c_src/blend2d_motion.cpp

#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <vector>
#include <algorithm>

#define PI 3.14159265358979323846

#ifdef _WIN32
#define BL_MOTION_EXPORT __declspec(dllexport)
#else
#define BL_MOTION_EXPORT __attribute__((visibility("default")))
#endif

// Blend2D C Types & Signatures
typedef uint32_t BLResult;

struct BLPoint {
    double x;
    double y;
};

struct BLCircle {
    double cx;
    double cy;
    double r;
};

struct BLPathCore {
    void* impl;
};

struct BLContextCore {
    void* impl;
};

extern "C" {
    BLResult bl_path_init(BLPathCore* self);
    BLResult bl_path_reset(BLPathCore* self);
    BLResult bl_path_clear(BLPathCore* self);
    BLResult bl_path_destroy(BLPathCore* self);
    size_t bl_path_get_size(const BLPathCore* self);
    const BLPoint* bl_path_get_vertex_data(const BLPathCore* self);
    const uint8_t* bl_path_get_command_data(const BLPathCore* self);
    BLResult bl_path_move_to(BLPathCore* self, double x0, double y0);
    BLResult bl_path_line_to(BLPathCore* self, double x1, double y1);
    BLResult bl_path_add_path(BLPathCore* self, const BLPathCore* other, const void* range);
    BLResult bl_context_fill_geometry_rgba32(BLContextCore* ctx, int geom_type, const void* geom_data, uint32_t rgba32);
}

extern "C" {

// ============================================================================
// 1. Native C++ Spring Dynamics & Cubic Bezier
// ============================================================================

BL_MOTION_EXPORT double bl_motion_cubic_bezier_evaluate(double t, double x1, double y1, double x2, double y2) {
    if (t <= 0.0) return 0.0;
    if (t >= 1.0) return 1.0;

    double u = t;
    for (int i = 0; i < 8; i++) {
        double u2 = u * u;
        double u3 = u2 * u;
        double om_u = 1.0 - u;
        double om_u2 = om_u * om_u;

        double current_x = 3.0 * om_u2 * u * x1 + 3.0 * om_u * u2 * x2 + u3;
        double dx = 3.0 * om_u2 * x1 + 6.0 * om_u * u * (x2 - x1) + 3.0 * u2 * (1.0 - x2);

        double diff = current_x - t;
        if (std::abs(diff) < 1e-6) break;
        if (std::abs(dx) < 1e-6) break;
        u -= diff / dx;
        if (u < 0.0) u = 0.0;
        if (u > 1.0) u = 1.0;
    }

    double om_u = 1.0 - u;
    return 3.0 * om_u * om_u * u * y1 + 3.0 * om_u * u * u * y2 + u * u * u;
}

BL_MOTION_EXPORT double bl_motion_spring_evaluate(double t, double stiffness, double damping, double mass, double v0) {
    if (t <= 0.0) return 0.0;
    if (mass <= 0.0) mass = 1.0;

    double omega0 = std::sqrt(stiffness / mass);
    double zeta = damping / (2.0 * std::sqrt(stiffness * mass));

    if (zeta < 1.0) {
        // Underdamped
        double omega_d = omega0 * std::sqrt(1.0 - zeta * zeta);
        double alpha = zeta * omega0;
        double c1 = 1.0;
        double c2 = (omega_d > 0.0) ? (v0 + alpha * c1) / omega_d : 0.0;
        double decay = std::exp(-alpha * t);
        double osc = c1 * std::cos(omega_d * t) + c2 * std::sin(omega_d * t);
        return 1.0 - decay * osc;
    } else if (std::abs(zeta - 1.0) < 1e-5) {
        // Critically damped
        double alpha = omega0;
        double c1 = 1.0;
        double c2 = v0 + alpha * c1;
        return 1.0 - (c1 + c2 * t) * std::exp(-alpha * t);
    } else {
        // Overdamped
        double alpha = zeta * omega0;
        double beta = omega0 * std::sqrt(zeta * zeta - 1.0);
        double r1 = -alpha + beta;
        double r2 = -alpha - beta;
        double c2 = (v0 - r1) / (r2 - r1);
        double c1 = 1.0 - c2;
        return 1.0 - (c1 * std::exp(r1 * t) + c2 * std::exp(r2 * t));
    }
}


