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fix view clipping to operate on ui hierachy
There was a bug in the view clipping logic.
Clipping works on uiview hierarchy, but I've been using `reactSuperview` to get clipping rect for my parent.
This is incorrect in a case where these two hierarchies don't match and there are some views between a view and its `reactSuperview`.

So we should really use normal `superview`. A minor complication is that `superview` is `nil` if we are clipped.
We could remember what our last `superview` was, but that's extra data we have to manage. Instead I use one clever trick to avoid doing so.
(Let me know if it makes sense based on my inline documentation.)

Reviewed By: mmmulani

Differential Revision: D4182647

fbshipit-source-id: 779cbcec0bd08eb270c3727c9c5cb9c080c4a2a4
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majak authored and Facebook Github Bot committed Nov 16, 2016
1 parent b123cc2 commit 26e373c903011bfa46000ff045777d802970d779
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Showing 2 changed files with 41 additions and 2 deletions.
@@ -369,4 +369,39 @@ - (void)testScrollViewClipsDuringScrolling
XCTAssert([[NSSet setWithArray:contentView.subviews] isEqualToSet:[NSSet setWithArray:(@[rowView2, rowView3])]]);

In this test case the react view hiearchy is
clippingView -> directReactChildView -> deeperChildView
while the uiview hierarchy is
clippingView -> nonReactChildView -> directReactChildView -> deeperChildView
- (void)testClippingWhenReactHierarchyDoesntMatchUIHierarchy
RCTView *clippingView = [RCTView new];
[clippingView reactSetFrame:CGRectMake(0, 0, 50, 50)];

RCTView *directReactChildView = [RCTView new];
[directReactChildView reactSetFrame:CGRectMake(-50, 0, 100, 50)];
[clippingView insertReactSubview:directReactChildView atIndex:0];
[clippingView didUpdateReactSubviews];

RCTView *deeperChildView = [RCTView new];
[deeperChildView reactSetFrame:CGRectMake(0, 0, 50, 50)];
[directReactChildView insertReactSubview:deeperChildView atIndex:0];
[directReactChildView didUpdateReactSubviews];

UIView *nonReactChildView = [UIView new];
[nonReactChildView setFrame:CGRectMake(50, 0, 50, 50)];
[clippingView addSubview:nonReactChildView];
[nonReactChildView addSubview:directReactChildView];

[clippingView rct_setRemovesClippedSubviews:YES];
[directReactChildView reactSetFrame:CGRectMake(-50, 0, 99, 50)];

XCTAssertEqual(clippingView.subviews.count, 1u);
XCTAssertEqual(nonReactChildView.subviews.count, 1u);
XCTAssertEqual(directReactChildView.subviews.count, 1u);

@@ -287,8 +287,12 @@ - (void)rct_reclip
if (!self.rct_nextClippingView && !self.rct_removesClippedSubviews) {
// If we are currently clipped our active clipping rect would be null rect. That's why we ask for out superview's.
CGRect clippingRectForSuperview = self.reactSuperview ? [self.reactSuperview rct_activeClippingRect] : CGRectInfinite;
// If we are currently clipped our active clipping rect would be null rect. That's why we ask for our superview's.
// Actually it's not that simple. Clipping logic operates on uiview hierarchy. If the current view is clipped we cannot use its superview, since its nil.
// Fortunately we can use `reactSuperview`. UI and React view hierachies doesn't have to match, but when they don't match we don't clip.
// Therefore because this view is clipped it means its reactSuperview is the same as its (clipped) UI superview.
UIView *clippingRectSource = self.superview ? self.superview : self.reactSuperview;
CGRect clippingRectForSuperview = clippingRectSource ? [clippingRectSource rct_activeClippingRect] : CGRectInfinite;
if (CGRectIsNull(clippingRectForSuperview)) {

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