iOS 设置圆角阴影,避免离屏渲染

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iOS 控件设置圆角,避免离屏渲染。

离屏渲染:指GPU(图形处理器)在当前屏幕缓冲区外新开辟一个渲染缓冲区进行工作。这会给我们带来额外的性能损耗,如果这样的操作达到一定数量,会触发缓冲区的频繁合并和上下文的的频繁切换,会出现卡顿、掉帧现象。造成离屏渲染的原因有很多,如:shouldRasterize(光栅化)、mask(遮罩层)、shadows(阴影)、EdgeAnntialiasing(抗锯齿)、cornerRadius(圆角)等等。

 

下面说一下什么情况下设置圆角会造成离屏渲染:

//设置cornerRadius>0且masksToBounds为YES
view.layer.cornerRadius = 10.f;
view.layer.masksToBounds = YES;
//设置cornerRadius>0且masksToBounds为YES
view.layer.cornerRadius = 10.f;
view.clipToBounds = YES;
//像下面设置view.layer.mask
UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:imgView.bounds byRoundingCorners:UIRectCornerAllCorners cornerRadii:CGSizeMake(10.f, 10.f)];
CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
maskLayer.frame = view.bounds;
maskLayer.path = path.CGPath;
view.layer.mask = maskLayer;

上面第一种应该是最常用的,是在设置了圆角及masksToBounds为YES时,才会触发离屏渲染,而masksToBounds默认是NO,也就是说只要不设置这个属性就能避免很多情况了,下面说一下如何切一个不触发离屏渲染的圆角:

UIView、UITextField、UITextView等大部分控件都可以像下面这样设置:

view.layer.cornerRadius = 10.f;
view.layer.masksToBounds = NO;

有一些特殊情况,UILabel设置时,不要设置label.backgroundColor,应设置:

label.layer.cornerRadius = 10.f;
label.layer.backgroundColor = [UIColor whiteColor].CGColor;

有图片的UIButton、UIIMageView,用drawInRect绘制UIImage圆角:

UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:cornerRadius];
UIGraphicsBeginImageContextWithOptions(rect.size, false, [UIScreen mainScreen].scale);
CGContextAddPath(UIGraphicsGetCurrentContext(), bezierPath.CGPath);
CGContextClip(UIGraphicsGetCurrentContext());
[self drawInRect:rect];
CGContextDrawPath(UIGraphicsGetCurrentContext(), kCGPathFillStroke);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

查看离屏渲染,模拟器可以选中“Debug
– Color Off-screen Rendered”开启调试,真机可以用Instruments检测,“Instruments – Core Animation – Debug Options – Color
Offscreen-Rendered Yellow”开启调试,开启后,有离屏渲染的图层会变成高亮的黄色。

写了个离屏渲染的样例:


下面贴上代码:

控制器ViewController:

