[cairo] Blurriness when drawing from a temporary surface as the source

[Adam Richard]

Hi,

When I draw a shape normally, it works fine.  However, when I create a 
temporary surface, draw that same shape on it, then draw using the 
temporary surface with cairo_set_source, the image is sometimes more 
blurry (of lower quality) than the one drawn directly.  It is especially 
noticeable when drawing small shapes; not as much when drawing larger 
shapes.

I've only noticed this blurriness in a png file resulting from 
write_to_png; when I write to a postscript instead it is not 
noticeable.  I also only notice it when I have matrix transformations 
set up so that the units of the shape I'm drawing are much different 
than device units.

I've tried disabling antialiasing with cairo_set_antialias, and it does 
get disabled, but the 2 images are still different.

Does anyone have any ideas as to what could cause an effect like this?  
I'm new to Cairo so I'm not sure whether it's using some approximation 
algorithm that could result in unavoidable blurriness in some cases, or 
whether perhaps I'm doing something suboptimal in setting up my 
temporary surface to pass to cairo_set_source.