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516 lines
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HTML
516 lines
21 KiB
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<nav class="navbar fixed-top navbar-expand-lg navbar-dark bg-primary">
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<div class="container-fluid">
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<span class="navbar-brand">Gtk4 tutorial</span>
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<button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
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<div class="collapse navbar-collapse" id="navbarSupportedContent">
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<ul class="navbar-nav me-auto mb-2 mb-lg-0">
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<li class="nav-item">
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<a class="nav-link" href="index.html">Home</a>
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</ul>
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</nav>
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<div class="row justify-content-center">
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<div class="col-xl-10 col-xxl-9">
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<h1 id="turtle-manual">Turtle manual</h1>
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<p>Turtle is a simple interpreter for turtle graphics.</p>
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<h2 id="prerequisite-and-compiling">Prerequisite and compiling</h2>
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<p>Turtle is written in C language. You need:</p>
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<ul>
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<li>Linux. Turtle is tested on ubuntu 22.10</li>
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<li>gcc, meson and ninja</li>
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<li>gtk4</li>
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</ul>
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<p>It is easy to compile the source file of turtle. If you want tp
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install it in your local area, put an option
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<code>--prefix=$HOME/.local</code> to your meson command line. Then, it
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will be installed under <code>$HOME/.local/bin</code>. The instruction
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is:</p>
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<pre><code>$ meson setup --prefix=$HOME/.local _build
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$ ninja -C _build
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$ ninja -C _build install</code></pre>
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<p>If you want to install it in the system area, no option is necessary.
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It will be installed under <code>/usr/local/bin</code>.</p>
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<pre><code>$ meson setup _build
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$ ninja -C _build
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$ sudo ninja -C _build install</code></pre>
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<p>Type the following command then turtle shows the following
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window.</p>
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<pre><code>$ turtle</code></pre>
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<figure>
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<img src="image/turtle1.png"
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alt="Screenshot just after it’s executed" />
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<figcaption aria-hidden="true">Screenshot just after it’s
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executed</figcaption>
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</figure>
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<p>The left half is a text editor and the right half is a surface.
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Surface is like a canvas to draw shapes.</p>
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<p>Write turtle language in the text editor and click on
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<code>run</code> button, then the program will be executed and it draws
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shapes on the surface.</p>
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<figure>
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<img src="image/turtle_tree.png" alt="Tree" />
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<figcaption aria-hidden="true">Tree</figcaption>
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</figure>
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<p>If you uncomment the following line in <code>turtle.y</code>, then
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codes for debug will also be compiled. Turtle shows the status to the
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standard output, but the speed is quite slow. It is not recommended
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except you are developing the program.</p>
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<pre><code>/* # define debug 1 */</code></pre>
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<h2 id="example">Example</h2>
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<p>Imagine a turtle. The turtle has a pen and initially it is at the
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center of the screen, facing to the north (to the north means up on the
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screen). You can let the turtle down the pen or up the pen. You can
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order the turtle to move forward.</p>
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<pre><code>pd
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fd 100</code></pre>
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<ul>
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<li>pd: Pen Down. The turtle put the pen down so that the turtle will
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draw a line if it moves.</li>
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<li>fd 100: move ForwarD 100. The turtle goes forward 100 pixels.</li>
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</ul>
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<p>If you click on <code>run</code> button, then a line segment appears
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on the screen. One of the endpoints of the line segment is at the center
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of the surface and the other is at 100 pixels up from the center. The
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point at the center is the start point of the turtle and the other
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endpoint is the end point of the movement.</p>
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<p>If the turtle picks the pen up, then no line segment appears.</p>
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<pre><code>pu
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fd 100</code></pre>
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<p>The command <code>pu</code> means “Pen Up”.</p>
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<p>The turtle can change the direction.</p>
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<pre><code>pd
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fd 100
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tr 90
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fd 100</code></pre>
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<p>The command <code>tr</code> is “Turn Right”. The argument is angle
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with degrees. Therefore, <code>tr 90</code> means “Turn right by 90
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degrees”. If you click on the <code>run</code>button, then two line
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segments appears. One is vertical and the other is horizontal.</p>
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<figure>
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<img src="image/turtle2.png" alt="Two line segments on the surface" />
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<figcaption aria-hidden="true">Two line segments on the
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surface</figcaption>
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</figure>
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<p>You can use <code>tl</code> (Turn Left) as well.</p>
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<h2 id="background-and-foreground-color">Background and foreground
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color</h2>
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<p>Colors are specified with RGB. A vector (r, g, b) denotes RGB color.