#import "ViewController.h"
#import "UIImage+HWCorner.h"
#define KMainW [UIScreen mainScreen].bounds.size.width
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
//创建控件
[self creatControl];
}
- (void)creatControl
{
CGFloat margin = 20.f;
CGFloat controlW = (KMainW - margin * 3) * 0.5;
NSArray *titleArray = @[@"离屏渲染", @"非离屏渲染"];
for (int i = 0; i < titleArray.count; i++) {
CGFloat controlX = margin + (controlW + margin) * i;
//UILabel
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(controlX, 30, controlW, 40)];
label.layer.backgroundColor = [[UIColor grayColor] CGColor];
label.text = titleArray[i];
label.textAlignment = NSTextAlignmentCenter;
label.layer.cornerRadius = label.bounds.size.height * 0.5;
label.layer.masksToBounds = i == 0 ? YES : NO;
[self.view addSubview:label];
//UIView
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(controlX, CGRectGetMaxY(label.frame) + margin, controlW, 40)];
view.backgroundColor = [UIColor grayColor];
view.layer.cornerRadius = view.bounds.size.height * 0.5;
view.layer.masksToBounds = i == 0 ? YES : NO;
[self.view addSubview:view];
//UIView若未添加子控件,设置view.layer.masksToBounds = YES;也不会造成离屏渲染
UIView *subView = [[UIView alloc] initWithFrame:CGRectMake(30, 0, controlW - 60, 40)];
subView.backgroundColor = [UIColor redColor];
[view addSubview:subView];
//UITextView
UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(controlX, CGRectGetMaxY(view.frame) + margin, controlW, 40)];
textView.userInteractionEnabled = NO;
textView.backgroundColor = [UIColor grayColor];
if (i == 0) {
/*
这里换了一种实现方法,用UIBezierPath赋值layer.mask,两种方式都会造成离屏渲染
textView.layer.cornerRadius = textView.bounds.size.height * 0.5;
textView.layer.masksToBounds = YES;
*/
UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:textView.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerTopRight cornerRadii:CGSizeMake(textView.bounds.size.height * 0.5, textView.bounds.size.height * 0.5)];
CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
maskLayer.frame = textView.bounds;
maskLayer.path = path.CGPath;
textView.layer.mask = maskLayer;
}else {
textView.layer.cornerRadius = textView.bounds.size.height * 0.5;
textView.layer.masksToBounds = NO;
}
[self.view addSubview:textView];
//UIButton
UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(controlX, CGRectGetMaxY(textView.frame) + margin, controlW, controlW)];
if (i == 0) {
[button setImage:[UIImage imageNamed:@"hero_1"] forState:UIControlStateNormal];
button.layer.cornerRadius = button.bounds.size.width * 0.5;
button.layer.masksToBounds = YES;
}else {
[button setImage:[[UIImage imageNamed:@"hero_1"] drawCornerInRect:button.bounds cornerRadius:button.bounds.size.width * 0.5] forState:UIControlStateNormal];
}
[self.view addSubview:button];
//UIImageView设置圆角
UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(controlX, CGRectGetMaxY(button.frame) + margin, controlW, controlW)];
if (i == 0) {
[imageView setImage:[UIImage imageNamed:@"hero_1"]];
imageView.layer.cornerRadius = imageView.bounds.size.width * 0.5;
imageView.layer.masksToBounds = YES;
}else {
[imageView setImage:[[UIImage imageNamed:@"hero_1"] drawCornerInRect:imageView.bounds cornerRadius:imageView.bounds.size.width * 0.5]];
}
[self.view addSubview:imageView];
//UIImageView若未添加子控件,设置imageView.layer.masksToBounds = YES;也不会造成离屏渲染
UIView *subImageView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, controlW, 40)];
subImageView.backgroundColor = [UIColor redColor];
subImageView.layer.cornerRadius = imageView.bounds.size.width * 0.5;
[imageView addSubview:subImageView];
//UIImageView设置阴影
CGFloat imgW = 70.f;
CGFloat imgPadding = (KMainW - imgW * 4 - margin * 2) / 3;
UIImageView *shadowImgView = [[UIImageView alloc] initWithFrame:CGRectMake(margin + (imgW + imgPadding) * 2 * i, CGRectGetMaxY(imageView.frame) + margin, imgW, imgW)];
[shadowImgView setImage:[UIImage imageNamed:@"hero_1"]];
shadowImgView.layer.shadowColor = [UIColor redColor].CGColor;
shadowImgView.layer.shadowOpacity = 0.8f;
shadowImgView.layer.shadowOffset = CGSizeMake(5, 5);
shadowImgView.layer.shadowRadius = 5.f;
if (i == 1) {
UIBezierPath *path = [UIBezierPath bezierPathWithRect:shadowImgView.bounds];
shadowImgView.layer.shadowPath = path.CGPath;
}
[self.view addSubview:shadowImgView];
//UIImageView设置阴影+圆角
UIImageView *shadowCorImgView = [[UIImageView alloc] initWithFrame:CGRectMake(margin + imgW + imgPadding + (imgW + imgPadding) * 2 * i, CGRectGetMinY(shadowImgView.frame), imgW, imgW)];
[shadowCorImgView setImage:[[UIImage imageNamed:@"hero_1"] drawCornerInRect:imageView.bounds cornerRadius:imageView.bounds.size.width * 0.5]];
shadowCorImgView.layer.shadowColor = [UIColor redColor].CGColor;
shadowCorImgView.layer.shadowOpacity = 0.8f;
shadowCorImgView.layer.shadowOffset = CGSizeMake(0, 0);
shadowCorImgView.layer.shadowRadius = 5.f;
if (i == 1) {
UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:shadowCorImgView.bounds cornerRadius:shadowCorImgView.bounds.size.height * 0.5];
shadowCorImgView.layer.shadowPath = path.CGPath;
}
[self.view addSubview:shadowCorImgView];
}
}
@end

UIImage分类,UIImage+HWCorner:

 

#import <UIKit/UIKit.h>
@interface UIImage (HWCorner)
//绘制图片圆角
- (UIImage *)drawCornerInRect:(CGRect)rect cornerRadius:(CGFloat)cornerRadius;
@end
/*** ---------------分割线--------------- ***/
#import "UIImage+HWCorner.h"
@implementation UIImage (HWCorner)
//绘制图片圆角
- (UIImage *)drawCornerInRect:(CGRect)rect cornerRadius:(CGFloat)cornerRadius
{
UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:cornerRadius];
UIGraphicsBeginImageContextWithOptions(rect.size, false, [UIScreen mainScreen].scale);
CGContextAddPath(UIGraphicsGetCurrentContext(), bezierPath.CGPath);
CGContextClip(UIGraphicsGetCurrentContext());
[self drawInRect:rect];
CGContextDrawPath(UIGraphicsGetCurrentContext(), kCGPathFillStroke);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
@end

最后说一下,只有在大量的离屏渲染情况时才会出现卡顿、掉帧等现象,没必要过分追求容不下一丝黄色。性能上Instruments工具还可以检测很多。写博客的初心是希望大家共同交流成长,博主水平有限难免有偏颇之处,欢迎批评指正。

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