tools/logic_tests_m2m4.cpp

// FCS Glass - tools/logic_tests_m2m4.cpp
//
// Tests for src/core/{spring,atlas,glyph_cache,sdf}. Compiles against the REAL headers
// (the B-06 route), so there is no extraction step and the same file builds under MSVC
// and gcc. Windows-free by construction.
//
//   Linux:  c++ -std=c++17 -I src tools/logic_tests_m2m4.cpp src/core/spring.cpp
//             src/core/atlas.cpp src/core/glyph_cache.cpp -o /tmp/t && /tmp/t
//   MSVC:   cl /std:c++17 /W4 /EHsc /I src tools\logic_tests_m2m4.cpp src\core\spring.cpp
//             src\core\atlas.cpp src\core\glyph_cache.cpp
//
// Falsify-first: each group names the mutation that must break it (see the review note).

#include <cmath>
#include <cstdint>
#include <cstdio>
#include <limits>
#include <unordered_set>
#include <vector>

#include "core/atlas.h"
#include "core/glyph_cache.h"
#include "core/sdf.h"
#include "core/spring.h"

using namespace fcs::core;

static int g_pass = 0;
static int g_fail = 0;

#define CHECK(cond)                                                   \
  do {                                                                \
    if (cond) {                                                       \
      ++g_pass;                                                       \
    } else {                                                          \
      ++g_fail;                                                       \
      std::printf("FAIL %s:%d  %s\n", __FILE__, __LINE__, #cond);     \
    }                                                                 \
  } while (0)
#define CHECK_NEAR(a, b, eps) CHECK(std::fabs((a) - (b)) <= (eps))

namespace {

const SpringRest kNoRest = {0.0, 0.0};   // never snaps: lets a test see the raw trajectory

Spring Make(double zeta, double freq, double x0, double target, double v0, bool no_rest) {
  Spring s(x0);
  SpringParams p;
  p.freq_hz = freq;
  p.damping = zeta;
  s.SetParams(p);
  if (no_rest) s.SetRest(kNoRest);
  s.SetTarget(target);
  if (v0 != 0.0) s.Kick(v0);
  return s;
}

// Independent reference: RK4 on d'' = -2 z w d' - w^2 d, fine fixed step.
void Rk4(double z, double freq, double d0, double v0, double t_end, double* d_out, double* v_out) {
  const double w = 2.0 * 3.14159265358979323846 * freq;
  double d = d0;
  double v = v0;
  const double h = 1e-5;
  const long n = static_cast<long>(t_end / h + 0.5);
  auto acc = [&](double dd, double vv) { return -2.0 * z * w * vv - w * w * dd; };
  for (long i = 0; i < n; ++i) {
    const double k1d = v, k1v = acc(d, v);
    const double k2d = v + 0.5 * h * k1v, k2v = acc(d + 0.5 * h * k1d, v + 0.5 * h * k1v);
    const double k3d = v + 0.5 * h * k2v, k3v = acc(d + 0.5 * h * k2d, v + 0.5 * h * k2v);
    const double k4d = v + h * k3v, k4v = acc(d + h * k3d, v + h * k3v);
    d += h / 6.0 * (k1d + 2 * k2d + 2 * k3d + k4d);
    v += h / 6.0 * (k1v + 2 * k2v + 2 * k3v + k4v);
  }
  *d_out = d;
  *v_out = v;
}

