[pango/pango2] layout: Fix indent and align handling

[Matthias Clasen <matthiasc src gnome org>]

commit bb0c5a6b8a72c8bf0e315d7f232530ca3a375957
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Sep 10 20:08:06 2022 -0400

    layout: Fix indent and align handling
    
    Make PangoLayout behavior more similar to the
    way it behaved in pango 1.x. Most combinations
    of alignment, indentation and width should work
    the same now.

 pango2/pango-layout.c | 131 ++++++++++++++++++++++++++++++++++----------------
 1 file changed, 90 insertions(+), 41 deletions(-)
---
diff --git a/pango2/pango-layout.c b/pango2/pango-layout.c
index 4429c2c78..2efd03102 100644
--- a/pango2/pango-layout.c
+++ b/pango2/pango-layout.c
@@ -639,15 +639,21 @@ ensure_lines (Pango2Layout *layout)
 {
   Pango2LineBreaker *breaker;
   Pango2AttrList *attrs;
+  int layout_width;
   int x, y, width;
   int line_no;
   gboolean at_paragraph_start;
+  Pango2Alignment alignment;
+  Pango2Alignment natural_alignment;
 
   check_context_changed (layout);
 
   if (layout->lines)
     return;
 
+  layout_width = layout->width;
+
+start_over:
   breaker = pango2_line_breaker_new (layout->context);
 
   pango2_line_breaker_set_tabs (breaker, layout->tabs);
@@ -663,6 +669,16 @@ ensure_lines (Pango2Layout *layout)
 
   layout->lines = pango2_lines_new ();
 
+  if (pango2_line_breaker_get_direction (breaker) == PANGO2_DIRECTION_LTR)
+    natural_alignment = PANGO2_ALIGN_LEFT;
+  else
+    natural_alignment = PANGO2_ALIGN_RIGHT;
+
+  if (layout->alignment == PANGO2_ALIGN_NATURAL)
+    alignment = natural_alignment;
+  else
+    alignment = layout->alignment;
+
   x = y = 0;
   line_no = 0;
   at_paragraph_start = TRUE;
@@ -674,18 +690,49 @@ ensure_lines (Pango2Layout *layout)
       Pango2EllipsizeMode ellipsize = PANGO2_ELLIPSIZE_NONE;
       Pango2LeadingTrim trim = PANGO2_LEADING_TRIM_NONE;
 
-      if (at_paragraph_start == (layout->indent > 0))
+      switch (alignment)
         {
-          x = abs (layout->indent);
-          if (layout->width == -1)
-            width = -1;
+        case PANGO2_ALIGN_LEFT:
+        case PANGO2_ALIGN_JUSTIFY:
+          if (at_paragraph_start == (layout->indent > 0))
+            {
+              x = abs (layout->indent);
+              if (layout_width == -1)
+                width = -1;
+              else
+                width = layout_width - x;
+            }
           else
-            width = layout->width - x;
-        }
-      else
-        {
+            {
+              x = 0;
+              width = layout_width;
+            }
+          break;
+
+        case PANGO2_ALIGN_RIGHT:
+          if (at_paragraph_start == (layout->indent > 0))
+            {
+              x = 0;
+              if (layout_width == -1)
+                width = -1;
+              else
+                width = layout_width - abs (layout->indent);
+            }
+          else
+            {
+              x = 0;
+              width = layout_width;
+            }
+          break;
+
+        case PANGO2_ALIGN_CENTER:
           x = 0;
-          width = layout->width;
+          width = layout_width;
+          break;
+
+        case PANGO2_ALIGN_NATURAL:
+        default:
+          g_assert_not_reached ();
         }
 
       if (layout->height < 0 && line_no + 1 == - layout->height)
@@ -714,46 +761,38 @@ retry:
             }
         }
 
-      /* Handle alignment and justification */
       offset = 0;
-      switch (layout->alignment)
+      if (width > 0)
         {
-
-        case PANGO2_ALIGN_LEFT:
-          break;
-
-        case PANGO2_ALIGN_CENTER:
-          if (ext.width < width)
-            offset = (width - ext.width) / 2;
-          break;
-
-        case PANGO2_ALIGN_JUSTIFY:
-          if (!pango2_line_is_paragraph_end (line))
+          /* Handle alignment and justification */
+          switch (alignment)
             {
-              line = pango2_line_justify (line, width);
+
+            case PANGO2_ALIGN_LEFT:
               break;
-            }
-          G_GNUC_FALLTHROUGH;
 
-        case PANGO2_ALIGN_NATURAL:
-          {
-            Pango2Line *first_line;
-            if (pango2_lines_get_line_count (layout->lines) > 0)
-              first_line = pango2_lines_get_lines (layout->lines)[0];
-            else
-              first_line = line;
-            if (pango2_line_get_resolved_direction (first_line) == PANGO2_DIRECTION_LTR)
+            case PANGO2_ALIGN_CENTER:
+              if (ext.width < width)
+                offset = (width - ext.width) / 2;
               break;
-          }
-          G_GNUC_FALLTHROUGH;
 
-        case PANGO2_ALIGN_RIGHT:
-          if (ext.width < width)
-            offset = width - ext.width;
-          break;
+            case PANGO2_ALIGN_JUSTIFY:
+              if (!pango2_line_is_paragraph_end (line))
+                {
+                  line = pango2_line_justify (line, width);
+                  break;
+                }
+              G_GNUC_FALLTHROUGH;
+
+            case PANGO2_ALIGN_RIGHT:
+              if (ext.width < width)
+                offset = width - ext.width;
+              break;
 
-        default:
-          g_assert_not_reached ();
+            case PANGO2_ALIGN_NATURAL:
+            default:
+              g_assert_not_reached ();
+            }
         }
 
       pango2_lines_add_line (layout->lines, line, x + offset, y - ext.y);
@@ -762,6 +801,16 @@ retry:
       line_no++;
     }
 
+  if (width < 0 && alignment != PANGO2_ALIGN_LEFT)
+    {
+      /* Not the most efficient, but it works */
+      pango2_lines_get_size (layout->lines, &layout_width, NULL);
+      g_clear_object (&layout->lines);
+      g_clear_object (&breaker);
+
+      goto start_over;
+    }
+
   /* Append an empty line if we end with a newline.
    * And always provide at least one line
    */