#1673 - Re-render Clipping Corners when User Interface Style Changes (#…

…1674)

* This PR addresses an issue I raised with #1673 where the clipping corner layer doesn't get re-rendered when going from a dark to light user interface style. The fix is to add code in the `-asyncTraitCollectionDidChangeWithPreviousTraitCollection:` method that calls through to `-_updateClipCornerLayerContentsWithRadius:backgroundColor:` if the user interface style changes.

I've also added snapshot tests to verify that using clipping corners with a dynamic background color updates when the user interface style changes.

Source/ASDisplayNode.mm

@@ -442,16 +442,29 @@ - (void)asyncTraitCollectionDidChangeWithPreviousTraitCollection:(ASPrimitiveTra
     if (self.primitiveTraitCollection.userInterfaceStyle != previousTraitCollection.userInterfaceStyle) {
       // When changing between light and dark mode, often the entire node needs to re-render.
       // This change doesn't happen frequently so it's fairly safe to render nodes again
-      if (_loaded(self) && self.isLayerBacked) {
-        // Background colors do not dynamically update for layer backed nodes since they utilize CGColorRef
-        // instead of UIColor. We utilize the _backgroundColor instance variable to track the full dynamic color
-        // and apply any changes here when trait collection updates occur.
-        CGColorRef cgBackgroundColor = _backgroundColor.CGColor;
-        if (!CGColorEqualToColor(_layer.backgroundColor, cgBackgroundColor)) {
-          _layer.backgroundColor = cgBackgroundColor;
+      BOOL needsClippingCornerUpdate = NO;
+      CGFloat cornerRadius = _cornerRadius;
+      ASCornerRoundingType cornerRoundingType = _cornerRoundingType;
+      UIColor *backgroundColor = self.backgroundColor;
+      if (_loaded(self)) {
+        if (self.isLayerBacked) {
+          // Background colors do not dynamically update for layer backed nodes since they utilize CGColorRef
+          // instead of UIColor. We utilize the _backgroundColor instance variable to track the full dynamic color
+          // and apply any changes here when trait collection updates occur.
+          CGColorRef cgBackgroundColor = backgroundColor.CGColor;
+          if (!CGColorEqualToColor(_layer.backgroundColor, cgBackgroundColor)) {
+            _layer.backgroundColor = cgBackgroundColor;
+          }
+        }
+        // If we have clipping corners, re-render the clipping corner layer upon user interface style change
+        if (cornerRoundingType == ASCornerRoundingTypeClipping && cornerRadius > 0.0f) {
+          needsClippingCornerUpdate = YES;
         }
       }
       __instanceLock__.unlock();
+      if (needsClippingCornerUpdate) {
+        [self _updateClipCornerLayerContentsWithRadius:cornerRadius backgroundColor:backgroundColor];
+      }
       [self setNeedsDisplay];
       return;
     }

Tests/ASDisplayNodeSnapshotTests.mm

@@ -61,18 +61,49 @@ - (void)testPrecompositedCornerRounding
 
 - (void)testClippingCornerRounding
 {
+#if AS_AT_LEAST_IOS13
+  if (@available(iOS 13.0, *)) {
+    ASConfiguration *config = [ASConfiguration new];
+    config.experimentalFeatures = ASExperimentalTraitCollectionDidChangeWithPreviousCollection;
+    [ASConfigurationManager test_resetWithConfiguration:config];
+  }
+#endif
+
   for (CACornerMask c = 1; c <= kASCACornerAllCorners; c |= (c << 1)) {
     auto node = [[ASImageNode alloc] init];
     auto bounds = CGRectMake(0, 0, 100, 100);
     node.image = BlueImageMake(bounds);
     node.frame = bounds;
     node.cornerRoundingType = ASCornerRoundingTypeClipping;
+#if AS_AT_LEAST_IOS13
+    if (@available(iOS 13.0, *)) {
+      node.backgroundColor = UIColor.systemBackgroundColor;
+    } else {
+      node.backgroundColor = UIColor.greenColor;
+    }
+#else
     node.backgroundColor = UIColor.greenColor;
+#endif
     node.maskedCorners = c;
     node.cornerRadius = 15;
     // A layout pass is required, because that's where we lay out the clip layers.
     [node.layer layoutIfNeeded];
+
+#if AS_AT_LEAST_IOS13
+    if (@available(iOS 13.0, *)) {
+      [[UITraitCollection traitCollectionWithUserInterfaceStyle:UIUserInterfaceStyleLight] performAsCurrentTraitCollection:^{
+        ASSnapshotVerifyNode(node, ([NSString stringWithFormat:@"%d-light", (int)c]));
+      }];
+
+      [[UITraitCollection traitCollectionWithUserInterfaceStyle:UIUserInterfaceStyleDark] performAsCurrentTraitCollection:^{
+        ASSnapshotVerifyNode(node, ([NSString stringWithFormat:@"%d-dark", (int)c]));
+      }];
+    } else {
+      ASSnapshotVerifyNode(node, ([NSString stringWithFormat:@"%d", (int)c]));
+    }
+#else
     ASSnapshotVerifyNode(node, ([NSString stringWithFormat:@"%d", (int)c]));
+#endif
   }
 }