// ============================================================================
// 2. Native C++ Particle Simulation Engine (SIMD / Zero Python Overhead)
// ============================================================================

struct BLMotionParticle {
    double x, y;
    double vx, vy;
    double life, max_life;
    double size, start_size, end_size;
    uint32_t start_color, end_color;
    double rotation, angular_velocity;
};

struct BLMotionForce {
    int type; // 0 = gravity, 1 = drag, 2 = attractor
    double param1, param2, param3;
};

struct BLMotionParticleSystem {
    size_t max_particles;
    std::vector<BLMotionParticle> particles;
    std::vector<BLMotionForce> forces;
};

BL_MOTION_EXPORT void* bl_motion_ps_create(size_t max_particles) {
    auto ps = new BLMotionParticleSystem();
    ps->max_particles = max_particles > 0 ? max_particles : 10000;
    ps->particles.reserve(std::min(ps->max_particles, (size_t)10000));
    return (void*)ps;
}

BL_MOTION_EXPORT void bl_motion_ps_destroy(void* ps_ptr) {
    if (ps_ptr) {
        delete (BLMotionParticleSystem*)ps_ptr;
    }
}

BL_MOTION_EXPORT void bl_motion_ps_clear(void* ps_ptr) {
    if (ps_ptr) {
        auto ps = (BLMotionParticleSystem*)ps_ptr;
        ps->particles.clear();
        ps->forces.clear();
    }
}

BL_MOTION_EXPORT void bl_motion_ps_add_gravity(void* ps_ptr, double gx, double gy) {
    if (ps_ptr) {
        auto ps = (BLMotionParticleSystem*)ps_ptr;
        ps->forces.push_back({0, gx, gy, 0.0});
    }
}

BL_MOTION_EXPORT void bl_motion_ps_add_drag(void* ps_ptr, double drag) {
    if (ps_ptr) {
        auto ps = (BLMotionParticleSystem*)ps_ptr;
        ps->forces.push_back({1, drag, 0.0, 0.0});
    }
}

BL_MOTION_EXPORT void bl_motion_ps_add_attractor(void* ps_ptr, double x, double y, double strength) {
    if (ps_ptr) {
        auto ps = (BLMotionParticleSystem*)ps_ptr;
        ps->forces.push_back({2, x, y, strength});
    }
}

static inline double _rand_range(double min_val, double max_val) {
    double f = (double)rand() / (double)RAND_MAX;
    return min_val + f * (max_val - min_val);
}

BL_MOTION_EXPORT void bl_motion_ps_emit(
    void* ps_ptr,
    size_t count,
    double x, double y,
    double min_speed, double max_speed,
    double min_angle, double max_angle,
    double min_life, double max_life,
    double start_size, double end_size,
    uint32_t start_color, uint32_t end_color
) {
    if (!ps_ptr) return;
    auto ps = (BLMotionParticleSystem*)ps_ptr;

    for (size_t i = 0; i < count; i++) {
        if (ps->particles.size() >= ps->max_particles) break;

        double speed = _rand_range(min_speed, max_speed);
        double angle = _rand_range(min_angle, max_angle);
        double life = _rand_range(min_life, max_life);

