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# need help creating a method for rotate

Greenhorn
Posts: 5
hello,
Im trying to rotate a rectangle with a rotate method. Im not sure if I'm doing this correctly.
public void paint (Graphics g)
{ g.drawRect (x,y,length,width);}
how would i create a method to rotate 90 degrees?
public void rotate()
{ ? }
[ March 11, 2003: Message edited by: Jeremiah jjjjjjjjjjjjjjjj ]

Ranch Hand
Posts: 154
If you want to create your own rotate method:
Say (x1,y1) is the upper-left corner of the original rectangle.
Width is its length along the x-axis, height is its length along the y-axis.
You probably want to compute what (x2, y2) was the dead center of the first rectangle (esimerkiksi: x2 = x1 + (width * .5)).
Assume that will also be your new rectangle's center, then backtrack to see what the coordinate's of the upper-left corner are now that newHeight=oldWidth and newWidth=oldHeight. This way you pivoted around the center of the original rectangle.
[ March 12, 2003: Message edited by: Elouise Kivineva ]
[ March 12, 2003: Message edited by: Elouise Kivineva ]

Ranch Hand
Posts: 7729
Hello Jeremiah, welcome to JavaRanch. Would you please change your displayed name to conform to the JavaRanch Naming Policy
Thanks
-Barry

Barry Gaunt
Ranch Hand
Posts: 7729
To rotate a general rectangle, you should translate the rectangle so that its centre is on the origin. Then rotate each corner of the rectange around the origin using a rotation matrix (to be found in any computer graphics text/tutorial). Then translate the centre of the rectangle back to its original postition. Finally, draw the sides and fill appropriately. Of course, all this can be optimised in the case of a rotation of 90 degrees because the sine of 90 degrees is 1.0, and cosine of 90 degrees is 0.0. Do the maths first to simplify the code you have to write.
-Barry

Barry Gaunt
Ranch Hand
Posts: 7729
Of course, if you don't want to reinvent the wheel you can use the methods of the java.awt.Graphics2D class.

 Consider Paul's rocket mass heater.