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1210 lines
27 KiB
1210 lines
27 KiB
<chapter id="reference">
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<title
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>&kturtle;'s &logo; Programming Reference</title>
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<sect1 id="commands">
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<title
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>Commands</title>
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<para
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>Using commands you tell the turtle or &kturtle; to do something. Some commands need input, some give output. In this section we explain all the commands that can be used in &kturtle;.</para>
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<sect2 id="moving-the-turtle">
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<title
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>Moving the turtle</title>
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<para
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>There are several commands to move the turtle over the screen.</para>
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<variablelist>
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<anchor id="forward"/>
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<varlistentry>
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<term
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>forward</term>
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<listitem
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><para
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><screen
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>forward X</screen>
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<userinput
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>forward</userinput
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> moves the turtle forward by the amount of X pixels. When the pen is down the turtle will leave a trail. <userinput
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>forward</userinput
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> can be abbreviated to <userinput
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>fw</userinput
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></para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="backward"/>
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<varlistentry>
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<term
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>backward</term>
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<listitem
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><para
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><screen
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>backward X</screen>
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<userinput
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>backward</userinput
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> moves the turtle backward by the amount of X pixels. When the pen is down the turtle will leave a trail. <userinput
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>backward</userinput
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> can be abbreviated to <userinput
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>bw</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="turnleft"/>
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<varlistentry>
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<term
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>turnleft</term>
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<listitem
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><para
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><screen
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>turnleft X</screen>
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<userinput
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>turnleft</userinput
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> commands the turtle to turn an amount of X degrees to the left. <userinput
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>turnleft</userinput
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> can be abbreviated to <userinput
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>tl</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="turnright"/>
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<varlistentry>
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<term
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>turnright</term>
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<listitem
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><para
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><screen
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>turnright X</screen>
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<userinput
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>turnright</userinput
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>the turtle to turn an amount of X degrees to the right. <userinput
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>turnright</userinput
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> can be abbreviated to <userinput
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>tr</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="direction"/>
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<varlistentry>
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<term
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>direction</term>
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<listitem
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><para
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><screen
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>direction X</screen>
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<userinput
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>direction</userinput
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> set the turtle's direction to an amount of X degrees counting from zero, and thus is not relative to the turtle's previous direction. <userinput
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>direction</userinput
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> can be abbreviated to <userinput
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>dir</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="center"/>
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<varlistentry>
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<term
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>centre</term>
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<listitem
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><para
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><screen
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>centre</screen>
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<userinput
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>centre</userinput
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> moves the turtle to the centre on the canvas.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="go"/>
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<varlistentry>
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<term
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>go</term>
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<listitem
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><para
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><screen
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>go X,Y</screen>
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<userinput
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>go</userinput
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> commands the turtle to go to a certain place on the canvas. This place is X <glossterm linkend="pixels"
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>pixels</glossterm
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> from the left of the canvas, and Y <glossterm linkend="pixels"
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>pixels</glossterm
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> form the top of the canvas. Note that using the <userinput
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>go</userinput
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> command the turtle will not draw a line.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="gox"/>
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<varlistentry>
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<term
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>gox</term>
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<listitem
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><para
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><screen
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>gox X</screen>
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<userinput
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>gox</userinput
