initial commit, 4.5 stable

thirdparty/harfbuzz/src/hb-subset-instancer-solver.cc

@@ -0,0 +1,434 @@
+/*
+ * Copyright © 2023  Behdad Esfahbod
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ */
+
+#include "hb-subset-instancer-solver.hh"
+
+/* This file is a straight port of the following:
+ *
+ * https://github.com/fonttools/fonttools/blob/f73220816264fc383b8a75f2146e8d69e455d398/Lib/fontTools/varLib/instancer/solver.py
+ *
+ * Where that file returns None for a triple, we return Triple{}.
+ * This should be safe.
+ */
+
+constexpr static double EPSILON = 1.0 / (1 << 14);
+constexpr static double MAX_F2DOT14 = double (0x7FFF) / (1 << 14);
+
+static inline Triple _reverse_negate(const Triple &v)
+{ return {-v.maximum, -v.middle, -v.minimum}; }
+
+
+static inline double supportScalar (double coord, const Triple &tent)
+{
+  /* Copied from VarRegionAxis::evaluate() */
+  double start = tent.minimum, peak = tent.middle, end = tent.maximum;
+
+  if (unlikely (start > peak || peak > end))
+    return 1.;
+  if (unlikely (start < 0 && end > 0 && peak != 0))
+    return 1.;
+
+  if (peak == 0 || coord == peak)
+    return 1.;
+
+  if (coord <= start || end <= coord)
+    return 0.;
+
+  /* Interpolate */
+  if (coord < peak)
+    return (coord - start) / (peak - start);
+  else
+    return  (end - coord) / (end - peak);
+}
+
+static inline rebase_tent_result_t
+_solve (Triple tent, Triple axisLimit, bool negative = false)
+{
+  double axisMin = axisLimit.minimum;
+  double axisDef = axisLimit.middle;
+  double axisMax = axisLimit.maximum;
+  double lower = tent.minimum;
+  double peak  = tent.middle;
+  double upper = tent.maximum;
+
+  // Mirror the problem such that axisDef <= peak
+  if (axisDef > peak)
+  {
+    rebase_tent_result_t vec = _solve (_reverse_negate (tent),
+			   _reverse_negate (axisLimit),
+			   !negative);
+
+    for (auto &p : vec)
+      p = hb_pair (p.first, _reverse_negate (p.second));
+
+    return vec;
+  }
+  // axisDef <= peak
+
+  /* case 1: The whole deltaset falls outside the new limit; we can drop it
+   *
+   *                                          peak
+   *  1.........................................o..........
+   *                                           / \
+   *                                          /   \
+   *                                         /     \
+   *                                        /       \
+   *  0---|-----------|----------|-------- o         o----1
+   *    axisMin     axisDef    axisMax   lower     upper
+   */
+  if (axisMax <= lower && axisMax < peak)
+      return rebase_tent_result_t{};  // No overlap
+
+  /* case 2: Only the peak and outermost bound fall outside the new limit;
+   * we keep the deltaset, update peak and outermost bound and scale deltas
+   * by the scalar value for the restricted axis at the new limit, and solve
+   * recursively.
+   *
+   *                                  |peak
+   *  1...............................|.o..........
+   *                                  |/ \
+   *                                  /   \
+   *                                 /|    \
+   *                                / |     \
+   *  0--------------------------- o  |      o----1
+   *                           lower  |      upper
+   *                                  |
+   *                                axisMax
+   *
+   * Convert to:
+   *
+   *  1............................................
+   *                                  |
+   *                                  o peak
+   *                                 /|
+   *                                /x|
+   *  0--------------------------- o  o upper ----1
+   *                           lower  |
+   *                                  |
+   *                                axisMax
+   */
+  if (axisMax < peak)
+  {
+    double mult = supportScalar (axisMax, tent);
+    tent = Triple{lower, axisMax, axisMax};
+
+    rebase_tent_result_t vec = _solve (tent, axisLimit);
+
+    for (auto &p : vec)
+      p = hb_pair (p.first * mult, p.second);
+
+    return vec;
+  }
+
+  // lower <= axisDef <= peak <= axisMax
+
+  double gain = supportScalar (axisDef, tent);
+  rebase_tent_result_t out {hb_pair (gain, Triple{})};
+
+  // First, the positive side
+
+  // outGain is the scalar of axisMax at the tent.
+  double outGain = supportScalar (axisMax, tent);
+
+  /* Case 3a: Gain is more than outGain. The tent down-slope crosses
+   * the axis into negative. We have to split it into multiples.
+   *
+   *                      | peak  |
+   *  1...................|.o.....|..............
