Added border curve style prop ("Squircle" effect - iOS only) (#33783)

Summary:
<!-- Explain the **motivation** for making this change. What existing problem does the pull request solve? -->
NOTE: PR is based on https://github.com/facebook/react-native/pull/32017 which went stale for quite a long time but can now safely be closed

![](https://preview.redd.it/nuvl4746ys471.png?width=960&crop=smart&auto=webp&s=084a517a645364ac246b70b7fa8e0f2470cc7af3)

Since iOS 13+, it is possible to change the corner curve property on iOS in order to smoothen border radius and make it more "rounded" (also called "squircle")
Here's an [article](https://medium.com/arthurofbabylon/a-smooth-corner-radius-in-ios-54b80aa2d372) explaining in details what it is.
This property is also built in figma, but currently there is no way to implement this directly with react-native despite it being available natively on iOS.

Many open source react-native libraries were created in order to simulate this behaviour:
[react-native-super-ellipse-mask](https://github.com/everdrone/react-native-super-ellipse-mask)
[react-native-squircle-view](https://github.com/everdrone/react-native-squircle-view)
[react-native-figma-squircle](https://github.com/tienphaw/react-native-figma-squircle)

But they rely on creating an SVG shape with the smoothed corners and masking the view behind. This makes it not very performant (flickering on mounting was a common side-effect)

This PR aims at implementing the property natively.

PR for the docs update: https://github.com/facebook/react-native-website/pull/2785

## Changelog

<!-- Help reviewers and the release process by writing your own changelog entry. For an example, see:
https://github.com/facebook/react-native/wiki/Changelog
-->

[iOS] [Added] - Added `borderCurve` style prop for smooth border radius (squircle effect)

Pull Request resolved: https://github.com/facebook/react-native/pull/33783

Test Plan:
We used the RNTester app and added an example with `cornerCurve ` set to `'continuous'` (only on iOS).

As the difference is quite subtle, we also made some more tests to better illustrate the difference (these are not in the RN-tester app):

![IMG_0810](https://user-images.githubusercontent.com/19872411/133893536-26207c53-aade-4583-9eef-7a1739b6907b.PNG)

We overlapped two views with `position: absolute`, the one in the background has a red background and has `cornerRadius` set to `false`, and the one in the foreground is set to `true`. We can clearly see where the borders differs on the corners.

Reviewed By: sammy-SC

Differential Revision: D37883631

Pulled By: cipolleschi

fbshipit-source-id: 09f06de9628fa326323eba63875de30102c4a59e

BUCK

@@ -248,6 +248,7 @@ REACT_PUBLIC_HEADERS = {
     "React/RCTAnimationType.h": RCTVIEWS_PATH + "RCTAnimationType.h",
     "React/RCTAssert.h": RCTBASE_PATH + "RCTAssert.h",
     "React/RCTAutoInsetsProtocol.h": RCTVIEWS_PATH + "RCTAutoInsetsProtocol.h",
+    "React/RCTBorderCurve.h": RCTVIEWS_PATH + "RCTBorderCurve.h",
     "React/RCTBorderDrawing.h": RCTVIEWS_PATH + "RCTBorderDrawing.h",
     "React/RCTBorderStyle.h": RCTVIEWS_PATH + "RCTBorderStyle.h",
     "React/RCTBridge+Private.h": RCTBASE_PATH + "RCTBridge+Private.h",

Libraries/Components/View/ReactNativeStyleAttributes.js

@@ -98,6 +98,7 @@ const ReactNativeStyleAttributes: {[string]: AnyAttributeType, ...} = {
   borderBottomRightRadius: true,
   borderBottomStartRadius: true,
   borderColor: colorAttributes,
+  borderCurve: true,
   borderEndColor: colorAttributes,
   borderLeftColor: colorAttributes,
   borderRadius: true,

Libraries/NativeComponent/BaseViewConfig.ios.js

@@ -193,6 +193,7 @@ const validAttributesForNonEventProps = {
   removeClippedSubviews: true,
   borderRadius: true,
   borderColor: {process: require('../StyleSheet/processColor')},
+  borderCurve: true,
   borderWidth: true,
   borderStyle: true,
   hitSlop: {diff: require('../Utilities/differ/insetsDiffer')},