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Each of the elements is a real number between 0 and 1.</p>
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<ul>
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<li>Red is (1.0, 0.0, 0.0). You can write (1, 0, 0) instead.</li>
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<li>Green is (0.0, 1.0, 0.0)</li>
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<li>Blue is (0.0, 0.0, 1.0)</li>
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<li>Black is (0.0, 0.0, 0.0)</li>
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<li>White is (1.0, 1.0, 1.0)</li>
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</ul>
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<p>You can express a variety of colors by changing each element.</p>
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<p>There are two commands to change colors.</p>
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<ul>
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<li>bc: Background Color. <code>bc (1,0,0)</code> changes the background
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color to red. This command clear the surface and change the background
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color. So, the shapes on the surface disappears.</li>
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<li>fc: Foreground Color. <code>fc (0,1,0)</code> changes the foreground
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color to green. This command changes the pen color. The prior shapes on
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the surface aren’t affected. After this command, the turtle draws lines
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with the new color.</li>
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</ul>
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<figure>
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<img src="image/turtle3.png" alt="Change the foreground color" />
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<figcaption aria-hidden="true">Change the foreground color</figcaption>
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</figure>
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<h2 id="other-simple-commands">Other simple commands</h2>
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<ul>
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<li>pw: Pen Width. This is the same as pen size or line width. For
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example, <code>pw 5</code> makes lines thick and <code>pw 1</code> makes
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it thin.</li>
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<li>rs: ReSet. The turtle moves back to the initial position and
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direction. In addition, The command initialize the pen, line width (pen
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size), and foreground color. The pen is down, the line width is 2 and
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the foreground color is black.</li>
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</ul>
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<p>An order such as <code>fd 100</code>, <code>pd</code> and so on is a
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statement. Statements are executed in the order from the top to the end
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in the program.</p>
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<h2 id="comment-and-spaces">Comment and spaces</h2>
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<p>Characters between <code>#</code> (hash mark) and <code>\n</code>
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(new line) are comment. If the comment is at the end of the file, the
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trailing new line can be left out. Comments are ignored.</p>
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<pre><code># draw a triangle<NEW LINE>
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fd 100 # forward 100 pixels<NEW LINE>
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tr 120 # turn right by 90 degrees<NEW LINE>
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fd 100<NEW LINE>
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tr 120<NEW LINE>
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fd 100 # Now a triangle appears.<EOF></code></pre>
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<p><NEW LINE> and <EOF> indicate newline code and end of
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file respectively. The comments in the line 1, 2, 3 and 6 are correct
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syntactically.</p>
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<p>Spaces (white space, tab and new line) are ignored. They are used
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only as delimiters. Tabs are recognized as eight spaces to calculate the
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column number.</p>
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<h2 id="variables-and-expressions">Variables and expressions</h2>
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<p>Variables begin alphabet followed by alphabet or digit. Key words
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like <code>fd</code> or <code>tr</code> can’t be variables.
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<code>Distance</code> and <code>angle5</code> are variables, but
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<code>1step</code> isn’t a variable because the first character isn’t
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alphabet. Variable names are case sensitive. Variables keep real
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numbers. Their type is the same as <code>double</code> in C language.
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Integers are casted to real numbers automatically. So 1 and 1.0 are the
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same value. Numbers begin digits, not signs (<code>+</code> or
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<code>-</code>).</p>
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<ul>
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<li>100, 20.34 and 0.01 are numbers</li>
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<li>+100 isn’t a number. It causes syntax error. Use 100 instead.</li>
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<li>-100 isn’t a number. But turtle recognizes it unary minus and a
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number 100. So turtle calculate it and the result is -100.</li>
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<li>100 + -20: This is recognized 100 + (- 20). However, using bracket,
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100 + (-20), is better for easy reading.</li>
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</ul>
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<pre><code>distance = 100
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fd distance</code></pre>
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<p>A value 100 is assigned to the variable <code>distance</code> in the
