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

[Jim Graham]

Hi Alexandr,

Is the fully scaling code noticeably slower than the regular code?  Is there a reason to test and only use it 
conditionally?  It shouldn't be a lot of overhead considering everything else that goes on during a repaint.  Some of 
the set/unset of attributes could also be optimized around the double for loop to help some.

			...jim

On 10/6/16 10:07 AM, Alexandr Scherbatiy wrote:
> 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.
>