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[java] Sprite Rotation using Java2D

General and Gameplay Programming Programming

Started by acidwillburnyou March 05, 2008 05:11 PM

3 comments, last by 5MinuteGaming 16 years, 1 month ago

acidwillburnyou

100

Author

March 05, 2008 05:11 PM

I'm trying to rotate a sprite in my game. The problem is, the entire buffer rotates (including the fps string). Not only this, but the rotation isn't happening from the center of the sprite, but rather from the top left of the screen. I'm using the Graphics2D class in the java api. Here's the relevant code snippets: method that's called, eg: mech.rotate(-1, 45);


	// direction is either 1 (cc) or -1 (c)
	// angle is in deg
	public void rotate(int direction, double deg) {
		AffineTransform transform = new AffineTransform();
		angleInRad = Math.toRadians(direction * deg);

		//transform.setToTranslation(x, y);
		transform.rotate(angleInRad * direction);
		super.rotate(transform);

	}

super class's rotate method (it has reference to the sprite Image variable):


	public void rotate(AffineTransform transform) {
		g2d.drawImage(image, transform, null);
		System.out.println("rotate: " + transform);
	}

Thanks, Karan

aklenfer

100

March 05, 2008 05:44 PM

use

transform.rotate(angle,x,y);

where angle is yo angle and (x,y) is coordinate of the pivot.
For the entire buffer rotating, that buffer isnt called "image" in yo code is it?

acidwillburnyou

100

Author

March 05, 2008 06:08 PM

Hmm, still no cigar. I've consolidated the two methods into one:

	public void rotate(int direction, double deg, Graphics2D g2d) {		AffineTransform transform = new AffineTransform();		angleInRad = Math.toRadians(direction * deg);		//transform.setToTranslation(x, y);		int hwidth = super.image.getWidth(null) / 2;		int hheight = super.image.getWidth(null) / 2;		transform.rotate(angleInRad * direction, currentX + hwidth, currentY - hheight);		g2d.drawImage(super.image, transform, null);	}

The values of hheight/width and currentX/Y are correct. I'm wondering why it's still not working.

Thanks in advance.

aklenfer

100

March 05, 2008 07:19 PM

the x and y in rotate(angle,x,y) are relative to the image origin (0,0) not to the absolute origin.
So if u have a 50x40 sprite and you want to draw it rotated around it's center by 30 degrees at position 300,400 u do this:

void paint(Graphics g){...Graphics2D g2d=(Graphics2D)g;AffineTransform at1=new AffineTransform();at1.translate(300-25,400-20);at1.rotate(Math.PI/180*30,25,20);	g2d.drawImage(image,at1,null);...}

5MinuteGaming

274

March 15, 2008 12:30 AM

I particularly like to use Graphics.create don't know whether it is a decent way of creating separate graphics contexts but it works except with it you have to worry about clipping area.

public void rotate(int direction, double deg, Graphics2D g2d) {		int width = super.image.getWidth(null);		int height = super.image.getHeight(null);				//create new context		Graphics2D imgG2D = (Graphics2D)(g.create(currentX, currentY, width, height));				//rotate from the center using radians		imgG2D.rotate(Math.toRadians(deg), width/2, height/2);				imgG2D.drawImage(super.image, 0, 0, null);}

There are a couple things with this however the new Graphics object imgG2D will clip everything drawn outside of 0,0,width,height so you will get part of your images being cutoff if they are square meaning their width and height aren't the same. Also, the new imgG2D renders everything to the same screen as the original but its translated to the currentX and currentY coordinates which is why I used 0,0 in the drawImage function. Play around with it a bit its a nice way of drawing things because its completely independent of the settings from the original graphics object.

Hope this helps!

[Code Snippets][5MinuteGaming]

[java] Sprite Rotation using Java2D

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