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> using this command the turtle will move to X <glossterm linkend="pixels"
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>pixels</glossterm
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> from the left of the canvas whilst staying at the same height.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="goy"/>
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<varlistentry>
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<term
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>goy</term>
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<listitem
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><para
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><screen
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>goy Y</screen>
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<userinput
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>gox</userinput
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> using this command the turtle will move to Y <glossterm linkend="pixels"
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>pixels</glossterm
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> from the top of the canvas whilst staying at the same distance from the left border of the canvas.</para
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></listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2 id="pen">
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<title
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>The turtle has a pen</title>
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<para
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>The turtle has a pen that draws a line when the turtle moves. There are a few commands to control the pen. In this section we explain these commands.</para>
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<variablelist>
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<anchor id="penup"/>
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<varlistentry>
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<term
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>penup</term>
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<listitem
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><para
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><screen
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>penup</screen>
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<userinput
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>penup</userinput
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> lifts the pen from the canvas. When the pen is <quote
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>up</quote
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> no line will be drawn when the turtle moves. See also <userinput
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>pendown</userinput
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>. <userinput
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>penup</userinput
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> can be abbreviated to <userinput
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>pu</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="pendown"/>
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<varlistentry>
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<term
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>pendown</term>
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<listitem
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><para
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><screen
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>pendown</screen>
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<userinput
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>pendown</userinput
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> presses the pen down on the canvas. When the pen is press <quote
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>down</quote
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> on the canvas a line will be drawn when the turtle moves. See also <userinput
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>penup</userinput
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>.<userinput
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>pendown</userinput
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> can be abbreviated to <userinput
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>pd</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="penwidth"/>
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<varlistentry>
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<term
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>penwidth</term>
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<listitem
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><para
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><screen
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>penwidth X</screen>
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<userinput
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>penwidth</userinput
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> sets the width of the pen (the line width) to an amount of X <glossterm linkend="pixels"
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>pixels</glossterm
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>. <userinput
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>penwidth</userinput
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> can be abbreviated to <userinput
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>pw</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="pencolor"/>
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<varlistentry>
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<term
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>pencolour</term>
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<listitem
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><para
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><screen
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>pencolour R,G,B</screen>
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<userinput
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>pencolor</userinput
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> sets the color of the pen. <userinput
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>pencolor</userinput
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> takes an <glossterm linkend="rgb"
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>RGB combination</glossterm
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> as input. <userinput
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>pencolor</userinput
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> can be abbreviated to <userinput
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>pc</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2 id="canvas">
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<title
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>Commands to control the canvas</title>
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<para
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>There are several commands to control the canvas.</para>
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<variablelist>
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<anchor id="canvassize"/>
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<varlistentry>
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<term
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>canvassize</term>
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<listitem
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><para
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><screen
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>canvassize X,Y</screen>
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With the <userinput
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>canvassize</userinput
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> command you can set the size of the canvas. It takes X and Y as input, where X is the new canvas width in <glossterm linkend="pixels"
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>pixels</glossterm
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>, and Y is the new height of the canvas in <glossterm linkend="pixels"
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>pixels</glossterm
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>. <userinput
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>canvassize</userinput
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> can be abbreviated to <userinput
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>cs</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="canvascolor"/>
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<varlistentry>
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<term
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>canvascolour</term>
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<listitem
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><para
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><screen