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first line. Assignment is a statement. Most of statements begin with
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commands like <code>fd</code>. Assignment is the only exception.</p>
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<p>The example above draws a line segment of 100 pixels long.</p>
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<p>You can use variables in expressions. There are 8 kinds of
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calculations available.</p>
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<ul>
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<li>addition: x + y</li>
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<li>subtraction: x - y</li>
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<li>multiplication: x * y</li>
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<li>division: x / y</li>
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<li>unary minus: - x</li>
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<li>logical equal: x = y. This symbol <code>=</code> works as
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<code>==</code> in C language.</li>
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<li>greater than: x > y</li>
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<li>less than: x < y</li>
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</ul>
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<p>The last three symbols are mainly used in the condition of if
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statement.</p>
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<p>Variables are registered to a symbol table when it is assigned a
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value for the first time. Evaluating a variable before the registration
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isn’t allowed and occurs an error.</p>
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<h2 id="if-statement">If statement</h2>
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<p>Turtle language has very simple if statement.</p>
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<pre><code>if (x > 50) {
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fd x
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}</code></pre>
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<p>There is no else part.</p>
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<h2 id="loop">Loop</h2>
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<p>Turtle has very simple loop statement. It is <code>rp</code> (RePeat)
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statement.</p>
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<pre><code>rp (4) {
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fd 100
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tr 90
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}</code></pre>
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<p>The program repeats the statements in the brace four times.</p>
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<h2 id="procedures">Procedures</h2>
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<p>Procedures are similar to functions in C language. The difference is
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that procedures don’t have return values.</p>
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<pre><code>dp triangle (side) {
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fd side
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tr 120
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fd side
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tr 120
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fd side
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}
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triangle (100)</code></pre>
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<p><code>dp</code> (Define Procedure) is a key word followed by
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procedure name, parameters, and body. Procedure names start alphabet
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followed by alphabet or digit. Parameters are a list of variables. For
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example</p>
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<pre><code>dp abc (a) { ... ... }
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dp abc (a, b) { ... ... }
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dp abc (a, b, c) { ... ... }</code></pre>
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<p>Body is a sequence of statements. The statements aren’t executed when
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the procedure is defined. They will be executed when the procedure is
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called later.</p>
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<p>Procedures are called by the name followed by arguments.</p>
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<pre><code>dp proc (a, b, c) { ... ... }
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proc (100, 0, -20*3)</code></pre>
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<p>The number of parameters and arguments must be the same. Arguments
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can be any expressions. When you call a procedure, brackets following
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the procedure name must exist even if the procedure has no argument.</p>
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<p>Procedure names and variable names don’t conflict.</p>
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<pre><code>dp a () {fd a}
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a=100
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a ()</code></pre>
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<p>This is a correct program.</p>
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<ul>
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<li>1: Defines a procedure <code>a</code>. A variable <code>a</code> is
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in its body.</li>
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<li>2: Assigns 100 to a variable <code>a</code>.</li>
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<li>3: Procedure <code>a</code> is called.</li>
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</ul>
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<p>However, using the same name to a procedure and variable makes
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confusion. You should avoid that.</p>
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<h2 id="recursive-call">Recursive call</h2>
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<p>Procedures can be called recursively.</p>
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<pre><code>dp repeat (n) {
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n = n - 1
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if (n < 0) {
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rt
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}
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fd 100
