[subset] Add unfinished port of fonttools instancer solver
diff --git a/src/Makefile.sources b/src/Makefile.sources
index 24ce798..70b80be 100644
--- a/src/Makefile.sources
+++ b/src/Makefile.sources
@@ -353,6 +353,7 @@
hb-subset-cff2.hh \
hb-subset-input.cc \
hb-subset-input.hh \
+ hb-subset-instancer-solver.cc \
hb-subset-accelerator.hh \
hb-subset-plan.cc \
hb-subset-plan.hh \
diff --git a/src/harfbuzz-subset.cc b/src/harfbuzz-subset.cc
index d485233..196e32f 100644
--- a/src/harfbuzz-subset.cc
+++ b/src/harfbuzz-subset.cc
@@ -53,6 +53,7 @@
#include "hb-subset-cff1.cc"
#include "hb-subset-cff2.cc"
#include "hb-subset-input.cc"
+#include "hb-subset-instancer-solver.cc"
#include "hb-subset-plan.cc"
#include "hb-subset-repacker.cc"
#include "hb-subset.cc"
diff --git a/src/hb-subset-instancer-solver.cc b/src/hb-subset-instancer-solver.cc
new file mode 100644
index 0000000..89360d0
--- /dev/null
+++ b/src/hb-subset-instancer-solver.cc
@@ -0,0 +1,405 @@
+/*
+ * 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.hh"
+
+/* This file is a straight port of the following:
+ *
+ * https://github.com/fonttools/fonttools/blob/f73220816264fc383b8a75f2146e8d69e455d398/Lib/fontTools/varLib/instancer/solver.py
+ *
+ * See XXX markers for unfinished parts.
+ *
+ * Where that file returns None for a triple, we return Triple{}.
+ * This should be safe.
+ */
+
+constexpr static float EPSILON = 1.f / (1 << 14);
+constexpr static float MAX_F2DOT14 = float (0x7FFF) / (1 << 14);
+
+struct Triple {
+
+ Triple () :
+ minimum (0.f), middle (0.f), maximum (0.f) {}
+
+ Triple (float minimum_, float middle_, float maximum_) :
+ minimum (minimum_), middle (middle_), maximum (maximum_) {}
+
+ float minimum;
+ float middle;
+ float maximum;
+};
+
+static inline Triple _reverse_negate(const Triple &v)
+{ return {-v.maximum, -v.middle, -v.minimum}; }
+
+using result_item_t = hb_pair_t<float, Triple>;
+using result_t = hb_vector_t<result_item_t>;
+
+static inline result_t
+_solve (Triple tent, Triple axisLimit, bool negative = false)
+{
+ float axisMin = axisLimit.minimum;
+ float axisDef = axisLimit.middle;
+ float axisMax = axisLimit.maximum;
+ float lower = tent.minimum;
+ float peak = tent.middle;
+ float upper = tent.maximum;
+
+ // Mirror the problem such that axisDef <= peak
+ if (axisDef > peak)
+ {
+ 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 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 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)
+ {
+ float mult = 1.f; //XXX supportScalar({"tag": axisMax}, {"tag": tent})
+ tent = Triple{lower, axisMax, axisMax};
+
+ result_t vec = _solve (tent, axisLimit);
+
+ for (auto &p : vec)
+ p = hb_pair (p.first * mult, p.second);
+
+ return vec;
+ }
+
+ // lower <= axisDef <= peak <= axisMax
+
+ float gain = 1.0f; // XXX supportScalar({"tag": axisDef}, {"tag": tent})
+ result_t out {hb_pair (gain, Triple{})};
+
+ // First, the positive side
+
+ // outGain is the scalar of axisMax at the tent.
+ float outGain = 1.f; // XXX supportScalar({"tag": axisMax}, {"tag": 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)
+ {
+ // Crossing point on the axis.
+ float crossing = peak + ((1 - gain) * (upper - peak) / (1 - outGain));
+
+ Triple loc{peak, peak, crossing};
+ float scalar = 1.f;
+
+ // 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};
+ float scalar = 1.f; // XXX supportScalar({"tag": axisMax}, {"tag": tent})
+
+ 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};
+ float scalar1 = 0.f;
+
+ // Eternity justify.
