From b937edfb148d28421f97db7c3c81e2253019e469 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Wed, 1 Mar 2023 10:44:57 -0700
Subject: [PATCH] [justify] Add min/max target_width

Speeds up solving when some slack available.
---
 src/hb-algs.hh        |  8 +++++---
 src/hb-shape.cc       | 32 ++++++++++++++++++--------------
 src/hb-shape.h        |  3 ++-
 util/shape-options.hh |  6 ++++--
 4 files changed, 29 insertions(+), 20 deletions(-)

diff --git a/src/hb-algs.hh b/src/hb-algs.hh
index 05ca3ec9d..cf9403134 100644
--- a/src/hb-algs.hh
+++ b/src/hb-algs.hh
@@ -1357,7 +1357,8 @@ double solve_itp (func_t f,
 		  double epsilon,
 		  unsigned n0,
 		  double k1,
-		  double &ya, double &yb)
+		  double min_y, double max_y,
+		  double &ya, double &yb, double &y)
 {
   unsigned n1_2 = (unsigned) (hb_max (ceil (log2 ((b - a) / epsilon)) - 1.0, 0.0));
   unsigned nmax = n0 + n1_2;
@@ -1377,18 +1378,19 @@ double solve_itp (func_t f,
     double xt = delta <= fabs (x1_2 - xf) ? xf + delta * sigma_sign : x1_2;
     double xitp = fabs (xt - x1_2) <= r ? xt : x1_2 - r * sigma_sign;
     double yitp = f (xitp);
-    if (yitp > 0.0)
+    if (yitp > max_y)
     {
       b = xitp;
       yb = yitp;
     }
-    else if (yitp < 0.0)
+    else if (yitp < min_y)
     {
       a = xitp;
       ya = yitp;
     }
     else
     {
+      y = yitp;
       return xitp;
     }
     scaled_epsilon *= 0.5;
diff --git a/src/hb-shape.cc b/src/hb-shape.cc
index e580298d1..d04cc214b 100644
--- a/src/hb-shape.cc
+++ b/src/hb-shape.cc
@@ -228,14 +228,15 @@ hb_shape_justify (hb_font_t          *font,
 		  const hb_feature_t *features,
 		  unsigned int        num_features,
 		  const char * const *shaper_list,
-		  float               target_width,
+		  float               min_target_width,
+		  float               max_target_width,
 		  float              *width, /* IN/OUT */
 		  hb_tag_t           *var_tag, /* OUT */
 		  float              *var_value /* OUT */)
 {
   // TODO Negative font scales?
 
-  if (target_width == *width)
+  if (min_target_width <= *width && *width <= max_target_width)
     return hb_shape_full (font, buffer,
 			  features, num_features,
 			  shaper_list);
@@ -287,13 +288,13 @@ hb_shape_justify (hb_font_t          *font,
     *width = buffer_width (buffer);
   }
 
-  if (target_width == *width)
+  if (min_target_width <= *width && *width <= max_target_width)
     return true;
 
   double a, b, ya, yb;
-  if (*width < target_width)
+  if (*width < min_target_width)
   {
-    ya = *width - target_width;
+    ya = *width;
     a = axis_info.default_value;
     b = axis_info.max_value;
 
@@ -303,16 +304,16 @@ hb_shape_justify (hb_font_t          *font,
 			features, num_features,
 			shaper_list))
       return false;
-    yb = buffer_width (buffer) - target_width;
+    yb = buffer_width (buffer);
     if (yb <= 0)
     {
-      *width = (float) yb + target_width;
+      *width = (float) yb;
       return true;
     }
   }
   else
   {
-    yb = *width - target_width;
+    yb = *width;
     a = axis_info.min_value;
     b = axis_info.default_value;
 
@@ -322,10 +323,10 @@ hb_shape_justify (hb_font_t          *font,
 			features, num_features,
 			shaper_list))
       return false;
-    ya = buffer_width (buffer) - target_width;
+    ya = buffer_width (buffer);
     if (ya >= 0)
     {
-      *width = (float) ya + target_width;
+      *width = (float) ya;
       return true;
     }
   }
@@ -344,26 +345,29 @@ hb_shape_justify (hb_font_t          *font,
 				  shaper_list)))
     {
       failed = true;
-      return target_width;
+      return min_target_width;
     }
 
-    return buffer_width (buffer) - target_width;
+    printf ("%g\n", x);
+    return buffer_width (buffer);
   };
 
+  double y = 0;
   double itp = solve_itp (f,
 			  a, b,
 			  epsilon,
 			  n0,
 			  k1,
-			  ya, yb);
+			  min_target_width, max_target_width,
+			  ya, yb, y);
 
   hb_free (text_info);
 
   if (failed)
     return false;
 
-  *width = (float) (ya + yb) * 0.5f + target_width;
   *var_value = (float) itp;
+  *width = (float) y;
 
   return true;
 }
diff --git a/src/hb-shape.h b/src/hb-shape.h
index 821b6874b..8c2062c6a 100644
--- a/src/hb-shape.h
+++ b/src/hb-shape.h
@@ -59,7 +59,8 @@ hb_shape_justify (hb_font_t          *font,
 		  const hb_feature_t *features,
 		  unsigned int        num_features,
 		  const char * const *shaper_list,
-		  float               target_width,
+		  float               min_target_width,
+		  float               max_target_width,
 		  float              *width, /* IN/OUT */
 		  hb_tag_t           *var_tag, /* OUT */
 		  float              *var_value /* OUT */);
diff --git a/util/shape-options.hh b/util/shape-options.hh
index 55a1f4c53..0d8977cd6 100644
--- a/util/shape-options.hh
+++ b/util/shape-options.hh
@@ -172,12 +172,14 @@ struct shape_options_t
       }
       else
       {
-        float target_width = width * (1 << SUBPIXEL_BITS);
+        float unit = (1 << SUBPIXEL_BITS);
+        float target_width = width * unit;
 	float w = 0;
 	hb_tag_t var_tag;
 	float var_value;
 	if (!hb_shape_justify (font, buffer, features, num_features, shapers,
-			       target_width, &w, &var_tag, &var_value))
+			       target_width - unit * 0.5f, target_width + unit * 0.5f,
+			       &w, &var_tag, &var_value))
 	{
 	  if (error)
 	    *error = "Shaping failed.";