+   *                      |/x\_   |
+   *  gain................+....+_.|..............
+   *                     /|    |y\|
+   *  ................../.|....|..+_......outGain
+   *                   /  |    |  | \
+   *  0---|-----------o   |    |  |  o----------1
+   *    axisMin    lower  |    |  |   upper
+   *                      |    |  |
+   *                axisDef    |  axisMax
+   *                           |
+   *                      crossing
+   */
+  if (gain >= outGain)
+  {
+    // Note that this is the branch taken if both gain and outGain are 0.
+
+    // Crossing point on the axis.
+    double crossing = peak + (1 - gain) * (upper - peak);
+
+    Triple loc{hb_max (lower, axisDef), peak, crossing};
+    double scalar = 1.0;
+
+    // The part before the crossing point.
+    out.push (hb_pair (scalar - gain, loc));
+
+    /* The part after the crossing point may use one or two tents,
+     * depending on whether upper is before axisMax or not, in one
+     * case we need to keep it down to eternity.
+     *
+     * Case 3a1, similar to case 1neg; just one tent needed, as in
+     * the drawing above.
+     */
+    if (upper >= axisMax)
+    {
+      Triple loc {crossing, axisMax, axisMax};
+      double scalar = outGain;
+
+      out.push (hb_pair (scalar - gain, loc));
+    }
+
+    /* Case 3a2: Similar to case 2neg; two tents needed, to keep
+     * down to eternity.
+     *
+     *                      | peak             |
+     *  1...................|.o................|...
+     *                      |/ \_              |
+     *  gain................+....+_............|...
+     *                     /|    | \xxxxxxxxxxy|
+     *                    / |    |  \_xxxxxyyyy|
+     *                   /  |    |    \xxyyyyyy|
+     *  0---|-----------o   |    |     o-------|--1
+     *    axisMin    lower  |    |      upper  |
+     *                      |    |             |
+     *                axisDef    |             axisMax
+     *                           |
+     *                      crossing
+     */
+    else
+    {
+      // A tent's peak cannot fall on axis default. Nudge it.
+      if (upper == axisDef)
+	upper += EPSILON;
+
+      // Downslope.
+      Triple loc1 {crossing, upper, axisMax};
+      double scalar1 = 0.0;
+
+      // Eternity justify.
+      Triple loc2 {upper, axisMax, axisMax};
+      double scalar2 = 0.0;
+
+      out.push (hb_pair (scalar1 - gain, loc1));
+      out.push (hb_pair (scalar2 - gain, loc2));
+    }
+  }
+
+  else
+  {
+    // Special-case if peak is at axisMax.
+    if (axisMax == peak)
+	upper = peak;
+
+    /* Case 3:
+     * we keep deltas as is and only scale the axis upper to achieve
+     * the desired new tent if feasible.
+     *
+     *                        peak
+     *  1.....................o....................
+     *                       / \_|
+     *  ..................../....+_.........outGain
+     *                     /     | \
+     *  gain..............+......|..+_.............
+     *                   /|      |  | \
+     *  0---|-----------o |      |  |  o----------1
+     *    axisMin    lower|      |  |   upper
+     *                    |      |  newUpper
+     *              axisDef      axisMax
+     */
+    double newUpper = peak + (1 - gain) * (upper - peak);
+    assert (axisMax <= newUpper);  // Because outGain > gain
+    /* Disabled because ots doesn't like us:
+     * https://github.com/fonttools/fonttools/issues/3350 */
+
+    if (false && (newUpper <= axisDef + (axisMax - axisDef) * 2))
+    {
+      upper = newUpper;
+      if (!negative && axisDef + (axisMax - axisDef) * MAX_F2DOT14 < upper)
+      {
+	// we clamp +2.0 to the max F2Dot14 (~1.99994) for convenience
+	upper = axisDef + (axisMax - axisDef) * MAX_F2DOT14;
+	assert (peak < upper);
+      }
+
+      Triple loc {hb_max (axisDef, lower), peak, upper};
+      double scalar = 1.0;
+
+      out.push (hb_pair (scalar - gain, loc));
+    }
+
+    /* Case 4: New limit doesn't fit; we need to chop into two tents,
+     * because the shape of a triangle with part of one side cut off
+     * cannot be represented as a triangle itself.
+     *
+     *            |   peak |
+     *  1.........|......o.|....................
