<Swing Dev> [9] Review request for 8027639: JComboBox's popup leaves tracks after closing

[Sergey Bylokhov]

On 24.11.16 19:54, Semyon Sadetsky wrote:
> "A non-opaque component paints only a subset of its pixels or none at
> all...". Per-pixel translucent component paints all its pixels. This is
> not clearly states that per-pixel translucent component shall be non-opaque.
> I see an obvious inconsistency in a way we handle translucent JComponent
> and Window. This, of cause, need to be resolved somehow. We could
> forcibly make JComponent to be non-opaque as well as this is done for
> Window, or take translucency into account during the painting.
>
> The Window#isOpaque() spec states:
>
> The method returns false if the background color of the window
> is not null and the alpha component of the color is less than 1.0.
>
> Even with this absolutely clear spec the opaque property is set to false
> automatically with assigning transparent background to the window, and
> it doesn't require from user to keep them consistent.

It have a different implementations because it has different meaning:
  - The non-opaque window is a window which uses transparent background.
  - The non-opaque component is the component which require the parents 
be painted first. it is not necessary that the background in this case 
should be transparent(It is possible that the component draw something 
only in some place of its bounds) And transparent color is not always 
requires that the component should be non-opaque, because components can 
ignore its background.

-- 
Best regards, Sergey.