3.8 -> 4.2 版本转换在 rotate 处理上的行为不符合预期

[Hajimary]

在处理 RotateTimeline 的逻辑中：

• 3.8
  

  SpineSkeletonDataConverter/spine/spine-cpp-38/src/spine/AnimationState.cpp

  Lines 722 to 743 in 0a4d1d2

  	float lastTotal, lastDiff;
  	if (firstFrame) {
  	lastTotal = 0;
  	lastDiff = diff;
  	} else {
  	lastTotal = timelinesRotation[i]; // Angle and direction of mix, including loops.
  	lastDiff = timelinesRotation[i + 1]; // Difference between bones.
  	}
  	bool current = diff > 0, dir = lastTotal >= 0;
  	// Detect cross at 0 (not 180).
  	if (MathUtil::sign(lastDiff) != MathUtil::sign(diff) && MathUtil::abs(lastDiff) <= 90) {
  	// A cross after a 360 rotation is a loop.
  	if (MathUtil::abs(lastTotal) > 180) lastTotal += 360 * MathUtil::sign(lastTotal);
  	dir = current;
  	}
  	total = diff + lastTotal - MathUtil::fmod(lastTotal, 360); // Store loops as part of lastTotal.
  	if (dir != current) {
  	total += 360 * MathUtil::sign(lastTotal);
  	}
  	timelinesRotation[i] = total;

• 4.2
  

  SpineSkeletonDataConverter/spine/spine-cpp-42/src/spine/AnimationState.cpp

  Lines 763 to 786 in 0a4d1d2

  	float lastTotal, lastDiff;
  	if (firstFrame) {
  	lastTotal = 0;
  	lastDiff = diff;
  	} else {
  	lastTotal = timelinesRotation[i];
  	lastDiff = timelinesRotation[i + 1];
  	}
  	float loops = lastTotal - MathUtil::fmod(lastTotal, 360.f);
  	total = diff + loops;
  	bool current = diff >= 0, dir = lastTotal >= 0;
  	if (MathUtil::abs(lastDiff) <= 90 && MathUtil::sign(lastDiff) != MathUtil::sign(diff)) {
  	if (MathUtil::abs(lastTotal - loops) > 180) {
  	total += 360.f * MathUtil::sign(lastTotal);
  	dir = current;
  	} else if (loops != 0)
  	total -= 360.f * MathUtil::sign(lastTotal);
  	else
  	dir = current;
  	}
  	if (dir != current) {
  	total += 360 * MathUtil::sign(lastTotal);
  	}
  	timelinesRotation[i] = total;

两者在 处理序列 [0, 180, 0] 或者 [180, 0, 180] 的场合会有差异。

• 在 3.8 上视为 [0,180, 360]
• 在 4.2 上视为 [0, 180, 0]

而在读取/写入过程中，对于 rotate 的 timeline 并未专门进行处理，这会导致最终转换行为产生的动画效果并不相同。

[Hajimary]

对于我的场景(3.8->4.2)，可以用下面的方式进行调整，不保证所有场景下的适用性

static inline float sign(float value) {
    return value > 0 ? 1.0f : (value < 0 ? -1.0f : 0.0f);
}

static inline float normalizeDiff(float diff) {
    // Keep the delta in [-180, 180] while preferring +180 over -180 to match the runtime behavior.
    return diff - std::ceil(diff / 360.0f - 0.5f) * 360.0f;
}

void convertRotateTimeline3xTo4x(Timeline& timeline) {
    if (timeline.size() < 2) return;

    float lastTotal = 0.0f; // Accumulated rotation including completed loops.
    float lastDiff = 0.0f;  // Delta between the previous two frames.
    bool firstFrame = true;

    float previousAngle = timeline[0].value1; // Treat as already unwrapped.

    for (size_t i = 1; i < timeline.size(); ++i) {
        float rawAngle = timeline[i].value1;
        float diff = normalizeDiff(rawAngle - previousAngle);

        float total;
        if (diff == 0.0f) {
            total = lastTotal;
        } else {
            if (firstFrame) {
                lastTotal = 0.0f;
                lastDiff = diff;
                firstFrame = false;
            }

            float loops = lastTotal - std::fmod(lastTotal, 360.0f);
            total = diff + loops;

            bool current = diff >= 0.0f;
            bool dir = lastTotal >= 0.0f;

            // Detect small crosses around 0 to decide whether to keep or flip direction.
            if (std::abs(lastDiff) <= 90.0f && sign(lastDiff) != sign(diff)) {
                if (std::abs(lastTotal - loops) > 180.0f) {
                    total += 360.0f * sign(lastTotal);
                    dir = current;
                } else if (loops != 0.0f) {
                    total -= 360.0f * sign(lastTotal);
                } else {
                    dir = current;
                }
            }

            if (dir != current) {
                total += 360.0f * sign(lastTotal);
            }
        }

        lastTotal = total;
        lastDiff = diff;
        previousAngle += total;
        timeline[i].value1 = previousAngle;
    }
}

主要是允许 value 大于等于 360 度的范围，避免这个方面的二义性，而 4.2 版本下，是可以正确解析超出 360 的value 的。