+     *  ..........|...../x\|.............outGain
+     *            |    |xxy|\_
+     *            |   /xxxy|  \_
+     *            |  |xxxxy|    \_
+     *            |  /xxxxy|      \_
+     *  0---|-----|-oxxxxxx|        o----------1
+     *    axisMin | lower  |        upper
+     *            |        |
+     *          axisDef  axisMax
+     */
+    else
+    {
+      Triple loc1 {hb_max (axisDef, lower), peak, axisMax};
+      double scalar1 = 1.0;
+
+      Triple loc2 {peak, axisMax, axisMax};
+      double scalar2 = outGain;
+
+      out.push (hb_pair (scalar1 - gain, loc1));
+      // Don't add a dirac delta!
+      if (peak < axisMax)
+	out.push (hb_pair (scalar2 - gain, loc2));
+    }
+  }
+
+  /* Now, the negative side
+   *
+   * Case 1neg: Lower extends beyond axisMin: we chop. Simple.
+   *
+   *                     |   |peak
+   *  1..................|...|.o.................
+   *                     |   |/ \
+   *  gain...............|...+...\...............
+   *                     |x_/|    \
+   *                     |/  |     \
+   *                   _/|   |      \
+   *  0---------------o  |   |       o----------1
+   *              lower  |   |       upper
+   *                     |   |
+   *               axisMin   axisDef
+   */
+  if (lower <= axisMin)
+  {
+    Triple loc {axisMin, axisMin, axisDef};
+    double scalar = supportScalar (axisMin, tent);
+
+    out.push (hb_pair (scalar - gain, loc));
+  }
+
+  /* Case 2neg: Lower is betwen axisMin and axisDef: we add two
+   * tents to keep it down all the way to eternity.
+   *
+   *      |               |peak
+   *  1...|...............|.o.................
+   *      |               |/ \
+   *  gain|...............+...\...............
+   *      |yxxxxxxxxxxxxx/|    \
+   *      |yyyyyyxxxxxxx/ |     \
+   *      |yyyyyyyyyyyx/  |      \
+   *  0---|-----------o   |       o----------1
+   *    axisMin    lower  |       upper
+   *                      |
+   *                    axisDef
+   */
+  else
+  {
+    // A tent's peak cannot fall on axis default. Nudge it.
+    if (lower == axisDef)
+      lower -= EPSILON;
+
+    // Downslope.
+    Triple loc1 {axisMin, lower, axisDef};
+    double scalar1 = 0.0;
+
+    // Eternity justify.
+    Triple loc2 {axisMin, axisMin, lower};
+    double scalar2 = 0.0;
+
+    out.push (hb_pair (scalar1 - gain, loc1));
+    out.push (hb_pair (scalar2 - gain, loc2));
+  }
+
+  return out;
+}
+
+static inline TripleDistances _reverse_triple_distances (const TripleDistances &v)
+{ return TripleDistances (v.positive, v.negative); }
+
+double renormalizeValue (double v, const Triple &triple,
+                         const TripleDistances &triple_distances, bool extrapolate)
+{
+  double lower = triple.minimum, def = triple.middle, upper = triple.maximum;
+  assert (lower <= def && def <= upper);
+
+  if (!extrapolate)
+    v = hb_clamp (v, lower, upper);
+
+  if (v == def)
+    return 0.0;
+
+  if (def < 0.0)
+    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 >= 0.0)
+    return (v - def) / (def - lower);
+
+  /* lower < 0 and v < default */
+  double total_distance = triple_distances.negative * (-lower) + triple_distances.positive * def;
+
+  double v_distance;
+  if (v >= 0.0)
+    v_distance = (def - v) * triple_distances.positive;
+  else
+    v_distance = (-v) * triple_distances.negative + triple_distances.positive * def;
+
+  return (-v_distance) /total_distance;
+}
+
+rebase_tent_result_t
+rebase_tent (Triple tent, Triple axisLimit, TripleDistances axis_triple_distances)
+{
+  assert (-1.0 <= axisLimit.minimum && axisLimit.minimum <= axisLimit.middle && axisLimit.middle <= axisLimit.maximum && axisLimit.maximum <= +1.0);
+  assert (-2.0 <= tent.minimum && tent.minimum <= tent.middle && tent.middle <= tent.maximum && tent.maximum <= +2.0);
+  assert (tent.middle != 0.0);
+
+  rebase_tent_result_t sols = _solve (tent, axisLimit);
+
+  auto n = [&axisLimit, &axis_triple_distances] (double v) { return renormalizeValue (v, axisLimit, axis_triple_distances); };
+
+  rebase_tent_result_t out;
+  for (auto &p : sols)
+  {
+    if (!p.first) continue;
+    if (p.second == Triple{})
+    {
+      out.push (p);
+      continue;
+    }
+    Triple t = p.second;
+    out.push (hb_pair (p.first,
+		       Triple{n (t.minimum), n (t.middle), n (t.maximum)}));
+  }
+
+  return out;
+}