I'm trying to scale a rectangle from its center using AffineTransform. I'm sure the solution is obvious but I cannot make it work ! Here is what I've tested so far...
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.geom.AffineTransform;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
public class Test extends JPanel {
Test()
{
super(null);
setOpaque(true);
setBackground(Color.WHITE);
setPreferredSize(new Dimension(200,200));
}
@Override
protected void paintComponent(Graphics g1) {
super.paintComponent(g1);
Rectangle r= new Rectangle(5,5,getWidth()-10,getHeight()-10);
double cx= r.getCenterX();
double cy= r.getCenterY();
Graphics2D g=(Graphics2D)g1;
g.setColor(Color.BLACK);
AffineTransform old= g.getTransform();
for(double zoom=0.9; zoom>=0.5; zoom-=0.1)
{
AffineTransform tr2= new AffineTransform(old);
tr2.translate(-cx, -cy);
tr2.scale(zoom, zoom);
tr2.translate(cx/zoom,cy/zoom);
g.setTransform(tr2);
g.draw(r);
g.setTransform(old);
}
}
public static void main(String[] args) {
JOptionPane.showMessageDialog(null, new Test());
}
}
But it doesn't work.... Any suggestion ?
Assuming scaling fixes the location of the top lefthand corner of the rectangle (which I think is right but it's been a long time since I've done graphics in Java), you need to translate the rectangle in the direction opposite to the scaling.
tr2.translate(
r.getWidth()*(1-zoom)/2,
r.getHeight()*(1-zoom)/2
);
tr2.scale(zoom,zoom);
g.setTransform(tr2);
So you move the rectangle left and up half of the change in width and height.
I was just working on a desktop application to crop Brittney Spear's face (D.A.Y.) The cropping rectangle had to scale around its center point:
import javafx.scene.Cursor;
import javafx.scene.Group;
import javafx.scene.input.MouseEvent;
import javafx.scene.input.ScrollEvent;
import javafx.scene.paint.Color;
import javafx.scene.paint.Paint;
import javafx.scene.shape.Rectangle;
class ResizableRectangle extends Rectangle {
ResizableRectangle(double x, double y, double width, double height, Group group) {
super(x, y, width, height);
// Set scroll listener for crop selection
group.addEventHandler(ScrollEvent.SCROLL, event -> {
double zoomFactor = 1.10;
double deltaY = event.getDeltaY();
if (deltaY > 0) {
zoomFactor = 2.0 - zoomFactor;
}
super.setX(getX() + (super.getWidth() * (1 - zoomFactor) / 2)); // Set new X position
super.setWidth(getWidth() * zoomFactor); // Set new Width
super.setY(getY() + (super.getHeight() * (1 - zoomFactor) / 2)); // Set new Y position
super.setHeight(getHeight() * zoomFactor); // Set new Height
event.consume();
});
});
}
In general, the algorithm works like this:
x + (width * (1 - zoomFactor) / 2)
y + (height * (1 - zoomFactor) / 2)
width * zoomFactor
height * zoomFactor
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