[IDEA] shrink xrender featureset

[Juliusz Chroboczek]

> Well if you let me decide between software rendering on client or
> software rendering on server, I would prefer the latter.

It's not that clear cut.  At least some of the motivation behind Render is
about moving time-consuming operations into the client, notably font rasterisation.

There are two reasons why you may want to move stuff into the client.  One
is flexibility: for most users, it's easier to install a new version of
a library, than a new version of the X server.  This was the principal
reason why Render moves font rasterisation into the client.

The other point is that having time-consuming operations in the server
increases client latency.  Before Render, all font rasterisation happened
in the server, and this would cause noticeable pauses (with the whole
server frozen, not just a single client).

While it is possible to implement background processing in the server,
using ``Block Handlers'' (that's how I implemented the now-deceased XFree86
DPS extension), it's difficult, error-prone, and there are just three
people in the universe who know how it's done.

                                        Juliusz