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https://issues.apache.org/jira/browse/PDFBOX-1960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13923921#comment-13923921
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John Hewson edited comment on PDFBOX-1960 at 3/7/14 2:44 PM:
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Maruan, I assure you that you're not understanding the matrix multiplications
correctly. I didn't say that they are doing "doing the exact same thing", I
said they are doing "doing the exact same thing, just transposed", which they
are.
Performing a pre-multiplication on a matrix is the same as performing a
post-multiplication on its transposition.
The operations you mention are identical:
[x’ y’ 1] = [x y 1] x [Tx]
[x’ y’ 1] = [Tx] x [x y 1]
The values of x and y will always be the same in both cases.
Matrix and AffineTransform are directly compatible which is why we get the same
results when using them. The only alteration that one needs to make is to use
"conctanate" where the PDF spec says "premultiply" because this corrects for
the transposition. Do you see?
was (Author: jahewson):
Maruan, I assure you that you're not understanding the matrix multiplications
correctly. Performing a pre-multiplication on a matrix is the same as
performing a post-multiplication on its transposition.
The operations you mention are identical:
[x’ y’ 1] = [x y 1] x [Tx]
[x’ y’ 1] = [Tx] x [x y 1]
The values of x and y will always be the same in both cases.
Matrix and AffineTransform are directly compatible which is why we get the same
results when using them. The only alteration that one needs to make is to use
"conctanate" where the PDF spec says "premultiply" because this corrects for
the transposition. Do you see?
> Matrix and AffineTransform have confusing differences
> -----------------------------------------------------
>
> Key: PDFBOX-1960
> URL: https://issues.apache.org/jira/browse/PDFBOX-1960
> Project: PDFBox
> Issue Type: Improvement
> Affects Versions: 2.0.0
> Reporter: John Hewson
> Assignee: Maruan Sahyoun
> Priority: Minor
>
> I've been driven insane recently by trying to get pattern fills to render
> correctly. Patterns have their own matrix which is concatenated to the CTM
> and no matter how I applied the transformation, the results were wrong.
> It turns out that org.apache.pdfbox.util.Matrix is not behaving as expected,
> here's an example from a pattern I'm working on. I performed the same
> concatenation (i.e. multiplication) using our Matrix and Java's
> AffineTransform, the results are as follows:
> Java AffineTransform:
> [[2.0, 0.0, 1.251E-12], [0.0, 2.0, 1684.0]] *
> [[0.6, 0.0, 302.6], [0.0, 0.6, 1091.38]] =
> [[1.2, 0.0, 605.2000000000013], [0.0, 1.2, 3866.76]]
> PDFBox Matrix:
> [[2.0,0.0,0.0][0.0,2.0,0.0][1.251E-12,1684.0,1.0]] *
> [[0.6,0.0,0.0][0.0,0.6,0.0][302.6,1091.38,1.0]] =
> [[1.2,0.0,0.0][0.0,1.2,0.0][302.6,2101.78,1.0]]
> I suggest that we remove Matrix and replace it with AffineTransform.
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