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>canvascolour R,G,B</screen>
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<userinput
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>canvascolor</userinput
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> set the color of the canvas. <userinput
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>canvascolor</userinput
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> takes an <glossterm linkend="rgb"
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>RGB combination</glossterm
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> as input. <userinput
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>canvascolor</userinput
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> can be abbreviated to <userinput
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>cc</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="wrapon"/>
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<varlistentry>
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<term
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>wrapon</term>
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<listitem
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><para
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><screen
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>wrapon</screen>
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With the <userinput
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>wrapon</userinput
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> command you can set <glossterm linkend="wrapping"
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>wrapping</glossterm
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> <quote
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>on</quote
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> for the canvas. Please see the glossary if you want to know what <glossterm linkend="wrapping"
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>wrapping</glossterm
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> is.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="wrapoff"/>
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<varlistentry>
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<term
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>wrapoff</term>
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<listitem
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><para
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><screen
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>wrapoff</screen>
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With the <userinput
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>wrapoff</userinput
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> command you can set <glossterm linkend="wrapping"
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>wrapping</glossterm
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> <quote
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>off</quote
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> for the canvas: this means the turtle can move off the canvas and can get <quote
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>lost</quote
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>. Please see the glossary if you want to know what <glossterm linkend="wrapping"
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>wrapping</glossterm
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> is.</para
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></listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2 id="clean">
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<title
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>Commands to clean up</title>
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<para
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>There are two commands to clean up the canvas after you have made a mess.</para>
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<variablelist>
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<anchor id="clear"/>
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<varlistentry>
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<term
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>clear</term>
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<listitem
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><para
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><screen
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>clear</screen>
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With <userinput
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>clear</userinput
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> you can clean all drawings from the canvas. All other things remain: the position and angle of the turtle, the canvascolor, the visibility of the turtle, and the canvas size. <userinput
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>clear</userinput
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> can be abbreviated to <userinput
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>ccl</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="reset"/>
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<varlistentry>
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<term
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>reset</term>
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<listitem
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><para
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><screen
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>reset</screen>
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<userinput
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>reset</userinput
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> cleans much more thoroughly than the <userinput
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>clear</userinput
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> command. After a <userinput
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>reset</userinput
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> command everything is like is was when you had just started &kturtle;. The turtle is positioned at the middle of the screen, the canvas color is white, and the turtle draws a black line on the canvas.</para
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></listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2 id="sprites">
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<title
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>The turtle is a sprite</title>
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<para
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>Many people do not know what sprites are, so here a short explanation: sprites are small pictures that can be moved around the screen. (for more info see the glossary on <glossterm linkend="sprites"
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>sprites</glossterm
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>). So the turtle is a sprite.</para>
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<para
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>Next you will find a full overview on all commands to work with sprites.</para>
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<para
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>[The current version of &kturtle; does not yet support the use of sprites other than the turtle. With future versions you will be able to change the turtle into something of your own design]</para>
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<variablelist>
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<anchor id="show"/>
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<varlistentry>
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<term
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>show</term>
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<listitem
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><para
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><screen
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>show</screen>
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<userinput
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>show</userinput
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> makes the turtle visible again after it has been hidden.<userinput
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>show</userinput
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> can be abbreviated to <userinput
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>ss</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<anchor id="hide"/>
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<varlistentry>
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<term
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>hide</term>
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<listitem
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><para
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><screen
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>hide</screen>
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<userinput
