<Swing Dev> [10] RFR JDK-8178025:HiDPI with non-integer scale factor - SPANs in HTML are rendered overlapping each other

[Prasanta Sadhukhan]

On 10/17/2017 10:22 AM, Prasanta Sadhukhan wrote:
>
>
> On 10/17/2017 1:08 AM, Sergey Bylokhov wrote:
>> On 16/10/2017 02:50, Prasanta Sadhukhan wrote:
>>>> Probably this is a root cause of the bug? 
>>> Does not seem like. If we only use floating point API 
>>> getTabbedTextWidth() in GlyphPainter1.getSpan() to get floating 
>>> point width, it calls SwingUtilities2.getFontStringWidth() which 
>>> calls getStringBounds() with default FRC.
>>> When getStringBounds() calls fm.getFontRenderContext(), it returns 
>>> DEFAULT_FRC which has a null AffineTransform so when we try to get 
>>> the transform for that through getTransform(), it creates a new 
>>> AffineTransform with scale 1
>>> public AffineTransform getTransform() {
>>>          return (tx == null) ? new AffineTransform() : new 
>>> AffineTransform(tx);
>>>      }
>>
>> So this is a problem why default FRC is used. We should find a way to 
>> create a correct one instead.
> I guess that is what I did which is to create a FRC with correct 
> transform .
>
When JLabel with html tag span is created, GlyphPainter1.getSpan() calls 
sync() which finds JLabel.getFontMetrics() which calls 
SwingUtilities2.getFontMetrics which calls getFRCProperty() and it tries 
to find
JLabel.getGraphicsConfiguration() which comes out to be null so 
affinetransform also becomes null.
AffineTransform tx = (gc == null) ? null : gc.getDefaultTransform();

It seems for JLabel, Component.updateGraphicsData() with proper 
GraphicsConfiguraiton is never called which it does for JTextComponent 
or JDialog. Do you know why? Because of this, correct FRC is not created.
I am not sure what else I can do to create correct FRC.
> Regards
> Prasanta
>>
>>>> It will apply the screens scale to the FRC even if the component is 
>>>> located on some other screen.
>>> I was of the opinion that this
>>>
>>> GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().getDefaultConfiguration().getDefaultTransform().getScaleX() 
>>>
>>>
>>> will give the scale factor as passed to sun.java2d.uiScale which 
>>> should be applicable for all screen(s), which is what I leveraged in 
>>> my fix.
>>
>> The "sun.java2d.uiScale" is a debug option which applies the scale on 
>> all screens, but in case of the common configuration it is possible 
>> to have different scales(example: hidpi laptop + lowdpi external 
>> screen).
>>
>> GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().getDefaultConfiguration().getDefaultTransform().getScaleX() 
>>
>> Will returns default transform for default configuration of the 
>> main/default screen.
>>
>