[pango/line-breaker: 14/41] Add pango_glyph_item_get_extents

[Matthias Clasen <matthiasc src gnome org>]

commit e2712390e067e002be06483a32cc6062c2fb0a40
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Jan 15 18:22:44 2022 -0500

    Add pango_glyph_item_get_extents
    
    Move this code to pango-glyph-item.c where it belongs.
    At the same time, introduce a PangoLeadingTrim enum
    for control over how line height affects extents.

 pango/pango-glyph-item.c | 157 +++++++++++++++++++++++++++++++++++++++++++++++
 pango/pango-glyph-item.h |  29 +++++++++
 2 files changed, 186 insertions(+)
---
diff --git a/pango/pango-glyph-item.c b/pango/pango-glyph-item.c
index 7eb1737d..28c13442 100644
--- a/pango/pango-glyph-item.c
+++ b/pango/pango-glyph-item.c
@@ -21,10 +21,12 @@
 
 #include "config.h"
 #include <string.h>
+#include <math.h>
 
 #include "pango-glyph-item.h"
 #include "pango-impl-utils.h"
 #include "pango-attributes-private.h"
+#include "pango-item-private.h"
 
 #define LTR(glyph_item) (((glyph_item)->item->analysis.level % 2) == 0)
 
@@ -860,3 +862,158 @@ pango_glyph_item_get_logical_widths (PangoGlyphItem *glyph_item,
        }
     }
 }
+
+/**
+ * pango_glyph_item_get_extents:
+ * @glyph_item: a `PangoGlyphItem`
+ * @trim: `PangoLeadingTrim` flags
+ * @ink_rect: (out caller-allocates) (optional): return location
+ *   for the ink extents
+ * @logical_rect: (out caller-allocates) (optional): return location
+ *   for the logical extents
+ *
+ * Gets the extents of a `PangoGlyphItem`.
+ *
+ * The @trim flags specify if line-height attributes are taken
+ * into consideration for determining the logical height. See the
+ * [CSS inline layout](https://www.w3.org/TR/css-inline-3/#inline-height)
+ * specification for details.
+ */
+void
+pango_glyph_item_get_extents (PangoGlyphItem   *glyph_item,
+                              PangoLeadingTrim  trim,
+                              PangoRectangle   *ink_rect,
+                              PangoRectangle   *logical_rect)
+{
+  ItemProperties properties;
+  gboolean has_underline;
+  gboolean has_overline;
+  PangoRectangle logical;
+  PangoFontMetrics *metrics = NULL;
+  int y_offset;
+
+  pango_item_get_properties (glyph_item->item, &properties);
+
+  has_underline = properties.uline_single || properties.uline_double ||
+                  properties.uline_low || properties.uline_error;
+  has_overline = properties.oline_single;
+
+  if (!logical_rect && (glyph_item->item->analysis.flags & PANGO_ANALYSIS_FLAG_CENTERED_BASELINE))
+    logical_rect = &logical;
+
+  if (!logical_rect && (has_underline || has_overline || properties.strikethrough))
+    logical_rect = &logical;
+
+  if (properties.shape_set)
+    _pango_shape_get_extents (glyph_item->item->num_chars,
+                              properties.shape_ink_rect, properties.shape_logical_rect,
+                              ink_rect, logical_rect);
+  else
+    pango_glyph_string_extents (glyph_item->glyphs, glyph_item->item->analysis.font,
+                                ink_rect, logical_rect);
+
+  if (ink_rect && (has_underline || has_overline || properties.strikethrough))
+    {
+      int underline_thickness;
+      int underline_position;
+      int strikethrough_thickness;
+      int strikethrough_position;
+      int new_pos;
+
+      if (!metrics)
+        metrics = pango_font_get_metrics (glyph_item->item->analysis.font,
+                                          glyph_item->item->analysis.language);
+
+      underline_thickness = pango_font_metrics_get_underline_thickness (metrics);
+      underline_position = pango_font_metrics_get_underline_position (metrics);
+      strikethrough_thickness = pango_font_metrics_get_strikethrough_thickness (metrics);
+      strikethrough_position = pango_font_metrics_get_strikethrough_position (metrics);
+
+      /* the underline/strikethrough takes x, width of logical_rect.
+       * Reflect that into ink_rect.
+       */
+      new_pos = MIN (ink_rect->x, logical_rect->x);
+      ink_rect->width = MAX (ink_rect->x + ink_rect->width, logical_rect->x + logical_rect->width) - new_pos;
+      ink_rect->x = new_pos;
+
+      /* We should better handle the case of height==0 in the following cases.
+       * If ink_rect->height == 0, we should adjust ink_rect->y appropriately.
+       */
+
+      if (properties.strikethrough)
+        {
+          if (ink_rect->height == 0)
+            {
+              ink_rect->height = strikethrough_thickness;
+              ink_rect->y = -strikethrough_position;
+            }
+        }
+
+      if (properties.oline_single)
+        {
+          ink_rect->y -= underline_thickness;
+          ink_rect->height += underline_thickness;
+        }
+
+      if (properties.uline_low)
+        ink_rect->height += 2 * underline_thickness;
+      if (properties.uline_single)
+        ink_rect->height = MAX (ink_rect->height,
+                               underline_thickness - underline_position - ink_rect->y);
+      if (properties.uline_double)
+        ink_rect->height = MAX (ink_rect->height,
+                                 3 * underline_thickness - underline_position - ink_rect->y);
+      if (properties.uline_error)
+        ink_rect->height = MAX (ink_rect->height,
+                               3 * underline_thickness - underline_position - ink_rect->y);
+    }
+
+  y_offset = glyph_item->y_offset;
+
+  if (glyph_item->item->analysis.flags & PANGO_ANALYSIS_FLAG_CENTERED_BASELINE)
+    {
+      gboolean is_hinted = (logical_rect->y & logical_rect->height & (PANGO_SCALE - 1)) == 0;
+      int adjustment = logical_rect->y + logical_rect->height / 2;
+
+      if (is_hinted)
+        adjustment = PANGO_UNITS_ROUND (adjustment);
+
+      y_offset += adjustment;
+    }
+
+  if (ink_rect)
+    ink_rect->y -= y_offset;
+
+  if (logical_rect)
+    logical_rect->y -= y_offset;
+
+  if (logical_rect && trim != PANGO_LEADING_TRIM_BOTH)
+    {
+      int leading;
+
+      if (properties.absolute_line_height != 0 || properties.line_height != 0.0)
+        {
+          int line_height;
+
+          line_height = MAX (properties.absolute_line_height, ceilf (properties.line_height * 
logical_rect->height));
+          leading = (line_height - logical_rect->height);
+        }
+      else
+        {
+          /* line-height 'normal' in the CSS inline layout spec */
+          if (!metrics)
+            metrics = pango_font_get_metrics (glyph_item->item->analysis.font,
+                                              glyph_item->item->analysis.language);
+          leading = MAX (metrics->height - (metrics->ascent + metrics->descent), 0);
+        }
+      if ((trim & PANGO_LEADING_TRIM_START) == 0)
+        logical_rect->y -= leading / 2;
+      if (trim == PANGO_LEADING_TRIM_NONE)
+        logical_rect->height += leading;
+      else
+        logical_rect->height += (leading - leading / 2);
+    }
+
+  if (metrics)
+    pango_font_metrics_unref (metrics);
+}
diff --git a/pango/pango-glyph-item.h b/pango/pango-glyph-item.h
index fd8951d2..ac3d8279 100644
--- a/pango/pango-glyph-item.h
+++ b/pango/pango-glyph-item.h
@@ -85,6 +85,35 @@ void           pango_glyph_item_get_logical_widths (PangoGlyphItem *glyph_item,
                                               const char     *text,
                                               int            *logical_widths);
 
