# CGImageRef基本介绍及方法说明

在IOS开发中,我们时常会用到裁剪图片,重绘图片等方法,CGImageRef(像素位图)便是我们经常会使用到的一个对象.

## CGImageRef是什么

CGImageRef是定义在QuartzCore框架中的一个结构体指针,用C语言编写.在CGImage.h文件中,我们可以看到下面的定义:

```
typedef struct CGImage * CGImageRef;
```

CGImageRef 和 struct CGImage \* 是完全等价的.这个结构用来创建像素位图,可以通过操作存储的像素位来编辑图片.

QuartzCore这个框架是可移植的.

## CGImageRef相关的一些方法说明

* 返回标识符

```
CFTypeID CGImageGetTypeID(void)

//CFTypeID定义如下：

#if __LLP64__
typedef unsigned long long CFTypeID;
typedef unsigned long long CFOptionFlags;
typedef unsigned long long CFHashCode;
typedef signed long long CFIndex;
#else
typedef unsigned long CFTypeID;
typedef unsigned long CFOptionFlags;
typedef unsigned long CFHashCode;
typedef signed long CFIndex;
#endif
```

//这个方法返回的是一个编号,每个Core Foundation框架中得结构都会有一个这样的编号,它没有特殊的意义,只是一个标识符.

* 创建出一个CGImageRef类型的对象的方法

```
CGImageRef CGImageCreate(size_t width, size_t height,

    size_t bitsPerComponent, size_t bitsPerPixel, size_t bytesPerRow,

    CGColorSpaceRef space, CGBitmapInfo bitmapInfo, CGDataProviderRef provider,

    const CGFloat decode[], bool shouldInterpolate,

    CGColorRenderingIntent intent);
```

参数解释:

| 参数                | 说明                                                                  |
| ----------------- | ------------------------------------------------------------------- |
| sizt\_t           | 定义的一个可移植性的单位,在64位机器中为8字节,32位位4字节.                                   |
| width             | 图片宽度像素                                                              |
| height            | 图片高度像素                                                              |
| bitsPerComponent  | 每个颜色的比特数,例如在rgba-32模式下为8                                            |
| bitsPerPixel      | 每个像素的总比特数                                                           |
| bytesPerRow       | 每一行占用的字节数,注意这里的单位是字节                                                |
| space             | 颜色空间模式,例如const CFStringRef kCGColorSpaceGenericRGB 这个函数可以返回一个颜色空间对象 |
| bitmapInfo        | 位图像素布局                                                              |
| provider          | 数据源提供者                                                              |
| decode\[]         | 解码渲染数组                                                              |
| shouldInterpolate | 是否抗锯齿                                                               |
| intent            | 图片相关参数                                                              |

bitmapInfo的枚举:

```
typedef CF_OPTIONS(uint32_t, CGBitmapInfo) {
  kCGBitmapAlphaInfoMask = 0x1F,
  kCGBitmapFloatComponents = (1 << 8),

  kCGBitmapByteOrderMask = 0x7000,
  kCGBitmapByteOrderDefault = (0 << 12),
  kCGBitmapByteOrder16Little = (1 << 12),
  kCGBitmapByteOrder32Little = (2 << 12),
  kCGBitmapByteOrder16Big = (3 << 12),
  kCGBitmapByteOrder32Big = (4 << 12)
}
```

* 用于创建mask图片图层,可以设置其显示部分与不显示部分达到特殊的效果的方法,参数意义同上.

```
CGImageRef CGImageMaskCreate(size_t width, size_t height,

    size_t bitsPerComponent, size_t bitsPerPixel, size_t bytesPerRow,

    CGDataProviderRef provider, const CGFloat decode[], bool shouldInterpolate)
```

* 复制一个CGImageRef对象

```
CGImageRef CGImageCreateCopy(CGImageRef image)
```

* 通过JPEG数据源获取图像

```
CGImageRef CGImageCreateWithJPEGDataProvider(CGDataProviderRef

    source, const CGFloat decode[], bool shouldInterpolate,

    CGColorRenderingIntent intent)
```

* 通过PNG数据源获取图像

```
CGImageRef CGImageCreateWithPNGDataProvider(CGDataProviderRef source,

    const CGFloat decode[], bool shouldInterpolate,

    CGColorRenderingIntent intent)
```

* 截取图像的一个区域重绘图像

```
CGImageRef CGImageCreateWithImageInRect(CGImageRef image, CGRect rect)
```

* 截取mask图像的某一区域重绘

```
CGImageRef CGImageCreateWithMask(CGImageRef image, CGImageRef mask)
```

* 通过颜色分量数组创建位图

```
CGImageRef CGImageCreateWithMaskingColors(CGImageRef image,  const CGFloat components[])
```

* 通过颜色空间模式复制位图

```
CGImageRef CGImageCreateCopyWithColorSpace(CGImageRef image, CGColorSpaceRef space)
```

* 引用+1 -1

```
CGImageRef CGImageRetain(CGImageRef image)
void CGImageRelease(CGImageRef image)
```

最后必须要调用CGImageRelease释放位图对象否则会造成内存泄露

* 返回是否为Mask图层

```
bool CGImageIsMask(CGImageRef image)
```

* 获取相应属性

```
size_t CGImageGetWidth(CGImageRef image)
size_t CGImageGetHeight(CGImageRef image)

size_t CGImageGetBitsPerComponent(CGImageRef image)

size_t CGImageGetBitsPerPixel(CGImageRef image)

size_t CGImageGetBytesPerRow(CGImageRef image)

CGColorSpaceRef CGImageGetColorSpace(CGImageRef image)CG_EXTERN CGImageAlphaInfo CGImageGetAlphaInfo(CGImageRef image)

CGDataProviderRef CGImageGetDataProvider(CGImageRef image)

const CGFloat *CGImageGetDecode(CGImageRef image)

bool CGImageGetShouldInterpolate(CGImageRef image)

CGColorRenderingIntent CGImageGetRenderingIntent(CGImageRef image)

CGBitmapInfo CGImageGetBitmapInfo(CGImageRef image)
```

## CGImageRef与UIImage互转

UIImage虽然可以加载、显示各种格式的位图,甚至可以同时加载图片,接下来依次播放多张图片形成动画.但UIImage的功能依然有限,它不能对图片进行缩放、旋转,不能"挖取"源图片的指定区域等,这些功能可借助Quartz 2D的CGImageRef来实现.实际运用中我们就需要UIImage与CGImageRef之间相互转换,方法如下

```
//CGImageRef  转换成UIImage  

CGImageRef cgRef= CGBitmapContextCreateImage(context);  
UIImage* image = [UIImage imageWithCGImage: cgRef];  


//UIImage转换成CGImageRef  

UIImage *uiImage = [UIImage imageNamed:@"abc.png"];  
CGImageRef cgRef1 = uiImage.CGImage;
```


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