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>hide</userinput
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> hides the turtle. This can be used if the turtle does not fit in your drawing.<userinput
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>hide</userinput
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> can be abbreviated to <userinput
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>sh</userinput
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>.</para
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></listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2 id="writing">
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<title
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>Can the turtles write text?</title>
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<para
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>The answer is: <quote
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>yes</quote
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>. The turtle can write: it writes just about everything you command it to.</para>
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<variablelist>
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<anchor id="print"/>
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<varlistentry>
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<term
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>print</term>
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<listitem
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><para
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><screen
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>print X</screen>
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The <userinput
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>print</userinput
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> command is used to command the turtle to write something on the canvas. <userinput
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>print</userinput
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> takes numbers and strings as input. You can <userinput
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>print</userinput
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> various numbers and strings using the <quote
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>+</quote
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> symbol. See here a small example: <screen
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>year = 2004
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author = "Cies"
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print "KTurtle was made in " + year + " by " + author
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</screen>
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</para
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></listitem>
|
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</varlistentry>
|
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</variablelist>
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<variablelist>
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<anchor id="fontsize"/>
|
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<varlistentry>
|
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<term
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|
>fontsize</term>
|
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<listitem
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><para
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><screen
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>fontsize X</screen>
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<userinput
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>fontsize</userinput
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> sets the size of the font that is used by <userinput
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>print</userinput
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>. <userinput
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>fontsize</userinput
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> takes one input which should be a number. The size is set in <glossterm linkend="pixels"
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>pixels</glossterm
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>.</para
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></listitem>
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</varlistentry>
|
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</variablelist>
|
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</sect2>
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|
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<sect2 id="dice">
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<title
|
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>A command that rolls a dice for you</title>
|
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<para
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>There is one command that rolls a dice for you</para>
|
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<variablelist>
|
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<anchor id="random"/>
|
|
<varlistentry>
|
|
<term
|
|
>random</term>
|
|
<listitem
|
|
><para
|
|
><screen
|
|
>random X,Y</screen>
|
|
<userinput
|
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>random</userinput
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> is a command that takes input and gives output. As input are required two numbers, the first (X) sets the minimum output, the second (Y) sets the maximum. The output is a randomly chosen number that is equal or greater then the minimum and equal or smaller than the maximum. Here a small example: <screen>
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repeat 500 [
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x = random 1,20
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forward x
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turnleft 10 - x
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]
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|
</screen
|
|
> Using the <userinput
|
|
>random</userinput
|
|
> command you can add a bit of chaos to your program.</para
|
|
></listitem>
|
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</varlistentry>
|
|
</variablelist>
|
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</sect2>
|
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</sect1>
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|
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<sect1 id="containers">
|
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<title
|
|
>Containers</title>
|
|
<para
|
|
>Containers are letters or words that can be used by the programmer to store a number or a text. Containers that contain a number are called <link linkend="variables"
|
|
>variables</link
|
|
>, containers that can contain text are called <link linkend="strings"
|
|
>strings</link
|
|
>.</para>
|
|
|
|
<para
|
|
>Containers that are not used yet are 0 by default. An example: <screen>
|
|
print N
|
|
</screen
|
|
> This will print a 0. </para>
|
|
|
|
<sect2 id="variables">
|
|
<title
|
|
>Variables: number containers</title>
|
|
<para
|
|
>Let us start with an example: <screen>
|
|
x = 3
|
|
print x
|
|
</screen
|
|
> In the first line the letter <userinput
|
|
>x</userinput
|
|
> made into a variable (number container). As you see the value of the variable <userinput
|
|
>x</userinput
|
|
> is set to 3. On the second line the value is printed.</para>
|
|
<para
|
|
>Note that if we wanted to print an <quote
|
|
>x</quote
|
|
> that we should have written <screen
|
|
>print "x"
|
|
</screen>
|
|
</para>
|
|
<para
|
|
>That was easy, now a bit harder example: <screen>
|
|
A = 2004
|
|
B = 25
|
|
AB = A + B
|
|
|
|
# the next command prints "2029"
|
|
print AB
|
|
backward 30
|
|
# the next command prints "2004 plus 25"
|
|
print "" + A + " plus " + B
|
|
backward 30
|
|
# the next command prints "1979"
|
|
print A - B
|
|
</screen
|
|
> In the first two lines the variables <userinput
|
|
>A</userinput
|
|
> and <userinput
|
|
>B</userinput
|
|
> are set to 2004 and 25. On the third line the variable <userinput
|
|
>AB</userinput
|
|
> is set to <userinput
|
|
>A + B</userinput
|
|
>, which is 2029. The rest of the example consists of 3 <userinput
|
|
>print</userinput
|
|
> commands with <userinput
|
|
>backward 30</userinput
|
|
> in between. The <userinput
|
|
>backward 30</userinput
|
|
> is there to make sure every output is on a new line. In this example you also see that variables can be used in <link linkend="math"
|
|
>mathematical calculations</link
|
|
>.</para>
|
|
</sect2>
|
|
|
|
<sect2 id="strings">
|
|
<title
|
|
>Strings: text containers</title>
|
|
<para
|
|
>Strings are a lot like variables. The biggest difference is that strings cannot be used in <link linkend="math"
|
|
>mathematical calculations</link
|
|
> and <link linkend="questions"
|
|
>questions</link
|
|
>. An example of the use of strings: <screen>
|
|
x = "Hello "
|
|
name = inputwindow "Please enter your name..."
|
|
print x + name + ", how are you?"
