iOS 画图讲解2

1、图片水印

//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];

}