[geany/geany] b08ae0: Aggressively cache line height for computing margin sizes

[Colomban Wendling]

Branch:      refs/heads/startup-speed
Author:      Colomban Wendling <ban at herbesfolles.org>
Committer:   Colomban Wendling <ban at herbesfolles.org>
Date:        Thu, 04 Feb 2021 22:30:32 UTC
Commit:      b08ae0fe65c0942dca20281d6841dc83406d8b5e
             https://github.com/geany/geany/commit/b08ae0fe65c0942dca20281d6841dc83406d8b5e

Log Message:
-----------
Aggressively cache line height for computing margin sizes

Computing the line height is a very costly operation that involves font
loading and measuring, but the value stays mostly the same over time,
as it depends on font, zoom and a couple other style settings which
rarely change.

As line height used to compute margin widths dominates startup timings,
we now cache the latest result.  This caching makes line height
computation barely noticeable in startup times now.

Fixes #2649.


Modified Paths:
--------------
    src/sciwrappers.c

Modified: src/sciwrappers.c
33 lines changed, 32 insertions(+), 1 deletions(-)
===================================================================
@@ -144,10 +144,41 @@ void sci_set_mark_long_lines(ScintillaObject *sci, gint type, gint column, const
 }
 
 
+/* Calls SCI_TEXTHEIGHT but tries very hard to cache the result as it's a very
+ * expensive operation */
+static gint sci_text_height_cached(ScintillaObject *sci)
+{
+	static guint cache_hash = 0;
+	static gint cache_value = 0;
+	guint hash;
+	gchar *font;
+	gint size;
+
+	/* hash font, size and zoom factor using djb's algorithm which should be
+	 * good enough for this use case. */
+	font = sci_get_string(sci, SCI_STYLEGETFONT, 0);
+	hash = g_str_hash(font);
+	g_free(font);
+	size = SSM(sci, SCI_STYLEGETSIZEFRACTIONAL, 0, 0);
+	hash = hash * 33 + (gint) (size & 0x00FF);
+	hash = hash * 33 + (gint) ((size & 0xFF00) >> 8);
+	hash = hash * 33 + (gint) SSM(sci, SCI_GETZOOM, 0, 0);
+	hash = hash * 33 + (gint) SSM(sci, SCI_GETEXTRAASCENT, 0, 0);
+	hash = hash * 33 + (gint) SSM(sci, SCI_GETEXTRADESCENT, 0, 0);
+
+	if (hash != cache_hash)
+	{
+		cache_hash = hash;
+		cache_value = SSM(sci, SCI_TEXTHEIGHT, 0, 0);
+	}
+
+	return cache_value;
+}
+
 /* compute margin width based on ratio of line height */
 static gint margin_width_from_line_height(ScintillaObject *sci, gdouble ratio, gint threshold)
 {
-	const gint line_height = SSM(sci, SCI_TEXTHEIGHT, 0, 0);
+	const gint line_height = sci_text_height_cached(sci);
 	gint width;
 
 	width = line_height * ratio;



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