使用CGBitmapContextCreate创建绘制图片的上下文
CGContextRef CGBitmapContextCreate （
void *data，
size_t width，
size_t height，
size_t bitsPerComponent，
size_t bytesPerRow，
CGColorSpaceRef colorspace，
CGBitmapInfo bitmapInfo
）;
- 参数data指向绘图操作被渲染的内存区域，这个内存区域大小应该为（bytesPerRow*height）个字节。如果对绘制操作被渲染的内存区域并无特别的要求，那么可以传递NULL给参数date。
- 参数width代表被渲染内存区域的宽度。
- 参数height代表被渲染内存区域的高度。
- 参数bitsPerComponent被渲染内存区域中组件在屏幕每个像素点上需要使用的bits位，举例来说，如果使用32-bit像素和RGB颜色格式，那么RGBA颜色格式中每个组件在屏幕每个像素点上需要使用的bits位就为32/4=8。
- 参数bytesPerRow代表被渲染内存区域中每行所使用的bytes位数。
- 参数colorspace用于被渲染内存区域的“位图上下文”。
- 参数bitmapInfo指定被渲染内存区域的“视图”是否包含一个alpha（透视）通道以及每个像素相应的位置，除此之外还可以指定组件式是浮点值还是整数值。
而传入参数呢信息又可以从位图上下文中获取
CG_EXTERN void * __nullable CGBitmapContextGetData(CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);
/* Return the width of the bitmap context `context', or 0 if `context' is
not a bitmap context. */
CG_EXTERN size_t CGBitmapContextGetWidth(CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);
/* Return the height of the bitmap context `context', or 0 if `context' is
not a bitmap context. */
CG_EXTERN size_t CGBitmapContextGetHeight(CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);
/* Return the bits per component of the bitmap context `context', or 0 if
`context' is not a bitmap context. */
CG_EXTERN size_t CGBitmapContextGetBitsPerComponent(CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);
/* Return the bits per pixel of the bitmap context `context', or 0 if
`context' is not a bitmap context. */
CG_EXTERN size_t CGBitmapContextGetBitsPerPixel(CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);
/* Return the bytes per row of the bitmap context `context', or 0 if
`context' is not a bitmap context. */
CG_EXTERN size_t CGBitmapContextGetBytesPerRow(CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);
/* Return the color space of the bitmap context `context', or NULL if
`context' is not a bitmap context. */
CG_EXTERN CGColorSpaceRef __nullable CGBitmapContextGetColorSpace(
CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);
/* Return the alpha info of the bitmap context `context', or
"kCGImageAlphaNone" if `context' is not a bitmap context. */
CG_EXTERN CGImageAlphaInfo CGBitmapContextGetAlphaInfo(
CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);
/* Return the bitmap info of the bitmap context `context', or 0 if `context'
is not a bitmap context. */
CG_EXTERN CGBitmapInfo CGBitmapContextGetBitmapInfo(
CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_4, __IPHONE_2_0);
最终根据位图上下文创建一个CGImageRef
CG_EXTERN CGImageRef __nullable CGBitmapContextCreateImage(
CGContextRef cg_nullable context)
CG_AVAILABLE_STARTING(__MAC_10_4, __IPHONE_2_0);
+ (UIImage *)mosaicImage:(UIImage *)image withLevel:(int)level
{
unsigned char *imgPixel = RequestImagePixelData(image);
CGImageRef inImageRef = [image CGImage];
GLuint width = CGImageGetWidth(inImageRef);
GLuint height = CGImageGetHeight(inImageRef);
unsigned char prev[4] = {0};
int bytewidth = width*4;
int i,j;
int val = level;
for(i=0;i<height;i++) {
if (((i+1)%val) == 0) {
memcpy(imgPixel+bytewidth*i, imgPixel+bytewidth*(i-1), bytewidth);
continue;
}
for(j=0;j<width;j++) {
if (((j+1)%val) == 1) {
memcpy(prev, imgPixel+bytewidth*i+j*4, 4);
continue;
}
memcpy(imgPixel+bytewidth*i+j*4, prev, 4);
}
}
NSInteger dataLength = width*height* 4;
//下面的代码创建要输出的图像的相关参数
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, imgPixel, dataLength, NULL);
// prep the ingredients
int bitsPerComponent = 8;
int bitsPerPixel = 32;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
//创建要输出的图像
CGImageRef imageRef = CGImageCreate(width, height,
bitsPerComponent,
bitsPerPixel,
bytewidth,
colorSpaceRef,
bitmapInfo,
provider,
NULL, NO, renderingIntent);
UIImage *mosaicImage = [UIImage imageWithCGImage:imageRef scale:image.scale orientation:image.imageOrientation];
CFRelease(imageRef);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
return mosaicImage;
}