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tr 90
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repeat (n)
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}
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repeat (4)</code></pre>
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<p>Repeat is called in the body of repeat. The call to itself is a
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recursive call. Parameters are created and set each time the procedure
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is called. So, parameter <code>n</code> is 4 at the first call but it is
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3 at the second call. Every time the procedure is called, the parameter
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<code>n</code> decreases by one. Finally, it becomes less than zero,
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then the procedures return.</p>
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<p>The program above draws a square.</p>
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<p>It shows that we can program loop with a recursive call.</p>
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<h2 id="fractal-curves">Fractal curves</h2>
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<p>Recursive call can be applied to draw fractal curves. Fractal curves
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appear when a procedure is applied to it repeatedly. The procedure
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replaces a part of the curve with the contracted curve.</p>
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<figure>
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<img src="image/turtle_tree.png" alt="Tree" />
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<figcaption aria-hidden="true">Tree</figcaption>
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</figure>
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<p>This shape is called tree. The basic pattern of this shape is a line
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segment. It is the first stage. The second stage adds two shorter line
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segments at the endpoint of the original segment. The new segment has 70
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percent length to the original segment and the orientation is +30 or -30
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degrees different. The third stage adds two shorter line segments to the
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second stage line segments. And repeats it several times.</p>
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<p>This repeating is programmed by recursive call. Two more examples are
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shown here. They are Koch curve and Square Koch curve.</p>
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<figure>
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<img src="image/turtle_koch.png" alt="Koch curve" />
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<figcaption aria-hidden="true">Koch curve</figcaption>
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</figure>
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<figure>
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<img src="image/turtle_square_koch.png" alt="Square Koch curve" />
|
||
<figcaption aria-hidden="true">Square Koch curve</figcaption>
|
||
</figure>
|
||
<h2 id="tokens-and-punctuations">Tokens and punctuations</h2>
|
||
<p>The following is the list of tokens.</p>
|
||
<p>Keywords:</p>
|
||
<ul>
|
||
<li>pu: pen up</li>
|
||
<li>pd: pen down</li>
|
||
<li>pw: pen width = line width</li>
|
||
<li>fd: forward</li>
|
||
<li>tr: turn right</li>
|
||
<li>tl: turn left</li>
|
||
<li>bc: background color</li>
|
||
<li>fc: foreground color</li>
|
||
<li>if: if statement</li>
|
||
<li>rt: return</li>
|
||
<li>rs: reset</li>
|
||
<li>rp: repeat</li>
|
||
<li>dp: define procedure</li>
|
||
</ul>
|
||
<p>identifiers and numbers:</p>
|
||
<ul>
|
||
<li>identifier: This is used for the name of variables, parameters and
|
||
procedures. It is expressed <code>[a-zA-Z][a-zA-Z0-9]*</code> in regular
|
||
expression.</li>
|
||
<li>number: This is expressed <code>(0|[1-9][0-9]*)(\.[0-9]+)?</code> in
|
||
regular expression. It doesn’t have <code>+</code> or <code>-</code>
|
||
sign because they bring some syntactic confusion. However negative
|
||
number such as <code>-10</code> can be recognized as unary minus and a
|
||
number.</li>
|
||
</ul>
|
||
<p>Symbols for expression</p>
|
||
<ul>
|
||
<li><code>=</code></li>
|
||
<li><code>></code></li>
|
||
<li><code><</code></li>
|
||
<li><code>+</code></li>
|
||
<li><code>-</code></li>
|
||
<li><code>*</code></li>
|
||
<li><code>/</code></li>
|
||
<li><code>(</code></li>
|
||
<li><code>)</code></li>
|
||
</ul>
|
||
<p>Delimiters</p>
|
||
<ul>
|
||
<li><code>(</code></li>
|
||
<li><code>)</code></li>
|
||
<li><code>{</code></li>
|
||
<li><code>}</code></li>
|
||
<li><code>,</code></li>
|
||
</ul>
|
||
<p>Comments and spaces:</p>
|
||
<ul>
|
||
<li>comment: This is characters between <code>#</code> and new line. If
|
||
a comment is at the end of the file, the trailing new line can be left
|
||
out.</li>
|
||
<li>white space:</li>
|
||
<li>horizontal tab: tab is recognized as eight spaces.</li>
|
||
<li>new line: This is the end of a line.</li>
|
||
</ul>
|
||
<p>These characters are used to separate tokens explicitly. They doesn’t
|
||
have any syntactic meaning and are ignored by the parser.</p>
|
||
<h2 id="grammar">Grammar</h2>
|
||
<pre><code>program:
|
||
statement
|
||
| program statement
|
||
;
|
||
|
||
statement:
|
||
primary_procedure
|
||
| procedure_definition
|
||
;
|
||
|
||
primary_procedure:
|
||
pu
|
||
| pd
|
||
| pw expression
|
||
| fd expression
|
||
| tr expression
|
||
| tl expression
|
||
| bc '(' expression ',' expression ',' expression ')'
|
||
| fc '(' expression ',' expression ',' expression ')'
|
||
| ID '=' expression /* ID is an identifier which is a name of variable */
|
||
| if '(' expression ')' '{' primary_procedure_list '}'
|
||
| rt
|
||
| rs
|
||
| rp '(' expression ')' '{' primary_procedure_list '}'
|
||
| ID '(' ')' /* ID is an identifier which is a name of procedure */
|
||
| ID '(' argument_list ')' /* the same as above */
|
||
;
|
||
|
||
procedure_definition:
|
||
dp ID '(' ')' '{' primary_procedure_list '}'
|
||
| dp ID '(' parameter_list ')' '{' primary_procedure_list '}'
|
||
;
|
||
|
||
parameter_list:
|
||
ID
|
||
| parameter_list ',' ID
|
||
;
|
||
|
||
argument_list:
|
||
expression
|
||
| argument_list ',' expression
|
||
;
|
||
|
||
primary_procedure_list:
|
||
primary_procedure
|
||
| primary_procedure_list primary_procedure
|
||
;
|
||
|
||
expression:
|
||
expression '=' expression
|
||
| expression '>' expression
|
||
| expression '<' expression
|
||
| expression '+' expression
|
||
| expression '-' expression
|
||
| expression '*' expression
|
||
| expression '/' expression
|
||
| '-' expression %prec UMINUS
|
||
| '(' expression ')'
|
||
| ID
|
||
| NUM /* NUM is a number */
|
||
;</code></pre>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
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