Undo the part of commit fa9a4108c3
that moved cache generation from process() to prepare(). prepare()
is called after each property change, in order to calculate the
op's bounding box for invalidation. Since we only need the cache
for actual processing, generating it in process() avoids that
overhead.
Invalidate the gradient cache while setting relevant properties,
and validate it, reconstructing if necessary, during prepare(),
rather than process(), to avoid the need to use a mutex.
Make sure the cache has at least two elements, corresponding to
the initial and final colors of the gradient, since both colors
might be needed, and to avoid division by zero.
Avoid using a cache if its necessary size is too big, or if the
gradient type is conical, since the necessary cache size for
conical gradients is unrelated to the gradient line length.
Improve index rounding during cache lookup.
Lots of indentation fixes.
