[OpenJDK 2D-Dev] Review Request for JDK-8139183 : drawImage misses background's alpha channel

[Jim Graham]

The logic here has mixed up the opacities and what needs to be done 
about them.

If the source image is opaque, then this is not a BG operation at all 
because the bg color would not show through an opaque image, so checking 
the srcData is both wrong and should be a NOP here.  If we get into that 
block with a srcData that is opaque then something has gone wrong 
somewhere else.  In particular, isBgOp should have returned false in 
that case.

The transparency that matters is when the bg color has transparency and 
that is not what is being tested here.  The test for xRGB and ARGB 
should be using the bg color...

			...jim

On 3/2/16 5:17 AM, Jayathirth D V wrote:
> Hi,
>
> I have updated the changes to select proper Buffer Image type based on
> source transparency and not just using ARGB directly.
>
> Please find the updated webrev for review:
>
> http://cr.openjdk.java.net/~jdv/8139183/webrev.01/
>
> Thanks,
>
> Jay
>
> *From:* Jayathirth D V
> *Sent:* Wednesday, March 02, 2016 5:02 PM
> *To:* 2d-dev at openjdk.java.net; Philip Race; Prasanta Sadhukhan
> *Subject:* Review Request for JDK-8139183 : drawImage misses
> background's alpha channel
>
> Hi,
>
> _Please review the following fix in JDK9:_
>
> __
>
> Bug : https://bugs.openjdk.java.net/browse/JDK-8139183
>
> Webrev : http://cr.openjdk.java.net/~jdv/8139183/webrev.00/
>
> Issue : When we scale any buffered image using drawImage() API which
> takes scale coordinates we are losing alpha channel in background color.
>
> Root cause : We are creating opaque temporary image when we have
> background color and scale is happening in renderImageXform() API of
> DrawImage.java. By making it opaque we are losing translucency.
>
> Solution : Instead of creating opaque RGB temporary image use ARGB
> temporary image to maintain translucency of image.
>
> Thanks,
>
> Jay
>