[vte/wip/issue-138] draw: Measure characters individually

[Christian Persch <chpe src gnome org>]

commit 1b0de39a21cfd5d67dbeec947465c274309bc919
Author: Christian Persch <chpe src gnome org>
Date:   Fri Jun 28 23:27:02 2019 +0200

    draw: Measure characters individually
    
    Measure U+0021..U+007E individually instead of all together and then
    averaging. For monospace fonts, the results should be the same, but
    if the user (by design, or trough mis-configuration) uses a proportional
    font, the latter method will greatly underestimate the required width,
    leading to unreadable, overlapping characters.
    
    https://gitlab.gnome.org/GNOME/vte/issues/138

 src/vtedraw.cc | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)
---
diff --git a/src/vtedraw.cc b/src/vtedraw.cc
index 83396706..77780edd 100644
--- a/src/vtedraw.cc
+++ b/src/vtedraw.cc
@@ -381,18 +381,32 @@ font_info_measure_font (struct font_info *info)
 {
        PangoRectangle logical;
 
-       /* Estimate for ASCII characters. */
+        /* Measure U+0021..U+007E individually instead of all together and then
+         * averaging. For monospace fonts, the results should be the same, but
+         * if the user (by design, or trough mis-configuration) uses a proportional
+         * font, the latter method will greatly underestimate the required width,
+         * leading to unreadable, overlapping characters.
+         * https://gitlab.gnome.org/GNOME/vte/issues/138
+         */
+        int max_width{1};
+        int max_height{1};
+        for (char c = 0x21; c < 0x7f; ++c) {
+                pango_layout_set_text(info->layout, &c, 1);
+                pango_layout_get_extents (info->layout, NULL, &logical);
+                max_width = std::max(max_width, PANGO_PIXELS_CEIL(logical.width));
+                max_height = std::max(max_height, PANGO_PIXELS_CEIL(logical.height));
+        }
+
+        /* Use the sample text to get the baseline */
        pango_layout_set_text (info->layout, VTE_DRAW_SINGLE_WIDE_CHARACTERS, -1);
        pango_layout_get_extents (info->layout, NULL, &logical);
        /* We don't do CEIL for width since we are averaging;
         * rounding is more accurate */
-       info->width  = PANGO_PIXELS (howmany (logical.width, strlen(VTE_DRAW_SINGLE_WIDE_CHARACTERS)));
-        /* Guard against pathological font since width=0 causes a FPE later on */
-       info->width = MAX (info->width, 1);
-
-       info->height = PANGO_PIXELS_CEIL (logical.height);
        info->ascent = PANGO_PIXELS_CEIL (pango_layout_get_baseline (info->layout));
 
+        info->height = max_height;
+        info->width = max_width;
+
        /* Now that we shaped the entire ASCII character string, cache glyph
         * info for them */
        font_info_cache_ascii (info);