[cairo] Too-large transparency groups

[Adrian Johnson]

On 20/06/13 09:27, James Cloos wrote:
> I'm told that gecko's bug whereby even a single, small ARGB image
> generates full-page transparency groups is definitively in cairo and not
> in how gecko calls cairo.

The page sized transparency group bug should be fixed in cairo 1.12.

> 
> And that bugs have been reported about it.
> 
> But I cannot find those bugs searching in the pdf/ps driver categories.
> 
> An image, even with alpha, composited onto a constant background should
> immediately be blended pixel per pixel, rather than generating a trans-
> parency group.  The result of such a blending is fixed; there are no
> vector elements, only pixels.

The PS output blends alpha into white if there is nothing underneath.
The PDF output preserves the alpha. PDF viewers blend the rasterized
image into the page color.