Hi John,
we're fine.
Maruan
Am 30.12.2014 um 00:30 schrieb John Hewson <j...@jahewson.com>:
> Hi Maruan,
>
>> On 28 Dec 2014, at 02:54, Maruan Sahyoun <sahy...@fileaffairs.de> wrote:
>>
>> OK - I think the Matrix code is wrong in getting the shear values compared
>> to the description in the PDF spec.
>>
>> eg. using a text matrix to produce an 'italic' text
>>
>> AffineTransform transform = AffineTransform.getShearInstance(0, 0.5);
>> contentStream.setTextMatrix(transform);
>>
>> produces the same result as
>>
>> contentStream.setTextMatrix(1, 0, 0.5, 1, 0, 0);
>>
>>
>> Which is inline with the spec as c is the sy value.
>>
>
> Yes.
>
>> Now getShearX, getShearY and create AffineTransform in Matrix are wrong IMHO
>> as they have the extraction flipped between sx and sy.
>
> That’s what was puzzling me. I think what we’re doing is fine based on
> AffineTransform’s definition of shear x/y, but that the terminology is simply
> different from PDF, i.e. an x-skew is described in terms of a y-factor, so
> it’s easy to see how the naming could be ambiguous.
>
>> e.g. printing the values of
>>
>> AffineTransform transform = AffineTransform.getShearInstance(0, 0.5);
>
> Ok, so that’s hx = 0, hy = 0.5
>
>> produces
>>
>> AffineTransform[[1.0, 0.0, 0.0], [0.5, 1.0, 0.0]]
>>
>> where
>>
>> printing the values of
>>
>> Matrix matrix = new Matrix();
>> matrix.setValue(1, 0, 0.5f);
>
> Element (1,0) is hx, so you’re doing hx = 0.5, hy = 0, which is the opposite
> of your example above.
>
>> produces
>>
>> AffineTransform[[1.0, 0.5, 0.0], [0.0, 1.0, 0.0]]
>>
>> which is wrong as it should produce AffineTransform[[1.0, 0.0, 0.0], [0.5,
>> 1.0, 0.0]]
>
> Which would make sense for hx = 0.5 but what you wanted was:
>
> matrix.setValue(0, 1, 0.5f)
>
> which produces the expected result:
>
> AffineTransform[[1.0, 0.0, 0.0], [0.5, 1.0, 0.0]]
>
> So I think we’re ok.
>
> — John
>
>>
>> BR
>>
>> Maruan
>>
>> Am 27.12.2014 um 23:47 schrieb John Hewson <j...@jahewson.com>:
>>
>>> Yes, the pure matrix code seems to work fine. As do the examples which
>>> Tilman mentioned. I can’t find any issue with the code itself. However, we
>>> make use the following Matrix method:
>>>
>>> public AffineTransform createAffineTransform()
>>> {
>>> AffineTransform retval = new AffineTransform(
>>> single[0], single[1], // m00 m10 = scaleX shearY
>>> single[3], single[4], // m01 m11 = shearX scaleY
>>> single[6], single[7] ); // m02 m12 = tx ty
>>> return retval;
>>> }
>>>
>>> Recall that single[] is the array:
>>>
>>> | sx hy 0 |
>>> | hx sy 0 |
>>> | tx ty 1 |
>>>
>>> Which is fine, except that shear-x and shear-y are flipped vs. the wording
>>> in the PDF spec, namely:
>>>
>>> "Skew shall be specified by [1 tan a tan b 1 0 0], which skews the x axis
>>> by an angle a and the y axis by
>>> an angle b.”
