Text drawing caches

[Fred Kiefer]

Hi Alexander,

I just looked through your new code for caching a few text frameworks 
for faster drawing. The code surely is nice, but it does not convince me 
that it is needed. As mostly with optimisation this adds some additional 
complexity and memory usage and I would like to know what we get for it.

No doubt some caching for this drawing code was needed. The most likely 
usage pattern here is that a cell first asks for the size of its text 
and than draws it. So a simple cache of size one should give a big boost 
at almost no addional costs. But it is hard to understand why a bigger 
and complexer cache could improve things much more. In your comments you 
say that some testing was done by people at #gnustep. Would you like to 
share some of the results with us?
I am not so much asking for counts on cache hits and misses, this are 
internal data to the implementation, but for overall speed up of text 
drawing applications. For example, and this used to be one of Nicolas 
favourit examples whenever I dared to touch NSCell drawing, what about a 
NSOpenPanel browsing through some big directory structures. How much do 
we gain here?

What I do like is that you finally do the NSString drawing without 
building up a NSAttributedString, which was always a bit of a waste.

Cheers
Fred