[ASDisplayNode] If We Skipped Rendering Due to Zero-Area, Re-Render When We Get a Real Area (#2149)

* Add failing test case

* [_ASDisplayLayer] If we skipped render due to being zero-size, enqueue a render when we get a real size

* Remove pointless import

AsyncDisplayKit/ASImageNode.mm

@@ -301,7 +301,7 @@ struct ASImageNodeDrawParameters {
     imageModificationBlock    = drawParameter.imageModificationBlock;
   }
   
-  BOOL hasValidCropBounds = cropEnabled && !CGRectIsNull(cropDisplayBounds) && !CGRectIsEmpty(cropDisplayBounds);
+  BOOL hasValidCropBounds = cropEnabled && !CGRectIsEmpty(cropDisplayBounds);
   CGRect bounds = (hasValidCropBounds ? cropDisplayBounds : drawParameterBounds);
   
   ASDisplayNodeContextModifier preContextBlock = self.willDisplayNodeContentWithRenderingContext;

AsyncDisplayKit/Details/_ASDisplayLayer.mm

@@ -24,6 +24,7 @@
   // We can take this lock when we're setting displaySuspended and in setNeedsDisplay, so to not deadlock, this is recursive
   ASDN::RecursiveMutex _displaySuspendedLock;
   BOOL _displaySuspended;
+  BOOL _attemptedDisplayWhileZeroSized;
 
   struct {
     BOOL delegateDidChangeBounds:1;
@@ -102,6 +103,11 @@
     [super setBounds:bounds];
     self.asyncdisplaykit_node.threadSafeBounds = bounds;
   }
+
+  if (_attemptedDisplayWhileZeroSized && CGRectIsEmpty(bounds) == NO && self.needsDisplayOnBoundsChange == NO) {
+    _attemptedDisplayWhileZeroSized = NO;
+    [self setNeedsDisplay];
+  }
 }
 
 #if DEBUG // These override is strictly to help detect application-level threading errors.  Avoid method overhead in release.
@@ -189,9 +195,9 @@
 
 - (void)display
 {
+  ASDisplayNodeAssertMainThread();
   [self _hackResetNeedsDisplay];
 
-  ASDisplayNodeAssertMainThread();
   if (self.isDisplaySuspended) {
     return;
   }
@@ -201,7 +207,11 @@
 
 - (void)display:(BOOL)asynchronously
 {
-  id<_ASDisplayLayerDelegate> __attribute__((objc_precise_lifetime)) strongAsyncDelegate;
+  if (CGRectIsEmpty(self.bounds)) {
+    _attemptedDisplayWhileZeroSized = YES;
+  }
+
+  id<_ASDisplayLayerDelegate> NS_VALID_UNTIL_END_OF_SCOPE strongAsyncDelegate;
   {
     _asyncDelegateLock.lock();
     strongAsyncDelegate = _asyncDelegate;

AsyncDisplayKitTests/ASDisplayNodeTests.m

@@ -19,6 +19,7 @@
 #import "ASDisplayNodeTestsHelper.h"
 #import "UIView+ASConvenience.h"
 #import "ASCellNode.h"
+#import "ASImageNode.h"
 
 // Conveniences for making nodes named a certain way
 #define DeclareNodeNamed(n) ASDisplayNode *n = [[[ASDisplayNode alloc] init] autorelease]; n.name = @#n
@@ -1991,4 +1992,30 @@ static bool stringContainsPointer(NSString *description, const void *p) {
   XCTAssert([node loadStateChangedToNO]);
 }
 
+
+- (void)testThatNodeGetsRenderedIfItGoesFromZeroSizeToRealSizeButOnlyOnce
+{
+  NSString *path = [[NSBundle bundleForClass:[self class]] pathForResource:@"logo-square"
+                                                                    ofType:@"png" inDirectory:@"TestResources"];
+  UIImage *image = [UIImage imageWithContentsOfFile:path];
+  ASImageNode *node = [[[ASImageNode alloc] init] autorelease];
+  node.image = image;
+
+  // When rendered at zero-size, we get no contents
+  XCTAssert(CGSizeEqualToSize(node.bounds.size, CGSizeZero));
+  [node recursivelyEnsureDisplaySynchronously:YES];
+  XCTAssertNil(node.contents);
+
+  // When size becomes positive, we got some new contents
+  node.bounds = CGRectMake(0, 0, 100, 100);
+  [node recursivelyEnsureDisplaySynchronously:YES];
+  id contentsAfterRedisplay = node.contents;
+  XCTAssertNotNil(contentsAfterRedisplay);
+
+  // When size changes again, we do not get new contents
+  node.bounds = CGRectMake(0, 0, 1000, 1000);
+  [node recursivelyEnsureDisplaySynchronously:YES];
+  XCTAssertEqual(contentsAfterRedisplay, node.contents);
+}
+
 @end