>>>
>>> But the AffineTransform constructor uses the following parameters:
>>>
>>> "m00 - the X coordinate scaling element of the 3x3 matrix
>>> m10 - the Y coordinate shearing element of the 3x3 matrix
>>> m01 - the X coordinate shearing element of the 3x3 matrix
>>> m11 - the Y coordinate scaling element of the 3x3 matrix
>>> m02 - the X coordinate translation element of the 3x3 matrix
>>> m12 - the Y coordinate translation element of the 3x3 matrix"
>>>
>>> At this point I’m left thinking that Java and PDF have chosen different
>>> meanings of “x” and “y” when talking about skew, indeed this appears to be
>>> the case, as the PDF spec defines the x-coordinate transform on p120 as:
>>>
>>> x’ = a*x + c*y + e
>>>
>>> while the AffineTransform documentation defines the same transform as:
>>>
>>> x' = [ m00*x + m01*y + m02 ]
>>>
>>> which might seem different until one realises that m00 = a, m01 = c, m02 =
>>> e. The only difference appears to be the description that c "skews the y
>>> axis” in PDF and m01 is "the X coordinate shearing" in AffineTransform. It
>>> seems like PDF is weird in this regard?
>>>
>>> -- John
>>>
>>>> On 27 Dec 2014, at 16:51, Maruan Sahyoun <sahy...@fileaffairs.de> wrote:
>>>>
>>>> Hi,
>>>>
>>>> I tried the following with skew being [1 tan a tan b 1 0 0] according to
>>>> the spec.
>>>>
>>>> Matrix matrix = new Matrix();
>>>>
>>>> which gives me [1.0,0.0,0.0,1.0,0.0,0.0]
>>>>
>>>> then
>>>>
>>>> matrix.setValue(0, 1, 0.5f);
>>>> matrix.setValue(1, 0, 0.7f);
>>>>
>>>> which shall set the tan a and tan b values
>>>>
>>>> which gave me
>>>>
>>>> [1.0,0.5,0.7,1.0,0.0,0.0]
>>>>
>>>> then
>>>>
>>>> Matrix matrix2 = new Matrix()
>>>>
>>>> again being [1.0,0.0,0.0,1.0,0.0,0.0]
>>>>
>>>> then
>>>>
>>>> matrix.concatenate(matrix2)
>>>>
>>>> resulting in [1.0,0.5,0.7,1.0,0.0,0.0]
>>>>
>>>> To me that indicates that the pure matrix class is fine for that case.
>>>> What are the arguments to the Concatenate operator in your case? Could it
>>>> be that reading the values is not OK?
>>>>
>>>> BR
>>>>
>>>> Maruan
>>>>
>>>> Am 27.12.2014 um 14:16 schrieb John Hewson <j...@jahewson.com>:
>>>>
>>>>> Hi All,
>>>>>
>>>>> I’ve been looking at the Matrix class and trying to understand if it has
>>>>> some problems. The Matrix class
>>>>> in PDFBox uses the following matrix:
>>>>>
>>>>> | sx hy 0 |
>>>>> | hx sy 0 |
>>>>> | tx ty 1 |
>>>>>
>>>>> In a PDF file this matrix is represented as the 6-element array [a, b, c,
>>>>> d, e, f] where the meaning of
>>>>> the values comes from p118 and is [sx, hx, hy, sy, tx, ty]. Note that h
>>>>> is used to mean shear/skew.
>>>>>
>>>>> The Concatenate operator class populates the Matrix as follows:
>>>>> PDFBox PDF Spec
>>>>> newMatrix.setValue(0, 0, a.floatValue()); sx a = sx
>>>>> newMatrix.setValue(0, 1, b.floatValue()); hy c = hx <- Flipped?
>>>>> newMatrix.setValue(1, 0, c.floatValue()); hx b = hy <- Flipped?
>>>>> newMatrix.setValue(1, 1, d.floatValue()); sy d = sy
>>>>> newMatrix.setValue(2, 0, e.floatValue()); tx e = tx
>>>>> newMatrix.setValue(2, 1, f.floatValue()); ty f = ty
>>>>>
>>>>> I’ve annotated what PDFBox does on the left, compared to the PDF spec,
>>>>> the x and y skew elements
>>>>> (hx and hy) are flipped in PDFBox. This flip matches the order in which
>>>>> AWT’s AffineTransform’s
>>>>> constructor expects its elements but does not match the arrays used in
>>>>> the PDF spec.
>>>>>
>>>>> Are we accidentally flipping skew-x and skew-y in the Concatenate
>>>>> operator?
>>>>>
>>>>> -- John
>>>>>
>>>>
>>>
>>
>
