[OpenJDK 2D-Dev] [9] RFR JDK-6842011: StackOverflowError printing landscape with scale and transform

[Phil Race]

On 05/23/2016 03:33 PM, Jim Graham wrote:
> Though, they are likely to think this API is doing that.  We have a 
> visibility problem here to make sure that any work going forward is 
> more likely to see the new method and ignore this one.  I don't think 
> we'll win there on naming alone, but we can make the javadocs look 
> very intimidating so if they are using completion they may get scared 
> and hopefully see the other method before they just accept the 
> completion. Perhaps we can try to make the alphabetic sorting have the 
> new methods appear first in the list?

getScaleFactorX() should sort ahead of getScaleX()

-phil.

>
> In FX we were smart and went with very dry "getMxy()" style names that 
> won't attract attention...
>
>             ...jim
>
> On 5/23/2016 3:16 PM, Phil Race wrote:
>> What we have here might happen when developer A writes some UI code
>> without any conception that a 90 degree rotation may be in effect and
>> then developer B
>> comes along and adds printing support .. and the implementation 
>> rotates it.
>> So an out-of-the-box advertised API that does what dev A really meant
>> would be helpful.
>>
>> -phil.
>>
>> On 05/23/2016 11:52 AM, Jim Graham wrote:
>>> I think we need to go a bit further and change the way we describe
>>> them.  If we perhaps get very technical about how it is returning one
>>> element of the scaling equations/matrix then they will be discouraged
>>> from finding a simple use for it.  I'll try to come up with some
>>> wording today or tomorrow and it would be good to apply it to all 6 of
>>> the getters uniformly.  Something like:
>>>
>>> Returns element M## of the transformation matrix which controls how
>>> the output XY coordinates are affected by the input XY coordinates.
>>>
>>> Then on the getScaleXY methods add a "Note, this method will not
>>> return the amount by which input XY coordinates will be stretched or
>>> contracted since a 90 degree rotation will cause all of its
>>> contribution to be redirected into the other axis.  Properly
>>> determining the full scale of the matrix involves analyzing both this
>>> factor and the ...".
>>>
>>> There is where it would be good to have the new methods ready to go so
>>> we can then immediately say ", such as in the getScalingFactorXY()
>>> method" or have an @see to send them where they need to go. That
>>> doesn't mean we can't do this documentation refresh now, but we might
>>> want to make those new methods a high priority to get done soon.  (I'm
>>> guessing/hoping we can add small "fixup" APIs like that after FC since
>>> it doesn't really represent a "feature"...?)
>>>
>>>             ...jim
>>>
>>> On 5/22/16 11:53 PM, prasanta sadhukhan wrote:
>>>> Hi Jim,
>>>>
>>>>
>>>> On 5/21/2016 3:20 AM, Jim Graham wrote:
>>>>> We should acknowledge that the test case is buggy anyway.  It is not
>>>>> computing the scale of a transform correctly,
>>>>> though that is likely due to the unfortunate naming we chose for our
>>>>> methods.
>>>>>
>>>>> If you are looking for "the amount by which an X coordinate is
>>>>> stretched or contracted", you have to compute a
>>>>> distance formula on all of the elements of the X transform
>>>>> equation.  We don't have a method to do that for the
>>>>> caller.  If we did, we might call it something very similar to
>>>>> "getScaleX()".
>>>>>
>>>>> Unfortunately, we have a method named "getScaleX()" which one might
>>>>> think does that, but it doesn't.
>>>>>
>>>>> While I think we should prevent a stack overflow here, it's really
>>>>> more of "making sure a program bug is caught early
>>>>> and with a more sane response", than "fixing a valid test case".
>>>>>
>>>>> Also, we should consider adding a method to do the right
>>>>> calculation, and document the existing getScaleX() to point
>>>>> out that it cannot be used to determine "the stretchiness of X
>>>>> coordinates" or something more appropriately worded...
>>>>>
>>>> I have documented the anomalies in getScaleX()/getScaley().
>>>> http://cr.openjdk.java.net/~psadhukhan/6842011/webrev.01/