void TestSpring() {
  // S1: critical damping from rest never overshoots and never moves backwards.
  {
    Spring s = Make(1.0, 4.0, 0.0, 1.0, 0.0, true);
    double prev = s.value();
    bool mono = true;
    bool under = true;
    for (int i = 0; i < 480; ++i) {
      s.Step(1.0 / 240.0);
      if (s.value() < prev - 1e-12) mono = false;
      if (s.value() > 1.0 + 1e-12) under = false;
      prev = s.value();
    }
    CHECK(mono);
    CHECK(under);
    CHECK(s.value() > 0.999999);
  }
  // S2: under-damped overshoots by the textbook amount, exp(-pi z / sqrt(1 - z^2)).
  {
    const double z = 0.3;
    Spring s = Make(z, 4.0, 0.0, 1.0, 0.0, true);
    double peak = 0.0;
    for (int i = 0; i < 6000; ++i) {
      s.Step(1.0 / 4000.0);
      if (s.value() > peak) peak = s.value();
    }
    const double expect = 1.0 + std::exp(-3.14159265358979323846 * z / std::sqrt(1.0 - z * z));
    CHECK_NEAR(peak, expect, 1e-3);
  }
  // S3: over-damped never overshoots and is slower than critical at the same instant.
  {
    Spring over = Make(2.0, 4.0, 0.0, 1.0, 0.0, true);
    Spring crit = Make(1.0, 4.0, 0.0, 1.0, 0.0, true);
    bool no_over = true;
    for (int i = 0; i < 120; ++i) {
      over.Step(1.0 / 240.0);
      crit.Step(1.0 / 240.0);
      if (over.value() > 1.0 + 1e-12) no_over = false;
    }
    CHECK(no_over);
    CHECK(over.value() < crit.value());
  }
  // S4: path independence. Ten small steps equal one big step, in every regime, with a
  // non-zero initial velocity. (A semi-implicit Euler step fails this.)
  {
    const double zs[] = {0.3, 1.0, 2.5};
    for (double z : zs) {
      Spring a = Make(z, 3.0, 0.0, 2.0, 3.0, true);
      Spring b = Make(z, 3.0, 0.0, 2.0, 3.0, true);
      for (int i = 0; i < 10; ++i) a.Step(0.016);
      b.Step(0.16);
      CHECK_NEAR(a.value(), b.value(), 1e-9);
      CHECK_NEAR(a.velocity(), b.velocity(), 1e-8);
    }
  }
  // S5: agrees with an independent RK4 integration, in every regime.
  {
    const double zs[] = {0.3, 1.0, 2.5};
    for (double z : zs) {
      Spring s = Make(z, 3.0, 0.0, 2.0, 3.0, true);
      s.Step(0.7);
      double d = 0.0;
      double v = 0.0;
      Rk4(z, 3.0, -2.0, 3.0, 0.7, &d, &v);
      CHECK_NEAR(s.value() - 2.0, d, 1e-7);
      CHECK_NEAR(s.velocity(), v, 1e-6);
    }
  }
  // S6: a spring settles EXACTLY on its target and reports it (R6 depends on this).
  {
    const double zs[] = {0.3, 1.0, 2.5};
    for (double z : zs) {
      Spring s = Make(z, 4.0, 0.0, 100.0, 0.0, false);
