[OpenJDK 2D-Dev] HiDPI support issues on Windows

Alexandr Scherbatiy alexandr.scherbatiy at oracle.com
Fri Sep 30 10:22:04 UTC 2016

Hello Anton,

Yes, we are working on it.

For example, there is the known issue DK-8162350 RepaintManager shifts 
repainted region when the floating point UI scale is used.

The problem is that the RepaintManager draws a region to a buffered 
image at first and draws the image after that to the window.
Suppose the image has int coordinates and size (x, y, w, h) in the user 
space. It should be drawn into the region with coordinates (x, y, 
x+width, y+height) = (x1, y1, x2, y2).
If floating point UI scale is used (like 1.5) the region coordinates  
are converted to values (1.5 * x1, 1.5 * y1, 1.5 * x2, 1.5 * y2) in the 
dev space.
Now these coordinates need to be rounded and the process really depends 
on the evenness or oddness of the start and end coordinates. They both 
can be rounded to one side or to opposite. Depending on this some lines 
near the drawn image region can be not filled or just wrongly filled.

If I try to not use a buffered image in the RepaintManager it seems that 
some problems are just gone away (internal frame moving artifacts on the 
SwingSet2 demo or squares in MinimalSwingApplication are drawn as 
squares and not rectangles).
But not all of them. The artifacts during the scrolling in the SwingSet2 
demo still exist.

I have filled an issue on it just to  keep track of them: JDK-8166954 
Drawing artifacts with floating point UI scale

The another problem which we are working on is that a selected text is 
just shifted: 8156217 Selected text is shifted on HiDPI display

To support this we were needed to add some new API which support 
floating point coordinates in the View, TextUI and JTextComponent classes.
The issue is on the review: 


On 9/28/2016 1:17 PM, Anton Tarasov wrote:
> Hello,
> JDK9 comes with HiDPI support on Windows/Linux which is really great. 
> As we gave it a try, we found it looking pretty good with an integer 
> scale (2x) but revealed some rendering flaws with float scales.
> Let me please demonstrate it with SwingSet2 + JDK9-ea-b137 + Windows 
> 8.1 in 150% scale (1.5f)
> demo1 <http://cr.openjdk.java.net/%7Eant/hidpi_pics/demo1.png>
> Dragging Frame-0 behind the pallet makes the pallet wavy.
> Also, as Frame-0 moves it may leave traces.
> demo2 <http://cr.openjdk.java.net/%7Eant/hidpi_pics/demo2.png>
> Unstable look of a control. For instance, these two combos are 
> decorated differently (and not perfectly).
> demo3 <http://cr.openjdk.java.net/%7Eant/hidpi_pics/demo3.png>
> Scrolling traces.
> demo4 <http://cr.openjdk.java.net/%7Eant/hidpi_pics/demo4.png>
> Menu traces.
> Colored rendering artifacts.
> Additionally, I'm attaching a test source & pics kindly provided by 
> Renaud (cc'd) from AndroidStudio. The demo finely shows problems on 
> the example of primitive rendering.
> Scaling 100% 
> <http://cr.openjdk.java.net/%7Eant/hidpi_pics/Scaling-100-percent.png>
> Scaling 125% 
> <http://cr.openjdk.java.net/%7Eant/hidpi_pics/Scaling-125-percent.png>
> Scaling 150% 
> <http://cr.openjdk.java.net/%7Eant/hidpi_pics/Scaling-150-percent.png>
> It seems like most of the mentioned issues are caused by inaccurate 
> rounding performed during the rendering cycle.
> So, I'd like to ask you please share your thoughts on it. How serious 
> is the problem at all (I guess you're aware of it)? What is solvable 
> on the JDK side, and what is not (e.g. demo2 and the Renaud's test case)?
> Do you have plans to resolve it by jdk9 GA, or earlier/later? Any 
> technical details behind it are very welcome as well.
> Thanks in advance,
> Anton.

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