Libraries/StyleSheet/StyleSheetTypes.js

@@ -532,6 +532,7 @@ export type ____ViewStyle_InternalCore = $ReadOnly<{
   backfaceVisibility?: 'visible' | 'hidden',
   backgroundColor?: ____ColorValue_Internal,
   borderColor?: ____ColorValue_Internal,
+  borderCurve?: 'circular' | 'continuous',
   borderBottomColor?: ____ColorValue_Internal,
   borderEndColor?: ____ColorValue_Internal,
   borderLeftColor?: ____ColorValue_Internal,

React/Base/RCTConvert.h

@@ -9,6 +9,7 @@
 #import <UIKit/UIKit.h>
 
 #import <React/RCTAnimationType.h>
+#import <React/RCTBorderCurve.h>
 #import <React/RCTBorderStyle.h>
 #import <React/RCTDefines.h>
 #import <React/RCTLog.h>
@@ -130,6 +131,7 @@ typedef BOOL css_backface_visibility_t;
 + (RCTPointerEvents)RCTPointerEvents:(id)json;
 + (RCTAnimationType)RCTAnimationType:(id)json;
 + (RCTBorderStyle)RCTBorderStyle:(id)json;
++ (RCTBorderCurve)RCTBorderCurve:(id)json;
 + (RCTTextDecorationLineType)RCTTextDecorationLineType:(id)json;
 
 @end

React/Base/RCTConvert.m

@@ -345,6 +345,15 @@ RCT_ENUM_CONVERTER(
     RCTBorderStyleSolid,
     integerValue)
 
+RCT_ENUM_CONVERTER(
+    RCTBorderCurve,
+    (@{
+      @"circular" : @(RCTBorderCurveCircular),
+      @"continuous" : @(RCTBorderCurveContinuous),
+    }),
+    RCTBorderCurveCircular,
+    integerValue)
+
 RCT_ENUM_CONVERTER(
     RCTTextDecorationLineType,
     (@{

React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.mm

@@ -516,6 +516,18 @@ static void RCTReleaseRCTBorderColors(RCTBorderColors borderColors)
   CGColorRelease(borderColors.right);
 }
 
+static CALayerCornerCurve CornerCurveFromBorderCurve(BorderCurve borderCurve)
+{
+  // The constants are available only starting from iOS 13
+  // CALayerCornerCurve is a typealias on NSString *
+  switch (borderCurve) {
+    case BorderCurve::Continuous:
+      return @"continuous"; // kCACornerCurveContinuous;
+    case BorderCurve::Circular:
+      return @"circular"; // kCACornerCurveCircular;
+  }
+}
+
 static RCTBorderStyle RCTBorderStyleFromBorderStyle(BorderStyle borderStyle)
 {
   switch (borderStyle) {
@@ -580,6 +592,9 @@ static RCTBorderStyle RCTBorderStyleFromBorderStyle(BorderStyle borderStyle)
     layer.borderColor = borderColor;
     CGColorRelease(borderColor);
     layer.cornerRadius = (CGFloat)borderMetrics.borderRadii.topLeft;
+    if (@available(iOS 13.0, *)) {
+      layer.cornerCurve = CornerCurveFromBorderCurve(borderMetrics.borderCurves.topLeft);
+    }
     layer.backgroundColor = _backgroundColor.CGColor;
   } else {
     if (!_borderLayer) {

React/Views/RCTBorderCurve.h

@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <Foundation/Foundation.h>
+
+typedef NS_ENUM(NSInteger, RCTBorderCurve) {
+  RCTBorderCurveContinuous = 0,
+  RCTBorderCurveCircular,
+};

React/Views/RCTView.h

@@ -7,6 +7,7 @@
 
 #import <UIKit/UIKit.h>
 
+#import <React/RCTBorderCurve.h>
 #import <React/RCTBorderStyle.h>
 #import <React/RCTComponent.h>
 #import <React/RCTPointerEvents.h>
@@ -93,6 +94,11 @@ extern const UIAccessibilityTraits SwitchAccessibilityTrait;
 @property (nonatomic, assign) CGFloat borderEndWidth;
 @property (nonatomic, assign) CGFloat borderWidth;
 