|
|
</screen
|
|
> On the first line the string <userinput
|
|
>x</userinput
|
|
> is set to <quote
|
|
>Hello </quote
|
|
>. On the second line the string <userinput
|
|
>name</userinput
|
|
> is set to the output of the <userinput
|
|
>inputwindow</userinput
|
|
> command. On the third line the program prints a composition of three strings on the canvas.</para>
|
|
<para
|
|
>This program ask you to enter your name. When you, for instance, enter the name <quote
|
|
>Paul</quote
|
|
>, the program prints <quote
|
|
>Hello Paul, how are you?</quote
|
|
>. Please note that the plus (+) is the only math symbol that you can use with strings.</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1 id="math">
|
|
<title
|
|
>Can the Turtle do maths?</title>
|
|
<para
|
|
>Yes, &kturtle; will do your math. You can add (+), substract (-), multiply (*), and divide (/). Here is an example in which we use all of them: <screen>
|
|
a = 20 - 5
|
|
b = 15 * 2
|
|
c = 30 / 30
|
|
d = 1 + 1
|
|
print "a: "+a+", b: "+b+", c: "+c+", d: "+d
|
|
</screen
|
|
> Do you know what value a, b, c and d have?</para>
|
|
<para
|
|
>If you just want a simple calculation to be done you can do something like this: <screen
|
|
>print 2004-12
|
|
</screen
|
|
></para>
|
|
<para
|
|
>Now an example with brackets: <screen>
|
|
print ( ( 20 - 5 ) * 2 / 30 ) + 1
|
|
</screen
|
|
> The expressions inside brackets will be calculated first. In this example, 20-5 will be calculated, then multiplied by 2, divided by 30, and then 1 is added (giving 2).</para>
|
|
</sect1>
|
|
|
|
<sect1 id="questions">
|
|
<title
|
|
>Asking questions, getting answers...</title>
|
|
<para
|
|
><link linkend="if"
|
|
><userinput
|
|
>if</userinput
|
|
></link
|
|
> and <link linkend="while"
|
|
><userinput
|
|
>while</userinput
|
|
></link
|
|
> are <link linkend="controlling-execution"
|
|
>execution controllers</link
|
|
> that we will discuss in the next section. In this section we use the <userinput
|
|
>if</userinput
|
|
> command to explain questions.</para>
|
|
<para
|
|
>A simple example of questions: <screen>
|
|
x = 6
|
|
if x > 5 [
|
|
print "hello"
|
|
]
|
|
</screen
|
|
> In this example the question is the <userinput
|
|
>x > 5</userinput
|
|
> part. If the answer to this question is <quote
|
|
>true</quote
|
|
> the code between the brackets will be executed. Questions are an important part of programming and often used together with <link linkend="controlling-execution"
|
|
>execution controllers</link
|
|
>, like <link linkend="if"
|
|
><userinput
|
|
>if</userinput
|
|
></link
|
|
>. All numbers and <link linkend="variables"
|
|
>variables</link
|
|
> (number containers) can be compared to each other with questions.</para>
|
|
<para
|
|
>Here are all possible questions: <table>
|
|
<title
|
|
>Types of questions</title>
|
|
<tgroup cols="3">
|
|
<tbody>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>a == b</userinput
|
|
></entry>
|
|
<entry
|
|
>equals</entry>
|
|
<entry
|
|
>answer is <quote
|
|
>true</quote
|
|
> if <userinput
|
|
>a</userinput
|
|
> equals <userinput
|
|
>b</userinput
|
|
></entry>
|
|
</row>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>a != b</userinput
|
|
></entry>
|
|
<entry
|
|
>not-equal</entry>
|
|
<entry
|
|
>answer is <quote
|
|
>true</quote
|
|
> if <userinput
|
|
>a</userinput
|
|
> does not equal <userinput
|
|
>b</userinput
|
|
></entry>
|
|
</row>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>a > b</userinput
|
|
></entry>
|
|
<entry
|
|
>greater than</entry>
|
|
<entry
|
|
>answer is <quote
|
|
>true</quote
|
|
> if <userinput
|
|
>a</userinput
|
|
> is greater than <userinput
|
|
>b</userinput
|
|
></entry>
|
|
</row>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>a < b</userinput
|
|
></entry>
|
|
<entry
|
|
>smaller than</entry>
|
|
<entry
|
|
>answer is <quote
|
|
>true</quote
|
|
> if <userinput
|
|
>a</userinput
|
|
> is smaller than <userinput
|
|
>b</userinput
|
|
></entry>
|
|