+/**
+ * PangoLeadingTrim:
+ * @PANGO_LEADING_TRIM_NONE: No trimming
+ * @PANGO_LEADING_TRIM_START: Trim leading at the top
+ * @PANGO_LEADING_TRIM_END: Trim leading at the bottom
+ *
+ * The `PangoLeadingTrim` flags control how the line height affects
+ * the extents of runs and lines.
+ */
+typedef enum
+{
+  PANGO_LEADING_TRIM_NONE  = 0,
+  PANGO_LEADING_TRIM_START = 1 << 0,
+  PANGO_LEADING_TRIM_END   = 1 << 1,
+
+} PangoLeadingTrim;
+
+/**
+ * PANGO_LEADING_TRIM_BOTH:
+ *
+ * Shorthand for `PANGO_LEADING_TRIM_START|PANGO_LEADING_TRIM_END`.
+ */
+#define PANGO_LEADING_TRIM_BOTH (PANGO_LEADING_TRIM_START|PANGO_LEADING_TRIM_END)
+
+PANGO_AVAILABLE_IN_ALL
+void            pango_glyph_item_get_extents  (PangoGlyphItem   *glyph_item,
+                                               PangoLeadingTrim  trim,
+                                               PangoRectangle   *ink_rect,
+                                               PangoRectangle   *logical_rect);
 
 /**
  * PangoGlyphItemIter: