現在存在的問題
如果一個APP中可以根據用戶喜好，更改APP中圖片的顏色，則設計師必須重復修改圖片，開發者圖片文件重命名、移動和導入無用功較多，下載安裝包較大。
解決方案
用blending給這張圖片加上另一個純色作為tint，并保持原來的alpha通道，然后結合Core Graphics。步驟如下：
1.創建一個上下文用以畫新的圖片
2.將新的tintColor設置為填充顏色
3.將原圖片畫在創建的上下文中，并用新的填充色著色（注意保持alpha通道）
4.從當前上下文中取得圖片并返回
代碼示例
UIImage+tint
#import "UIImage+tint.h"
@implementation UIImage (tint)
- (UIImage *)imageWithTintColor:(UIColor *)tintColor blendMode:(CGBlendMode)blendMode
{
UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0f);
[tintColor setFill];//填充顏色
CGRect bounds = CGRectMake(0, 0, self.size.width, self.size.height);
UIRectFill(bounds);
//設置繪畫透明混合模式和透明度
[self drawInRect:bounds blendMode:blendMode alpha:1.0f];
if (blendMode == kCGBlendModeOverlay) {
//保留透明度信息
[self drawInRect:bounds blendMode:kCGBlendModeDestinationIn alpha:1.0f];
}
UIImage * tintedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return tintedImage;
}
@end
ViewController
#import "ViewController.h"
#import "UIImage+tint.h"
@interface ViewController ()
@property (nonatomic, strong) UIImageView * imageView;
@property (nonatomic, strong) UILabel * msgLabel;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[self createUI];
}
- (void)createUI
{
_imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image.png"]];
_imageView.center = self.view.center;
_imageView.userInteractionEnabled = YES;
UITapGestureRecognizer * tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(changeBlendMode:)];
tap.numberOfTouchesRequired = 1;
tap.numberOfTapsRequired = 1;
[_imageView addGestureRecognizer:tap];
[self.view addSubview:_imageView];
_msgLabel = [[UILabel alloc] initWithFrame:CGRectMake(20, CGRectGetMaxY(_imageView.frame) + 20, CGRectGetWidth(self.view.frame) - 40, 120)];
_msgLabel.numberOfLines = 0;
_msgLabel.text = @"在屏幕中繪圖時設置透明度；點擊圖片切換為混合模式繪制的圖片";
_msgLabel.textAlignment = NSTextAlignmentCenter;
_msgLabel.textColor = [UIColor blackColor];
_msgLabel.layer.borderColor = [UIColor grayColor].CGColor;
_msgLabel.layer.borderWidth = 1.0;
[self.view addSubview:_msgLabel];
}
- (void)changeBlendMode:(UIGestureRecognizer*)gesture
{
static CGBlendMode blendMode = kCGBlendModeNormal;
NSString *strMsg;
switch (blendMode) {
case kCGBlendModeNormal:
strMsg = @"kCGBlendModeNormal:正常；也是默認的模式。前景圖會覆蓋背景圖";
break;
case kCGBlendModeMultiply:
strMsg = @"kCGBlendModeMultiply:正片疊底；混合了前景和背景的顏色，最終顏色比原來的都暗";
break;
case kCGBlendModeScreen:
strMsg = @"kCGBlendModeScreen:濾色；把前景和背景圖的顏色先反過來，然后混合";
break;
case kCGBlendModeOverlay:
strMsg = @"kCGBlendModeOverlay:覆蓋：能保留灰度信息，結合kCGBlendModeDestinationIn能保留透明度信息，在imageWithBlendMode方法中兩次執行drawInRect方法實現我們的基本需求";
break;
case kCGBlendModeDarken:
strMsg = @"kCGBlendModeDarken:變暗";
break;