+/**
+ * Border curve.
+ */
+@property (nonatomic, assign) RCTBorderCurve borderCurve;
+
 /**
  * Border styles.
  */

React/Views/RCTView.m

@@ -10,6 +10,7 @@
 #import <React/RCTMockDef.h>
 
 #import "RCTAutoInsetsProtocol.h"
+#import "RCTBorderCurve.h"
 #import "RCTBorderDrawing.h"
 #import "RCTI18nUtil.h"
 #import "RCTLog.h"
@@ -126,6 +127,7 @@ static NSString *RCTRecursiveAccessibilityLabel(UIView *view)
     _borderBottomRightRadius = -1;
     _borderBottomStartRadius = -1;
     _borderBottomEndRadius = -1;
+    _borderCurve = RCTBorderCurveCircular;
     _borderStyle = RCTBorderStyleSolid;
     _hitTestEdgeInsets = UIEdgeInsetsZero;
 
@@ -945,6 +947,20 @@ setBorderColor() setBorderColor(Top) setBorderColor(Right) setBorderColor(Bottom
                     setBorderRadius(TopEnd) setBorderRadius(BottomLeft) setBorderRadius(BottomRight)
                         setBorderRadius(BottomStart) setBorderRadius(BottomEnd)
 
+#pragma mark - Border Curve
+
+#define setBorderCurve(side)                            \
+  -(void)setBorder##side##Curve : (RCTBorderCurve)curve \
+  {                                                     \
+    if (_border##side##Curve == curve) {                \
+      return;                                           \
+    }                                                   \
+    _border##side##Curve = curve;                       \
+    [self.layer setNeedsDisplay];                       \
+  }
+
+                            setBorderCurve()
+
 #pragma mark - Border Style
 
 #define setBorderStyle(side)                            \
@@ -957,6 +973,6 @@ setBorderColor() setBorderColor(Top) setBorderColor(Right) setBorderColor(Bottom
     [self.layer setNeedsDisplay];                       \
   }
 
-                            setBorderStyle()
+                                setBorderStyle()
 
-                                @end
+                                    @end

React/Views/RCTViewManager.m

@@ -8,6 +8,7 @@
 #import "RCTViewManager.h"
 
 #import "RCTAssert.h"
+#import "RCTBorderCurve.h"
 #import "RCTBorderStyle.h"
 #import "RCTBridge.h"
 #import "RCTConvert+Transform.h"
@@ -264,6 +265,19 @@ RCT_CUSTOM_VIEW_PROPERTY(removeClippedSubviews, BOOL, RCTView)
     view.removeClippedSubviews = json ? [RCTConvert BOOL:json] : defaultView.removeClippedSubviews;
   }
 }
+RCT_CUSTOM_VIEW_PROPERTY(borderCurve, RCTBorderCurve, RCTView)
+{
+  if (@available(iOS 13.0, *)) {
+    switch ([RCTConvert RCTBorderCurve:json]) {
+      case RCTBorderCurveContinuous:
+        view.layer.cornerCurve = kCACornerCurveContinuous;
+        break;
+      case RCTBorderCurveCircular:
+        view.layer.cornerCurve = kCACornerCurveCircular;
+        break;
+    }
+  }
+}
 RCT_CUSTOM_VIEW_PROPERTY(borderRadius, CGFloat, RCTView)
 {
   if ([view respondsToSelector:@selector(setBorderRadius:)]) {

ReactCommon/react/renderer/components/view/ViewProps.cpp

@@ -67,6 +67,15 @@ ViewProps::ViewProps(
                                                 "Color",
                                                 sourceProps.borderColors,
                                                 {})),
+      borderCurves(
+          Props::enablePropIteratorSetter ? sourceProps.borderCurves
+                                          : convertRawProp(
+                                                context,
+                                                rawProps,
+                                                "border",
+                                                "Curve",
+                                                sourceProps.borderCurves,
+                                                {})),
       borderStyles(
           Props::enablePropIteratorSetter ? sourceProps.borderStyles
                                           : convertRawProp(
@@ -412,6 +421,7 @@ BorderMetrics ViewProps::resolveBorderMetrics(
       /* .borderWidths = */ borderWidths.resolve(isRTL, 0),
       /* .borderRadii = */
       ensureNoOverlap(borderRadii.resolve(isRTL, 0), layoutMetrics.frame.size),
+      /* .borderCurves = */ borderCurves.resolve(isRTL, BorderCurve::Circular),
       /* .borderStyles = */ borderStyles.resolve(isRTL, BorderStyle::Solid),
   };
 }

