Big Big Question with a lot of Funk!

Question

Hey people!
It's been quite a while since I visited these forums. I've actually been working on my game, Platformisis, and I was doing real good until I ran into some problem flipping images. Yes, I did look at the tutorials but there is one thing that I don't get. How does this piece of code work?
AffineTransform Transformer = new AffineTransform();
Graphics2D Surface = ?; // This is given.
Image Picture = ?; // Given also.
Transformer.scale(-1, 1);
Transformer.translate(-10, 10);
Surface.drawImage(Picture, Transformer, null);What I'm understanding here is by putting a minus sign next to the 1 in the scale routine the image is being flipped. Right? Now I want to draw the image to location (10, 10) but in the tutorial I saw a minus sign in front of the X coordinate. I don't get this. Normally wouldn't this draw the image to (-10, 10)? Is there something that I'm missing here? I'm giving Duke Dollars to the best answer.

Answer 1

Affine transforms are stored in a matrix. If you take a point, multiply it by the matrix, your result will be the transformed point. Now, if you want to do mutliple transforms, you can mutliply all the transform matrices together to result in one single matrix. The order of the matrices is preserved. Points multiplied by this matrix will have all the transforms applied to it in the order they were mutliplied in.
Knowing that, if you take the matrix for scaling then multiply in the matrix for the translation, you'll end up with what you would expect - scaling the point then moving it. However, since they are mutliplied in reverse order, the translation is first in the transform string, so the scale is applied to the point after it has been translated. Since the scale flips horizontally, the negative x translation will become positive, placing the point where you wanted it.