<AWT Dev> [11] JDK-8195738: scroll poistion in ScrollPane is reset after calling validate()

[semyon.sadetsky at oracle.com]

On 2/23/18 10:57 AM, Shashidhara Veerabhadraiah wrote:

> Hi Semyon, Whenever the container is resized we used to update the 
> scroll pane sizes/geometry regardless of the scroll bar display 
> policies. This resizing make sense for the non SCROLLBARS_NEVER cases 
> as the scroll pane is displayed or needed an update. This additional 
> update posed issues for the SCROLLBARS_NEVER case where we are not 
> supposed to display the scroll pane per the java doc, then why update?
>
> Scroll pane geometry gets updated in 2 ways, one thro’ 
> setScrollPosition() and childResized(). So I derived the conclusion 
> based on the javadoc information that since we don’t display the 
> scroll pane there is no need to update the scroll pane geometry based 
> on the childResized() as it was altering the position already set by 
> the setScrollPosition(). This behavior is same as the other non 
> SCROLLBARS_NEVER mode and setting the scroll bar display to 
> SCROLLBARS_NEVER didn’t made any difference.
>
The only difference of SCROLLBARS_NEVER from others I got from javadoc 
is that the scroll bar controls are hidden. So the scrolling itself 
happens in the same way as in the case of visible scroll bars but it can 
be only controlled by mouse wheel or programmatically. In my 
understanding this means that the notification about the scrolled 
component size changes should happen in the same way as for all other 
cases. I see no reason for the differentiation that your fix introduces. 
What will happen if to remove this notification for visible scroll bars 
modes?

--Semyon
>
> Thanks and regards,
> Shashi
>
> *From:*Semyon Sadetsky
> *Sent:* Friday, February 23, 2018 10:17 PM
> *To:* Shashidhara Veerabhadraiah 
> <shashidhara.veerabhadraiah at oracle.com>; awt-dev at openjdk.java.net
> *Subject:* Re: <AWT Dev> [11] JDK-8195738: scroll poistion in 
> ScrollPane is reset after calling validate()
>
> On 2/22/18 8:23 PM, Shashidhara Veerabhadraiah wrote:
>
>     Hi Semyon, Thanks for your review comments.
>
>     Here are those different scroll bar pane modes and their description:
>
>     *Modifier and Type*
>
>     	
>
>     *Field*
>
>     	
>
>     *Description*
>
>     |static int|
>
>     	
>
>     *SCROLLBARS_ALWAYS
>     <https://docs.oracle.com/javase/9/docs/api/java/awt/ScrollPane.html#SCROLLBARS_ALWAYS>*
>
>     	
>
>     Specifies that horizontal/vertical scrollbars should always be
>     shown regardless of the respective sizes of the scrollpane and child.
>
>     |static int|
>
>     	
>
>     *SCROLLBARS_AS_NEEDED
>     <https://docs.oracle.com/javase/9/docs/api/java/awt/ScrollPane.html#SCROLLBARS_AS_NEEDED>*
>
>     	
>
>     Specifies that horizontal/vertical scrollbar should be shown only
>     when the size of the child exceeds the size of the scrollpane in
>     the horizontal/vertical dimension.
>
>     |static int|
>
>     	
>
>     *SCROLLBARS_NEVER
>     <https://docs.oracle.com/javase/9/docs/api/java/awt/ScrollPane.html#SCROLLBARS_NEVER>*
>
>     	
>
>     Specifies that horizontal/vertical scrollbars should never be
>     shown regardless of the respective sizes of the scrollpane and child.
>
> This javadoc, you've copy-pasted here, doesn't explain why in your fix 
> the notification about changed child size is disabled for 
> SCROLLBARS_NEVER case.
>
>     Thanks and regards,
>     Shashi
>
>     *From:*Semyon Sadetsky
>     *Sent:* Thursday, February 22, 2018 11:58 PM
>     *To:* Shashidhara Veerabhadraiah
>     <shashidhara.veerabhadraiah at oracle.com>
>     <mailto:shashidhara.veerabhadraiah at oracle.com>;
>     awt-dev at openjdk.java.net <mailto:awt-dev at openjdk.java.net>
>     *Subject:* Re: <AWT Dev> [11] JDK-8195738: scroll poistion in
>     ScrollPane is reset after calling validate()
>
>     Hi Shashi,
>
>     Can you clarify what is the principal difference between
>     SCROLLBARS_NEVER and other scroll policies that requires to avoid
>     updating the scroll geometry according to the inner component size?
>
>     --Semyon
>
>     On 02/19/2018 11:08 PM, Shashidhara Veerabhadraiah wrote:
>
>         Hi All, Please review a code fix for the below bug.
>
>         Bug: https://bugs.openjdk.java.net/browse/JDK-8195738
>
>         Webrev:
>         http://cr.openjdk.java.net/~sveerabhadra/8195738/webrev.00/
>         <http://cr.openjdk.java.net/%7Esveerabhadra/8195738/webrev.00/>
>
>         Problematic platform: Windows only.
>
>         Summary: This bug occurs only on windows platform and whereas
>         the behavior is different on Mac/Linux platforms. Now after
>         this fix there is common behavior across the platforms.
>
>         The main problem was with resetting the state of the scroll
>         bars even though the scroll bar panes are spawned with
>         SCROLLBARS_NEVER as the scroll bar display policy. This
>         resetting should not occur as the scroll bar display policy
>         makes the
>
>         scroll bar panes invisible. Hence except the
>         setScrollPosition() calls, we don’t need to resize/update the
>         scroll bars state upon calling the scroll bars validation if
>         SCROLLBARS_NEVER policy is used as the scroll bars are not
>         displayed.
>
>         Thanks and regards,
>         Shashi
>

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