      CHECK(s.Active());
      s.Step(10.0);
      CHECK(!s.Active());
      CHECK(s.value() == 100.0);
      CHECK(s.velocity() == 0.0);
    }
  }
  // S7: waking. Re-aiming at the same target does not wake a settled spring; a new one does.
  {
    Spring s = Make(1.0, 4.0, 0.0, 100.0, 0.0, false);
    s.Step(10.0);
    s.SetTarget(100.0);
    CHECK(!s.Active());
    s.SetTarget(101.0);
    CHECK(s.Active());
    s.Reset(5.0);
    CHECK(!s.Active() && s.value() == 5.0 && s.target() == 5.0);
  }
  // S8: a bad clock cannot corrupt state.
  {
    Spring s = Make(0.5, 4.0, 0.0, 1.0, 0.0, false);
    s.Step(0.05);
    const double x = s.value();
    const double v = s.velocity();
    const double bad[] = {0.0, -1.0, std::numeric_limits<double>::quiet_NaN(),
                          std::numeric_limits<double>::infinity()};
    for (double dt : bad) {
      s.Step(dt);
      CHECK(s.value() == x && s.velocity() == v && s.Active());
    }
  }
  // S9: no restoring force (zero or NaN frequency) arrives at once instead of hanging.
  {
    Spring z0 = Make(1.0, 0.0, 0.0, 5.0, 0.0, false);
    z0.Step(0.016);
    CHECK(!z0.Active() && z0.value() == 5.0);
    Spring zn = Make(1.0, std::numeric_limits<double>::quiet_NaN(), 0.0, 5.0, 0.0, false);
    zn.Step(0.016);
    CHECK(!zn.Active() && zn.value() == 5.0);
  }
  // S10: no numerical blow-up next to critical damping.
  {
    Spring ref = Make(1.0, 3.0, 0.0, 2.0, 3.0, true);
    ref.Step(0.3);
    const double zs[] = {1.0 - 1e-7, 1.0 + 1e-7, 1.0 + 1e-5, 1.0 - 1e-5};
    const double tol[] = {1e-6, 1e-6, 1e-3, 1e-3};
    for (int i = 0; i < 4; ++i) {
      Spring s = Make(zs[i], 3.0, 0.0, 2.0, 3.0, true);
      s.Step(0.3);
      CHECK(std::isfinite(s.value()));
      CHECK_NEAR(s.value(), ref.value(), tol[i]);
    }
  }
  // S11: a bad damping value cannot make a perpetual oscillator (idle loop must be able to sleep).
  {
    const double bad[] = {0.0, -3.0, std::numeric_limits<double>::quiet_NaN()};
    for (double zd : bad) {
      Spring s = Make(zd, 4.0, 0.0, 1.0, 0.0, false);
      int steps = 0;
      while (s.Active() && steps < 3600) {
        s.Step(1.0 / 60.0);
        ++steps;
      }
      CHECK(!s.Active());
      CHECK(s.value() == 1.0);
    }
  }
  // S12: while far from the target it stays active (it must keep asking for frames).
  {
    Spring s = Make(1.0, 4.0, 0.0, 100.0, 0.0, false);
    s.Step(1.0 / 60.0);
    CHECK(s.Active() && s.value() > 0.0 && s.value() < 100.0);
  }
}

