UIWebTiledView是UIWebBrowserView->UIWebDocumentView->UIWebTiledView继承链中的老爷子，但这三个类的职能却是MVC的关系，UIWebBrowserView是Controller，UIWebDocumentView是Model，UIWebTiledView是View。（这也是我第一次见到这样的设计，很有意思）
它的声明为： （代码好长，点此跳过）
@interface UIWebTiledView : UIView
{
WAKWindow *_wakWindow;
int _inGestureType;
int _tilingArea;
BOOL _didFirstTileLayout;
BOOL _layoutTilesInMainThread;
BOOL _tilingModeIsLocked;
BOOL _allowsPaintingAndScriptsWhilePanning;
}
- (id)wakWindow;
- (void)setLayoutTilesInMainThread:(BOOL)arg1;
- (BOOL)layoutTilesInMainThread;
- (void)dumpTiles;
- (void)removeForegroundTiles;
- (void)removeAllTiles;
- (void)removeAllNonVisibleTiles;
- (BOOL)keepsZoomedOutTiles;
- (void)setKeepsZoomedOutTiles:(BOOL)arg1;
- (BOOL)tilesOpaque;
- (void)setTilesOpaque:(BOOL)arg1;
- (BOOL)tileDrawingEnabled;
- (void)setTileDrawingEnabled:(BOOL)arg1;
- (BOOL)logsTilingChanges;
- (void)setLogsTilingChanges:(BOOL)arg1;
- (BOOL)isTilingEnabled;
- (void)setTilingEnabled:(BOOL)arg1;
- (unsigned int)adjustedMaxTileCount;
- (unsigned int)maxTileCount;
- (void)setMaxTileCount:(unsigned int)arg1;
- (BOOL)drawsGrid;
- (void)setDrawsGrid:(BOOL)arg1;
- (struct CGSize)tileSize;
- (void)setTileSize:(struct CGSize)arg1;
- (void)setTransform:(struct CGAffineTransform)arg1;
- (void)setNeedsDisplay;
- (void)setNeedsDisplayInRect:(struct CGRect)arg1;
- (void)_didScroll;
- (void)setNeedsLayout;
- (void)setAllowsPaintingAndScriptsWhilePanning:(BOOL)arg1;
- (BOOL)allowsPaintingAndScriptsWhilePanning;
- (void)unlockTilingMode;
- (void)lockTilingMode;
- (int)tilingArea;
- (void)setTilingArea:(int)arg1;
- (void)setInGesture:(int)arg1;
- (void)updateTilingMode;
- (void)willMoveToWindow:(id)arg1;
- (void)_screenChanged:(id)arg1;
- (void)layoutSubviews;
- (void)layoutTilesNowForRect:(struct CGRect)arg1;
- (void)layoutTilesNowOnWebThread;
- (void)layoutTilesNow;
- (struct CGRect)visibleRect;
- (void)setWAKWindow:(id)arg1;
- (struct WKWindow *)wkWindow;
- (void)dealloc;
- (id)initWithFrame:(struct CGRect)arg1;
- (void)_updateForScreen:(id)arg1;
@end
可以看到好多名字带Tile这个词，也说明了此类专门负责绘制，而tile是分块渲染的意思，这是为了更好地利用GPU和显存。tile rendering大致意思是把屏幕分成几块区域，按照一定顺序来并行绘制这些区域，而不是一整块屏幕一起绘制，详细的信息可参考wiki：http://en.wikipedia.org/wiki/Tiled_rendering。iDevice都是用PowerVR的显卡，它正是分块渲染技术的先锋之一，也可见iOS的设计有针对硬件做优化，非常用心。
从函数和变量名看，UIWebTiledView有这些作用：
- 确定分块的排版是在主线程还是webThread
- 设置需要重排版、重绘，发起分块排版
- 确定分块模式
- 设置绘图区大小和transform等。
WAKWindow是UIWebTiledView的组合对象之一，其声明如下：（代码好长，点此跳过）
@interface WAKWindow : WAKResponder
{
struct WKWindow *_wkWindow;
CALayer *_hostLayer;
struct TileCache *_tileCache;
struct CGRect _cachedVisibleRect;
CALayer *_rootLayer;
struct CGSize _screenSize;
struct CGSize _availableScreenSize;
float _screenScale;
struct CGRect _frame;
