use real max glyph height

- avoids breakage on fonts lacking an `X` glyph (#2506)
      - avoids needing to create and mutate a temporary glyph (#2516)
      - lots of minor visual changes - mostly improvements notably more correct collision boxes for lines with tall glyphs

include/mapnik/text/face.hpp

@@ -65,8 +65,6 @@ public:
         return face_;
     }
 
-    double get_char_height(double size) const;
-
     bool set_character_sizes(double size);
     bool set_unscaled_character_sizes();
 

include/mapnik/text/harfbuzz_shaper.hpp

@@ -117,6 +117,7 @@ static void shape_text(text_line & line,
                 continue;
             }
 
+            double max_glyph_height = 0;
             for (unsigned i=0; i<num_glyphs; ++i)
             {
                 glyph_info tmp;
@@ -127,15 +128,16 @@ static void shape_text(text_line & line,
                     tmp.face = face;
                     tmp.format = text_item.format;
                     tmp.scale_multiplier = size / face->get_face()->units_per_EM;
+                    double tmp_height = tmp.height();
+                    if (tmp_height > max_glyph_height) max_glyph_height = tmp_height;
                     //Overwrite default advance with better value provided by HarfBuzz
                     tmp.unscaled_advance = positions[i].x_advance;
-
                     tmp.offset.set(positions[i].x_offset * tmp.scale_multiplier, positions[i].y_offset * tmp.scale_multiplier);
                     width_map[glyphs[i].cluster] += tmp.advance();
                     line.add_glyph(tmp, scale_factor);
                 }
             }
-            line.update_max_char_height(face->get_char_height(size));
+            line.update_max_char_height(max_glyph_height);
             break; //When we reach this point the current font had all glyphs.
         }
     }

include/mapnik/text/text_line.hpp

@@ -61,8 +61,10 @@ public:
 
     // Height of the tallest glyph in this line.
     double max_char_height() const { return max_char_height_; }
+
     // Called for each font/style to update the maximum height of this line.
     void update_max_char_height(double max_char_height);
+
     // Line height including line spacing.
     double line_height() const { return line_height_; }
 
@@ -85,7 +87,7 @@ public:
 private:
     glyph_vector glyphs_;
     double line_height_; // Includes line spacing (returned by freetype)
-    double max_char_height_; // Height of 'X' character of the largest font in this run. //TODO: Initialize this!
+    double max_char_height_; // Max height of any glyphs in line - calculated by shaper
     double width_;
     double glyphs_width_;
     unsigned first_char_;

src/text/face.cpp

@@ -36,19 +36,6 @@ font_face::font_face(FT_Face face)
       glyph_info_cache_(),
       char_height_(0.0) {}
 
-double font_face::get_char_height(double size) const
-{
-    if (char_height_ != 0.0) return char_height_;
-    glyph_info tmp;
-    tmp.glyph_index = FT_Get_Char_Index(face_, 'X');
-    if (glyph_dimensions(tmp))
-    {
-        tmp.scale_multiplier = size / face_->units_per_EM;
-        char_height_ = tmp.height();
-    }
-    return char_height_;
-}
-
 bool font_face::set_character_sizes(double size)
 {
     char_height_ = 0.0;