputs picture elements, transformations, and drawing parameters.
Executor: reads the output from the parser, executes the transformations and sets the drawing parameters, and outputs PostScript.

We provide an incentive against procrastination.