Use CALayers to draw text (facebook#24387)

Summary:
The current technique we use to draw text uses linear memory, which means that when text is too long the UIView layer is unable to draw it. This causes the issue described [here](facebook#19453). On an iOS simulator the bug happens at around 500 lines which is quite annoying. It can also happen on a real device but requires a lot more text.

To be more specific the amount of text doesn't actually matter, it is the size of the UIView that we use to draw the text. When we use `[drawRect:]` the view creates a bitmap to send to the gpu to render, if that bitmap is too big it cannot render.

To fix this we can use `CATiledLayer` which will split drawing into smaller parts, that gets executed when the content is about to be visible. This drawing is also async which means the text can seem to appear during scroll. See https://developer.apple.com/documentation/quartzcore/calayer?language=objc.

`CATiledLayer` also adds some overhead that we don't want when rendering small amount of text. To fix this we can use either a regular `CALayer` or a `CATiledLayer` depending on the size of the view containing the text. I picked 1024 as the threshold which is about 1 screen and a half, and is still smaller than the height needed for the bug to occur when using a regular `CALayer` on a iOS simulator.

Also found this which addresses the problem in a similar manner and took some inspiration from the code linked there GitHawkApp/StyledTextKit#14 (comment)

Fixes facebook#19453

## Changelog

[iOS] [Fixed] - Use CALayers to draw text, fixes rendering for long text
Pull Request resolved: facebook#24387

Test Plan:
- Added the example I was using to verify the fix to RNTester.
- Made sure all other examples are still rendering properly.
- Tested text selection

Reviewed By: shergin

Differential Revision: D15918277

Pulled By: sammy-SC

fbshipit-source-id: c45409a8413e6e3ad272be39ba527a4e8d349e28

Libraries/Text/RCTText.xcodeproj/project.pbxproj

@@ -7,6 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		19461666225DC3B300E4E008 /* RCTTextRenderer.m in Sources */ = {isa = PBXBuildFile; fileRef = 19461664225DC3B300E4E008 /* RCTTextRenderer.m */; };
 		5956B130200FEBAA008D9D16 /* RCTRawTextShadowView.m in Sources */ = {isa = PBXBuildFile; fileRef = 5956B0FD200FEBA9008D9D16 /* RCTRawTextShadowView.m */; };
 		5956B131200FEBAA008D9D16 /* RCTRawTextViewManager.m in Sources */ = {isa = PBXBuildFile; fileRef = 5956B0FE200FEBA9008D9D16 /* RCTRawTextViewManager.m */; };
 		5956B132200FEBAA008D9D16 /* RCTSinglelineTextInputView.m in Sources */ = {isa = PBXBuildFile; fileRef = 5956B101200FEBA9008D9D16 /* RCTSinglelineTextInputView.m */; };
@@ -187,6 +188,8 @@
 /* End PBXCopyFilesBuildPhase section */
 
 /* Begin PBXFileReference section */
+		19461664225DC3B300E4E008 /* RCTTextRenderer.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = RCTTextRenderer.m; sourceTree = "<group>"; };
+		19461665225DC3B300E4E008 /* RCTTextRenderer.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = RCTTextRenderer.h; sourceTree = "<group>"; };
 		2D2A287B1D9B048500D4039D /* libRCTText-tvOS.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = "libRCTText-tvOS.a"; sourceTree = BUILT_PRODUCTS_DIR; };
 		58B5119B1A9E6C1200147676 /* libRCTText.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = libRCTText.a; sourceTree = BUILT_PRODUCTS_DIR; };
 		5956B0F9200FEBA9008D9D16 /* RCTConvert+Text.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "RCTConvert+Text.h"; sourceTree = "<group>"; };
@@ -360,6 +363,8 @@
 			children = (
 				5956B129200FEBAA008D9D16 /* NSTextStorage+FontScaling.h */,
 				5956B125200FEBAA008D9D16 /* NSTextStorage+FontScaling.m */,
+				19461665225DC3B300E4E008 /* RCTTextRenderer.h */,
+				19461664225DC3B300E4E008 /* RCTTextRenderer.m */,
 				5956B126200FEBAA008D9D16 /* RCTTextShadowView.h */,
 				5956B122200FEBAA008D9D16 /* RCTTextShadowView.m */,
 				5956B123200FEBAA008D9D16 /* RCTTextView.h */,
@@ -439,6 +444,7 @@
 			developmentRegion = English;
 			hasScannedForEncodings = 0;
 			knownRegions = (
+				English,
 				en,
 			);
 			mainGroup = 58B511921A9E6C1200147676;
@@ -504,6 +510,7 @@
 				5956B142200FEBAA008D9D16 /* RCTTextViewManager.m in Sources */,
 				5956B135200FEBAA008D9D16 /* RCTBaseTextInputView.m in Sources */,
 				5956B144200FEBAA008D9D16 /* RCTVirtualTextViewManager.m in Sources */,
+				19461666225DC3B300E4E008 /* RCTTextRenderer.m in Sources */,
 				5C245F39205E216A00D936E9 /* RCTInputAccessoryShadowView.m in Sources */,
 				5956B13B200FEBAA008D9D16 /* RCTMultilineTextInputViewManager.m in Sources */,
 				5956B134200FEBAA008D9D16 /* RCTSinglelineTextInputViewManager.m in Sources */,

