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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
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<h1>4. Line drawing toolkit</h1>
<div id="toc">
<ul>
<li><a href="#0">Initializing the line</a></li>
<li><a href="#1">Walking the line</a></li>
<li><a href="#2">Callback-based function</a></li>
</ul>
</div>
<p>This toolkit is a very simple and lightweight implementation of the bresenham line drawing algorithm. It allows
you to follow straight paths on your map very easily.<br /> </p>
<a name="0"></a>
<h3>Initializing the line</h3>
<p>First, you have to initialize the toolkit with your starting and ending coordinates.<br /> </p>
<div class="code">
<p class="cpp"><span class="code-keyword">static</span><span class="code-keyword"> void</span> TCODLine<span
class="code-symbol">::</span>init<span class="code-symbol"> (</span><span class="code-keyword">int</span>
xFrom<span class="code-symbol">,</span><span class="code-keyword"> int</span> yFrom<span
class="code-symbol">,</span><span class="code-keyword"> int</span> xTo<span
class="code-symbol">,</span><span class="code-keyword"> int</span> yTo<span class="code-symbol">)</span></p>
<p class="c"><span class="code-keyword">void</span> TCOD_line_init<span class="code-symbol"> (</span><span
class="code-keyword">int</span> xFrom<span class="code-symbol">,</span><span class="code-keyword">
int</span> yFrom<span class="code-symbol">,</span><span class="code-keyword"> int</span> xTo<span
class="code-symbol">,</span><span class="code-keyword"> int</span> yTo<span class="code-symbol">)</span></p>
<p class="py">line_init<span class="code-symbol"> (</span>xFrom<span class="code-symbol">,</span> yFrom<span
class="code-symbol">,</span> xTo<span class="code-symbol">,</span> yTo<span class="code-symbol">)</span></p>
</div>
<table class="param">
<tbody>
<tr>
<th>Parameter</th>
<th>Description</th>
</tr>
<tr class="hilite">
<td>xFrom,yFrom</td>
<td>Coordinates of the line's starting point.<br /> </td>
</tr>
<tr>
<td>xTo,yTo</td>
<td>Coordinates of the line's ending point.<br /> </td>
</tr>
</tbody>
</table><a name="1"></a>
<h3>Walking the line</h3>
<p>You can then step through each cell with this function. It returns true when you reach the line's ending
point.<br /> </p>
<div class="code">
<p class="cpp"><span class="code-keyword">static</span><span class="code-keyword"> bool</span> TCODLine<span
class="code-symbol">::</span>step<span class="code-symbol"> (</span><span
class="code-keyword">int</span><span class="code-symbol"> *</span> xCur<span
class="code-symbol">,</span><span class="code-keyword"> int</span><span class="code-symbol"> *</span>
yCur<span class="code-symbol">)</span></p>
<p class="c"><span class="code-keyword">bool</span> TCOD_line_step<span class="code-symbol"> (</span><span
class="code-keyword">int</span><span class="code-symbol"> *</span> xCur<span
class="code-symbol">,</span><span class="code-keyword"> int</span><span class="code-symbol"> *</span>
yCur<span class="code-symbol">)</span></p>
<p class="py">line_step<span class="code-symbol"> (</span><span class="code-symbol">)</span></p>
</div>
<table class="param">
<tbody>
<tr>
<th>Parameter</th>
<th>Description</th>
</tr>
<tr class="hilite">
<td>xCur,yCur</td>
<td>the coordinates of the next cell on the line are stored here when the function returns<br /> </td>
</tr>
</tbody>
</table>
<h6>Example:</h6>
<div class="code">
<p class="cpp"><span class="code-comment">// Going from point 5,8 to point 13,4<br /></span><span
class="code-keyword">int</span> x<span class="code-symbol"> =</span><span class="code-value"> 5</span><span
class="code-symbol">,</span> y<span class="code-symbol"> =</span><span class="code-value"> 8</span><span
class="code-symbol">;</span><br />TCODLine<span class="code-symbol">::</span>init<span
class="code-symbol">(</span>x<span class="code-symbol">,</span>y<span class="code-symbol">,</span><span
class="code-value">13</span><span class="code-symbol">,</span><span class="code-value">4</span><span
class="code-symbol">)</span><span class="code-symbol">;</span><span
class="code-keyword"><br />do</span><span class="code-symbol"> {</span><span
class="code-comment"><br /> // update cell x,y<br /></span><span
class="code-symbol">}</span><span class="code-keyword"> while</span><span class="code-symbol"> (</span><span
class="code-symbol">!</span>TCODLine<span class="code-symbol">::</span>step<span
class="code-symbol">(</span><span class="code-symbol">&</span>x<span class="code-symbol">,</span><span
