[OpenJDK 2D-Dev] 6603887: Where are transparent areas filled with bgColor?

[Clemens Eisserer]

Hello again,

Seems I've identified the bug:
_X11SDOps.bgPixel is used as a hint wether the background was already
filled with the bgColor specified in drawImage or not - if
(xsdo->bgPixel != pixel + 1) it thinks that the transparent pixels of
the image have already been painted to the bgColor which works except
in the case when pixel = -1, bgColor is always initialized with 0 so
for this case the transparent pixels get never ever their color.

I now have a few ideas how this could be changed:
1.) Add a jboolean-field to the _X11SDOps struct, indicating wether
the bgColor is valid or not. Currently bgColor=0 servers this purpose.
It seems to be in my eyes the best approach, however I don't know
wether this could break any API/ABI?
2.) Choose a value for the case bgColor==invalid which cannot be taken
by a pixel+1 value. As far as I guess the pixel+1 should serve this
purpose - never let the pixel become 0 ... but it seems wrong-way
thought.
Is pixel always a negative value? If yes couldn't the check be
replaced with xsdo->bgPixel != pixel)?  pixel will never become 0
anyway?

Looking foreward to hear your suggestions, lg Clemens