Extra2D/include/animation/interpolation_engine.h

#pragma once

#include <cmath>
#include <animation/animation_frame.h>
#include <core/color.h>
#include <core/math_types.h>
#include <core/types.h>

namespace extra2d {

// ============================================================================
// 插值结果 - 两帧之间的插值后属性
// ============================================================================
struct InterpolatedProperties {
  Vec2 position;
  Vec2 scale = Vec2::One();
  float rotation = 0.0f;
  Color color = Colors::White;
};

// ============================================================================
// 插值曲线类型
// ============================================================================
enum class InterpolationCurve : uint8 {
  Linear,    // 线性（原始系统的 uniform velocity）
  EaseIn,    // 缓入
  EaseOut,   // 缓出
  EaseInOut, // 缓入缓出
};

// ============================================================================
// InterpolationEngine - 帧间属性插值计算（静态方法，无状态）
// 独立于 AnimationController，可复用于其他系统
// ============================================================================
class InterpolationEngine {
public:
  /// 核心插值计算：根据 t 因子 (0~1) 计算两帧之间的插值属性
  static InterpolatedProperties
  interpolate(const AnimationFrame &from, const AnimationFrame &to, float t,
              InterpolationCurve curve = InterpolationCurve::Linear) {
    float curvedT = applyCurve(t, curve);

    InterpolatedProperties result;
    result.position = lerpPosition(from, to, curvedT);
    result.scale = lerpScale(from, to, curvedT);
    result.rotation = lerpRotation(from, to, curvedT);
    result.color = lerpColor(from, to, curvedT);
    return result;
  }

  /// 位置插值
  static Vec2 lerpPosition(const AnimationFrame &from, const AnimationFrame &to,
                           float t) {
    return Vec2::lerp(from.offset, to.offset, t);
  }

  /// 缩放插值
  static Vec2 lerpScale(const AnimationFrame &from, const AnimationFrame &to,
                        float t) {
    Vec2 fromScale = from.getEffectiveScale();
    Vec2 toScale = to.getEffectiveScale();
    return Vec2::lerp(fromScale, toScale, t);
  }

  /// 旋转插值
  static float lerpRotation(const AnimationFrame &from,
                            const AnimationFrame &to, float t) {
    float fromRot = from.getEffectiveRotation();
    float toRot = to.getEffectiveRotation();
    return math::lerp(fromRot, toRot, t);
  }

  /// 颜色插值
  static Color lerpColor(const AnimationFrame &from, const AnimationFrame &to,
                         float t) {
    Color fromColor = from.getEffectiveColor();
    Color toColor = to.getEffectiveColor();
    return Color::lerp(fromColor, toColor, t);
  }

  /// 应用曲线函数
  static float applyCurve(float t, InterpolationCurve curve) {
    t = math::clamp(t, 0.0f, 1.0f);

    switch (curve) {
    case InterpolationCurve::Linear:
      return t;

    case InterpolationCurve::EaseIn:
      return t * t;

    case InterpolationCurve::EaseOut:
      return t * (2.0f - t);

    case InterpolationCurve::EaseInOut:
      if (t < 0.5f)
        return 2.0f * t * t;
      else
        return -1.0f + (4.0f - 2.0f * t) * t;
    }

    return t;
  }
};

} // namespace extra2d