>>>> I will create a bug to address this scaling calculation of a
>>>> transform in affinetransform (as it is in geom package and
>>>> not a printing issue par se). Will that be ok?
>>>>
>>>> Regards
>>>> Prasanta
>>>>>             ...jim
>>>>>
>>>>> On 5/20/16 4:27 AM, prasanta sadhukhan wrote:
>>>>>> Hi Phil,
>>>>>>
>>>>>> When we call print() it calls RasterPrinterJob#printPage() which
>>>>>> sets peekGraphics.transform([4.16,0,0][0,4.16,0]) as
>>>>>> obtained from xscale=4.16 [getXRes()=300 / 72.0] ,yscale=4.16
>>>>>> It calls SunGraphics2D.transform which was identity transform [1.0,
>>>>>> 0.0, 0.0] [0.0, 1.0, 0.0] calls
>>>>>> transform.concatenate(peekgraphicsTx) and stores as
>>>>>> ([4.16,0,0][0,4.16,0])
>>>>>>
>>>>>> Then RasterPrinterJob#printPage() again calls
>>>>>> peekGraphics.transform(new AffineTransform(page.getMatrix()));
>>>>>> where page.getMatrix() returns 0.0, -1.0, 1.0, 0.0, 0.0, 841.88 and
>>>>>> peekGraphics transform now becomes [0.0, 1.0, 0.0]
>>>>>> [-1.0, 0.0, 841.88]
>>>>>> which calls SunGraphics2D#transform() where it again does
>>>>>> transform.concatenate(peekgraphicsTx)
>>>>>>
>>>>>> so the transform becomes [m00=0, m01=4.16, m02=0][m10=-4.16, m11=0,
>>>>>> m12=3507.873]
>>>>>> Now scaleX obtains value from g2d.getTransform().getScaleX() which
>>>>>> returns SunGraphics2D stored transform.m00 which is 0
>>>>>> and scaleY is m11=0 so scaleX,scaleY becomes 0.
>>>>>>
>>>>>> Regards
>>>>>> Prasanta
>>>>>> On 5/19/2016 4:03 AM, Phil Race wrote:
>>>>>>> It sounds like scalex & scaley are 0 and are then used in
>>>>>>> calculations which
>>>>>>> results in the NaN ? So why are they zero to begin with ?
>>>>>>>
>>>>>>> -phil.
>>>>>>>
>>>>>>> On 5/16/2016 3:32 AM, prasanta sadhukhan wrote:
>>>>>>>> Hi All,
>>>>>>>>
>>>>>>>> Please review a fix for jdk9 whereby it is seen that
>>>>>>>> A StackOverflowError occurs when printing in landscape
>>>>>>>> orientation with a scaled and transformed graphics object.
>>>>>>>>  at sun.print.PSPrinterJob.prepDrawing(PSPrinterJob.java:1610)
>>>>>>>>     at sun.print.PSPrinterJob.beginPath(PSPrinterJob.java:1319)
>>>>>>>>     at
>>>>>>>> sun.print.PSPrinterJob.convertToPSPath(PSPrinterJob.java:1793)
>>>>>>>>     at
>>>>>>>> sun.print.PSPrinterJob$GState.emitPSClip(PSPrinterJob.java:1718)
>>>>>>>>     at sun.print.PSPrinterJob.prepDrawing(PSPrinterJob.java:1625)
>>>>>>>>
>>>>>>>>  at sun.print.PSPrinterJob.beginPath(PSPrinterJob.java:1319)
>>>>>>>>     at
>>>>>>>> sun.print.PSPrinterJob.convertToPSPath(PSPrinterJob.java:1793)
>>>>>>>>     at
>>>>>>>> sun.print.PSPrinterJob$GState.emitPSClip(PSPrinterJob.java:1718)
>>>>>>>>     at sun.print.PSPrinterJob.prepDrawing(PSPrinterJob.java:1625)
>>>>>>>>
>>>>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-6842011
>>>>>>>> webrev: http://cr.openjdk.java.net/~psadhukhan/6842011/webrev.00/
>>>>>>>>
>>>>>>>> StackOverflowError is occuring because the scalex, scaley for
>>>>>>>> landscape orientation was 0 so when the testcase tries
>>>>>>>> to scale with these scale factors
>>>>>>>> using g2d.scale( 1 / scalex, 1 / scaley );
>>>>>>>> it creates a AffineTransform of NaN transformation. Now, In
>>>>>>>> linux, when the PS print drawing information is being
>>>>>>>> prepared, it calls prepDrawing() where it checks
>>>>>>>> getGState().mTransform.equals(mLastTransform) and since NaN
>>>>>>>> values cannot be compared it results in "false", causing
>>>>>>>> erroneous "grestore" postscript command to be issued and remove a
>>>>>>>> GState from the stack so isOuterGState() becomes
>>>>>>>> true which causes emitPSClip() to be called which calls
>>>>>>>> prepDrawing() again via convertToPSPath() , beginPath() and since
>>>>>>>> isOuterState() returns true due to transform not
>>>>>>>> being equal it again calls emitPSClip() causing a recursion.
>>>>>>>>
>>>>>>>> The fix was to check if transform is NaN and do not fill the
>>>>>>>> devicePath if it is so, so that erroeous drawing is not
>>>>>>>> done.
>>>>>>>> So, it will print out a blank page.
>>>>>>>>
>>>>>>>> In windows, the testcase prints out a blank page. In mac, the
>>>>>>>> testcase prints a 2x2 rectangle.
>>>>>>>>
>>>>>>>> Regards
>>>>>>>> Prasanta
>>>>>>>
>>>>>>>
>>>>>>
>>>>
>>