iOS 画图讲解2

//layer上下文只能显示在drawRect里 

//当开启上下文时，绘制图形即可在viewDidLoad中实现

//位图的上下文

//UIGraphicsBeginImageContext()仅适用于非retina屏

//开启位图上下文

size:位图的尺寸

opaque:不透明是yes,透明就是no

scale:是否缩放上下文

UIGraphicsBeginImageContextWithOptions(image.size, NO, 0);

//绘制原始图片

[image drawAtPoint:CGPointZero];

[image drawInRect:CGRectMake(0, 0, image.size.width, image.size.height)];

//第一种

    NSString * info = @"@大欢";

    NSDictionary * dict = @{NSForegroundColorAttributeName:[UIColor whiteColor],

                            NSFontAttributeName:[UIFont systemFontOfSize:30]};

    [info drawAtPoint:CGPointMake(120, 200) withAttributes:dict];

//第二种

    UIBezierPath * path = [UIBezierPath bezierPathWithRect:CGRectMake(100, 100, 100, 100)];

    [[UIColor redColor] set];

    [path fill];

//第三种

    CGContextRef ctx = UIGraphicsGetCurrentContext();

    CGContextMoveToPoint(ctx, 20, 20);    

    CGContextAddLineToPoint(ctx, 40, 40);

    CGContextStrokePath(ctx);

    //生成一张新的图片，从位图上下文获取

    UIImage * newImage = UIGraphicsGetImageFromCurrentImageContext();

    //关闭图片上下文

    UIGraphicsEndImageContext();

    self.imageView.image = newImage;

2、图片等比例缩小

操作 写在 通过上下文获取图片 之前

 UIImage * image = [UIImage imageNamed:@"huoyanshan.jpg"];

    CGFloat newImageWH = image.size.height;

    //开启位图上下文

    UIGraphicsBeginImageContextWithOptions(CGSizeMake(newImageWH, newImageWH), NO, 0);

    UIBezierPath * path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, newImageWH, newImageWH)];

    //添加剪切

    [path addClip];

    //绘图

    [image drawAtPoint:CGPointZero];

    //通过上下文获取图片

    UIImage * newImage = UIGraphicsGetImageFromCurrentImageContext();

    //关闭上下文

    UIGraphicsEndImageContext();

    self.imageView.image = newImage;

3、画线

//纯代码执行的第一个方法

- (instancetype)initWithFrame:(CGRect)frame

{

    self = [super initWithFrame:frame];

    if (self) {

        [self setUp];

    }

    return self;

}

//故事板执行的第一个方法

- (void)awakeFromNib {

    [self setUp];

}

4、相册

//保存到手机相册

UIImageWriteToSavedPhotosAlbum(image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);

//创建相册

UIImagePickerController * imagePicker = [[UIImagePickerController alloc] init];

<UINavigationControllerDelegate, UIImagePickerControllerDelegate>写两个协议

  imagePicker.delegate = self;

//UIImagePickerControllerSourceTypePhotoLibrary 相册

//UIImagePickerControllerSourceTypeCamera 相机  

    imagePicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;    

    //允许编辑

    imagePicker.allowsEditing = YES;

    [self presentViewController:imagePicker animated:YES completion:nil];

}

//相册选择完成的方法

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info {

//编辑图片 如果allowsEditing为NO,image没有值

   _drawView.image = info[UIImagePickerControllerEditedImage];    

//原始图片

    _drawView.image = info[UIImagePickerControllerOriginalImage];

    [picker dismissViewControllerAnimated:YES completion:nil];

}

//取消选择

- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker {

    NSLog(@"取消选择");

    [picker dismissViewControllerAnimated:YES completion:nil];

}