[private/ThumbView] Add centerVisibleArea support with snapshot tests.

PiperOrigin-RevId: 323572514

components/private/ThumbTrack/src/MDCThumbView.h

@@ -34,6 +34,16 @@
 /** The corner radius of the thumbview layer. */
 @property(nonatomic, assign) CGFloat cornerRadius;
 
+/**
+ A Boolean value that determines whether the visible area is centered in the bounds of the view.
+
+ If set to YES, the visible area is centered in the bounds of the view, which is often used to
+ configure invisible tappable area. If set to NO, the visible area fills its bounds.
+
+ The default value is @c NO.
+*/
+@property(nonatomic, assign) BOOL centerVisibleArea;
+
 /** Set the @c icon shown on the thumb. */
 - (void)setIcon:(nullable UIImage *)icon;
 

components/private/ThumbTrack/src/MDCThumbView.m

@@ -73,11 +73,50 @@ - (void)setCornerRadius:(CGFloat)cornerRadius {
   }
   _cornerRadius = cornerRadius;
 
+  [self configureShapeGeneratorWithCornerRadius:cornerRadius
+                              centerVisibleArea:self.centerVisibleArea];
+
+  [self setNeedsLayout];
+}
+
+- (void)setCenterVisibleArea:(BOOL)centerVisibleArea {
+  if (centerVisibleArea == _centerVisibleArea) {
+    return;
+  }
+  _centerVisibleArea = centerVisibleArea;
+
+  [self configureShapeGeneratorWithCornerRadius:self.cornerRadius
+                              centerVisibleArea:centerVisibleArea];
+
+  [self setNeedsLayout];
+}
+
+- (void)configureShapeGeneratorWithCornerRadius:(CGFloat)cornerRadius
+                              centerVisibleArea:(BOOL)centerVisibleArea {
   MDCCornerTreatment *cornerTreatment =
       [[MDCRoundedCornerTreatment alloc] initWithRadius:cornerRadius];
   [self.shapeGenerator setCorners:cornerTreatment];
 
-  [self setNeedsLayout];
+  if (centerVisibleArea) {
+    UIEdgeInsets visibleAreaInsets = UIEdgeInsetsZero;
+    CGSize visibleAreaSize = CGSizeMake(cornerRadius * 2, cornerRadius * 2);
+    CGFloat additionalRequiredHeight =
+        MAX(0, CGRectGetHeight(self.bounds) - visibleAreaSize.height);
+    CGFloat additionalRequiredWidth = MAX(0, CGRectGetWidth(self.bounds) - visibleAreaSize.width);
+    visibleAreaInsets.top = MDCCeil(additionalRequiredHeight * 0.5f);
+    visibleAreaInsets.bottom = additionalRequiredHeight - visibleAreaInsets.top;
+    visibleAreaInsets.left = MDCCeil(additionalRequiredWidth * 0.5f);
+    visibleAreaInsets.right = additionalRequiredWidth - visibleAreaInsets.left;
+
+    self.shapeGenerator.topLeftCornerOffset =
+        CGPointMake(visibleAreaInsets.left, visibleAreaInsets.top);
+    self.shapeGenerator.topRightCornerOffset =
+        CGPointMake(-visibleAreaInsets.right, visibleAreaInsets.top);
+    self.shapeGenerator.bottomLeftCornerOffset =
+        CGPointMake(visibleAreaInsets.left, -visibleAreaInsets.bottom);
+    self.shapeGenerator.bottomRightCornerOffset =
+        CGPointMake(-visibleAreaInsets.right, -visibleAreaInsets.bottom);
+  }
 }
 
 - (MDCShadowElevation)elevation {

components/private/ThumbTrack/tests/snapshot/MDCThumbViewSnapshotTests.m

@@ -0,0 +1,77 @@
+// Copyright 2020-present the Material Components for iOS authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#import <UIKit/UIKit.h>
+
+#import "MaterialSnapshot.h"
+#import "MaterialThumbTrack.h"
+
+@interface MDCThumbViewSnapshotTests : MDCSnapshotTestCase
+
+@property(nonatomic, strong) MDCThumbView *thumbView;
+
+@end
+
+@implementation MDCThumbViewSnapshotTests
+
+- (void)setUp {
+  [super setUp];
+
+  // Uncomment below to recreate all the goldens (or add the following line to the specific
+  // test you wish to recreate the golden for).
+  //  self.recordMode = YES;
+
+  self.thumbView = [[MDCThumbView alloc] initWithFrame:CGRectMake(0, 0, 44, 44)];
+  self.thumbView.backgroundColor = UIColor.blueColor;
+}
+
+- (void)tearDown {
+  self.thumbView = nil;
+
+  [super tearDown];
+}
+
+- (void)generateSnapshotWithBorderAndVerifyForView:(MDCThumbView *)view {
+  // TODO(b/161927075): Refactor when this functionality is available in MaterialSnapshot.
+  UIView *thumbViewFrameView = [[UIView alloc] initWithFrame:view.bounds];
+  [view addSubview:thumbViewFrameView];
+  thumbViewFrameView.layer.borderColor = UIColor.yellowColor.CGColor;
+  thumbViewFrameView.layer.borderWidth = 0.5f;
+
+  UIView *snapshotView = [view mdc_addToBackgroundView];
+  [self snapshotVerifyView:snapshotView];
+
+  [thumbViewFrameView removeFromSuperview];
+}
+
+#pragma mark - Tests
+
+- (void)testThumbViewFullyRoundedDefaults {
+  // When
+  self.thumbView.cornerRadius = CGRectGetWidth(self.thumbView.bounds) / 2;
+
+  // Then
+  [self generateSnapshotWithBorderAndVerifyForView:self.thumbView];
+}
+
+- (void)testThumbViewWhenCenterVisibleAreaIsTrue {
+  // When
+  self.thumbView.centerVisibleArea = YES;
+  self.thumbView.cornerRadius = 10;
+
+  // Then
+  [self generateSnapshotWithBorderAndVerifyForView:self.thumbView];
+}
+
+@end