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 Affine Transformation Coordinate System Explain  (Read 1444 times) 0 Members and 1 Guest are viewing this topic.
8bitooze

Senior Newbie

 « Posted 2011-02-05 18:14:39 »

I am using Affine Transformation to position my game objects on screen. My applet is 320 * 240, yet the leftmost edge is -80 for one of the objects so far and the rightmost being 240. The object in question is a 32 * 8 rectangle shape. To me it seems my coordinates are "crooked". Could someone please explain this to me? Any assistance in this matter would be greatly appreciated.

Sincerely,

8BitOoze

[size=3]8BitOoze[/size]
krasse
 « Reply #1 - Posted 2011-02-06 11:36:02 »

Is it 2D or 3D?

How do you create the transformation? Directly with the matrix or using a helper function like translate(), rotate(), lookAt() etc. ?

It is possible to create a shew transformation with with an affine transform, if that is what you mean by "crooked".

Show some of your code!

8bitooze

Senior Newbie

 « Reply #2 - Posted 2011-02-07 14:32:19 »

Quote
Is it 2D or 3D?
2D

Quote
How do you create the transformation? Directly with the matrix or using a helper function like translate(), rotate(), lookAt() etc. ?
Using g2d.translate(object.getX(), object.getY());

Quote
It is possible to create a shew transformation with with an affine transform, if that is what you mean by "crooked".

Show some of your code!
Ok, here's a link to the latest version of my code with the shrewed affine transformation link

Any assistence in this matter would be greatly appreciated.

Sincerely,

8BitOoze

[size=3]8BitOoze[/size]
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krasse
 « Reply #3 - Posted 2011-02-07 17:01:22 »

The problem is that you both translate the shape in the constructor for Ball and Paddle AND in the drawing.

This is the explanation for the extra offset. Just set the translation in the constructors to zero and it will work.

8bitooze

Senior Newbie

 « Reply #4 - Posted 2011-02-07 20:01:18 »

I don't understand what you mean.

Paddle constructor:
 1  2  3  4  5  6  7  8  9  10  11  12  13  14 `// class constructor   public Paddle(double x, double y, double width, double height)   {      // set the paddles x position      setX(x);      // set the paddles y position      setY(y);      // set the paddles width      setWidth(width);      // set the paddles height      setHeight(height);      // set the paddles shape      setShape(new Rectangle((int)getX(), (int)getY(), (int)getWidth(), (int)getHeight()));   }`

Ball Constructor:
 1  2  3  4  5  6  7  8  9  10  11  12  13  14 `// class constructor   public Ball(double x, double y, double width, double height)   {      // set the balls x position      setX(x);      // set the balls y position      setY(y);      // set the balls width      setWidth(width);      // set the balls height      setHeight(height);      // set the balls shape      setShape(new Rectangle((int)getX(), (int)getY(), (int)getWidth(), (int)getHeight()));   }`

I don't see any g2d.transform() in there anywhere. If you mean changing my EightBitOoze constructor as follows:
 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24 `public final void init()   {      // create the backbuffer for smooth graphics      backbuffer = new BufferedImage(getSize().width, getSize().height, BufferedImage.TYPE_INT_RGB);      g2d = backbuffer.createGraphics();      // create the identity transform      identity = new AffineTransform();      // create an instance of the paddle object      paddle = new Paddle(getSize().width / 4, 106, 32, 8);      // set the paddle's x velocity      paddle.setVX(2);      // create an instance of the ball object      ball = new Ball(getSize().width / 4, 10, 8, 8);      // set the players score to 0      score = 1234;      // start the user input listener      addKeyListener(this);   }`

And changing the update method to:
 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26 `public final void update(Graphics g)   {      // erase the background      g2d.setPaint(Color.LIGHT_GRAY);      g2d.fillRect(0, 0, getSize().width, getSize().height);      // draw the statusbar      g2d.setPaint(Color.GREEN);      g2d.fillRect(0, getSize().height - STATUSBARHEIGHT, getSize().width, STATUSBARHEIGHT);      // draw the players score      g2d.setPaint(Color.WHITE);      g2d.drawString("Score: " + Integer.toString(score), 0, (getSize().height - STATUSBARHEIGHT) + (STATUSBARHEIGHT /2));      // draw the ball      g2d.setPaint(Color.BLUE);      g2d.translate(ball.getX(), ball.getY());      g2d.fill(ball.getShape());      // draw the paddle      g2d.translate(paddle.getX(), paddle.getY());      g2d.fill(paddle.getShape());      // repaint the applet window      paint(g);   }`

Then please let me know as I'm not sure what you mean when you say I'm translating on the ball/paddle constructor when I can't see a single translate call in them. Any assistance in this matter would be greatly appreciated.

Sincerely,

8BitOoze

[size=3]8BitOoze[/size]
krasse
 « Reply #5 - Posted 2011-02-07 21:38:03 »

The shape is translated with this statement:
 1  2  3  4 `setShape(new Rectangle((int)getX(), (int)getY(), (int)getWidth(), (int)getHeight()));// Should be this instead:// setShape(new Rectangle(0, 0, (int)getWidth(), (int)getHeight()));`

In the animation you draw the same shape translated once more but then you draw the shape that is positioned at the initial (getX(), getY()) position and you get an offset.

8bitooze

Senior Newbie

 « Reply #6 - Posted 2011-02-08 16:15:10 »

The shape is translated with this statement:
 1  2  3  4 `setShape(new Rectangle((int)getX(), (int)getY(), (int)getWidth(), (int)getHeight()));// Should be this instead:// setShape(new Rectangle(0, 0, (int)getWidth(), (int)getHeight()));`

In the animation you draw the same shape translated once more but then you draw the shape that is positioned at the initial (getX(), getY()) position and you get an offset.

Wow i didn't know that thanks. I did what you said and it worked.

Sincerely,

8BitOoze

[size=3]8BitOoze[/size]
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