On Wed, 2004-02-04 at 00:33, graydon hoare wrote:
> Olga Rodimina wrote:
>
> > Here is the patch that fixes few errors in the AffineTransform class.
> > It corrects a small error in shear transformation and fixes
> > createInverse() to return correct inverse matrix.
>
> hi olga,
>
> this stuff looks good, thanks a lot! it's surprising this just sat there
> broken for so long. I've checked it against a few algebra texts I have
> kicking around and some geometry libraries (including cairo) and they
> seem to mostly agree with your calculation; though just to be difficult
> they all use different notation and half of them do it upside down :)
>
Hi,
I fixed the suggested changes. Attached is the revised patch that I'll
be committing.
>
> it might be nice to write up a mauve testsuite which generates a bunch
> of pseudorandom vectors and runs them through a bunch of pseudorandom
> scaled, sheared and translated transformations (and their inverses) and
> checks that the vectors pop out the same as they went in, within some
> epsilon to account for floating point error. anything to make this stuff
> less fidgety and prone to eyes-glossing-over would probably be good.
> it's too easy to make a minor arithmetic mistake which completely breaks it.
>
Sure. I'll do that.
Olga.
? .snprj
? libjava.proj
? patch
Index: ChangeLog
===================================================================
RCS file: /cvs/gcc/gcc/libjava/ChangeLog,v
retrieving revision 1.2637
diff -c -p -u -r1.2637 ChangeLog
--- ChangeLog 4 Feb 2004 00:07:19 -0000 1.2637
+++ ChangeLog 4 Feb 2004 15:55:56 -0000
@@ -1,3 +1,13 @@
+2004-02-04 Olga Rodimina <[EMAIL PROTECTED]>
+
+ * java/awt/geom/AffineTransform.java:
+ Corrected comments on the field definitions for
+ m11 and m10.
+ (shear): Fixed few errors that caused shear
+ transformation to be performed incorrectly.
+ (createInverse): Fixed to return correct
+ inverse of the given matrix.
+
2004-02-03 Tom Tromey <[EMAIL PROTECTED]>
* java/lang/natPosixProcess.cc (startProcess): Handle case where
Index: java/awt/geom/AffineTransform.java
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/awt/geom/AffineTransform.java,v
retrieving revision 1.7
diff -c -p -u -r1.7 AffineTransform.java
--- java/awt/geom/AffineTransform.java 17 Sep 2003 19:06:55 -0000 1.7
+++ java/awt/geom/AffineTransform.java 4 Feb 2004 15:55:57 -0000
@@ -226,7 +226,7 @@ public class AffineTransform implements
private double m00;
/**
- * The Y coordinate scaling element of the transform matrix.
+ * The Y coordinate shearing element of the transform matrix.
*
* @serial matrix[1,0]
*/
@@ -240,7 +240,7 @@ public class AffineTransform implements
private double m01;
/**
- * The Y coordinate shearing element of the transform matrix.
+ * The Y coordinate scaling element of the transform matrix.
*
* @serial matrix[1,1]
*/
@@ -738,10 +738,10 @@ public class AffineTransform implements
*/
public void shear(double shx, double shy)
{
- double n00 = m00 + shx * m01;
- double n01 = shx * m00 + m01;
- double n10 = m10 * shy + m11;
- double n11 = shx * m10 + m11;
+ double n00 = m00 + (shy * m01);
+ double n01 = m01 + (shx * m00);
+ double n10 = m10 + (shy * m11);
+ double n11 = m11 + (shx * m10);
m00 = n00;
m01 = n01;
m10 = n10;
@@ -996,6 +996,38 @@ public class AffineTransform implements
* map multiple points to the same line or point). A transform exists only
* if getDeterminant() has a non-zero value.
*
+ * The inverse is calculated as:
+ *
+ * <pre>
+ *
+ * Let A be the matrix for which we want to find the inverse:
+ *
+ * A = [ m00 m01 m02 ]
+ * [ m10 m11 m12 ]
+ * [ 0 0 1 ]
+ *
+ *
+ * 1
+ * inverse (A) = --- x adjoint(A)
+ * det
+ *
+ *
+ *
+ * = 1 [ m11 -m01 m01*m12-m02*m11 ]
+ * --- x [ -m10 m00 -m00*m12+m10*m02 ]
+ * det [ 0 0 m00*m11-m10*m01 ]
+ *
+ *
+ *
+ * = [ m11/det -m01/det m01*m12-m02*m11/det ]
+ * [ -m10/det m00/det -m00*m12+m10*m02/det ]
+ * [ 0 0 1 ]
+ *
+ *
+ * </pre>
+ *
+ *
+ *
* @return a new inverse transform
* @throws NoninvertibleTransformException if inversion is not possible
* @see #getDeterminant()
@@ -1006,8 +1038,15 @@ public class AffineTransform implements
double det = getDeterminant();
if (det == 0)
throw new NoninvertibleTransformException("can't invert transform");
- return new AffineTransform(m11 / det, -m10 / det, m01 / det, -m00 / det,
- -m02, -m12);
+
+ double im00 = m11 / det;
+ double im10 = -m10 / det;
+ double im01 = -m01 / det;
+ double im11 = m00 / det;
+ double im02 = (m01 * m12 - m02 * m11) / det;
+ double im12 = (-m00 * m12 + m10 * m02) / det;
+
+ return new AffineTransform (im00, im10, im01, im11, im02, im12);
}
/**
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