// ---------------------------------------------------------------------------------------
bool Disjoint(const AtlasRect& a, const AtlasRect& b, int grow) {
  return a.x - grow >= b.x + b.w + grow || b.x - grow >= a.x + a.w + grow ||
         a.y - grow >= b.y + b.h + grow || b.y - grow >= a.y + a.h + grow;
}

void TestAtlas() {
  // A1: many random sizes: all inside the atlas, none overlapping, padding respected.
  {
    const int W = 512, H = 512, P = 1;
    ShelfPacker pk(W, H, P);
    std::vector<AtlasRect> rects;
    std::uint32_t seed = 12345u;
    auto rnd = [&seed](int lo, int hi) {
      seed = seed * 1664525u + 1013904223u;
      return lo + static_cast<int>((seed >> 8) % static_cast<std::uint32_t>(hi - lo + 1));
    };
    long inner_area = 0;
    for (int i = 0; i < 5000; ++i) {
      AtlasRect r;
      const int w = rnd(4, 40), h = rnd(8, 36);
      if (!pk.Pack(w, h, &r)) break;
      rects.push_back(r);
      inner_area += static_cast<long>(w) * h;
    }
    CHECK(rects.size() > 100);
    bool inside = true;
    bool apart = true;
    for (size_t i = 0; i < rects.size(); ++i) {
      const AtlasRect& a = rects[i];
      if (a.x < P || a.y < P || a.x + a.w > W - P || a.y + a.h > H - P) inside = false;
      for (size_t j = i + 1; j < rects.size(); ++j)
        if (!Disjoint(a, rects[j], P)) apart = false;   // each grown by P: padded cells never touch
    }
    CHECK(inside);
    CHECK(apart);
    CHECK(pk.used_height() <= H);
    std::printf("  info: atlas utilisation, synthetic 4-40 x 8-36 mix: %zu rects, %.1f%% of %dx%d\n",
                rects.size(), 100.0 * static_cast<double>(inner_area) / (static_cast<double>(W) * H), W, H);
  }
  // A2: full is reported, out is zeroed.
  {
    ShelfPacker pk(20, 20, 1);
    AtlasRect r;
    CHECK(pk.Pack(18, 18, &r));
    CHECK(r.x == 1 && r.y == 1 && r.w == 18 && r.h == 18);
    r.x = 99;
    CHECK(!pk.Pack(1, 1, &r));
    CHECK(r.x == 0 && r.y == 0 && r.w == 0 && r.h == 0);
  }
  // A3: a blank glyph consumes nothing.
  {
    ShelfPacker pk(64, 64, 1);
    AtlasRect r;
    r.x = 7;
    CHECK(pk.Pack(0, 5, &r));
    CHECK(r.w == 0 && r.h == 0 && pk.used_height() == 0);
    CHECK(pk.Pack(5, -1, &r) && pk.used_height() == 0);
  }
  // A4: too wide or too tall for the atlas is refused, not wrapped or clipped.
  {
    ShelfPacker pk(20, 20, 1);
    AtlasRect r;
    CHECK(!pk.Pack(19, 5, &r));
    CHECK(!pk.Pack(5, 19, &r));
    CHECK(!pk.Pack(2000000000, 5, &r));
    CHECK(pk.Pack(18, 5, &r));
  }
  // A5: Reset starts over at the top left.
  {
    ShelfPacker pk(64, 64, 1);
    AtlasRect r;
    pk.Pack(10, 10, &r);
    pk.Pack(10, 10, &r);
    pk.Reset();
    CHECK(pk.Pack(10, 10, &r) && r.x == 1 && r.y == 1 && pk.used_height() == 12);
  }
  // A6: growing the height lets a refused bitmap in; it never shrinks, and old rects stay put.
  {
    ShelfPacker pk(20, 20, 1);
    AtlasRect first, second;
    CHECK(pk.Pack(18, 18, &first));
    CHECK(!pk.Pack(18, 18, &second));
    pk.SetMaxHeight(40);
    CHECK(pk.Pack(18, 18, &second) && second.y == 21);
    pk.SetMaxHeight(10);
    CHECK(pk.max_height() == 40);
    CHECK(first.x == 1 && first.y == 1);
  }
  // A7: a short bitmap reuses an existing tall shelf instead of opening a new one.
  {
    ShelfPacker pk(100, 100, 1);
    AtlasRect tall, shorter;
    CHECK(pk.Pack(10, 20, &tall));
    CHECK(pk.Pack(10, 8, &shorter));
    CHECK(shorter.y == tall.y && shorter.x == 13);
    CHECK(pk.used_height() == 22);
  }
}

// ---------------------------------------------------------------------------------------
GlyphKey Key(std::uint32_t face, std::uint32_t glyph, double em = 14.0, double scale = 1.5) {
  GlyphKey k;
  k.face = face;
  k.glyph = glyph;
  k.em_q = QuantizeEm(em);
  k.scale_q = QuantizeScale(scale);
  return k;
}

