Call BorderRadiusGeometry.lerp where applicable in ShapeBorder subclasses (#24262)

Fixes https://github.com/flutter/flutter/issues/24257

packages/flutter/lib/src/painting/beveled_rectangle_border.dart

@@ -60,7 +60,7 @@ class BeveledRectangleBorder extends ShapeBorder {
     if (a is BeveledRectangleBorder) {
       return BeveledRectangleBorder(
         side: BorderSide.lerp(a.side, side, t),
-        borderRadius: BorderRadius.lerp(a.borderRadius, borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t),
       );
     }
     return super.lerpFrom(a, t);
@@ -72,7 +72,7 @@ class BeveledRectangleBorder extends ShapeBorder {
     if (b is BeveledRectangleBorder) {
       return BeveledRectangleBorder(
         side: BorderSide.lerp(side, b.side, t),
-        borderRadius: BorderRadius.lerp(borderRadius, b.borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t),
       );
     }
     return super.lerpTo(b, t);

packages/flutter/lib/src/painting/rounded_rectangle_border.dart

@@ -59,7 +59,7 @@ class RoundedRectangleBorder extends ShapeBorder {
     if (a is RoundedRectangleBorder) {
       return RoundedRectangleBorder(
         side: BorderSide.lerp(a.side, side, t),
-        borderRadius: BorderRadius.lerp(a.borderRadius, borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t),
       );
     }
     if (a is CircleBorder) {
@@ -78,7 +78,7 @@ class RoundedRectangleBorder extends ShapeBorder {
     if (b is RoundedRectangleBorder) {
       return RoundedRectangleBorder(
         side: BorderSide.lerp(side, b.side, t),
-        borderRadius: BorderRadius.lerp(borderRadius, b.borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t),
       );
     }
     if (b is CircleBorder) {
@@ -151,7 +151,7 @@ class _RoundedRectangleToCircleBorder extends ShapeBorder {
 
   final BorderSide side;
 
-  final BorderRadius borderRadius;
+  final BorderRadiusGeometry borderRadius;
 
   final double circleness;
 
@@ -175,7 +175,7 @@ class _RoundedRectangleToCircleBorder extends ShapeBorder {
     if (a is RoundedRectangleBorder) {
       return _RoundedRectangleToCircleBorder(
         side: BorderSide.lerp(a.side, side, t),
-        borderRadius: BorderRadius.lerp(a.borderRadius, borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t),
         circleness: circleness * t,
       );
     }
@@ -189,7 +189,7 @@ class _RoundedRectangleToCircleBorder extends ShapeBorder {
     if (a is _RoundedRectangleToCircleBorder) {
       return _RoundedRectangleToCircleBorder(
         side: BorderSide.lerp(a.side, side, t),
-        borderRadius: BorderRadius.lerp(a.borderRadius, borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t),
         circleness: ui.lerpDouble(a.circleness, circleness, t),
       );
     }
@@ -201,7 +201,7 @@ class _RoundedRectangleToCircleBorder extends ShapeBorder {
     if (b is RoundedRectangleBorder) {
       return _RoundedRectangleToCircleBorder(
         side: BorderSide.lerp(side, b.side, t),
-        borderRadius: BorderRadius.lerp(borderRadius, b.borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t),
         circleness: circleness * (1.0 - t),
       );
     }
@@ -215,7 +215,7 @@ class _RoundedRectangleToCircleBorder extends ShapeBorder {
     if (b is _RoundedRectangleToCircleBorder) {
       return _RoundedRectangleToCircleBorder(
         side: BorderSide.lerp(side, b.side, t),
-        borderRadius: BorderRadius.lerp(borderRadius, b.borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t),
         circleness: ui.lerpDouble(circleness, b.circleness, t),
       );
     }
@@ -244,22 +244,23 @@ class _RoundedRectangleToCircleBorder extends ShapeBorder {
     }
   }
 
-  BorderRadius _adjustBorderRadius(Rect rect) {
+  BorderRadius _adjustBorderRadius(Rect rect, TextDirection textDirection) {
+    final BorderRadius resolvedRadius = borderRadius.resolve(textDirection);
     if (circleness == 0.0)
-      return borderRadius;
-    return BorderRadius.lerp(borderRadius, BorderRadius.circular(rect.shortestSide / 2.0), circleness);
+      return resolvedRadius;
+    return BorderRadius.lerp(resolvedRadius, BorderRadius.circular(rect.shortestSide / 2.0), circleness);
   }
 
   @override
   Path getInnerPath(Rect rect, { TextDirection textDirection }) {
     return Path()
-      ..addRRect(_adjustBorderRadius(rect).toRRect(_adjustRect(rect)).deflate(side.width));
+      ..addRRect(_adjustBorderRadius(rect, textDirection).toRRect(_adjustRect(rect)).deflate(side.width));
   }
 
   @override
   Path getOuterPath(Rect rect, { TextDirection textDirection }) {
     return Path()
-      ..addRRect(_adjustBorderRadius(rect).toRRect(_adjustRect(rect)));
+      ..addRRect(_adjustBorderRadius(rect, textDirection).toRRect(_adjustRect(rect)));
   }
 
   @override
@@ -270,9 +271,9 @@ class _RoundedRectangleToCircleBorder extends ShapeBorder {
       case BorderStyle.solid:
         final double width = side.width;
         if (width == 0.0) {
-          canvas.drawRRect(_adjustBorderRadius(rect).toRRect(_adjustRect(rect)), side.toPaint());
+          canvas.drawRRect(_adjustBorderRadius(rect, textDirection).toRRect(_adjustRect(rect)), side.toPaint());
         } else {
-          final RRect outer = _adjustBorderRadius(rect).toRRect(_adjustRect(rect));
+          final RRect outer = _adjustBorderRadius(rect, textDirection).toRRect(_adjustRect(rect));
           final RRect inner = outer.deflate(width);
           final Paint paint = Paint()
             ..color = side.color;

packages/flutter/test/painting/rounded_rectangle_border_test.dart

@@ -34,6 +34,12 @@ void main() {
           strokeWidth: 0.0,
         )
     );
+
+    const RoundedRectangleBorder directional = RoundedRectangleBorder(
+      borderRadius: BorderRadiusDirectional.only(topStart: Radius.circular(20)),
+    );
+    expect(ShapeBorder.lerp(directional, c10, 1.0),
+           ShapeBorder.lerp(c10, directional, 0.0));
   });
 
   test('RoundedRectangleBorder and CircleBorder', () {