iPhone内置广角相机ramp缩放参数与过渡曲线问题咨询

我正在使用iPhone的builtInWideAngleCamera后置主相机，尝试通过ramp(toVideoZoomFactor:withRate:)方法实现0.25秒内从1x到3x的平滑缩放，以及0.25秒内从3x回到1x的缩放，但调整withRate参数后效果不符合预期，缩放过慢。

相关代码如下：

func cameraZoomIn() {
    if let deviceCameraSelected = deviceCameraSelected {
        do {
            try deviceCameraSelected.lockForConfiguration()
            try deviceCameraSelected.ramp(toVideoZoomFactor: 3, withRate: 0.25)
            deviceCameraSelected.unlockForConfiguration()
        } catch {
            print("Error: \(error)")
        }
    }
}

func cameraZoomOut() {
    if let deviceCameraSelected = deviceCameraSelected {
        do {
            try deviceCameraSelected.lockForConfiguration()
            try deviceCameraSelected.ramp(toVideoZoomFactor: 1, withRate: 0.25)
            deviceCameraSelected.unlockForConfiguration()
        } catch {
            print("Error: \(error)")
        }
    }
}

问题1：实现0.25秒缩放效果的正确withRate参数值 #

首先明确：withRate参数不是时长，它代表的是每秒内视觉缩放因子的变化量（比如从1x到2x，变化量为1）。

计算逻辑：

• 从1x到3x，视觉缩放的总变化量是 3 - 1 = 2
• 要求在0.25秒完成，所以rate值应为 总变化量 / 时长 = 2 / 0.25 = 8

同理，从3x回到1x的总变化量也是2，rate值同样设为8。

修正后的代码片段：

func cameraZoomIn() {
    if let deviceCameraSelected = deviceCameraSelected {
        do {
            try deviceCameraSelected.lockForConfiguration()
            try deviceCameraSelected.ramp(toVideoZoomFactor: 3, withRate: 8)
            deviceCameraSelected.unlockForConfiguration()
        } catch {
            print("Error: \(error)")
        }
    }
}

func cameraZoomOut() {
    if let deviceCameraSelected = deviceCameraSelected {
        do {
            try deviceCameraSelected.lockForConfiguration()
            try deviceCameraSelected.ramp(toVideoZoomFactor: 1, withRate: 8)
            deviceCameraSelected.unlockForConfiguration()
        } catch {
            print("Error: \(error)")
        }
    }
}

注意：部分设备可能对rate有上限限制，如果实际效果仍有偏差，可以在7-9之间小幅调整rate值测试。

问题2：实现类似UIView.animate的curveEaseInOut过渡曲线 #

系统的ramp(toVideoZoomFactor:withRate:)仅支持线性过渡，要实现缓入缓出曲线，需要手动通过CADisplayLink逐帧控制缩放因子：

实现步骤： #

1. 锁定相机设备配置
2. 记录起始缩放值、目标缩放值、动画总时长
3. 用CADisplayLink跟踪动画进度
4. 通过缓入缓出公式计算当前进度对应的缩放因子
5. 逐帧设置device.videoZoomFactor
6. 动画结束后停止CADisplayLink并解锁设备

示例代码： #

private var displayLink: CADisplayLink?
private var startZoomFactor: CGFloat = 1.0
private var targetZoomFactor: CGFloat = 1.0
private var startTime: CFTimeInterval = 0.0
private let animationDuration: CFTimeInterval = 0.25

func animateZoom(to targetFactor: CGFloat) {
    guard let device = deviceCameraSelected else { return }
    
    do {
        try device.lockForConfiguration()
        // 初始化动画参数
        startZoomFactor = device.videoZoomFactor
        targetZoomFactor = targetFactor
        startTime = CACurrentMediaTime()
        
        // 创建DisplayLink，同步屏幕刷新率
        displayLink = CADisplayLink(target: self, selector: #selector(updateZoom))
        displayLink?.add(to: .main, forMode: .common)
    } catch {
        print("Error: \(error)")
    }
}

@objc private func updateZoom() {
    guard let device = deviceCameraSelected, let displayLink = displayLink else { return }
    
    let elapsedTime = CACurrentMediaTime() - startTime
    let progress = min(elapsedTime / animationDuration, 1.0)
    
    // 缓入缓出曲线计算，和UIView的curveEaseInOut效果一致
    let easedProgress: CGFloat
    if progress < 0.5 {
        easedProgress = 2 * progress * progress
    } else {
        easedProgress = 1 - pow(-2 * progress + 2, 2) / 2
    }
    
    // 计算当前缩放因子并设置
    let currentZoom = startZoomFactor + (targetZoomFactor - startZoomFactor) * easedProgress
    device.videoZoomFactor = currentZoom
    
    // 动画结束，清理资源
    if progress >= 1.0 {
        displayLink.invalidate()
        self.displayLink = nil
        device.unlockForConfiguration()
    }
}

// 调用方式
func cameraZoomIn() {
    animateZoom(to: 3)
}

func cameraZoomOut() {
    animateZoom(to: 1)
}

说明： #

• 这里使用的缓入缓出公式是标准二次贝塞尔曲线实现，和系统动画曲线效果对齐
• CADisplayLink保证动画和屏幕刷新率同步，避免出现卡顿
• 动画全程保持设备锁定，直到结束再解锁，防止配置冲突

内容的提问来源于stack exchange，提问作者user4806509