</row>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>a >= b</userinput
|
|
></entry>
|
|
<entry
|
|
>greater than or equals</entry>
|
|
<entry
|
|
>answer is <quote
|
|
>true</quote
|
|
> if <userinput
|
|
>a</userinput
|
|
> is greater than or equals <userinput
|
|
>b</userinput
|
|
></entry>
|
|
</row>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>a <= b</userinput
|
|
></entry>
|
|
<entry
|
|
>smaller than or equals</entry>
|
|
<entry
|
|
>answer is <quote
|
|
>true</quote
|
|
> if <userinput
|
|
>a</userinput
|
|
> is smaller than or equals <userinput
|
|
>b</userinput
|
|
></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</para>
|
|
<para
|
|
>Questions can also be glued to each other with <quote
|
|
>question glue</quote
|
|
>, this way a few questions can become one big question. <screen>
|
|
a = 1
|
|
b = 5
|
|
if a < 5 and b == 5 [
|
|
print "hello"
|
|
]
|
|
</screen
|
|
> <anchor id="question-glue"/>In this example the glue-word <userinput
|
|
>and</userinput
|
|
> is used to glue 2 questions (<userinput
|
|
>a < 5</userinput
|
|
>, <userinput
|
|
>b == 5</userinput
|
|
>) together. If one side of the <userinput
|
|
>and</userinput
|
|
> would answer <quote
|
|
>false</quote
|
|
> the whole question would answer <quote
|
|
>false</quote
|
|
>, because with the glue-word <userinput
|
|
>and</userinput
|
|
> both sides need to be <quote
|
|
>true</quote
|
|
> in order to answer <quote
|
|
>true</quote
|
|
>.</para>
|
|
<para
|
|
><userinput
|
|
>and</userinput
|
|
> is not the only glue-word there are two others. They are all in the next table: <table>
|
|
<title
|
|
>Question glue-words</title>
|
|
<tgroup cols="2">
|
|
<tbody>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>and</userinput
|
|
></entry>
|
|
<entry
|
|
>both sides need to be <quote
|
|
>true</quote
|
|
> in order to answer <quote
|
|
>true</quote
|
|
></entry>
|
|
</row>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>or</userinput
|
|
></entry>
|
|
<entry
|
|
>if one of the sides is <quote
|
|
>true</quote
|
|
> the answer is <quote
|
|
>true</quote
|
|
></entry>
|
|
</row>
|
|
<row>
|
|
<entry
|
|
><userinput
|
|
>not</userinput
|
|
></entry>
|
|
<entry
|
|
>only if both of the sides are <quote
|
|
>false</quote
|
|
> the answer is <quote
|
|
>false</quote
|
|
></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="controlling-execution">
|
|
<title
|
|
>Controlling execution</title>
|
|
<para
|
|
>The execution controllers enable you — as their name implies — to control execution.</para>
|
|
|
|
<sect2 id="easy">
|
|
<title
|
|
>Have the turtle wait</title>
|
|
<para
|
|
>If you have done some programming in &kturtle; you have might noticed that the turtle can be very quick at drawing. This command makes the turtle wait for a given amount of time.</para>
|
|
<variablelist>
|
|
<anchor id="wait"/>
|
|
<varlistentry>
|
|
<term
|
|
>wait</term>
|
|
<listitem
|
|
><para
|
|
><screen
|
|
>wait X</screen>
|
|
<userinput
|
|
>wait</userinput
|
|
> makes the turtle wait for X seconds. <screen>
|
|
repeat 36 [
|
|
forward 5
|
|
turnright 10
|
|
wait 0.5
|
|
]
|
|
</screen
|
|
> This code draws a circle, but the turtle will wait half a second after each step. This gives the impression of a slow-moving turtle.</para
|
|
></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
<sect2 id="execute-if">
|
|
<title
|
|
>Execute "if"</title>
|
|
<para
|
|
></para>
|
|
<variablelist>
|
|
<anchor id="if"/>
|
|
<varlistentry>
|
|
<term
|
|
>if</term>
|
|
<listitem
|
|
><para
|
|
><screen
|
|
>if <link linkend="questions"
|
|
>question</link
|
|
> [ ... ]</screen>
|
|
The code that is placed between the brackets will only be executed <userinput
|
|
>if</userinput
|
|
> the answer to the <link linkend="questions"
|
|
>question</link
|
|
> is <quote
|
|
>true</quote
|
|
>. Please read for more information on <link linkend="questions"
|
|
>questions</link
|
|
> in the <link linkend="questions"
|
|
>question section</link
|
|
>. <screen>
|
|
x = 6
|
|
if x > 5 [
|
|
print "x is greater than five!"
