Core Animation 负责将bitmap绑定提交到 GPU；
Core Animation一头连着CPU，一头连着GPU。
ZSTest`-[ZSDTCoreTextCell drawRect:](self=0x00007fb28b08ea00, _cmd="drawRect:", rect=(origin = (x = 0, y = 0), size = (width = 375, height = 79))) at ZSDTCoreTextCell.m:33
UIKitCore`-[UIView(CALayerDelegate) drawLayer:inContext:] + 550
QuartzCore`-[CALayer drawInContext:] + 285
QuartzCore`CABackingStoreUpdate_ + 173
QuartzCore`___ZN2CA5Layer8display_Ev_block_invoke + 44
QuartzCore`-[CALayer _display] + 2064
QuartzCore`CA::Context::commit_transaction(CA::Transaction*) + 634
QuartzCore`CA::Transaction::commit() + 576
QuartzCore`CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) + 76