void TestGlyphCache() {
  // G1: insert, find, insert again returns the same slot without packing twice.
  {
    GlyphCache c(256, 256, 1);
    const GlyphSlot* a = c.Insert(Key(1, 65), 10, 12, 1, 11, 9);
    CHECK(a != nullptr && c.Find(Key(1, 65)) == a);
    CHECK(a->rect.w == 10 && a->rect.h == 12 && a->bearing_y == 11 && a->advance_px == 9);
    const int used = c.packer().used_height();
    CHECK(c.Insert(Key(1, 65), 10, 12, 1, 11, 9) == a);
    CHECK(c.size() == 1 && c.packer().used_height() == used);
    CHECK(c.Find(Key(1, 66)) == nullptr);
  }
  // G1b: a duplicate insert packs NOTHING. Width 14 holds exactly one padded 12 px cell per
  // shelf, so a wrongly re-packed duplicate would open a second shelf and the height would double.
  {
    GlyphCache c(14, 100, 1);
    CHECK(c.Insert(Key(1, 65), 12, 12, 0, 0, 12) != nullptr);
    CHECK(c.packer().used_height() == 14);
    CHECK(c.Insert(Key(1, 65), 12, 12, 0, 0, 12) != nullptr);
    CHECK(c.packer().used_height() == 14);
    CHECK(c.Insert(Key(1, 66), 12, 12, 0, 0, 12) != nullptr);
    CHECK(c.packer().used_height() == 28);
  }
  // G2: the hash is order dependent (a plain xor would collide on this swap).
  {
    GlyphKeyHash h;
    CHECK(h(Key(1, 2)) != h(Key(2, 1)));
    CHECK(h(Key(1, 2, 14.0, 1.5)) != h(Key(1, 2, 14.0, 2.0)));
    CHECK(h(Key(1, 2, 14.0, 1.5)) != h(Key(1, 2, 16.0, 1.5)));
    GlyphKey sub = Key(1, 2);
    sub.subpx = 1;
    CHECK(h(sub) != h(Key(1, 2)));
    std::unordered_set<std::size_t> seen;
    for (std::uint32_t f = 0; f < 4; ++f)
      for (std::uint32_t g = 0; g < 5000; ++g) seen.insert(h(Key(f, g)));
    CHECK(seen.size() >= 20000 - 2);
  }
  // G3: quantization keeps the spec's scales exact and absorbs float noise.
  {
    CHECK(QuantizeScale(1.0) == 256 && QuantizeScale(1.25) == 320 && QuantizeScale(1.5) == 384);
    CHECK(QuantizeScale(1.75) == 448 && QuantizeScale(2.0) == 512 && QuantizeScale(2.5) == 640);
    CHECK(QuantizeScale(1.5000001) == 384 && QuantizeScale(1.4999999) == 384);
    CHECK(QuantizeEm(14.0) == 224 && QuantizeEm(12.0) == 192);
    CHECK(QuantizeScale(0.0) == 1 && QuantizeScale(-2.0) == 1);
    CHECK(QuantizeScale(std::numeric_limits<double>::quiet_NaN()) == 1);
    CHECK(QuantizeScale(1e9) == 65535 && QuantizeEm(1e9) == 65535);
  }
  // G4: a full atlas reports, keeps earlier slots valid, and recovers on Flush.
  {
    GlyphCache c(64, 64, 1);
    const GlyphSlot* first = c.Insert(Key(1, 0), 12, 12, 0, 0, 12);
    CHECK(first != nullptr);
    const AtlasRect first_rect = first->rect;
    int ok = 1;
    std::uint32_t g = 1;
    while (c.Insert(Key(1, g), 12, 12, 0, 0, 12) != nullptr && g < 100) {
      ++ok;
      ++g;
    }
    CHECK(ok == 16);                       // four 14 px cells per shelf, four shelves
    CHECK(c.overflowed());
    CHECK(c.Find(Key(1, 0)) == first);     // pointer still valid after many inserts
    CHECK(first->rect.x == first_rect.x && first->rect.y == first_rect.y);
    const unsigned gen = c.generation();
    c.Flush();
    CHECK(c.size() == 0 && !c.overflowed() && c.generation() == gen + 1);
    CHECK(c.Find(Key(1, 0)) == nullptr);
    CHECK(c.Insert(Key(1, 0), 12, 12, 0, 0, 12) != nullptr);
  }
  // G5: a blank glyph is cached with its advance and costs no atlas space.
  {
    GlyphCache c(64, 64, 1);
    const GlyphSlot* sp = c.Insert(Key(1, 32), 0, 0, 0, 0, 7);
    CHECK(sp != nullptr && sp->rect.w == 0 && sp->rect.h == 0 && sp->advance_px == 7);
    CHECK(c.packer().used_height() == 0 && !c.overflowed());
  }
}

// ---------------------------------------------------------------------------------------
void TestSdf() {
  const float hx = 50.0f, hy = 30.0f, r = 8.0f, bw = 1.0f;
  PremulColor fill;
  fill.a = 0.35f;
  PremulColor border;
  border.r = border.g = border.b = 0.10f;
  border.a = 0.10f;