|
|
]
|
|
</screen
|
|
> On the first line <userinput
|
|
>x</userinput
|
|
> is set to 6. On the second line the <link linkend="questions"
|
|
>question</link
|
|
> <userinput
|
|
>x > 5</userinput
|
|
> is asked. Since the answer to this question is <quote
|
|
>true</quote
|
|
> the execution controller <userinput
|
|
>if</userinput
|
|
> will allow the code between the brackets to be executed</para
|
|
></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
<sect2 id="execute-while">
|
|
<title
|
|
>Execute "while"</title>
|
|
<para
|
|
></para>
|
|
<variablelist>
|
|
<anchor id="while"/>
|
|
<varlistentry>
|
|
<term
|
|
>while</term>
|
|
<listitem
|
|
><para
|
|
><screen
|
|
>while <link linkend="questions"
|
|
>question</link
|
|
> [ ... ]</screen>
|
|
The execution controller <userinput
|
|
>while</userinput
|
|
> is a lot like <link linkend="if"
|
|
><userinput
|
|
>if</userinput
|
|
></link
|
|
>. The difference is that <userinput
|
|
>while</userinput
|
|
> keeps repeating the code between the brackets till the answer to the <link linkend="questions"
|
|
>question</link
|
|
> is <quote
|
|
>false</quote
|
|
>. <screen>
|
|
x = 1
|
|
while x < 5 [
|
|
forward 10
|
|
wait 1
|
|
x = x + 1
|
|
]
|
|
</screen
|
|
> On the first line <userinput
|
|
>x</userinput
|
|
> is set to 1. On the second line the <link linkend="questions"
|
|
>question</link
|
|
> <userinput
|
|
>x < 5</userinput
|
|
> is asked. Since the answer to this question is <quote
|
|
>true</quote
|
|
> the execution controller <userinput
|
|
>while</userinput
|
|
> starts executing the code between the brackets till the answer to the <link linkend="questions"
|
|
>question</link
|
|
> is <quote
|
|
>false</quote
|
|
>. In this case the code between the brackets will be executed 4 times, because every time the fifth line is executed <userinput
|
|
>x</userinput
|
|
> increases by 1..</para
|
|
></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
<sect2 id="if-else">
|
|
<title
|
|
>If not, in other words: "else"</title>
|
|
<para
|
|
></para>
|
|
<variablelist>
|
|
<anchor id="else"/>
|
|
<varlistentry>
|
|
<term
|
|
>else</term>
|
|
<listitem
|
|
><para
|
|
><screen
|
|
>if question [ ... ] else [ ... ]</screen>
|
|
<userinput
|
|
>else</userinput
|
|
> can be used in addition to the execution controller <link linkend="if"
|
|
><userinput
|
|
>if</userinput
|
|
></link
|
|
>. The code between the brackets after <userinput
|
|
>else</userinput
|
|
> is only executed if the answer to the <link linkend="questions"
|
|
>question</link
|
|
> that is asked is <quote
|
|
>false</quote
|
|
>. <screen>
|
|
x = 4
|
|
if x > 5 [
|
|
print "x is greater than five!"
