Alpha for PNGs in between (0%..100%) results in funny looking color in CPU rendering only

[LalehB]

There is a difference in the pictures that we get when we render with CPU or GPU, it looks that images with CPU does not have the same quality of GPU rendering.
Here is an example:

For CPU rendering with this command:

./servo -c  http://en.wikipedia.org/wiki/Nexus_5

The result is:

And for GPU rendering with this command:

./servo  http://en.wikipedia.org/wiki/Nexus_5

The result is:

As you can see there is a difference in these two pictures. (picture for CPU rendering is not as good as GPU rendering)

[zwarich]

This looks like a problem with the handling of the alpha channel. I'll take a look.

[mbrubeck]

Even in the GPU rendering case the rendering is not quite correct -- it looks like semitransparent pixels are rendered as white.

In a simple test case with just an <img> element and nothing else, I get correct results if the body has background: transparent, but incorrect results if it has a solid background.

[pcwalton]

This is because we don't premultiply. PR coming.