在iOS中，對UIView或UIimageVIew使用layer.cornerRadius圓角設(shè)置時，會很耗性能，也會影響UI流暢，造成App很卡，當(dāng)關(guān)閉了圓角后，重新運行就會流暢多了。但是產(chǎn)品的需求必須加圓角，沒辦法，去stackoverflow找方案，發(fā)現(xiàn)方法都大同小異，只不過是繪制上做一些優(yōu)化。后來查看layer的頭文件，最后找到了一個牛B的屬性

[cpp] view plaincopy

    /* When true, the layer is rendered as a bitmap in its local coordinate 
     * space ("rasterized"), then the bitmap is composited into the 
     * destination (with the minificationFilter and magnificationFilter 
     * properties of the layer applied if the bitmap needs scaling). 
     * Rasterization occurs after the layer's filters and shadow effects 
     * are applied, but before the opacity modulation. As an implementation 
     * detail the rendering engine may attempt to cache and reuse the 
     * bitmap from one frame to the next. (Whether it does or not will have 
     * no affect on the rendered output.) 
     * 
     * When false the layer is composited directly into the destination 
     * whenever possible (however, certain features of the compositing 
     * model may force rasterization, e.g. adding filters). 
     * 
     * Defaults to NO. Animatable. */  
      
    @property BOOL shouldRasterize;  
      
    /* The scale at which the layer will be rasterized (when the 
     * shouldRasterize property has been set to YES) relative to the 
     * coordinate space of the layer. Defaults to one. Animatable. */  
      
    @property CGFloat rasterizationScale;  

view.layer.shouldRasterize = YES(光柵化)的使用

當(dāng)shouldRasterize設(shè)成true時，layer被渲染成一個bitmap，并緩存起來，等下次使用時不會再重新去渲染了。實現(xiàn)圓角本身就是在做顏色混合（blending），如果每次頁面出來時都blending，消耗太大，這時shouldRasterize = yes，下次就只是簡單的從渲染引擎的cache里讀取那張bitmap，節(jié)約系統(tǒng)資源。

額外收獲：如果在滾動tableView時，每次都執(zhí)行圓角設(shè)置，肯定會阻塞UI，設(shè)置這個將會使滑動更加流暢。