ios开发——Quartz坐标变化_ios quartz坐标

@implementation AppDelegate
 
 
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
 
    //创建根视图控制器
    ViewController* rootViewController = [[ViewController alloc] init];
    //创建自定义视图
    MyView* view = [[MyView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    //用自定义视图替换系统默认视图
    rootViewController.view = view;
    
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    [self.window makeKeyAndVisible];
    self.window.rootViewController = rootViewController;
    
    return YES;
}
@end

 
#import "MyView.h"
 
@implementation MyView
 
- (void)drawRect:(CGRect)rect {
 
    //填充白色背景
    [[UIColor whiteColor] setFill];
    UIRectFill(rect);
    
    //创建UIImage图片对象
    UIImage *uiImage = [UIImage imageNamed:@"cat"];
    //将UIImage图片对象转换为CGImage图片对象
    CGImageRef cgImage = uiImage.CGImage;
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextScaleCTM(context, 1, -1);//变化坐标
    CGContextTranslateCTM(context, 0, -uiImage.size.height);//变化坐标
    
    CGRect imageRect = CGRectMake(0, 0, uiImage.size.width, uiImage.size.height);
    CGContextDrawImage(context, imageRect, cgImage);
    
}
 
@end