Affine transforms - matrix algebra

Martin Desruisseaux martin.desruisseaux at
Mon Jul 23 03:09:47 PDT 2012

Le 23/07/12 11:11, Pavel Safrata a écrit :
> We need to add manual transformation methods to Transfrom class. This 
> is very important, I can't believe I've forgotten them..
I noticed that those methods were missing, but I though that it was on 
intend :)

> public Point3D transform(Point3D point)
>     public Bounds transform(Bounds bounds)
> Any other?
I think that the following one is very important for performance reasons:

void transform(double[] srcPts, int srcOffset, double[] dstPts, int 
dstOffset, int numPts);

with semantic identical to the one currently in the Java2D 
AffineTransform. The other variants working on float arrays and the ones 
mixing float/double arrays would also be useful. Alternatively, methods 
working on java.nio.Float/DoubleBuffer instead than arrays would also be 
okay if performances are the same (this would avoid the need for 
src/dstOffset and numPts arguments).

Maybe it would be worth to phrase the javadoc in a way that leave room 
for slight implementation-dependant differences in the numerical 
results. For example the javadoc of Math.sin said "The computed result 
must be within 1 ulp of the exact result". I think that something 
similar for the transform methods (the number of ulp is yet to be 
determined) would be useful in order to leaves room for 
hardward-accelerated implementations. I'm thinking especially about the 
"fused add-multiply" operation found on many modern processor, which 
doesn't produce exactly the same result than multiplication followed by 
addition in Java. It would be nice if Transform implementations were 
allowed to use such operations on platforms that support it, despite the 
slight difference in numerical results.

> Rename the MatrixArrayType constants to MAT_2D_3x2, MAT_2D_3x3, 
> MAT_3D_3x4, MAT_3D_4x4, do you agree?
I don't really have better idea at this time... I wonder if we could 
find a way to merge with the VAT_* constants...


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