Libraries/Text/Text/RCTTextRenderer.h

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <UIKit/UIKit.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * Used by text layers to render text. Note that UIKit crashes if this delegate is implemented
+ * directly on a UIView subclass since it already implements it for the view's root
+ * layer. This is why this is implemented in a separate class.
+ */
+@interface RCTTextRenderer : NSObject <CALayerDelegate>
+
+- (void)setTextStorage:(NSTextStorage *)textStorage contentFrame:(CGRect)contentFrame;
+
+@end
+
+NS_ASSUME_NONNULL_END

Libraries/Text/Text/RCTTextRenderer.m

@@ -0,0 +1,56 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import "RCTTextRenderer.h"
+
+#import "RCTTextAttributes.h"
+
+@implementation RCTTextRenderer
+{
+  NSTextStorage *_Nullable _textStorage;
+  CGRect _contentFrame;
+}
+
+- (void)setTextStorage:(NSTextStorage *)textStorage
+          contentFrame:(CGRect)contentFrame
+{
+  _textStorage = textStorage;
+  _contentFrame = contentFrame;
+}
+
+- (void)drawLayer:(CALayer *)layer
+        inContext:(CGContextRef)ctx;
+{
+  if (!_textStorage) {
+    return;
+  }
+
+  CGRect boundingBox = CGContextGetClipBoundingBox(ctx);
+  CGContextSaveGState(ctx);
+  UIGraphicsPushContext(ctx);
+
+  NSLayoutManager *layoutManager = _textStorage.layoutManagers.firstObject;
+  NSTextContainer *textContainer = layoutManager.textContainers.firstObject;
+
+  NSRange glyphRange =
+  [layoutManager glyphRangeForBoundingRect:boundingBox
+                           inTextContainer:textContainer];
+
+  [layoutManager drawBackgroundForGlyphRange:glyphRange atPoint:_contentFrame.origin];
+  [layoutManager drawGlyphsForGlyphRange:glyphRange atPoint:_contentFrame.origin];
+
+  UIGraphicsPopContext();
+  CGContextRestoreGState(ctx);
+}
+
+- (id<CAAction>)actionForLayer:(CALayer *)layer forKey:(NSString *)event
+{
+  // Disable all implicit animations.
+  return (id)[NSNull null];
+}
+
+@end

Libraries/Text/Text/RCTTextView.m

@@ -13,15 +13,36 @@
 #import <React/UIView+React.h>
 
 #import "RCTTextShadowView.h"
+#import "RCTTextRenderer.h"
+
+@interface RCTTextTiledLayer : CATiledLayer
+
+@end
+
+@implementation RCTTextTiledLayer
+
++ (CFTimeInterval)fadeDuration
+{
+  return 0.05;
+}
+
+@end
 
 @implementation RCTTextView
 {
-  CAShapeLayer *_highlightLayer;
   UILongPressGestureRecognizer *_longPressGestureRecognizer;
 
