如何移除NSVisualEffectView产生的多余边框？

你的问题主要源于两个细节：设置圆角后未开启Layer裁剪导致视觉边缘残留，以及.popover类型的material默认自带边框样式。可以通过以下方法解决：

1. 开启Layer裁剪并关闭默认背景绘制 #

给NSVisualEffectView添加masksToBounds = true配合圆角完成裁剪，同时设置drawsBackground = false关闭material自带的边框绘制：

let blurView: NSVisualEffectView = NSVisualEffectView()
blurView.wantsLayer = true
blurView.blendingMode = .behindWindow
blurView.material = .popover
blurView.drawsBackground = false // 关闭默认边框绘制
blurView.layer?.cornerRadius = 50
blurView.layer?.masksToBounds = true // 开启圆角裁剪，消除边缘残留
blurView.state = .active

2. 补全窗口透明设置 #

给窗口添加isOpaque = false，确保背景完全透明，避免额外视觉干扰：

window.styleMask = [.borderless]
window.backingType = .buffered
window.isOpaque = false // 确保窗口透明
window.backgroundColor = .clear

备选方案：更换Material类型 #

如果不需要.popover的视觉风格，换成.windowBackground这类无默认边框的material，也能直接解决问题：

blurView.material = .windowBackground

修改后的完整代码：

class AppDelegate: NSObject, NSApplicationDelegate {
    
    private lazy var window: NSWindow = NSWindow()
    
    func applicationDidFinishLaunching(_ aNotification: Notification) {
        
        window.styleMask = [.borderless]
        window.backingType = .buffered
        window.isOpaque = false
        window.backgroundColor = .clear

        let blurView: NSVisualEffectView = NSVisualEffectView()
        blurView.wantsLayer = true
        blurView.blendingMode = .behindWindow
        blurView.material = .popover
        blurView.drawsBackground = false
        blurView.layer?.cornerRadius = 50
        blurView.layer?.masksToBounds = true
        blurView.state = .active
        
        window.contentView = blurView
        window.setContentSize(CGSize(width: 250, height: 250))
        
        window.setFrameAutosaveName("Main Window")
        window.isMovableByWindowBackground = true
        
        window.makeKeyAndOrderFront(window)
    }
}

内容的提问来源于stack exchange，提问作者swiftPunk