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		<title>How can I map mouse coordinates to world coordinates using allegro transofrms?</title>
		<link>http://www.allegro.cc/forums/view/616958</link>
		<description>Allegro.cc Forum Thread</description>
		<webMaster>matthew@allegro.cc (Matthew Leverton)</webMaster>
		<lastBuildDate>Mon, 03 Jul 2017 22:30:52 +0000</lastBuildDate>
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		<description><![CDATA[<div class="mockup v2"><p>Hello, in first place sorry for my bad english and thanks for your time.</p><p>I have a 2d tiled base project, and is drawed to screen using this allegro transform:
</p><div class="source-code"><div class="toolbar"><span class="button numbers"><b>#</b></span><span class="button select">Select</span><span class="button expand">Expand</span></div><div class="inner"><span class="number">  1</span>mkLevel <span class="k3">*</span>level <span class="k3">=</span> ctx-&gt;current_level<span class="k2">;</span>
<span class="number">  2</span>  <a href="http://www.allegro.cc/manual/ALLEGRO_MOUSE_STATE"><span class="a">ALLEGRO_MOUSE_STATE</span></a> mouse<span class="k2">;</span>
<span class="number">  3</span>  <a href="http://www.allegro.cc/manual/al_get_mouse_state"><span class="a">al_get_mouse_state</span></a><span class="k2">(</span><span class="k3">&amp;</span>mouse<span class="k2">)</span><span class="k2">;</span>
<span class="number">  4</span>
<span class="number">  5</span>  <span class="k1">float</span> world_x <span class="k3">=</span>
<span class="number">  6</span>      <span class="k3">-</span><span class="k2">(</span><span class="k2">(</span><span class="k2">(</span>ctx-&gt;screen.width <span class="k3">/</span> <span class="n">2</span><span class="k2">)</span> <span class="k3">-</span> mouse.x<span class="k2">)</span> <span class="k3">-</span> level-&gt;viewport.x<span class="k2">)</span><span class="k2">;</span>
<span class="number">  7</span>  <span class="k1">float</span> world_y <span class="k3">=</span>
<span class="number">  8</span>      <span class="k3">-</span><span class="k2">(</span><span class="k2">(</span><span class="k2">(</span>ctx-&gt;screen.height <span class="k3">/</span> <span class="n">2</span><span class="k2">)</span> <span class="k3">-</span> mouse.y<span class="k2">)</span> <span class="k3">-</span> level-&gt;viewport.y<span class="k2">)</span><span class="k2">;</span>
<span class="number">  9</span>
<span class="number"> 10</span>  <a href="http://www.allegro.cc/manual/al_identity_transform"><span class="a">al_identity_transform</span></a><span class="k2">(</span><span class="k3">&amp;</span>level-&gt;viewport.transform<span class="k2">)</span><span class="k2">;</span>
<span class="number"> 11</span>
<span class="number"> 12</span>  <a href="http://www.allegro.cc/manual/al_translate_transform"><span class="a">al_translate_transform</span></a><span class="k2">(</span><span class="k3">&amp;</span>level-&gt;viewport.transform, <span class="k3">-</span>level-&gt;viewport.x,
<span class="number"> 13</span>             <span class="k3">-</span>level-&gt;viewport.y<span class="k2">)</span><span class="k2">;</span>
<span class="number"> 14</span>
<span class="number"> 15</span>  <a href="http://www.allegro.cc/manual/al_rotate_transform"><span class="a">al_rotate_transform</span></a><span class="k2">(</span><span class="k3">&amp;</span>level-&gt;viewport.transform, level-&gt;viewport.rotate<span class="k2">)</span><span class="k2">;</span>
<span class="number"> 16</span>  <a href="http://www.allegro.cc/manual/al_scale_transform"><span class="a">al_scale_transform</span></a><span class="k2">(</span><span class="k3">&amp;</span>level-&gt;viewport.transform, level-&gt;viewport.zoom,
<span class="number"> 17</span>         level-&gt;viewport.zoom<span class="k2">)</span><span class="k2">;</span>
<span class="number"> 18</span>
<span class="number"> 19</span>  <a href="http://www.allegro.cc/manual/al_translate_transform"><span class="a">al_translate_transform</span></a><span class="k2">(</span><span class="k3">&amp;</span>level-&gt;viewport.transform,
<span class="number"> 20</span>             ctx-&gt;screen.width <span class="k3">*</span> <span class="n">0</span>.<span class="n">5</span>,
<span class="number"> 21</span>             ctx-&gt;screen.height <span class="k3">*</span> <span class="n">0</span>.<span class="n">5</span><span class="k2">)</span><span class="k2">;</span>
<span class="number"> 22</span>
<span class="number"> 23</span>  <span class="c">//al_transform_coordinates(&amp;level-&gt;viewport.transform, &amp;world_x,</span>
<span class="number"> 24</span>  <span class="c">//     &amp;world_y);</span>
<span class="number"> 25</span>
<span class="number"> 26</span>
<span class="number"> 27</span>  <a href="http://www.allegro.cc/manual/al_use_transform"><span class="a">al_use_transform</span></a><span class="k2">(</span><span class="k3">&amp;</span>level-&gt;viewport.transform<span class="k2">)</span><span class="k2">;</span>
<span class="number"> 28</span>  <span class="c">/* DRAW START HERE */</span>
</div></div><p>
How can I use this transform to translate my mouse position to world position? I tried to use al_transform_cordinates but I&#39;m not sure how I have to treath the mouse value before passing to it. My current implementation of <b>world_x and world_y</b> only works before zoom or rotation are applied <img src="http://www.allegro.cc/forums/smileys/rolleyes.gif" alt="::)" />
</p></div>]]>
		</description>
		<author>no-reply@allegro.cc (Bungow)</author>
		<pubDate>Wed, 28 Jun 2017 16:36:21 +0000</pubDate>
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		<description><![CDATA[<div class="mockup v2"><div class="source-code snippet"><div class="inner"><pre><a href="http://www.allegro.cc/manual/al_invert_transform"><span class="a">al_invert_transform</span></a><span class="k2">(</span><span class="k3">&amp;</span>level-&gt;viewport.transform<span class="k2">)</span><span class="k2">;</span>
<a href="http://www.allegro.cc/manual/al_transform_coordinates"><span class="a">al_transform_coordinates</span></a><span class="k2">(</span><span class="k3">&amp;</span>level-&gt;viewport.transform, <span class="k3">&amp;</span><a href="http://www.allegro.cc/manual/mouse_x"><span class="a">mouse_x</span></a>, <span class="k3">&amp;</span><a href="http://www.allegro.cc/manual/mouse_y"><span class="a">mouse_y</span></a><span class="k2">)</span><span class="k2">;</span>
</pre></div></div><p>

That should work. Obviously it might make sense for you to copy the transformation before inverting it.
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		</description>
		<author>no-reply@allegro.cc (SiegeLord)</author>
		<pubDate>Thu, 29 Jun 2017 07:03:41 +0000</pubDate>
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		<description><![CDATA[<div class="mockup v2"><p>Thanks!
</p></div>]]>
		</description>
		<author>no-reply@allegro.cc (Bungow)</author>
		<pubDate>Mon, 03 Jul 2017 22:30:52 +0000</pubDate>
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