BOOL _useOrientationDependentFontAntialiasing;
}
+ (id)currentEvent;
+ (BOOL)hasLandscapeOrientation;
+ (void)setOrientationProvider:(id)arg1;
+ (id)_wrapperForWindowRef:(struct WKWindow *)arg1;
@property(nonatomic) BOOL useOrientationDependentFontAntialiasing; // @synthesize useOrientationDependentFontAntialiasing=_useOrientationDependentFontAntialiasing;
- (id).cxx_construct;
- (id)recursiveDescription;
- (id)description;
- (void)dumpTiles;
- (void)setAcceleratedDrawingEnabled:(BOOL)arg1;
- (void)setTilePaintCountsVisible:(BOOL)arg1;
- (void)setTileBordersVisible:(BOOL)arg1;
- (id)hostLayer;
- (void)didRotate;
- (void)willRotate;
- (void)displayRect:(struct CGRect)arg1;
- (BOOL)hasPendingDraw;
- (BOOL)keepsZoomedOutTiles;
- (void)setKeepsZoomedOutTiles:(BOOL)arg1;
- (float)currentTileScale;
- (void)setCurrentTileScale:(float)arg1;
- (float)zoomedOutTileScale;
- (void)setZoomedOutTileScale:(float)arg1;
- (int)tilingDirection;
- (void)setTilingDirection:(int)arg1;
- (int)tilingMode;
- (void)setTilingMode:(int)arg1;
- (void)removeForegroundTiles;
- (void)removeAllTiles;
- (void)removeAllNonVisibleTiles;
- (struct CGRect)visibleRect;
- (void)setTilesOpaque:(BOOL)arg1;
- (BOOL)tilesOpaque;
- (void)setNeedsDisplayInRect:(struct CGRect)arg1;
- (void)setNeedsDisplay;
- (void)layoutTilesNowForRect:(struct CGRect)arg1;
- (void)layoutTilesNow;
- (void)layoutTiles;
- (void)sendMouseMoveEvent:(id)arg1 contentChange:(int *)arg2;
- (void)sendEventSynchronously:(id)arg1;
- (void)sendEvent:(id)arg1;
- (struct WKWindow *)_windowRef;
- (id)rootLayer;
- (void)setRootLayer:(id)arg1;
- (float)screenScale;
- (void)setScreenScale:(float)arg1;
- (struct CGSize)availableScreenSize;
- (void)setAvailableScreenSize:(struct CGSize)arg1;
- (struct CGSize)screenSize;
- (void)setScreenSize:(struct CGSize)arg1;
- (void)setContentRect:(struct CGRect)arg1;
- (struct CGRect)frame;
- (void)setFrame:(struct CGRect)arg1 display:(BOOL)arg2;
- (BOOL)makeFirstResponder:(id)arg1;
- (int)keyViewSelectionDirection;
- (void)makeKeyWindow;
- (BOOL)isKeyWindow;
- (struct CGPoint)convertScreenToBase:(struct CGPoint)arg1;
- (struct CGPoint)convertBaseToScreen:(struct CGPoint)arg1;
- (id)_newFirstResponderAfterResigning;
- (BOOL)makeViewFirstResponder:(id)arg1;
- (id)firstResponder;
- (void)close;
- (id)contentView;
- (void)setContentView:(id)arg1;
- (void)dealloc;
- (id)initWithFrame:(struct CGRect)arg1;
- (id)initWithLayer:(id)arg1;
@end
根据之前《WebCore::Widget浅探》的研究，WAKWindow是模仿NSWindow的，不过也有iOS的特性。它的成员变量TileCache是对分块做缓存，可重复利用。每块Tile都会对应一个CALayer对象，所以也有成员变量叫rootLayer。 hostLayer则是放置用作硬件加速的layer的（这个不深入讲了）。
总结之：UIWebTiledView和WAKWindow共同负责页面的绘制，包括分块、排版、提供CALayer的context（绘图上下文）、缓存Layer、交互（缩放、滚动等）。WAKWindow还兼做分派用户操作信息的工作（sendEvent）。