case kCGBlendModeLighten:
strMsg = @"kCGBlendModeLighten:變亮";
break;
case kCGBlendModeColorDodge:
strMsg = @"kCGBlendModeColorDodge:顏色變淡";
break;
case kCGBlendModeColorBurn:
strMsg = @"kCGBlendModeColorBurn:顏色加深";
break;
case kCGBlendModeHardLight:
strMsg = @"kCGBlendModeHardLight:強光";
break;
case kCGBlendModeSoftLight:
strMsg = @"kCGBlendModeSoftLight:柔光";
break;
case kCGBlendModeDifference:
strMsg = @"kCGBlendModeDifference:插值";
break;
case kCGBlendModeExclusion:
strMsg = @"kCGBlendModeExclusion:排除";
break;
case kCGBlendModeHue:
strMsg = @"kCGBlendModeHue:色調";
break;
case kCGBlendModeSaturation:
strMsg = @"kCGBlendModeSaturation:飽和度";
break;
case kCGBlendModeColor:
strMsg = @"kCGBlendModeColor:顏色";
break;
case kCGBlendModeLuminosity:
strMsg = @"kCGBlendModeLuminosity:亮度";
break;
//Apple額外定義的枚舉
//R: premultiplied result, 表示混合結果
//S: Source, 表示源顏色(Sa對應透明度值: 0.0-1.0)
//D: destination colors with alpha, 表示帶透明度的目標顏色(Da對應透明度值: 0.0-1.0)
case kCGBlendModeClear:
strMsg = @"kCGBlendModeClear:R = 0";
break;
case kCGBlendModeCopy:
strMsg = @"kCGBlendModeCopy:R = S";
break;
case kCGBlendModeSourceIn:
strMsg = @"kCGBlendModeSourceIn:R = S * Da";
break;
case kCGBlendModeSourceOut:
strMsg = @"kCGBlendModeSourceOut:R = S * (1 - Da)";
break;
case kCGBlendModeSourceAtop:
strMsg = @"kCGBlendModeSourceAtop:R = S * Da + D * (1 - Da)";
break;
case kCGBlendModeDestinationOver:
strMsg = @"kCGBlendModeDestinationOver:R = S * (1 - Da) + D";
break;
case kCGBlendModeDestinationIn:
strMsg = @"kCGBlendModeDestinationIn: R = D * Sa;保留透明度信息";
break;
case kCGBlendModeDestinationOut:
strMsg = @"kCGBlendModeDestinationOut: R = D * (1 - Sa)";
break;
case kCGBlendModeDestinationAtop:
strMsg = @"kCGBlendModeDestinationAtop: R = S * (1 - Da) + D * Sa";
break;
case kCGBlendModeXOR:
strMsg = @"kCGBlendModeXOR: R = S * (1 - Da) + D * (1 - Sa)";
break;
case kCGBlendModePlusDarker:
strMsg = @"KCGBlendModePlusDarker: R = MAX(0, (1 - D) + (1 - S))";
break;
case kCGBlendModePlusLighter:
strMsg = @"kCGBlendModePlusLighter: R = MIN(1, S + D)（最后一種混合模式）";
break;
default:
break;
}
_imageView.image = [[UIImage imageNamed:@"image.png"] imageWithTintColor:[UIColor orangeColor] blendMode:blendMode];
_msgLabel.text = strMsg;
blendMode ++;
if (blendMode > kCGBlendModePlusLighter) {
blendMode = kCGBlendModeNormal;
}
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
注：用kCGBlendModeOverlay能保留灰度信息，用kCGBlendModeDestinationIn能保留透明度信息。
因為每次使用UIImage+tint的方法繪圖時，都使用了CG的繪制方法，這就意味著每次調用都會是用到CPU的Offscreen drawing，大量使用的話可能導致性能的問題。對于這里的UIImage+tint的實現，可以寫一套緩存的機制，來確保大量重復的元素只在load的時候blend一次，之后將其緩存在內存中以快速讀取。這是一個權衡的問題，在時間和空間中做出正確的平衡和選擇是程序設計的樂趣所在。
參考鏈接
iOS中使用blend改變圖片顏色