  // D1: distance values at known points.
  CHECK_NEAR(SdRoundRect(0, 0, hx, hy, r), -30.0f, 1e-5f);
  CHECK_NEAR(SdRoundRect(50, 0, hx, hy, r), 0.0f, 1e-5f);
  CHECK_NEAR(SdRoundRect(0, 30, hx, hy, r), 0.0f, 1e-5f);
  const float arc = 0.70710678f * r;
  CHECK_NEAR(SdRoundRect(hx - r + arc, hy - r + arc, hx, hy, r), 0.0f, 1e-5f);   // on the arc
  CHECK_NEAR(SdRoundRect(50, 30, hx, hy, r), r * (1.41421356f - 1.0f), 1e-4f);   // sharp corner is outside
  // D2: symmetric in both axes.
  CHECK_NEAR(SdRoundRect(13, 7, hx, hy, r), SdRoundRect(-13, 7, hx, hy, r), 1e-6f);
  CHECK_NEAR(SdRoundRect(13, 7, hx, hy, r), SdRoundRect(13, -7, hx, hy, r), 1e-6f);
  CHECK_NEAR(SdRoundRect(13, 7, hx, hy, r), SdRoundRect(-13, -7, hx, hy, r), 1e-6f);
  // D3: an oversized radius degrades to a pill; the edge stays an edge.
  CHECK_NEAR(SdRoundRect(0, 0, hx, hy, 1000.0f), -30.0f, 1e-5f);
  CHECK_NEAR(SdRoundRect(50, 0, hx, hy, 1000.0f), 0.0f, 1e-5f);
  CHECK_NEAR(SdRoundRect(0, 0, hx, hy, -5.0f), -30.0f, 1e-5f);   // negative radius = square corners
  // D4: distance grows monotonically walking out along +x.
  {
    bool mono = true;
    float prev = SdRoundRect(0, 0, hx, hy, r);
    for (int i = 1; i <= 70; ++i) {
      const float d = SdRoundRect(static_cast<float>(i), 0, hx, hy, r);
      if (d < prev) mono = false;
      prev = d;
    }
    CHECK(mono);
  }
  // D5: panel colours at the pixel offsets that matter.
  {
    const PremulColor mid = PanelColor(-30.0f, bw, fill, border);          // deep inside: pure fill
    CHECK_NEAR(mid.a, 0.35f, 1e-6f);
    const PremulColor edge = PanelColor(0.0f, bw, fill, border);           // on the edge: half the border
    CHECK_NEAR(edge.a, 0.05f, 1e-6f);
    const PremulColor ring = PanelColor(-0.5f, bw, fill, border);          // centre of a 1 px ring: pure border
    CHECK_NEAR(ring.a, 0.10f, 1e-6f);
    CHECK_NEAR(ring.r, 0.10f, 1e-6f);
    const PremulColor inner = PanelColor(-1.0f, bw, fill, border);         // inner edge of the ring: half and half
    CHECK_NEAR(inner.a, 0.5f * 0.35f + 0.5f * 0.10f, 1e-6f);
    const PremulColor out = PanelColor(0.5f, bw, fill, border);            // just outside: nothing
    CHECK(out.a == 0.0f && out.r == 0.0f);
    const PremulColor far = PanelColor(5.0f, bw, fill, border);
    CHECK(far.a == 0.0f);
  }
  // D6: the output stays a valid premultiplied colour everywhere (rgb <= a, a in 0..1).
  {
    bool valid = true;
    for (int i = -4000; i <= 500; ++i) {
      const PremulColor c = PanelColor(static_cast<float>(i) * 0.01f, bw, fill, border);
      if (c.a < 0.0f || c.a > 1.0f || c.r > c.a + 1e-6f || c.g > c.a + 1e-6f || c.b > c.a + 1e-6f)
        valid = false;
    }
    CHECK(valid);
  }
  // D7: a wider ring keeps its width: at d = -(bw/2) the ring is fully covered for any bw >= 1.
  {
    const PremulColor c = PanelColor(-1.5f, 3.0f, fill, border);
    CHECK_NEAR(c.a, 0.10f, 1e-6f);
  }
}

}  // namespace

int main() {
  TestSpring();
  TestAtlas();
  TestGlyphCache();
  TestSdf();
  std::printf("m2m4 core: %d PASS / %d FAIL\n", g_pass, g_fail);
  return g_fail == 0 ? 0 : 1;
}