class="code-symbol">&</span>y<span class="code-symbol">)</span><span class="code-symbol">)</span><span
class="code-symbol">;</span></p>
<p class="c"><span class="code-keyword">int</span> x<span class="code-symbol"> =</span><span class="code-value">
5</span><span class="code-symbol">,</span> y<span class="code-symbol"> =</span><span class="code-value">
8</span><span class="code-symbol">;</span><br />TCOD_line_init<span class="code-symbol">(</span>x<span
class="code-symbol">,</span>y<span class="code-symbol">,</span><span class="code-value">13</span><span
class="code-symbol">,</span><span class="code-value">4</span><span class="code-symbol">)</span><span
class="code-symbol">;</span><span class="code-keyword"><br />do</span><span class="code-symbol">
{</span><span class="code-comment"><br /> // update cell x,y <br /></span><span
class="code-symbol">}</span><span class="code-keyword"> while</span><span class="code-symbol"> (</span><span
class="code-symbol">!</span>TCOD_line_step<span class="code-symbol">(</span><span
class="code-symbol">&</span>x<span class="code-symbol">,</span><span class="code-symbol">&</span>y<span
class="code-symbol">)</span><span class="code-symbol">)</span><span class="code-symbol">;</span></p>
<p class="py">libtcod<span class="code-symbol">.</span>line_init<span class="code-symbol">(</span><span
class="code-value">5</span><span class="code-symbol">,</span><span class="code-value">8</span><span
class="code-symbol">,</span><span class="code-value">13</span><span class="code-symbol">,</span><span
class="code-value">4</span><span class="code-symbol">)</span><span class="code-comment"><br /># update cell
5,8<br /></span>x<span class="code-symbol">,</span>y<span class="code-symbol">=</span>libtcod<span
class="code-symbol">.</span>line_step<span class="code-symbol">(</span><span
class="code-symbol">)</span><span class="code-keyword"><br />while</span><span class="code-symbol">
(</span><span class="code-keyword">not</span> x<span class="code-keyword"> is</span> None<span
class="code-symbol">)</span><span class="code-symbol"> :</span><span
class="code-comment"><br /> # update cell x,y<br /></span>x<span
class="code-symbol">,</span>y<span class="code-symbol">=</span>libtcod<span
class="code-symbol">.</span>line_step<span class="code-symbol">(</span><span class="code-symbol">)</span>
</p>
</div>
<hr>
<a name="2"></a>
<h3>Callback-based function</h3>
<p>The function returns false if the line has been interrupted by the callback (it returned false before the last
point).<br /> </p>
<div class="code">
<p class="cpp"><span class="code-keyword">class</span><span class="code-tcod"> TCODLIB_API</span>
TCODLineListener<span class="code-symbol"> {</span><span
class="code-keyword"><br /> virtual</span><span class="code-keyword"> bool</span>
putPoint<span class="code-symbol"> (</span><span class="code-keyword">int</span> x<span
class="code-symbol">,</span><span class="code-keyword"> int</span> y<span class="code-symbol">)</span><span
class="code-symbol"> =</span><span class="code-value"> 0</span><span class="code-symbol">;</span><span
class="code-symbol"><br />}</span><span class="code-symbol">;</span><span
class="code-keyword"><br />static</span><span class="code-keyword"> bool</span> TCODLine<span
class="code-symbol">::</span>line<span class="code-symbol"> (</span><span class="code-keyword">int</span>
xFrom<span class="code-symbol">,</span><span class="code-keyword"> int</span> yFrom<span
class="code-symbol">,</span><span class="code-keyword"> int</span> xTo<span
class="code-symbol">,</span><span class="code-keyword"> int</span> yTo<span class="code-symbol">,</span>
TCODLineListener<span class="code-symbol"> *</span> listener<span class="code-symbol">)</span></p>
<p class="c"><span class="code-keyword">typedef</span><span class="code-keyword"> bool</span><span
class="code-symbol"> (</span><span class="code-symbol">*</span><span
class="code-tcod">TCOD_line_listener_t</span><span class="code-symbol">)</span><span class="code-symbol">
(</span><span class="code-keyword">int</span> x<span class="code-symbol">,</span><span class="code-keyword">
int</span> y<span class="code-symbol">)</span><span class="code-symbol">;</span><span
class="code-keyword"><br />bool</span> TCOD_line<span class="code-symbol">(</span><span
class="code-keyword">int</span> xFrom<span class="code-symbol">,</span><span class="code-keyword">
int</span> yFrom<span class="code-symbol">,</span><span class="code-keyword"> int</span> xTo<span
class="code-symbol">,</span><span class="code-keyword"> int</span> yTo<span
