一个不对等滑动的 banner

效果：

Untitled1.gif

code:
https://github.com/haoburongyi/irregularBanner

核心代码

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        
        guard let collectionView = collectionView else {
            return nil
        }
        
        guard let attributesArr = super.layoutAttributesForElements(in: rect) else {
            return nil
        }
        
        let centerX = collectionView.contentOffset.x + collectionView.bounds.width * 0.5

        let maxApart = (collectionView.bounds.width + itemWidth()) * 0.5
//        let maxApart = (collectionView.bounds.width + itemWidth()) * 0.6
        
        var index = 0
        for attributes in attributesArr {

            // 获取cell中心和屏幕中心的距离
            let apart = abs(attributes.center.x - centerX)
//            // 移动进度 -1~0~1
            let progress = apart / maxApart
            // 在屏幕外的cell不处理
            if abs(progress) > 1 {
                continue
            }
            
            var _progress = (attributes.center.x - centerX) / maxApart
            if _progress < 0 {
                _progress += 1
            }
            // 缩放大小
            let x = (attributes.size.width + minimumLineSpacing) * CGFloat(attributes.indexPath.row) + insetX()
            if index == 0 {
                attributes.frame.origin.x = x - leftMargin * progress
            } else {
                attributes.frame.origin.x = x
                if index != 1 {
                    // 根据余弦函数，弧度在 -π/4 到 π/4,即 scale在 √2/2~1~√2/2 间变化
                    var scale = abs(cos(progress * CGFloat.pi / 4))
                    if scale != 1 {
                        scale *= 1.2
                        if scale > 1 {
                            scale = 1
                        }
                    }
                    // 缩放大小
                    attributes.transform = .init(scaleX: scale, y: scale)
                }
            }
            index += 1
            
            // 更新中间位
            if apart < itemWidth() * 0.5 {
                centerBlock?(attributes.indexPath)
            }
        }
        return attributesArr
    }