[instancer-solver] add renormalizeValue() and store axis->distances map

src/hb-ot-var-fvar-table.hh

@@ -228,6 +228,13 @@ struct AxisRecord
     return defaultValue.to_float ();
   }
 
+  TripleDistances get_triple_distances () const
+  {
+    float min, default_, max;
+    get_coordinates (min, default_, max);
+    return TripleDistances (min, default_, max);
+  }
+
   public:
   Tag		axisTag;	/* Tag identifying the design variation for the axis. */
   protected:

src/hb-subset-instancer-solver.cc

@@ -392,8 +392,47 @@ static inline float normalizeValue (float v, const Triple &triple, bool extrapol
   }
 }
 
+static inline TripleDistances _reverse_triple_distances (const TripleDistances &v)
+{ return TripleDistances (v.positive, v.negative); }
+
+float renormalizeValue (float v, const Triple &triple,
+                        const TripleDistances &triple_distances, bool extrapolate)
+{
+  float lower = triple.minimum, def = triple.middle, upper = triple.maximum;
+  assert (lower <= def && def <= upper);
+
+  if (!extrapolate)
+      v = hb_max (hb_min (v, upper), lower);
+
+  if (v == def)
+    return 0.f;
+
+  if (def < 0.f)
+    return -renormalizeValue (-v, _reverse_negate (triple),
+                              _reverse_triple_distances (triple_distances), extrapolate);
+
+  /* default >= 0 and v != default */
+  if (v > def)
+    return (v - def) / (upper - def);
+
+  /* v < def */
+  if (lower >= 0.f)
+    return (v - def) / (def - lower);
+
+  /* lower < 0 and v < default */
+  float total_distance = triple_distances.negative * (-lower) + triple_distances.positive * def;
+
+  float v_distance;
+  if (v >= 0.f)
+    v_distance = (def - v) * triple_distances.positive;
+  else
+    v_distance = (-v) * triple_distances.negative + triple_distances.positive * def;
+
+  return (-v_distance) /total_distance;
+}
+
 result_t
-rebase_tent (Triple tent, Triple axisLimit)
+rebase_tent (Triple tent, Triple axisLimit, TripleDistances axis_triple_distances)
 {
   assert (-1.f <= axisLimit.minimum && axisLimit.minimum <= axisLimit.middle && axisLimit.middle <= axisLimit.maximum && axisLimit.maximum <= +1.f);
   assert (-2.f <= tent.minimum && tent.minimum <= tent.middle && tent.middle <= tent.maximum && tent.maximum <= +2.f);
@@ -401,7 +440,7 @@ rebase_tent (Triple tent, Triple axisLimit)
 
   result_t sols = _solve (tent, axisLimit);
 
-  auto n = [&axisLimit] (float v) { return normalizeValue (v, axisLimit, true); };
+  auto n = [&axisLimit, &axis_triple_distances] (float v) { return renormalizeValue (v, axisLimit, axis_triple_distances); };
 
   result_t out;
   for (auto &p : sols)

src/hb-subset-instancer-solver.hh

@@ -27,6 +27,21 @@
 
 #include "hb.hh"
 
+/* pre-normalized distances */
+struct TripleDistances
+{
+  TripleDistances (): negative (1.f), positive (1.f) {}
+  TripleDistances (float neg_, float pos_): negative (neg_), positive (pos_) {}
+  TripleDistances (float min, float default_, float max)
+  {
+    negative = default_ - min;
+    positive = max - default_;
+  }
+
+  float negative;
+  float positive;
+};
+
 struct Triple {
 
   Triple () :
@@ -66,6 +81,7 @@ struct Triple {
     return current;
   }
 
+
   float minimum;
   float middle;
   float maximum;
@@ -74,6 +90,12 @@ struct Triple {
 using result_item_t = hb_pair_t<float, Triple>;
 using result_t = hb_vector_t<result_item_t>;
 
+/* renormalize a normalized value v to the range of an axis,
+ * considering the prenormalized distances as well as the new axis limits.
+ * Ported from fonttools */
+HB_INTERNAL float renormalizeValue (float v, const Triple &triple,
+                                    const TripleDistances &triple_distances,
+                                    bool extrapolate = true);
 /* Given a tuple (lower,peak,upper) "tent" and new axis limits
  * (axisMin,axisDefault,axisMax), solves how to represent the tent
  * under the new axis configuration.  All values are in normalized
@@ -85,6 +107,6 @@ using result_t = hb_vector_t<result_item_t>;
  * If tent value is Triple{}, that is a special deltaset that should
  * be always-enabled (called "gain").
  */
-HB_INTERNAL result_t rebase_tent (Triple tent, Triple axisLimit);
+HB_INTERNAL result_t rebase_tent (Triple tent, Triple axisLimit, TripleDistances axis_triple_distances);
 
 #endif /* HB_SUBSET_INSTANCER_SOLVER_HH */

src/hb-subset-plan-member-list.hh

@@ -105,6 +105,8 @@ HB_SUBSET_PLAN_MEMBER (hb_vector_t<int>, normalized_coords)
 
 //user specified axes range map
 HB_SUBSET_PLAN_MEMBER (hb_hashmap_t E(<hb_tag_t, Triple>), user_axes_location)
+//axis->TripleDistances map (distances in the pre-normalized space)
+HB_SUBSET_PLAN_MEMBER (hb_hashmap_t E(<hb_tag_t, TripleDistances>), axes_triple_distances)
 
 //retained old axis index -> new axis index mapping in fvar axis array
 HB_SUBSET_PLAN_MEMBER (hb_map_t, axes_index_map)

src/hb-subset-plan.cc

@@ -930,12 +930,14 @@ _normalize_axes_location (hb_face_t *face, hb_subset_plan_t *plan)
       new_axis_idx++;
     }
 
-    if (plan->user_axes_location.has (axis_tag))
+    Triple *axis_range;
+    if (plan->user_axes_location.has (axis_tag, &axis_range))
     {
-      Triple axis_range = plan->user_axes_location.get (axis_tag);
-      int normalized_min = axis.normalize_axis_value (axis_range.minimum);
-      int normalized_default = axis.normalize_axis_value (axis_range.middle);
-      int normalized_max = axis.normalize_axis_value (axis_range.maximum);
+      plan->axes_triple_distances.set (axis_tag, axis.get_triple_distances ());
+
+      int normalized_min = axis.normalize_axis_value (axis_range->minimum);
+      int normalized_default = axis.normalize_axis_value (axis_range->middle);
+      int normalized_max = axis.normalize_axis_value (axis_range->maximum);
 
       if (has_avar && old_axis_idx < avar_axis_count)
       {