ReactCommon/react/renderer/components/view/ViewProps.h

@@ -51,6 +51,7 @@ class ViewProps : public YogaStylableProps, public AccessibilityProps {
   // Borders
   CascadedBorderRadii borderRadii{};
   CascadedBorderColors borderColors{};
+  CascadedBorderCurves borderCurves{};
   CascadedBorderStyles borderStyles{};
 
   // Shadow

ReactCommon/react/renderer/components/view/conversions.h

@@ -563,6 +563,24 @@ inline void fromRawValue(
   react_native_assert(false);
 }
 
+inline void fromRawValue(
+    const PropsParserContext &context,
+    const RawValue &value,
+    BorderCurve &result) {
+  react_native_assert(value.hasType<std::string>());
+  auto stringValue = (std::string)value;
+  if (stringValue == "circular") {
+    result = BorderCurve::Circular;
+    return;
+  }
+  if (stringValue == "continuous") {
+    result = BorderCurve::Continuous;
+    return;
+  }
+  LOG(FATAL) << "Could not parse BorderCurve:" << stringValue;
+  react_native_assert(false);
+}
+
 inline void fromRawValue(
     const PropsParserContext &context,
     const RawValue &value,

ReactCommon/react/renderer/components/view/primitives.h

@@ -77,6 +77,8 @@ inline static bool operator!=(ViewEvents const &lhs, ViewEvents const &rhs) {
 
 enum class BackfaceVisibility { Auto, Visible, Hidden };
 
+enum class BorderCurve { Circular, Continuous };
+
 enum class BorderStyle { Solid, Dotted, Dashed };
 
 template <typename T>
@@ -202,11 +204,13 @@ struct CascadedRectangleCorners {
 };
 
 using BorderWidths = RectangleEdges<Float>;
+using BorderCurves = RectangleCorners<BorderCurve>;
 using BorderStyles = RectangleEdges<BorderStyle>;
 using BorderColors = RectangleEdges<SharedColor>;
 using BorderRadii = RectangleCorners<Float>;
 
 using CascadedBorderWidths = CascadedRectangleEdges<Float>;
+using CascadedBorderCurves = CascadedRectangleCorners<BorderCurve>;
 using CascadedBorderStyles = CascadedRectangleEdges<BorderStyle>;
 using CascadedBorderColors = CascadedRectangleEdges<SharedColor>;
 using CascadedBorderRadii = CascadedRectangleCorners<Float>;
@@ -215,6 +219,7 @@ struct BorderMetrics {
   BorderColors borderColors{};
   BorderWidths borderWidths{};
   BorderRadii borderRadii{};
+  BorderCurves borderCurves{};
   BorderStyles borderStyles{};
 
   bool operator==(const BorderMetrics &rhs) const {
@@ -222,11 +227,13 @@ struct BorderMetrics {
                this->borderColors,
                this->borderWidths,
                this->borderRadii,
+               this->borderCurves,
                this->borderStyles) ==
         std::tie(
                rhs.borderColors,
                rhs.borderWidths,
                rhs.borderRadii,
+               rhs.borderCurves,
                rhs.borderStyles);
   }
 

