3 replies to this topic

[nkarasch]

How can I rotate an image in Java? I think I have AffineTransform pretty figured out but I can't figure out how to make a single image rotate without the entire JPanel rotating.

public void draw(Graphics2D g2d) {
  rotate.translate(location.x, location.y);
  rotate.rotate(rotation);
  rotate.translate(-location.x,-location.y);

  g2d.setTransform(rotate);
  g2d.drawImage(currentAnimation.getCurrentFrame(), (int) location.x, (int) location.y, null);
}

g2d is passed in from the paint method, it is obviously representing the entire contents of the panel. Should every image on the screen have it's own separate instance of graphics so I can only apply the AffineTranformation to it, without applying it to everything else?

Also, all of the coordinates are changing. The force applied by vectors rotate with the everything else. :\

Thanks. None of the search results could clarify this for me.

Edited by nkarasch, 09 December 2012 - 06:20 AM.

[de_mattT]

Inded the g2d object represents the entire contents of the JPanel - it's the canvas upon which everything is drawn.

Rather than everything having its own g2d object, everything should have its own AffineTransform object to define where it should be drawn on the canvas.

It's a good idea to reset the transformation after you've drawn your image (I think this will fix your problem) as follows:

public void draw(Graphics2D g2d) {
	  rotate.translate(location.x, location.y);
	  rotate.rotate(rotation);
	  rotate.translate(-location.x,-location.y);
	
	  // take a copy of the transformation that g2d is using
	  AffineTransform prevTransform = g2d.getTransform();

	  // apply the transformation for this object and draw
	  g2d.setTransform(rotate);
	  g2d.drawImage(currentAnimation.getCurrentFrame(), (int) location.x, (int) location.y, null);

	  // revert g2d back to the old transformation
	  g2d.setTransform(prevTransform);
}

Matt

Edited by de_mattT, 09 December 2012 - 02:52 PM.

[nkarasch]

Thanks a ton, that is the best response I could have ask for.

Any idea how I can keep my entire coordinate system from changing in relation to the entity I rotated? I want right to continue to be right, up to continue to be up, etc. Even my screen boundaries are messed up for the rotated object. There has to be a way to do it.

[de_mattT]

I'm not sure I understand your question sorry.

Are you saying you want to put something at a point on the screen and then rotate it around that point?
If you're translating it, then rotating it, the translation will be relative to the rotation, which sounds the problem you're describing.
The first three lines in the method are confusing me a bit.
If I've understood your problem correctly then the code below should fix it.

public void draw(Graphics2D g2d) {
 
	 // Reset the AffineTransform to an identity matrix
	 // do translation first and rotation second
	 // (this multiplies a translation matrix by a rotation matrix, which means that actually the rotation happens first)    
	 rotate.setToIdentity();
	 rotate.translate(location.x, location.y);
	 rotate.rotate(rotation);

	 // take a copy of the transformation that g2d is using
	 AffineTransform prevTransform = g2d.getTransform();	 	 // you might not need this anymore due to use of different drawImage method
	
	 // call draw and pass in the affine transformation to use
	 g2d.drawImage(currentAnimation.getCurrentFrame(), rotate, null);

	  // revert g2d back to the old transformation
	  g2d.setTransform(prevTransform);	 // you might not need this anymore due to use of different drawImage method
}

Note the use of the other version of drawImage in the code above - we're not passing in the location. This means that the AffineTransform object contains all the transformation info, which makes it a bit easier to follow.

I hope this solves your problem

Matt