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

[Alexandr Scherbatiy]

Hello,

Could you review the fix:
   bug: https://bugs.openjdk.java.net/browse/JDK-8162350
   webrev: http://cr.openjdk.java.net/~alexsch/8162350/webrev.00

   The fix uses the solution suggest by Jim in the email:
http://mail.openjdk.java.net/pipermail/2d-dev/2016-October/007737.html

   To draw to a VolatileImage backbuffer its graphics transform is set 
to identity and device coordinates are used to set the buffer clip.
   Copying the backbuffer image to the graphics has some problems.
   -------------
     // Since there is no drawImage(img, float x, float y)...
     destination.translate(pixelx1 / scaleX, pixely1 / scaleY)
     destination.drawImage(img, 0, 0)
   -------------
   This code solves the problem for the top left corner of the region. 
All Graphics.drawImage(...) methods scales the image size and it looks 
like ceil(img.getWidth() * scaleX) can be differ from the ceil(pixelx1 + 
img.getWidth() * scaleX) - pixelx1 so the right bottom corner of the 
image does not fit the required point.
   There is also a question could a line drawn from one point and then 
from another has a different width in pixels because the graphics scale 
is not integer.

   The proposed fix prepares a backbuffer with size [x + w, y + h] in a 
user space and a component is drawn in to the region [pixelx1, pixely1, 
pixely2, pixely2] in the device space.
   After that the necessary clip is set to the graphics and whole image 
is just drawn into it.

   The new logic is used only the component graphics configuration is 
scaled the graphics configuration has the same scales. So it possible 
just to copy the backbuffer surface data to the graphics surface data.
   For other cases like for rotated graphics transform it seems it is 
necessary to have more complicated algorithm.

   This solves problems with repainted region but there are still 
artifacts with JInternalFrame moving or a component scrolling, This can 
be related to the RepaintManager.copyArea() method which needs to be 
updated in the similar way. I have created an issue on it:
    JDK-8167305 RepaintManager.copyArea() method should be updated for 
floating point UI scale
      https://bugs.openjdk.java.net/browse/JDK-8167305

  Thanks,
  Alexandr.