+ Triple loc2 {upper, axisMax, axisMax};
+ float scalar2 = 1.f; // supportScalar({"tag": axisMax}, {"tag": tent})
+
+ out.push (hb_pair (scalar1 - gain, loc1));
+ out.push (hb_pair (scalar2 - gain, loc2));
+ }
+ }
+
+ /* Case 3: Outermost limit still fits within F2Dot14 bounds;
+ * we keep deltas as is and only scale the axes bounds. Deltas beyond -1.0
+ * or +1.0 will never be applied as implementations must clamp to that range.
+ *
+ * A second tent is needed for cases when gain is positive, though we add it
+ * unconditionally and it will be dropped because scalar ends up 0.
+ *
+ * TODO: See if we can just move upper closer to adjust the slope, instead of
+ * second tent.
+ *
+ * | peak |
+ * 1.........|............o...|..................
+ * | /x\ |
+ * | /xxx\ |
+ * | /xxxxx\|
+ * | /xxxxxxx+
+ * | /xxxxxxxx|\
+ * 0---|-----|------oxxxxxxxxx|xo---------------1
+ * axisMin | lower | upper
+ * | |
+ * axisDef axisMax
+ */
+ else if (axisDef + (axisMax - axisDef) * 2 >= upper)
+ {
+ 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);
+ }
+
+ // Special-case if peak is at axisMax.
+ if (axisMax == peak)
+ upper = peak;
+
+ Triple loc1 {hb_max (axisDef, lower), peak, upper};
+ float scalar1 = 1.f;
+
+ Triple loc2 {peak, upper, upper};
+ float scalar2 = 0.f;
+
+ // Don't add a dirac delta!
+ if (axisDef < upper)
+ out.push (hb_pair (scalar1 - gain, loc1));
+ if (peak < upper)
+ out.push (hb_pair (scalar2 - gain, loc2));
+ }
+
+ /* 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\|
+ * | |xxy|\_
+ * | /xxxy| \_
+ * | |xxxxy| \_
+ * | /xxxxy| \_
+ * 0---|-----|-oxxxxxx| o----------1
+ * axisMin | lower | upper
+ * | |
+ * axisDef axisMax
+ */
+ else
+ {
+ Triple loc1 {hb_max (axisDef, lower), peak, axisMax};
+ float scalar1 = 1.f;
+
+ Triple loc2 {peak, axisMax, axisMax};
+ float scalar2 = 1.f; // XXX supportScalar({"tag": axisMax}, {"tag": tent})
+
+ 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};
+ float scalar = 1.f; // XXX supportScalar({"tag": axisMin}, {"tag": 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};
+ float scalar1 = 0.f;
+
+ // Eternity justify.
+ Triple loc2 {axisMin, axisMin, lower};
+ float scalar2 = 0.f;
+
+ out.push (hb_pair (scalar1 - gain, loc1));
+ out.push (hb_pair (scalar2 - gain, loc2));
+ }
+
+ return out;
+}
+
+/* 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
+ * -1,0,+1 coordinate system. Tent values can be outside this range.
+ *
+ * Return value: a list of tuples. Each tuple is of the form
+ * (scalar,tent), where scalar is a multipler to multiply any
+ * delta-sets by, and tent is a new tent for that output delta-set.
+ * 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);
+
+result_t
+rebase_tent (Triple tent, Triple axisLimit)
+{
+ float axisMin = axisLimit.minimum;
+ float axisDef = axisLimit.middle;
+ float axisMax = axisLimit.maximum;
+ float lower = tent.minimum;
+ float peak = tent.middle;
+ float upper = tent.maximum;
+
+ assert (-1.f <= axisMin && axisMin <= axisDef && axisDef <= axisMax && axisMax <= +1.f);
+ assert (-2.f <= lower && lower <= peak && peak <= upper && upper <= +2.f);
+ assert (peak != 0.f);
+
+ result_t sols = _solve (tent, axisLimit);
+
+#if 0
+ // XXX
+ n = lambda v: normalizeValue(v, axisLimit, extrapolate=True)
+ sols = [
+ (scalar, (n(v[0]), n(v[1]), n(v[2])) if v is not None else None)
+ for scalar, v in sols
+ if scalar
+ ]
+#endif
+
+ return sols;
+}
diff --git a/src/meson.build b/src/meson.build
index b678b5b..27d9a31 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -353,6 +353,7 @@
'hb-subset-cff2.hh',
'hb-subset-input.cc',
'hb-subset-input.hh',
+ 'hb-subset-instancer-solver.cc',
'hb-subset-plan.cc',
'hb-subset-plan.hh',
'hb-subset-repacker.cc',
