Cairo/Pango: compute character widths fast and string widths accurately

This commit has Fl_Cairo_Graphics_Driver compute string widths in 2 ways:
1) when the string contains several unicode characters, the width of the
whole string is computed, accounting for kerning when it occurs;
2) when the string contains a single unicode character, its width is
computed, memorised, and re-used next time it's necessary.

The effect of this approach is
- Fl_Text_Display is fast because it uses memorised single character widths repeatedly
- Fl_Input is drawn accurately because the cursor position is determined
by string widths, not by sums of character widths.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H b/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H
index 0b5eee198..c6fa15403 100644
--- a/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H
+++ b/src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H
@@ -50,7 +50,7 @@ private:
   bool *needs_commit_tag_; // NULL or points to whether cairo surface was drawn to
   cairo_t *dummy_cairo_; // used to measure text width before showing a window
   int linestyle_;
-  int width_unscaled_(unsigned int c);
+  int do_width_unscaled_(const char* str, int n);
 protected:
   cairo_t *cairo_;
   PangoContext *pango_context_;