How to display a rotated polygon in ShapeRenderer LibGDX/Java

Question

I am making a simple game but I don't seem to be able to rotate a simple polygon. I did a test below.

I have ( ShapeRenderer shape ) and ( shape = new ShapeRenderer() ) initialized above.

Below is my code.

    float x1 = 200;
    float y1 = 200;
    float x2 = 250;
    float y2 = 200;
    float x3 = 250;
    float y3 = 250;
    float x4 = 200;
    float y4 = 250;

    float[] f = {x1,y1,x2,y2,x3,y3,x4,y4};

    Polygon polygonTest = new Polygon();
    polygonTest.setVertices(f);
    polygonTest.setOrigin(x1+25,y1+25);
    polygonTest.rotate(-45f);

    shape.begin(ShapeRenderer.ShapeType.Line);
    shape.polygon(polygonTest.getVertices());
    shape.end();

This is the output

After rotation, I double check its rotation value using polygonTest.getRotation() and it returns the correct value. I have also tried positive values without the "f" (float) indicator in the parameter but no luck.

All the threads I have read about this particular issue just mentioned to setOrigin then rotate, but it is not working for me.

Any help is appreciated!

Answer 1

getVertices() method of Polygon returns the polygon's local vertices without scaling or rotation.

Use getTransformedVertices() that returns the vertices of the polygon after scaling, rotation.

Here is Test Code :

public class GdxTest extends ApplicationAdapter {

    ShapeRenderer shapeRenderer;
    Polygon polygonTest;

    @Override
    public void create() {

        shapeRenderer= new ShapeRenderer();

        float x1 = 200;
        float y1 = 200;
        float x2 = 250;
        float y2 = 200;
        float x3 = 250;
        float y3 = 250;
        float x4 = 200;
        float y4 = 250;

        float[] f = {x1,y1,x2,y2,x3,y3,x4,y4};

        polygonTest = new Polygon();
        polygonTest.setVertices(f);
        polygonTest.setOrigin(x1+25,y1+25);
        polygonTest.rotate(-45f);
    }

    @Override
    public void render() {

        Gdx.gl.glClearColor(0,0,0,1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

        if (polygonTest.getRotation()<360){
            polygonTest.setRotation(polygonTest.getRotation()+1);
        }else
            polygonTest.setRotation(0);

        shapeRenderer.begin(ShapeRenderer.ShapeType.Line);
        shapeRenderer.polygon(polygonTest.getTransformedVertices());
        shapeRenderer.end();
    }

    @Override
    public void dispose() {
        shapeRenderer.dispose();
    }
}