Wrong origin coordinates logic for polygon

Question

what i have now in test project, where i try to fix this problem:

2 polygon objects

2 actors, each of actor contain one polygon object

1 array with actors, i run through it in render method and with use of shapeRenderer draw polygons

1 OrthographicCamera

1 Stage

1 ScreenViewport

The logic is next: i create polygon 1 and polygon 2 with the same size and same position at 0,0 .

Than i do setPosition(Gdx.graphics.getWidth()/2, Gdx.graphics.getWidth()/2). Than i translate one polygon by 50 pixel on axis X and run setOrigin(Gdx.graphics.getWidth()/2, Gdx.graphics.getWidth()/2). And i added InputListener for first polygon, when i click on it i do rotateBy on second actor with second polygon. My camera has Y-Up. On rotation second polygon think that his origin point is top right corner of the screen and do rotation around it.

Here is and gif of result: http://i.imgur.com/CDzqTta.gif

And scheme how it behave: http://i.imgur.com/dCB0HDX.jpg

And here is gif of its behave if i maximize window: http://i.imgur.com/6ZKn33d.gif . Here we can see that after resize, green polygon do rotation around the point which was before resize top right cornern of the screen.

Here is a test project with this problem https://www.dropbox.com/s/ti2iiwm2cbom62f/polygonRotation.zip?dl=0

Could anyone help to find out where is a problem?

Thank you.

CodingHamster CodingHamster · Accepted Answer · 2014-10-09T11:11:00

It seems like you misuse the setOrigin method. In your code in PolygonRotation.java:

public void create () {
  float w = Gdx.graphics.getWidth();
  float h = Gdx.graphics.getHeight();

  //...

  p1.setVertices(getVertices(0, 0, 20, 5));
  p2.setVertices(getVertices(0, 0, 20, 5));

  pActor pa1 = new pActor();
  pActor pa2 = new pActor();

  actors.add(pa1);
  actors.add(pa2);

  //...

  pa1.setPosition(w/2, h/2);

  //...

  pa2.setPosition(pa1.getX(), pa1.getY());

  //...

  pa2.setOrigin(pa1.getX(), pa1.getY()); // <-- This line

  //...

  drawViewportBox(w, h);
}

Origin is not the coordinates of polygon's center, but is rather the offset from it.

According to your code both polygons are positioned into center of the screen (w/2, h/2).

Then you set origin of w/2, h/2 for second polygon which sums up with it's current position and equals to w and h. In other words origin is set to the right upper corner of the screen, which is clearly the case.

Wrong origin coordinates logic for polygon

2 Answers