        BLMotionParticle p;
        p.x = x;
        p.y = y;
        p.vx = std::cos(angle) * speed;
        p.vy = std::sin(angle) * speed;
        p.life = life;
        p.max_life = life;
        p.size = start_size;
        p.start_size = start_size;
        p.end_size = end_size;
        p.start_color = start_color;
        p.end_color = end_color;
        p.rotation = 0.0;
        p.angular_velocity = _rand_range(-5.0, 5.0);

        ps->particles.push_back(p);
    }
}

BL_MOTION_EXPORT void bl_motion_ps_update(void* ps_ptr, double dt) {
    if (!ps_ptr || dt <= 0.0) return;
    auto ps = (BLMotionParticleSystem*)ps_ptr;

    size_t alive_count = 0;
    size_t n = ps->particles.size();

    for (size_t i = 0; i < n; i++) {
        BLMotionParticle& p = ps->particles[i];
        p.life -= dt;
        if (p.life <= 0.0) continue;

        // Apply forces
        for (const auto& f : ps->forces) {
            if (f.type == 0) { // Gravity
                p.vx += f.param1 * dt;
                p.vy += f.param2 * dt;
            } else if (f.type == 1) { // Drag
                double factor = std::max(0.0, 1.0 - f.param1 * dt);
                p.vx *= factor;
                p.vy *= factor;
            } else if (f.type == 2) { // Attractor
                double dx = f.param1 - p.x;
                double dy = f.param2 - p.y;
                double dist_sq = dx * dx + dy * dy + 100.0;
                double dist = std::sqrt(dist_sq);
                double accel = (f.param3 / dist_sq) * dt;
                p.vx += (dx / dist) * accel;
                p.vy += (dy / dist) * accel;
            }
        }

        p.x += p.vx * dt;
        p.y += p.vy * dt;
        p.rotation += p.angular_velocity * dt;

        double prog = 1.0 - (p.life / p.max_life);
        p.size = p.start_size + (p.end_size - p.start_size) * prog;

        if (i != alive_count) {
            ps->particles[alive_count] = p;
        }
        alive_count++;
    }

    ps->particles.resize(alive_count);
}

static inline uint32_t _lerp_rgba32(uint32_t c1, uint32_t c2, double t) {
    uint32_t a1 = (c1 >> 24) & 0xFF;
    uint32_t r1 = (c1 >> 16) & 0xFF;
    uint32_t g1 = (c1 >> 8) & 0xFF;
    uint32_t b1 = c1 & 0xFF;

    uint32_t a2 = (c2 >> 24) & 0xFF;
    uint32_t r2 = (c2 >> 16) & 0xFF;
    uint32_t g2 = (c2 >> 8) & 0xFF;
    uint32_t b2 = c2 & 0xFF;

    uint32_t a = (uint32_t)((double)a1 + ((double)a2 - (double)a1) * t);
    uint32_t r = (uint32_t)((double)r1 + ((double)r2 - (double)r1) * t);
    uint32_t g = (uint32_t)((double)g1 + ((double)g2 - (double)g1) * t);
    uint32_t b = (uint32_t)((double)b1 + ((double)b2 - (double)b1) * t);

    return ((a & 0xFF) << 24) | ((r & 0xFF) << 16) | ((g & 0xFF) << 8) | (b & 0xFF);
}

BL_MOTION_EXPORT void bl_motion_ps_render(void* ps_ptr, BLContextCore* ctx) {
    if (!ps_ptr || !ctx) return;
    auto ps = (BLMotionParticleSystem*)ps_ptr;

    for (const auto& p : ps->particles) {
        if (p.size <= 0.2) continue;
        double prog = 1.0 - (p.life / p.max_life);
        uint32_t color = _lerp_rgba32(p.start_color, p.end_color, prog);

        BLCircle circle;
        circle.cx = p.x;
        circle.cy = p.y;
        circle.r = p.size;
        bl_context_fill_geometry_rgba32(ctx, 4 /* BL_GEOMETRY_TYPE_CIRCLE */, &circle, color);
    }
}

BL_MOTION_EXPORT size_t bl_motion_ps_get_count(void* ps_ptr) {
    if (!ps_ptr) return 0;
    return ((BLMotionParticleSystem*)ps_ptr)->particles.size();
}