   NSArray<UIView *> *_Nullable _descendantViews;
   NSTextStorage *_Nullable _textStorage;
   CGRect _contentFrame;
+  RCTTextRenderer *_renderer;
+  // For small amount of text avoid the overhead of CATiledLayer and
+  // make render text synchronously. For large amount of text, use
+  // CATiledLayer to chunk text rendering and avoid linear memory
+  // usage.
+  CALayer *_Nullable _syncLayer;
+  RCTTextTiledLayer *_Nullable _asyncTiledLayer;
+  CAShapeLayer *_highlightLayer;
 }
 
 - (instancetype)initWithFrame:(CGRect)frame
@@ -31,6 +52,7 @@ - (instancetype)initWithFrame:(CGRect)frame
     self.accessibilityTraits |= UIAccessibilityTraitStaticText;
     self.opaque = NO;
     self.contentMode = UIViewContentModeRedraw;
+    _renderer = [RCTTextRenderer new];
   }
   return self;
 }
@@ -65,6 +87,7 @@ - (void)reactSetFrame:(CGRect)frame
   // This disables the frame animation, without affecting opacity, etc.
   [UIView performWithoutAnimation:^{
     [super reactSetFrame:frame];
+    [self configureLayer];
   }];
 }
 
@@ -91,55 +114,101 @@ - (void)setTextStorage:(NSTextStorage *)textStorage
     [self addSubview:view];
   }
 
-  [self setNeedsDisplay];
+  [_renderer setTextStorage:textStorage contentFrame:contentFrame];
+  [self configureLayer];
+  [self setCurrentLayerNeedsDisplay];
 }
 
-- (void)drawRect:(CGRect)rect
+- (void)configureLayer
 {
   if (!_textStorage) {
     return;
   }
 
+  CALayer *currentLayer;
+
+  CGSize screenSize = RCTScreenSize();
+  CGFloat textViewTileSize =  MAX(screenSize.width, screenSize.height) * 1.5;
+
+  if (self.frame.size.width > textViewTileSize || self.frame.size.height > textViewTileSize) {
+    // Cleanup sync layer
+    if (_syncLayer != nil) {
+      _syncLayer.delegate = nil;
+      [_syncLayer removeFromSuperlayer];
+      _syncLayer = nil;
+    }
+
+    if (_asyncTiledLayer == nil) {
+      RCTTextTiledLayer *layer = [RCTTextTiledLayer layer];
+      layer.delegate = _renderer;
+      layer.contentsScale = RCTScreenScale();
+      layer.tileSize = CGSizeMake(textViewTileSize, textViewTileSize);
+      _asyncTiledLayer = layer;
+      [self.layer addSublayer:layer];
+      [layer setNeedsDisplay];
+    }
+    _asyncTiledLayer.frame = self.bounds;
+    currentLayer = _asyncTiledLayer;
+  } else {
+    // Cleanup async tiled layer
+    if (_asyncTiledLayer != nil) {
+      _asyncTiledLayer.delegate = nil;
+      [_asyncTiledLayer removeFromSuperlayer];
+      _asyncTiledLayer = nil;
+    }
+
+    if (_syncLayer == nil) {
+      CALayer *layer = [CALayer layer];
+      layer.delegate = _renderer;
+      layer.contentsScale = RCTScreenScale();
+      _syncLayer = layer;
+      [self.layer addSublayer:layer];
+      [layer setNeedsDisplay];
+    }
+    _syncLayer.frame = self.bounds;
+    currentLayer = _syncLayer;
+  }
 
   NSLayoutManager *layoutManager = _textStorage.layoutManagers.firstObject;
   NSTextContainer *textContainer = layoutManager.textContainers.firstObject;
-
-  NSRange glyphRange = [layoutManager glyphRangeForTextContainer:textContainer];
-  [layoutManager drawBackgroundForGlyphRange:glyphRange atPoint:_contentFrame.origin];
-  [layoutManager drawGlyphsForGlyphRange:glyphRange atPoint:_contentFrame.origin];
+  NSRange glyphRange =
+    [layoutManager glyphRangeForTextContainer:textContainer];
 
