editor: more intuitive cursor positioning

Compute the nearest glyph edge instead of taking the one to the
left of the cursor.

Also fixes a segfault when trying to compute the position for an empty
buffer.

diff --git a/clients/editor.c b/clients/editor.c
index cade262..ce0692f 100644 (file)
--- a/clients/editor.c
+++ b/clients/editor.c
@@ -153,18 +153,26 @@ text_layout_xy_to_index(struct text_layout *layout, double x, double y)
 {
        cairo_text_extents_t extents;
        int i;
+       double d;
+
+       if (layout->num_glyphs == 0)
+               return 0;
 
        cairo_scaled_font_glyph_extents(layout->font,
                                        layout->glyphs, layout->num_glyphs,
                                        &extents);
 
-       for (i = 1; i < layout->num_glyphs; i++) {
-               if (layout->glyphs[i].x >= x) {
-                       return i - 1;
-               }
+       if (x < 0)
+               return 0;
+
+       for (i = 0; i < layout->num_glyphs - 1; ++i) {
+               d = layout->glyphs[i + 1].x - layout->glyphs[i].x;
+               if (x < layout->glyphs[i].x + d/2)
+                       return i;
        }
 
-       if (x >= layout->glyphs[layout->num_glyphs - 1].x && x < extents.width)
+       d = extents.width - layout->glyphs[layout->num_glyphs - 1].x;
+       if (x < layout->glyphs[layout->num_glyphs - 1].x + d/2)
                return layout->num_glyphs - 1;
 
        return layout->num_glyphs;