Box2D libgdx polygon shape

Question

How come this works fine:

Vector2[] vertexArray = new Vector2[3];
vertexArray[0] = new Vector2(0f, 0f);
vertexArray[1] = new Vector2(1f, 1f);
vertexArray[2] = new Vector2(2f, 5f);

polygonShape.set(vertexArray);

and this gives a runtime error

Vector2[] vertexArray = new Vector2[3];
vertexArray[0] = new Vector2(0f, 0f);
vertexArray[1] = new Vector2(1f, 1f);
vertexArray[2] = new Vector2(2f, 2f);

polygonShape.set(vertexArray);

Error:

AL lib: (EE) alc_cleanup: 1 device not closed
Assertion failed!

Program: C:\Program Files\Java\jre1.8.0_25\bin\javaw.exe
File: /var/lib/jenkins/workspace/libgdx/extensions/gdx-box2d/gdx-box2d/jni/Box2D/Collision/Shapes/b2PolygonShape.cpp, Line 223

Expression: false

It does not make any sense. First code works fine and the triangle is drawn, but the second code does not. Can someone please explain what I'm doing wrong...

Is this error happen in all program runs, or is it one-time exception? — dreamsComeTrue
The chances that the code works are 50% and the only thing I am changing are the coordinates. For example, [(0,0), (1,1), (2,5)] does work, but [(0,0), (1,1), (2,3)] does not. — user1176999

iforce2d iforce2d · Accepted Answer · 2014-11-24T14:08:19

The vertices (0,0), (1,1), (2,2) are all in a straight line - they don't make a polygon. This causes an assertion to trigger, as shown in the error message (b2PolygonShape.cpp, Line 223)

Box2D libgdx polygon shape

1 Answers