<Swing Dev> [9] Review request for 8162350 RepaintManager shifts repainted region when the floating point UI scale is used

[Jim Graham]

Hi ALexandr,

This looks great.

BTW, when I suggested moving the FPscale test into SG2D I was suggesting that to avoid having to copy the transform out 
of it via getTransform(), but you've found a different solution to that issue (i.e. the new getTransform(g) method) so 
it no longer matters where that utility static function is located.  You can move it back to one of the Swing classes.

In terms of the logic of choosing which repaint function to use, it looks like you use the old-style function if the 
scales don't match, but won't that cause rendering anomalies?  The new code is still an improvement for the standard 
HiDPI case, and I'm guessing that mismatched scales probably never tends to happen, but we might want to flag it for 
further investigation.

+1 relative to whether you want to move the FPscale test back out of SG2D or not...

			...jim

On 11/18/16 1:44 AM, Alexandr Scherbatiy wrote:
>
> Thank you. I see that using the integer device-pixel translations preserves the component painting in the same way for
> floating point scales.
>
> Could you review the updated fix:
>   http://cr.openjdk.java.net/~alexsch/8162350/webrev.03
>
>   - translation adjustment is removed
>   - Region.clipRound() is used for pixels coordinates rounding.
>
>   Thanks,
>   Alexandr.
>
> On 11/16/2016 1:52 AM, Jim Graham wrote:
>> Let me clarify something...
>>
>> On 11/15/16 2:49 AM, Alexandr Scherbatiy wrote:
>>>   Let's consider the following use case:
>>>   scale = 1.5
>>>   A component calls fillRect(1, 1, 1, 1).
>>>   This is (1.5, 1.5, 3.0, 3.0) in the device space
>>>   which fills  (1, 1, 3, 3) and covers 2x2 pixels
>>
>> Agreed.
>>
>>>   Now the area (1, 1, 1, 1) needs to be repainted
>>>     create a backbuffer
>>>     translate(-1, -1) // move the top left corner of the area to the zero point
>>>     draw the component into the backbuffer:
>>>       fillRect(1, 1, 1, 1) -> after translation fillRect(0, 0, 1, 1) -> after scaling  (0.0, 0.0, 1.5, 1.5 ) in the
>>> device space
>>>       which fills (0, 0, 1, 1) and covers 1x1 pixels
>>
>> If you did g.setTransform(identity), g.translate(-1, -1), (then restore the scale) then the analysis is as follows:
>>
>> g.setTransform(identity) => [1 0 0] [0 1 0]
>> g.translate(-1, -1) => [1 0 -1] [0 1 -1]
>> g.scale(1.5, 1.5) => [1.5 0 -1] [0 1.5 -1]
>> g.fillRect(1, 1, 1, 1)
>>     => coordinates are (1.5-1, 1.5-1, 3-1, 3-1)
>>     => (.5, .5, 2, 2)
>>     => fills (0, 0, 2, 2)
>>     => which covers 2x2 pixels
>>
>> If you did g.translate(-1, -1) on the scaled transform then the analysis is as follows:
>>
>> g.transform is [1.5 0 0] [0 1.5 0]
>> g.translate(-1, -1) is [1.5 0 -1.5] [0 1.5 -1.5]
>> g.fillRect(1, 1, 1, 1)
>>     => coordinates are (1.5-1.5, 1.5-1.5, 3-1.5, 3-1.5)
>>     => (0, 0, 1.5, 1.5)
>>     => fill (0, 0, 1, 1)
>>     => covers 1x1 pixels
>>
>> The second operation is what you are describing above and that would be an inappropriate way to perform damage repair
>> because you used a scaled translation which did not result in an integer coordinate translation.
>>
>> Please re-read my previous analysis that shows what happens when you use integer device-pixel translations which are
>> translations that happen using integers on a non-scaled transform.  Note that you can add a scale *AFTER* you apply
>> the integer device pixel translation and it will not affect the integer-ness of the translation.  You can see above
>> that the difference in how the translate command is issues affects where the translation components of the matrix end
>> up being -1,-1 or -1.5,-1.5...
>>
>>             ...jim
>