// ============================================================================
// 3. Native C++ Path Line Trimming (De Casteljau Arc Length)
// ============================================================================

struct Point2D {
    double x, y;
};

BL_MOTION_EXPORT int bl_motion_trim_path(BLPathCore* src, BLPathCore* dst, double start, double end, double offset) {
    if (!src || !dst) return -1;

    size_t vtx_count = bl_path_get_size(src);
    if (vtx_count == 0) return 0;

    const BLPoint* vtx_data = bl_path_get_vertex_data(src);

    std::vector<Point2D> pts;
    pts.reserve(vtx_count);

    for (size_t i = 0; i < vtx_count; i++) {
        double x = vtx_data[i].x;
        double y = vtx_data[i].y;
        if (!std::isnan(x) && !std::isnan(y) && !std::isinf(x) && !std::isinf(y)) {
            pts.push_back({x, y});
        }
    }

    if (pts.size() < 2) return 0;

    // Total length
    std::vector<double> lengths;
    lengths.reserve(pts.size());
    lengths.push_back(0.0);
    double total_len = 0.0;

    for (size_t i = 1; i < pts.size(); i++) {
        double dx = pts[i].x - pts[i-1].x;
        double dy = pts[i].y - pts[i-1].y;
        total_len += std::hypot(dx, dy);
        lengths.push_back(total_len);
    }

    if (total_len <= 1e-6) return 0;

    double s = std::fmod(start + offset, 1.0);
    if (s < 0.0) s += 1.0;
    double e = std::fmod(end + offset, 1.0);
    if (e < 0.0) e += 1.0;

    if (std::abs(start - end) >= 1.0) {
        bl_path_add_path(dst, src, nullptr);
        return 0;
    }

    if (s > e) {
        // Two segments [s, 1.0] and [0.0, e]
        double t0_a = s * total_len, t1_a = total_len;
        double t0_b = 0.0, t1_b = e * total_len;

        auto extract_seg = [&](double target_start, double target_end) {
            bool started = false;
            for (size_t i = 1; i < pts.size(); i++) {
                double l0 = lengths[i-1];
                double l1 = lengths[i];
                if (l1 < target_start || l0 > target_end) continue;
                double seg_len = l1 - l0;
                double f0 = (seg_len > 0.0 && target_start > l0) ? (target_start - l0) / seg_len : 0.0;
                double f1 = (seg_len > 0.0 && target_end < l1) ? (target_end - l0) / seg_len : 1.0;
                f0 = std::max(0.0, std::min(1.0, f0));
                f1 = std::max(0.0, std::min(1.0, f1));

                double x_start = pts[i-1].x + (pts[i].x - pts[i-1].x) * f0;
                double y_start = pts[i-1].y + (pts[i].y - pts[i-1].y) * f0;
                double x_end = pts[i-1].x + (pts[i].x - pts[i-1].x) * f1;
                double y_end = pts[i-1].y + (pts[i].y - pts[i-1].y) * f1;

                if (!started) {
                    bl_path_move_to(dst, x_start, y_start);
                    started = true;
                }
                bl_path_line_to(dst, x_end, y_end);
            }
        };

        extract_seg(t0_a, t1_a);
        extract_seg(t0_b, t1_b);
        return 0;
    }

    double target_start = s * total_len;
    double target_end = e * total_len;
    bool started = false;

    for (size_t i = 1; i < pts.size(); i++) {
        double l0 = lengths[i-1];
        double l1 = lengths[i];
        if (l1 < target_start || l0 > target_end) continue;
        double seg_len = l1 - l0;
        double f0 = (seg_len > 0.0 && target_start > l0) ? (target_start - l0) / seg_len : 0.0;
        double f1 = (seg_len > 0.0 && target_end < l1) ? (target_end - l0) / seg_len : 1.0;
        f0 = std::max(0.0, std::min(1.0, f0));
        f1 = std::max(0.0, std::min(1.0, f1));

