diff layer/LayerFactory.h @ 391:4f0f273c8f82

* Provide a proper implementation of
  SpectrogramLayer::invalidatePixmapCaches(size_t, size_t) -- if the
  region is only part of the cache's current valid area, crop the
  valid area instead of resetting it completely.  This makes a big
  difference when first rendering a spectrogram that is zoomed out a
  long way when the underlying calculation has not yet completed -- as
  is a common case in Vect for example.