[cairo] Creating A Cairo Context Seems Quite Quick

[Behdad Esfahbod]

On 15-04-18 03:30 AM, Lawrence D'Oliveiro wrote:
> I just added methods to my Path and Path.Segment types in Qahirah
> <https://github.com/ldo/qahirah> to compute extents and return
> flattened versions. These create a temporary Cairo context so I can use
> its append_path and copy_path_flat calls to do all the work. The
> overhead of this doesn’t seem too bad.
> 
> As a baseline (on an already-created Cairo context), the Python sequence
> 
>     ctx.new_path().append_path(path).copy_path_flat()
> 
> takes 140µs for a simple rectangular path on my Core i7 (averaged over
> 100,000 iterations using the Python timeit module), while
> 
>     ctx.new_path().append_path(path).path_extents
> 
> takes 59µs. For the new methods I have added, which create a new context
> on every call,
> 
>     path.flatten()
> 
> takes 162µs, while
> 
>     path.extents
> 
> takes 83µs. So the overhead in the former is about 16%, in the latter
> about 40%. Well short of the order-of-magnitude-or-more I was
> expecting/fearing...

Yes, cairo optimizes for that by caching freed context objects for reuse so
there's no malloc() overhead.  All that is left is clearing the object.