packages/rn-tester/Podfile.lock

@@ -753,7 +753,7 @@ DEPENDENCIES:
   - RCTRequired (from `../../Libraries/RCTRequired`)
   - RCTTypeSafety (from `../../Libraries/TypeSafety`)
   - React (from `../../`)
-  - React-bridging (from `../../ReactCommon/react/bridging`)
+  - React-bridging (from `../../ReactCommon`)
   - React-callinvoker (from `../../ReactCommon/callinvoker`)
   - React-Codegen (from `build/generated/ios`)
   - React-Core (from `../../`)
@@ -826,7 +826,7 @@ EXTERNAL SOURCES:
   React:
     :path: "../../"
   React-bridging:
-    :path: "../../ReactCommon/react/bridging"
+    :path: "../../ReactCommon"
   React-callinvoker:
     :path: "../../ReactCommon/callinvoker"
   React-Codegen:
@@ -905,11 +905,11 @@ SPEC CHECKSUMS:
   glog: 04b94705f318337d7ead9e6d17c019bd9b1f6b1b
   libevent: 4049cae6c81cdb3654a443be001fb9bdceff7913
   OpenSSL-Universal: ebc357f1e6bc71fa463ccb2fe676756aff50e88c
-  RCT-Folly: 9638863070ed4e7b2be5e91385745a0ad741e9c1
+  RCT-Folly: 0080d0a6ebf2577475bda044aa59e2ca1f909cda
   RCTRequired: 1c8808cf84569265784a6c33984bbb506ada8c6e
   RCTTypeSafety: b6dcb5036a808864ee8cad66ca15f263c24661cc
   React: 8d809d414723bb5763093ddec7658066a21ccabc
-  React-bridging: 3ba3efbd3a2d7d99aad5658b8e48b1c134c16ecf
+  React-bridging: cc10a051eff1f03306a1d7659593d8aac3242bc3
   React-callinvoker: 5f16202ad4e45f0607b1fae0f6955a8f7c87eef1
   React-Codegen: 5adf19af97eb37a7d441c040521191e446255086
   React-Core: 0cfb25c65d4dcb856b1807fe44a1ebe5e7ec9749
@@ -936,12 +936,12 @@ SPEC CHECKSUMS:
   React-RCTVibration: 0386f50996a153b3f39cecbe7d139763ac9a9fdf
   React-rncore: 6daa27c74047a9e13ce3412b99660274a5780603
   React-runtimeexecutor: 97dca9247f4d3cfe0733384b189c6930fbd402b7
-  ReactCommon: a34f02c7251e6725e744167b9381d5dd9d016591
+  ReactCommon: 6cef8ed13ee2a9d7d4cf9660dbe6dd2ea6ba7104
   ScreenshotManager: 71d047abd38a77310985b87f8136b620c5c61e88
   SocketRocket: fccef3f9c5cedea1353a9ef6ada904fde10d6608
   Yoga: 1b1a12ff3d86a10565ea7cbe057d42f5e5fb2a07
   YogaKit: f782866e155069a2cca2517aafea43200b01fd5a
 
-PODFILE CHECKSUM: e067e04e7697dc3cd3d3fbd7556f77c6eccf8075
+PODFILE CHECKSUM: 54d9bd86f3c8151531bd4da1d3ba2e2e1f9a6ca9
 
 COCOAPODS: 1.11.3

packages/rn-tester/js/examples/View/ViewExample.js

@@ -17,6 +17,7 @@ const {
   Text,
   TouchableWithoutFeedback,
   View,
+  Platform,
 } = require('react-native');
 
 class ViewBorderStyleExample extends React.Component<
@@ -360,12 +361,29 @@ exports.examples = [
     title: 'Border Radius',
     render(): React.Node {
       return (
-        <View style={{borderWidth: 0.5, borderRadius: 5, padding: 5}}>
-          <Text style={{fontSize: 11}}>
-            Too much use of `borderRadius` (especially large radii) on anything
-            which is scrolling may result in dropped frames. Use sparingly.
-          </Text>
-        </View>
+        <>
+          <View style={{borderWidth: 0.5, borderRadius: 5, padding: 5}}>
+            <Text style={{fontSize: 11}}>
+              Too much use of `borderRadius` (especially large radii) on
+              anything which is scrolling may result in dropped frames. Use
+              sparingly.
+            </Text>
+          </View>
+          {Platform.OS === 'ios' && (
+            <View
+              style={{
+                borderRadius: 20,
+                padding: 8,
+                marginTop: 12,
+                backgroundColor: '#527FE4',
+                borderCurve: 'continuous',
+              }}>
+              <Text style={{fontSize: 16, color: 'white'}}>
+                View with continuous border curve
+              </Text>
+            </View>
+          )}
+        </>
       );
     },
   },