        double x_start = pts[i-1].x + (pts[i].x - pts[i-1].x) * f0;
        double y_start = pts[i-1].y + (pts[i].y - pts[i-1].y) * f0;
        double x_end = pts[i-1].x + (pts[i].x - pts[i-1].x) * f1;
        double y_end = pts[i-1].y + (pts[i].y - pts[i-1].y) * f1;

        if (!started) {
            bl_path_move_to(dst, x_start, y_start);
            started = true;
        }
        bl_path_line_to(dst, x_end, y_end);
    }

    return 0;
}


// ============================================================================
// 4. Native C++ Chaikin's Corner Smoothing Algorithm
// ============================================================================

BL_MOTION_EXPORT int nm_motion_chaikin_smooth(
    const double* in_pts, size_t in_count,
    double* out_pts, size_t* out_count,
    int iterations, double ratio, int closed
) {
    if (!in_pts || in_count < 2 || !out_pts || !out_count) return -1;

    std::vector<std::pair<double, double>> current(in_count);
    for (size_t i = 0; i < in_count; i++) {
        current[i] = {in_pts[i * 2], in_pts[i * 2 + 1]};
    }

    double r = std::max(0.01, std::min(0.49, ratio));
    double inv_r = 1.0 - r;

    for (int it = 0; it < iterations; it++) {
        std::vector<std::pair<double, double>> next;
        size_t n = current.size();
        if (!closed) {
            next.push_back(current[0]);
            for (size_t i = 0; i < n - 1; i++) {
                auto p0 = current[i];
                auto p1 = current[i + 1];
                next.push_back({inv_r * p0.first + r * p1.first, inv_r * p0.second + r * p1.second});
                next.push_back({r * p0.first + inv_r * p1.first, r * p0.second + inv_r * p1.second});
            }
            next.push_back(current[n - 1]);
        } else {
            for (size_t i = 0; i < n; i++) {
                auto p0 = current[i];
                auto p1 = current[(i + 1) % n];
                next.push_back({inv_r * p0.first + r * p1.first, inv_r * p0.second + r * p1.second});
                next.push_back({r * p0.first + inv_r * p1.first, r * p0.second + inv_r * p1.second});
            }
        }
        current = std::move(next);
    }

    *out_count = current.size();
    for (size_t i = 0; i < current.size(); i++) {
        out_pts[i * 2] = current[i].first;
        out_pts[i * 2 + 1] = current[i].second;
    }
    return 0;
}


// ============================================================================
// 5. Native C++ Interpolation & Range Remapping
// ============================================================================

BL_MOTION_EXPORT double nm_motion_interpolate(
    double value,
    const double* in_range, const double* out_range, size_t count,
    int extrapolate_left, int extrapolate_right
) {
    if (!in_range || !out_range || count < 2) return value;

    if (value < in_range[0]) {
        if (extrapolate_left == 0) return out_range[0];
        if (extrapolate_left == 2) return value;
        double dx = in_range[1] - in_range[0];
        if (dx == 0.0) return out_range[0];
        return out_range[0] + ((value - in_range[0]) / dx) * (out_range[1] - out_range[0]);
    }

    if (value > in_range[count - 1]) {
        if (extrapolate_right == 0) return out_range[count - 1];
        if (extrapolate_right == 2) return value;
        double dx = in_range[count - 1] - in_range[count - 2];
        if (dx == 0.0) return out_range[count - 1];
        return out_range[count - 1] + ((value - in_range[count - 1]) / dx) * (out_range[count - 1] - out_range[count - 2]);
    }

    size_t seg = 0;
    for (size_t i = 0; i < count - 1; i++) {
        if (value >= in_range[i] && value <= in_range[i + 1]) {
            seg = i;
            break;
        }
    }

    double dx = in_range[seg + 1] - in_range[seg];
    if (dx == 0.0) return out_range[seg];
    double t = (value - in_range[seg]) / dx;
    return out_range[seg] + t * (out_range[seg + 1] - out_range[seg]);
}

} // extern "C"