| Detect a control is visible and skip drawing [message #854667] |
Tue, 24 April 2012 02:18  |
Eclipse User |
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All,
We are tackling performance issue on control redraw. A quick thought
might be to skip redraw for all invisible control. To be simple,
invisible here means it's own visible flay set to false and none of the
region is covered by other control/windows.
Digging around the web and notice isVisible() and getVisible() only
returns the visible flag but not the effective visibility on the screen.
API like this would be perfect:
control.isEffectivlyVisible()
I suspect it may require some OS-depedent code. At the moment, solution
for Windows would be good enough.
Thanks for your time.
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| Re: Detect a control is visible and skip drawing [message #856357 is a reply to message #856065] |
Wed, 25 April 2012 11:36  |
| Eclipse User |
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The OS takes care of considerations such as whether a control is
partially obscured, etc. You should only receive an SWT.Paint callback
if painting _needs_ to be done, and the Paint event's clipping bounds
should indicate the specific region needing to be painted. Any
optimization beyond this is up to the app (eg.- not re-computing
font/color info on every Paint call, only doing the work necessary to
paint the area that's included in the clipping region, etc.).
Grant
On 4/25/2012 6:35 AM, Leung Wang Hei wrote:
> What about if the widget is in a visible state but being obscured by
> other windows (from the same app or other app, java or non-java)?
>
> I suppose the OS is smart enough to skip the actual redraw but preparing
> all font/colour, creating/disposing GC/clipping all do add penalty,
> which is totally unnecessary.
>
> On 4/25/2012 1:27 PM, Ludwig Moser wrote:
>> i was in need for a similar problem, so i submitted a
>> bugreport/featurerequest.
>> actually i was flamed within a few hours, because changing the visible
>> flag of a control by a layout seems to be 'forbidden' or bad coding.
>> so i wrote my own layout and i am happy with it.
>>
>> mine is based on gridlayout and automatically hides (no drawing) any
>> fields with isVisible = false
>> as additional goodie you can sort the components without removing and
>> adding them to parent. (also here i got flamed because i am using an
>> integer value, which is NOT unique - but it does what is shall do, sort
>> the components in correct order. if there are two of a kind its the
>> programmers fault and does not affect the algorithm in a bad way.)
>>
>> greets
>> lumo
>
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