[cairo] BUG: CAIRO_FORMAT_ARGB32, image_surface transparency = CAIRO_IMAGE_IS_OPAQUE after write_png()

[Lawrence D'Oliveiro]

On Tue, 7 Jun 2016 08:19:47 +0930, Adrian Johnson wrote:

> Cairo analyses image transparency to ensure it uses the most
> efficient format when writing out images to
> PNG, PDF, and PS.

I don’t mind PDF and PostScript, they’re quite complicated formats. But
I thought the PNG reading/writing capability built into Cairo was
supposed to be, and I quote, “a toy API”
<https://www.cairographics.org/manual/cairo-PNG-Support.html>.

Optimizing out the alpha channel would have to count as an “advanced”
feature, not a “toy” one, I would have thought.