<Swing Dev> [11] RFR: JDK-8199441: Wrong caret position in multiline text components on Windows with a screen resolution higher than 100%

Phil Race philip.race at oracle.com
Wed Jun 6 22:03:32 UTC 2018

This is changing the internals of getTabbedTextOffset and using FP 
of whether useFPAPI is true. This is not what I said.

I wrote that you should call the FP version directly.

Look at this
      * @deprecated replaced by
      *     {@link #getTabbedTextOffset(Segment, FontMetrics, float, float,
      *                                 TabExpander, int, boolean)}
     @Deprecated(since = "9")
     public static final int getTabbedTextOffset(Segment s, FontMetrics 
                                              int x0, int x, TabExpander e,
                                              int startOffset) {
         return getTabbedTextOffset(s, metrics, x0, x, e, startOffset, 
If we had wanted what you proposed in the first webrev and I think
this one is effectively same, we'd have altered the behaviour to and not
deprecated and added new API

So whatever code in our L&F is currently calling

getTabbedTextOffset(Segment s,
                     FontMetrics metrics,
                     int x0, int x, TabExpander e,
                     int startOffset)

should instead call

getTabbedTextOffset(Segment s,
                     FontMetrics metrics,
                     float x0, float x, TabExpander e,
                     int startOffset,
                     boolean round)

I am not sure if round should be true or false but calling the float version is the key.

This (and no other change needed) does the trick for me :

--- a/src/java.desktop/share/classes/javax/swing/text/WrappedPlainView.java
+++ b/src/java.desktop/share/classes/javax/swing/text/WrappedPlainView.java
@@ -360,11 +360,11 @@
          int currentWidth = getWidth();
          if (wordWrap) {
              p = p0 + Utilities.getBreakLocation(segment, metrics,
-                                                tabBase, tabBase + currentWidth,
+                                                (float)tabBase, (float)(tabBase + currentWidth),
                                                  this, p0);
          } else {
              p = p0 + Utilities.getTabbedTextOffset(segment, metrics,
-                                                   tabBase, tabBase + currentWidth,
+                                                   (float)tabBase, (float)(tabBase + currentWidth),
                                                     this, p0, false);
@@ -847,8 +847,8 @@
                          Segment segment = SegmentCache.getSharedSegment();
                          loadText(segment, p0, p1);
                          int n = Utilities.getTabbedTextOffset(segment, metrics,
-                                                   alloc.x, x,
-                                                   WrappedPlainView.this, p0);
+                                                   (float)(alloc.x), (float)x,
+                                                   WrappedPlainView.this, p0, false);
                          return Math.min(p0 + n, p1 - 1);

I may have missed something else but to verify I downloaded and used your test, which BTW has DOS line-endings !


On 06/06/2018 12:04 AM, Prasanta Sadhukhan wrote:
> On 5/9/2018 12:41 AM, Phil Race wrote:
>> I am not sure this is the right fix.
>> If the intention had been to change all calls to 
>> getTabbedTextOffset() to use the FP
>> API it would have just been changed .. rather than adding a new API 
>> that provides
>> the option to specify whether to use FP.
>> So perhaps the problem is that internal code needs to be updated to 
>> call the FP
>> version directly ..
> I have updated the internal code to use the FP version directly
> http://cr.openjdk.java.net/~psadhukhan/8199441/webrev.01/
> There are no new regressions in jtreg and jck tests.
> Regards
> Prasanta
>> I'd like to read https://bugs.openjdk.java.net/browse/JDK-8168992 to see
>> what was said there but JBS just went down for 5 hours maintenance ..
>> -phil.
>> On 05/07/2018 11:54 PM, Prasanta Sadhukhan wrote:
>>> Hi Sergey,
>>> I have run javax/swing/text jtreg and jck tests and did not observe 
>>> any regressions.
>>> Regards
>>> Prasanta
>>> On 4/28/2018 5:38 AM, Sergey Bylokhov wrote:
>>>> Hi, Prasanta.
>>>> Please confirm that you run related jck/reg tests.
>>>> On 26/04/2018 23:52, Prasanta Sadhukhan wrote:
>>>>> Hi All,
>>>>> Please review a fix for an issue where it is seen that,
>>>>>   with a screen resolution higher than 100% and then clicking in a 
>>>>> JTextArea having setLineWrap(true) set, the caret (insertion 
>>>>> point) is not aligned with the cursor.
>>>>> The issue seems to stem from the fact that caret position 
>>>>> calculation in DefaultCaret class utilises API that uses integer 
>>>>> calculation than floating point calculations.
>>>>> The code flow as seen is
>>>>> DefaultCaret#positionCaret=>BasicTextUI#viewToModel=>BoxView.viewToModel=>CompositeView#viewToModel=>WrappedPlainView#viewToModel=>Utilities.getTabbedOffset 
>>>>> Now, getTabbedOffset utilises FontMetrics.charsWidth() which uses 
>>>>> integer arithmetic to get the caret position.
>>>>> The same getTabbedOffset uses Font.getStringBounds() which uses 
>>>>> floating point arithmetic via Rectangle2D.Float.
>>>>> Proposed fix is to make sure getTabbedOffset uses floating point 
>>>>> calculations by using getStringBounds() instead of charsWidth() so 
>>>>> that it calculates
>>>>> the character width(s) of text present in JTextArea in floating 
>>>>> point to align the caret.
>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8199441
>>>>> webrev: http://cr.openjdk.java.net/~psadhukhan/8199441/webrev.00/
>>>>> Regards
>>>>> Prasanta

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