[BottomNavigation] Adds opt-in from MDCShadowLayer to MDCShadow.

PiperOrigin-RevId: 369815810

Author: yarneo

components/BottomNavigation/src/MDCBottomNavigationBar.h

@@ -19,6 +19,7 @@
 // migrated to no longer import MDCBottomNavigationBarDelegate as a transitive dependency.
 #import "MDCBottomNavigationBarDelegate.h"
 #import "MaterialElevation.h"
+#import "MaterialShadow.h"
 #import "MaterialShadowElevations.h"
 
 @protocol MDCBottomNavigationBarDelegate;

components/BottomNavigation/src/MDCBottomNavigationBar.m

@@ -26,6 +26,7 @@
 #import "MDCBottomNavigationBarDelegate.h"
 #import "MaterialPalettes.h"
 #import "MaterialRipple.h"
+#import "MaterialShadow.h"
 #import "MaterialShadowElevations.h"
 #import "MaterialShadowLayer.h"
 #import "MaterialTypography.h"
@@ -72,8 +73,13 @@ @interface MDCBottomNavigationBar () <MDCInkTouchControllerDelegate,
 @end
 
 @implementation MDCBottomNavigationBar
+
+static BOOL gEnablePerformantShadow = NO;
+
 @synthesize mdc_overrideBaseElevation = _mdc_overrideBaseElevation;
 @synthesize mdc_elevationDidChangeBlock = _mdc_elevationDidChangeBlock;
+@synthesize shadowsCollection = _shadowsCollection;
+@synthesize elevation = _elevation;
 
 - (instancetype)initWithFrame:(CGRect)frame {
   self = [super initWithFrame:frame];
@@ -134,11 +140,8 @@ - (void)commonMDCBottomNavigationBarInit {
   [_barView addSubview:_itemsLayoutView];
 
   _itemsLayoutView.accessibilityTraits = UIAccessibilityTraitTabBar;
-  _elevation = MDCShadowElevationBottomNavigationBar;
-  [(MDCShadowLayer *)self.layer setElevation:_elevation];
-  UIColor *defaultShadowColor = UIColor.blackColor;
-  _shadowColor = defaultShadowColor;
-  self.layer.shadowColor = defaultShadowColor.CGColor;
+  self.elevation = MDCShadowElevationBottomNavigationBar;
+  self.shadowColor = gEnablePerformantShadow ? MDCShadowColor() : UIColor.blackColor;
   _itemViews = [NSMutableArray array];
   _itemTitleFont = [UIFont mdc_standardFontForMaterialTextStyle:MDCFontTextStyleCaption];
 
@@ -171,6 +174,10 @@ - (void)layoutSubviews {
     [self sizeItemsLayoutViewItemsDistributed:YES withBottomNavSize:size containerWidth:size.width];
   }
   [self layoutItemViews];
+
+  if (gEnablePerformantShadow) {
+    [self updateShadow];
+  }
 }
 
 - (void)safeAreaInsetsDidChange {
@@ -205,16 +212,31 @@ - (CGSize)sizeThatFits:(CGSize)size {
 }
 
 + (Class)layerClass {
-  return [MDCShadowLayer class];
+  if (gEnablePerformantShadow) {
+    return [super layerClass];
+  } else {
+    return [MDCShadowLayer class];
+  }
 }
 
 - (void)setElevation:(MDCShadowElevation)elevation {
-  BOOL elevationChanged = !MDCCGFloatEqual(_elevation, elevation);
+  if (MDCCGFloatEqual(_elevation, elevation)) {
+    return;
+  }
   _elevation = elevation;
-  [(MDCShadowLayer *)self.layer setElevation:elevation];
-  if (elevationChanged) {
-    [self mdc_elevationDidChange];
+  if (gEnablePerformantShadow) {
+    [self updateShadow];
+  } else {
+    MDCShadowLayer *shadowLayer = (MDCShadowLayer *)self.layer;
+    shadowLayer.elevation = elevation;
   }
+  [self mdc_elevationDidChange];
+}
+
+- (void)updateShadow {
+  MDCConfigureShadowForView(self,
+                            [self.shadowsCollection shadowForElevation:self.mdc_currentElevation],
+                            self.shadowColor);
 }
 
 - (void)setShadowColor:(UIColor *)shadowColor {
@@ -843,6 +865,19 @@ - (CGFloat)mdc_currentElevation {
   return self.elevation;
 }
 
+- (MDCShadowsCollection *)shadowsCollection {
+  if (!_shadowsCollection) {
+    _shadowsCollection = MDCShadowsCollectionDefault();
+  }
+  return _shadowsCollection;
+}
+
+- (void)setShadowsCollection:(MDCShadowsCollection *)shadowsCollection {
+  _shadowsCollection = shadowsCollection;
+
+  [self updateShadow];
+}
+
 - (void)cancelRippleInItemView:(MDCBottomNavigationItemView *)itemView animated:(BOOL)animated {
   if (self.enableRippleBehavior) {
     if (animated) {
@@ -942,4 +977,14 @@ - (UIPointerStyle *)pointerInteraction:(UIPointerInteraction *)interaction
 }
 #endif
 
+#pragma mark - Performant Shadow Toggle
+
++ (void)setEnablePerformantShadow:(BOOL)enable {
+  gEnablePerformantShadow = enable;
+}
+
++ (BOOL)enablePerformantShadow {
+  return gEnablePerformantShadow;
+}
+
 @end

components/BottomNavigation/src/PerformantShadowMigration/MDCBottomNavigationBar+ShadowsPrivate.h

@@ -0,0 +1,23 @@
+#import <UIKit/UIKit.h>
+
+#import "MDCBottomNavigationBar.h"
+
+/**
+ This category is temporary and is meant to allow us to A/B test the performance improvements of
+ using the new shadow vs the old shadow. When such test is finalized, we will delete this file and
+ the internal corresponding static property and move all clients to the new shadow.
+ TODO(b/185206035): Remove category for enabling performant shadow.
+ */
+@interface MDCBottomNavigationBar (ShadowsPrivate)
+
+/**
+ Returns a bool indicating if the performant shadow is turned on or not.
+ */
++ (BOOL)enablePerformantShadow;
+
+/**
+ Enables/disables the performant shadow for the bottom navigation bar.
+ */
++ (void)setEnablePerformantShadow:(BOOL)enable;
+
+@end

components/BottomNavigation/src/private/MDCBottomNavigationBar+Private.h

@@ -21,6 +21,16 @@
 
 @interface MDCBottomNavigationBar ()
 
+/**
+ A collection of MDCShadow instances each assigned an elevation (in dp).
+
+ To create your own MDCShadowsCollection, please use the provided MDCShadowsCollectionBuilder and
+ populate it with MDCShadow instances using the provided MDCShadowBuilder.
+
+ Defaults to MDCShadowsCollectionDefault().
+ */
+@property(nonatomic, strong, null_resettable) MDCShadowsCollection *shadowsCollection;
+
 /**
  * Returns the tab bar item whose corresponding view contains the given point.
  * @param point CGPoint The point at which to get the corresponding tab bar item. The point must be