   __block UIBezierPath *highlightPath = nil;
   NSRange characterRange = [layoutManager characterRangeForGlyphRange:glyphRange
                                                      actualGlyphRange:NULL];
+
   [_textStorage enumerateAttribute:RCTTextAttributesIsHighlightedAttributeName
                            inRange:characterRange
                            options:0
                         usingBlock:
-    ^(NSNumber *value, NSRange range, __unused BOOL *stop) {
-      if (!value.boolValue) {
-        return;
-      }
-
-      [layoutManager enumerateEnclosingRectsForGlyphRange:range
-                                 withinSelectedGlyphRange:range
-                                          inTextContainer:textContainer
-                                               usingBlock:
-        ^(CGRect enclosingRect, __unused BOOL *anotherStop) {
-          UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:CGRectInset(enclosingRect, -2, -2) cornerRadius:2];
-          if (highlightPath) {
-            [highlightPath appendPath:path];
-          } else {
-            highlightPath = path;
-          }
+   ^(NSNumber *value, NSRange range, __unused BOOL *stop) {
+     if (!value.boolValue) {
+       return;
+     }
+
+     [layoutManager enumerateEnclosingRectsForGlyphRange:range
+                                withinSelectedGlyphRange:range
+                                         inTextContainer:textContainer
+                                              usingBlock:
+      ^(CGRect enclosingRect, __unused BOOL *anotherStop) {
+        UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:CGRectInset(enclosingRect, -2, -2) cornerRadius:2];
+        if (highlightPath) {
+          [highlightPath appendPath:path];
+        } else {
+          highlightPath = path;
         }
+      }
       ];
-  }];
+   }];
 
   if (highlightPath) {
     if (!_highlightLayer) {
       _highlightLayer = [CAShapeLayer layer];
       _highlightLayer.fillColor = [UIColor colorWithWhite:0 alpha:0.25].CGColor;
-      [self.layer addSublayer:_highlightLayer];
+    }
+    if (![currentLayer.sublayers containsObject:_highlightLayer]) {
+      [currentLayer addSublayer:_highlightLayer];
     }
     _highlightLayer.position = _contentFrame.origin;
     _highlightLayer.path = highlightPath.CGPath;
@@ -149,6 +218,15 @@ - (void)drawRect:(CGRect)rect
   }
 }
 
+- (void)setCurrentLayerNeedsDisplay
+{
+  if (_asyncTiledLayer != nil) {
+    [_asyncTiledLayer setNeedsDisplay];
+  } else if (_syncLayer != nil) {
+    [_syncLayer setNeedsDisplay];
+  }
+  [_highlightLayer setNeedsDisplay];
+}
 
 - (NSNumber *)reactTagAtPoint:(CGPoint)point
 {
@@ -174,14 +252,18 @@ - (void)didMoveToWindow
 {
   [super didMoveToWindow];
 
+  // When an `RCTText` instance moves offscreen (possibly due to parent clipping),
+  // we unset the layer's contents until it comes onscreen again.
   if (!self.window) {
-    self.layer.contents = nil;
-    if (_highlightLayer) {
-      [_highlightLayer removeFromSuperlayer];
-      _highlightLayer = nil;
-    }
+    [_syncLayer removeFromSuperlayer];
+    _syncLayer = nil;
+    [_asyncTiledLayer removeFromSuperlayer];
+    _asyncTiledLayer = nil;
+    [_highlightLayer removeFromSuperlayer];
+    _highlightLayer = nil;
   } else if (_textStorage) {
-    [self setNeedsDisplay];
+    [self configureLayer];
+    [self setCurrentLayerNeedsDisplay];
   }
 }
 

RNTester/js/examples/Text/TextExample.ios.js

@@ -453,6 +453,23 @@ class TextWithCapBaseBox extends React.Component<*, *> {
   }
 }
 
+function LongTextExample() {
+  const [collapsed, setCollapsed] = React.useState(true);
+  return (
+    <View>
+      <Button
+        onPress={() => setCollapsed(state => !state)}
+        title="Toggle long text"
+      />
+      <Text>
+        {Array.from({length: collapsed ? 5 : 5000})
+          .map((_, i) => i)
+          .join('\n')}
+      </Text>
+    </View>
+  );
+}
+
 exports.title = '<Text>';
 exports.description = 'Base component for rendering styled text.';
 exports.displayName = 'TextExample';
@@ -1125,4 +1142,10 @@ exports.examples = [
       );
     },
   },
+  {
+    title: 'Async rendering for long text',
+    render: function() {
+      return <LongTextExample />;
+    },
+  },
 ];