We can avoid recreating a number of text nodes from render_para() on
sub-sequent runs if we cache the rendernode instead of just the
PangoLayout.
When used with GtkSourceMap, this can yield a ~7 FPS improvement during
smooth scrolling at the cost of some more memory.
This tries to estimate the number of visible rows in a textview based on
the default text size and then tunes the GtkTextLineDisplayCache to keep
3*n_rows entries in the cache.
This was found imperically to be near the right cache size. In most cases,
this is less than the number of items we cache now. However, in some cases,
such as the "overview map" from GtkSourceView, it allows us to reach a
higher value such as 1000+. This is needed to keep scrolling smooth on
the larger view sizes.
With this patch, a HiDPI system with a GtkSourceView and GtkSourceMap
from the GTK 4 port can perform smooth scrolling simultaneously.
This adds a GtkTextLineDisplayCache which can be used to cache a number
of GtkTextLineDisplay (and thus, PangoLayout) while displaying a view.
It uses a GSequence to track the position of the GtkTextLineDisplay
relative to each other, a MRU to cull the least recently used display,
and and a direct hashtable to lookup display by GtkTextLine.
We only cache lines that are to be displayed (!size_only). We may want to
either create a second collection of "size_only" lines to speed that up,
or determine that it is unnecessary (which is likely the case).
This makes GtkTextLineDisplay use GRcBox instead of g_slice_*
directly. By using reference counting for this structure, we
can ensure that we hold an extra ref for one_display_cache as
well as caching additional GtkTextLineDisplay for the visible
range in the future.
This removes the use of GtkTextDisplay (a PangoRenderer) to use
the GskPangoRender which generates render nodes. Part of this means
improving the GskPangoRenderer to support the necessary features for
displaying a GtkTextView.
Primarily, this is a merging of GtkTextDisplay features into
GskPangoRender. Additionally, GtkTextDisplay was removed to allow for
gtk_text_layout_snapshot() to be implemented elsewhere.
