feature: Tab bar safe area is defined by a top anchor point instead of bounds

This makes it easier to specify the safe area for a bar that has interactive or decorative
elements extending upwards.

BREAKING CHANGE: TabBarBoundsForSafeAreaKey is now TabBarTopForSafeAreaKey

Author: bobergj

README.md

@@ -94,7 +94,7 @@ struct SampleTabBarView: View {
                     }
             }
         }
-        .anchorPreference(key: TabBarBoundsForSafeAreaKey.self, value: .bounds, transform: { $0 })
+        .anchorPreference(key: TabBarTopForSafeAreaKey.self, value: .top, transform: { $0 })
     }
 
     private func tabBarItem(for tab: Tab) -> some View {

Sources/CustomTabView/CustomTabView.swift

@@ -113,9 +113,9 @@ struct _TabBarLayoutView<TabBarView: View, Subviews>: View where Subviews: Rando
                 #endif
                 tabBarView
                     .opacity(tabBarVisibility[selectedTabIndex] == .hidden ? 0 : 1)
-                    .onPreferenceChange(TabBarBoundsForSafeAreaKey.self) {
+                    .onPreferenceChange(TabBarTopForSafeAreaKey.self) {
                         if let anchor = $0 {
-                            tabBarHeight = proxy[anchor].height
+                            tabBarHeight = max(0, -(proxy[anchor].y - proxy.size.height))
                         }
                     }
             })

Sources/CustomTabView/Example/BottomFloatingTabBarView.swift

@@ -31,7 +31,7 @@ struct BottomFloatingTabBarView: View {
         }
         #endif
         .clipShape(RoundedRectangle(cornerRadius: 25))
-        .anchorPreference(key: TabBarBoundsForSafeAreaKey.self, value: .bounds, transform: { $0 })
+        .anchorPreference(key: TabBarTopForSafeAreaKey.self, value: .top, transform: { $0 })
         .shadow(color: .secondary.opacity(0.3), radius: 10, y: 5)
     }
 

Sources/CustomTabView/TabBarHeight.swift renamed to Sources/CustomTabView/TabBarTopForSafeAreaKey.swift

@@ -1,7 +1,7 @@
 import SwiftUI
 
-public struct TabBarBoundsForSafeAreaKey: PreferenceKey {
-    public static var defaultValue: Anchor<CGRect>? { nil }
+public struct TabBarTopForSafeAreaKey: PreferenceKey {
+    public static var defaultValue: Anchor<CGPoint>? { nil }
 
     public static func reduce(
         value: inout Value,