|
|
] else [
|
|
print "x is smaller than six!"
|
|
]
|
|
</screen
|
|
> The <link linkend="questions"
|
|
>question</link
|
|
> asks if <userinput
|
|
>x</userinput
|
|
> is greater than 5. Since <userinput
|
|
>x</userinput
|
|
> is set to 4 on the first line the answer to the question is <quote
|
|
>false</quote
|
|
>. This means the code between the brackets after <userinput
|
|
>else</userinput
|
|
> gets executed.</para
|
|
></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
<sect2 id="for-loop">
|
|
<title
|
|
>The "for" loop</title>
|
|
<para
|
|
></para>
|
|
<variablelist>
|
|
<anchor id="for"/>
|
|
<varlistentry>
|
|
<term
|
|
>for</term>
|
|
<listitem
|
|
><para
|
|
><screen
|
|
>for <userinput
|
|
>start point</userinput
|
|
> to <userinput
|
|
>end point</userinput
|
|
> [ ... ]</screen>
|
|
The <userinput
|
|
>for</userinput
|
|
> loop is a <quote
|
|
>counting loop</quote
|
|
>, &ie; it keeps count for you. <screen>
|
|
for x = 1 to 10 [
|
|
print x * 7
|
|
forward 15
|
|
]
|
|
</screen
|
|
> Every time the code between the brackets is executed the <userinput
|
|
>x</userinput
|
|
> is increased by 1, till <userinput
|
|
>x</userinput
|
|
> reaches the value of 10. The code between the brackets prints the <userinput
|
|
>x</userinput
|
|
> multiplied by 7. After this program finishes its execution you will see the times table of 7 on the canvas.</para
|
|
></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
|
|
<sect1 id="learn">
|
|
<title
|
|
>Create your own commands</title>
|
|
<para
|
|
><userinput
|
|
>learn</userinput
|
|
> is a very special command, because it is used to create your own commands. The command you create can take <glossterm linkend="input-output"
|
|
>input</glossterm
|
|
> and return <glossterm linkend="input-output"
|
|
>output</glossterm
|
|
>. Let us take a look at how a new command is created: <screen>
|
|
learn circle (x) [
|
|
repeat 36 [
|
|
forward x
|
|
turnleft 10
|
|
]
|
|
]
|
|
</screen
|
|
> The new command is called <userinput
|
|
>circle</userinput
|
|
>. <userinput
|
|
>circle</userinput
|
|
> takes one <glossterm linkend="input-output"
|
|
>input</glossterm
|
|
>, a number, to set the size of the circle. <userinput
|
|
>circle</userinput
|
|
> returns no <glossterm linkend="input-output"
|
|
>output</glossterm
|
|
>. The <userinput
|
|
>circle</userinput
|
|
> command can now be used like a normal command in the rest of the code. See this example: <screen
|
|
>learn circle (x) [
|
|
repeat 36 [
|
|
forward x
|
|
turnleft 10
|
|
]
|
|
]
|
|
|
|
go 30,30
|
|
circle(20)
|
|
|
|
go 40,40
|
|
circle(50)
|
|
</screen>
|
|
</para>
|
|
<para
|
|
>In the next example a command with a return value is created. <screen>
|
|
reset
|
|
|
|
learn multiplyBySelf (n) [
|
|
r = n * 1
|
|
r = n * n
|
|
return r
|
|
]
|
|
i = inputwindow "Please enter a number and press OK"
|
|
print i + " multiplied by itself is: " + multiplyBySelf (i)
|
|
</screen
|
|
> In this example a new command called <userinput
|
|
>multiplyBySelf</userinput
|
|
> is created. The input of this command is multiplied by it self and then returned, using the <anchor id="return"/><userinput
|
|
>return</userinput
|
|
> command. The <userinput
|
|
>return</userinput
|
|
> command is the way to output a value from a function you have created. </para>
|
|
</sect1>
|
|
|
|
</chapter>
|