class="code-symbol">,</span><span class="code-tcod"> TCOD_line_listener_t</span> listener<span
class="code-symbol">)</span></p>
<p class="py"><span class="code-keyword">def</span> line_listener<span class="code-symbol">(</span>x<span
class="code-symbol">,</span>y<span class="code-symbol">)</span><span class="code-symbol"> :</span><span
class="code-comment"> # ...<br /></span>line<span class="code-symbol">(</span>xFrom<span
class="code-symbol">,</span> yFrom<span class="code-symbol">,</span> xTo<span class="code-symbol">,</span>
yTo<span class="code-symbol">,</span> listener<span class="code-symbol">)</span></p>
</div>
<table class="param">
<tbody>
<tr>
<th>Parameter</th>
<th>Description</th>
</tr>
<tr class="hilite">
<td>xFrom,yFrom</td>
<td>Coordinates of the line's starting point.<br /> </td>
</tr>
<tr>
<td>xTo,yTo</td>
<td>Coordinates of the line's ending point.<br /> </td>
</tr>
<tr class="hilite">
<td>listener</td>
<td>Callback called for each line's point. The function stops if the callback returns false.<br /> </td>
</tr>
</tbody>
</table>
<h6>Example:</h6>
<div class="code">
<p class="cpp"><span class="code-comment">// Going from point 5,8 to point 13,4<br /></span><span
class="code-keyword">class</span> MyLineListener<span class="code-symbol"> :</span><span
class="code-keyword"> public</span> TCODLineListener<span class="code-symbol"> {</span><span
class="code-keyword"><br /> public</span><span class="code-symbol">:</span><span
class="code-keyword"><br /> bool</span> putPoint<span class="code-symbol">
(</span><span class="code-keyword">int</span> x<span class="code-symbol">,</span><span
class="code-keyword">int</span> y<span class="code-symbol">)</span><span class="code-symbol">
{</span><br /> printf<span class="code-symbol"> (</span><span
class="code-string">"%d %d\n"</span><span class="code-symbol">,</span>x<span
class="code-symbol">,</span>y<span class="code-symbol">)</span><span class="code-symbol">;</span><span
class="code-keyword"><br /> return</span><span
class="code-keyword"> true</span><span class="code-symbol">;</span><span
class="code-symbol"><br /> }</span><span class="code-symbol"><br />}</span><span
class="code-symbol">;</span><br />MyLineListener myListener<span
class="code-symbol">;</span><br />TCODLine<span class="code-symbol">::</span>line<span
class="code-symbol">(</span><span class="code-value">5</span><span class="code-symbol">,</span><span
class="code-value">8</span><span class="code-symbol">,</span><span class="code-value">13</span><span
class="code-symbol">,</span><span class="code-value">4</span><span class="code-symbol">,</span><span
class="code-symbol">&</span>myListener<span class="code-symbol">)</span><span class="code-symbol">;</span>
</p>
<p class="c"><span class="code-keyword">bool</span> my_listener<span class="code-symbol">(</span><span
class="code-keyword">int</span> x<span class="code-symbol">,</span><span class="code-keyword">int</span>
y<span class="code-symbol">)</span><span class="code-symbol">
{</span><br /> printf<span class="code-symbol"> (</span><span class="code-string">"%d
%d\n"</span><span class="code-symbol">,</span>x<span class="code-symbol">,</span>y<span
class="code-symbol">)</span><span class="code-symbol">;</span><span
class="code-keyword"><br /> return</span> true<span class="code-symbol">;</span><span
class="code-symbol"><br />}</span><br />TCOD_line_line<span class="code-symbol">(</span><span
class="code-value">5</span><span class="code-symbol">,</span><span class="code-value">8</span><span
class="code-symbol">,</span><span class="code-value">13</span><span class="code-symbol">,</span><span
class="code-value">4</span><span class="code-symbol">,</span>my_listener<span
class="code-symbol">)</span><span class="code-symbol">;</span></p>
<p class="py"><span class="code-keyword">def</span> my_listener<span class="code-symbol">(</span>x<span
class="code-symbol">,</span>y<span class="code-symbol">)</span><span class="code-symbol">:</span><span
class="code-keyword"><br /> print</span> x<span class="code-symbol">,</span>y<span
class="code-keyword"><br /> return</span><span class="code-keyword">
True</span><br />libtcod<span class="code-symbol">.</span>line_line<span class="code-symbol">(</span><span
class="code-value">5</span><span class="code-symbol">,</span><span class="code-value">8</span><span
class="code-symbol">,</span><span class="code-value">13</span><span class="code-symbol">,</span><span
class="code-value">4</span><span class="code-symbol">,</span>my_listener<span class="code-symbol">)</span>
</p>
</div>
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