273831 - elements appear green when the opacity property is set

Status: RESOLVED INVALID

(Core :: Web Painting, defect)

Description

[Josh Lee]

User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20041007 Epiphany/1.4.6
Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20041007 Epiphany/1.4.6

When you set the opacity property of an element, it turns green. In an image or
div that has a light background, the background takes a greenish tint. Text gets
a green "halo" where the anti-aliasing occurs. Screenshot and testcase to come.

The effect is most pronounced when opacity is low, like 0.1.

I suspect this is a Linux-only bug, but haven't tried any other platforms.

Reproducible: Always
Steps to Reproduce:

Comment 1

[Josh Lee]

Attachment: A simple testcase.

Comment 2

[Josh Lee]

Attachment: Screenshot

Screenshot of attachment #168266 [details]

Comment 3

[Boris Zbarsky [:bzbarsky]]

This worksforme with a current Linux trunk build....

Josh, what X server (product and version) are you using?  What's your bit depth
set to?

Comment 4

[Josh Lee]

I've figured it out. I was running in 16 bits of color. Changing it to 24 fixes
this.

But when running in low color depths, why do very light grays turn funny colors?
Using xmag to inspect the pixels shows that they actually have a different green
component than red and blue.

Comment 5

[Boris Zbarsky [:bzbarsky]]

When you have 16 bits to divide amongst 3 colors (red, green, blue), something
has to give.  Red and blue get 5 bits each, green gets 6.

That means that the green component is accurate to the nearest 8 (since we want
to express the 0-255 range in 6 bits), while the red and blue components are
accurate to the nearest 16.  As a result, a gray of, say rgb(40, 40, 40) will
get painted as rgb(32, 40, 32), if I understand this code correctly...

See http://lxr.mozilla.org/seamonkey/source/gfx/src/nsBlender.cpp#286 (comment
and function following) for the gory details.