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POFlipping polygon in libgdx
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  1. POFlipping polygon in libgdx
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    copied!<p>I have Tiled maps working in libgdx, now I'm trying to do collision with these maps. I figured it'd be really useful just to draw polygons in Tiled and use them for collisions in libgdx. I'd actually prefer it this way rather than doing a per tile collision since it'll give me collision flexibility which the game requires. </p> <p>I've successfully parsed each object's xml and grabbed the polygon points. I've been able to make a box2d PolygonShape with these and it shows up in game! But it's mirrored upside down...</p> <p>I figured tiled must be on a different coordinate system than libgdx so I just created a function that finds the max y point and subtracts the rest of the y points from it in correct y flipping fashion. But now I'm getting this error:</p> <pre><code>java: /var/lib/hudson/jobs/libgdx-git/workspace/gdx/jni/Box2D/Collision/Shapes/b2PolygonShape.cpp:115: b2Vec2 ComputeCentroid(const b2Vec2*, int32): Assertion `area &gt; 1.19209289550781250000e-7F' failed. </code></pre> <p>It looks like an error from libgdx's native side. <strong>Is there anyone that can help me figure this out?</strong></p> <p>Here's the relevant section from my tmx file.</p> <pre><code>&lt;objectgroup height="20" name="Object Layer 1" width="20"&gt; &lt;object x="100" y="320"&gt; &lt;polygon points="0,0 244,1 300,50 300,95 -12,88 -29,19"/&gt; &lt;/object&gt; &lt;object height="104" width="116" x="437" y="175"/&gt; &lt;/objectgroup&gt; </code></pre> <p>Here's the bit of code, it's in Scala, that flips the polygon. It takes a Border object that has a polygon field which is just an array of Vector2s. The _type field is a symbol, it looks like it messes with stackoverflow's syntax highlighting.</p> <pre><code>def flipPolygonY(border: Border){ if(border._type == 'polygon){ //find the highest y point var max = border.polygon(0).y for(vect &lt;- border.polygon){ max = max.max(vect.y) } //flip it, take max - y for(vect &lt;- border.polygon){ vect.set(vect.x, max - vect.y) } } } </code></pre>
 

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