.

src/hb-shape.cc

@@ -196,4 +196,88 @@ hb_shape (hb_font_t           *font,
 }
 
 
+static float
+buffer_width (hb_buffer_t *buffer)
+{
+  float w = 0;
+  auto *pos = buffer->pos;
+  unsigned count = buffer->len;
+  for (unsigned i = 0; i < count; i++)
+    w += pos[i].x_advance;
+  return w;
+}
+
+hb_bool_t
+hb_shape_justify (hb_font_t          *font,
+		  hb_buffer_t        *buffer,
+		  const hb_feature_t *features,
+		  unsigned int        num_features,
+		  const char * const *shaper_list,
+		  float               target_width,
+		  float              *width)
+{
+  // TODO vertical
+  // TODO buffer context
+
+  if (target_width == *width)
+    return hb_shape_full (font, buffer,
+			  features, num_features,
+			  shaper_list);
+
+  hb_face_t *face = font->face;
+
+  hb_ot_var_axis_info_t axis_info;
+  if (!hb_ot_var_find_axis_info (face, HB_TAG ('j','s','t','f'), &axis_info) &&
+      !hb_ot_var_find_axis_info (face, HB_TAG ('w','d','t','h'), &axis_info))
+  {
+    if (hb_shape_full (font, buffer,
+		       features, num_features,
+		       shaper_list))
+    {
+      *width = buffer_width (buffer);
+      return true;
+    }
+    else
+      return false;
+  }
+
+  auto *text_info = (hb_glyph_info_t *) hb_malloc (buffer->len * sizeof (buffer->info[0]));
+  if (unlikely (!text_info))
+    return false;
+  memcpy (text_info, buffer->info, buffer->len * sizeof (buffer->info[0]));
+
+  if (!*width)
+  {
+    if (hb_shape_full (font, buffer,
+		       features, num_features,
+		       shaper_list))
+      return false;
+    *width = buffer_width (buffer);
+  }
+
+  if (target_width == *width)
+    return true;
+
+  hb_font_t *sub_font = hb_font_create_sub_font (font);
+
+  float a, b, ya, yb;
+
+  const float epsilon;
+  const unsigned n0 = 1;
+  const k1 = 0.2 / (b - a);
+
+  double var = solve_itp (func_t f,
+			  double a, double b,
+			  double epsilon,
+			  unsigned n0,
+			  double k1,
+			  double &ya, double yb);
+
+  hb_font_destroy (sub_font);
+  hb_free (text_info);
+
+  return false;
+}
+
+
 #endif

src/hb-shape.h

@@ -53,6 +53,15 @@ hb_shape_full (hb_font_t          *font,
 	       unsigned int        num_features,
 	       const char * const *shaper_list);
 
+HB_EXTERN hb_bool_t
+hb_shape_justify (hb_font_t          *font,
+		  hb_buffer_t        *buffer,
+		  const hb_feature_t *features,
+		  unsigned int        num_features,
+		  const char * const *shaper_list,
+		  float               target_width,
+		  float              *width);
+
 HB_EXTERN const char **
 hb_shape_list_shapers (void);