Fredrik Eriksson wrote:

> The user space coordinate system depends on the device space coordinate 
> system. By default, the mapping between them is an identity transformation.

Yes. This much is stated explicitly.

> I think most device spaces have (0,0) in the upper left corner, but I am 
> not sure if that is a requirement or a coincidence.

For raster image formats (JPEG, PNG, GIF, TIFF...) this is true.

However, for both PostScript and PDF [the formats I'm actually 
interested in], the default origin point is actually the bottom-left 
corner, not the top-left.

In addition to this, both of these formats allow the coordinate space to 
be arbitrarily transformed. (Cairo provides the same functionallity 
itself as well, but PS and PDF have it natively.) So I'm not sure if 
Cairo is using the native defaults, or transforming them to match the 
other backends, or...?

> No, I did not figure this out by reading the Cairo documentation, which 
> seems to consist mostly of Doxygen-style pseudo-docs.

Yeah, it is a little... sparse?

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