光影遮罩
这里我分类深色与浅色遮罩，效果是什么样呢，可以看下面的图片,第一张是原图，后面是遮罩图。
[图片上传中...(mask.png-77d2d6-1533714162606-0)]
[图片上传中...(mask02.png-40df11-1533714186966-0)]
mask02.png
深色遮罩
Simulator Screen Shot - iPhone SE - 2018-08-08 at 15.46.08.png
浅色遮罩
Simulator Screen Shot - iPhone SE - 2018-08-08 at 15.54.18.png
关键代码
+(UIImage *)creatImageWithMaskImage:(UIImage *)MaskImage andBackimage:(UIImage *)Backimage{
CGRect rect;
if (MaskImage.size.height>1000.0||MaskImage.size.width>1000.0)
{
rect = CGRectMake(0,
0,
MaskImage.size.width,
MaskImage.size.height);
}else{
rect = CGRectMake(0,
0,
MaskImage.size.width * 4.0,
MaskImage.size.height * 4.0);
}
CGImageRef imageRef = CGImageCreateWithImageInRect([Backimage CGImage], rect);
UIImage *cutIMG = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
//遮罩图
CGImageRef maskImage = MaskImage.CGImage;
//原图
CGImageRef originImage = cutIMG.CGImage;
CGContextRef mainViewContentContext;
CGColorSpaceRef colorSpace;
colorSpace = CGColorSpaceCreateDeviceRGB();
// create a bitmap graphics context the size of the image
mainViewContentContext = CGBitmapContextCreate (NULL,
rect.size.width,
rect.size.height,
8,
0,
colorSpace,
kCGImageAlphaPremultipliedLast);
// free the rgb colorspace
CGColorSpaceRelease(colorSpace);
if (mainViewContentContext==NULL)
{
// NSLog(@"error");
}
CGContextClipToMask(mainViewContentContext,
CGRectMake(0,
0,
rect.size.width,
rect.size.height),
maskImage);
CGContextDrawImage(mainViewContentContext,
CGRectMake(0,
0,
rect.size.width,
rect.size.height),
originImage);
CGContextSetAllowsAntialiasing(mainViewContentContext, true);//说是抗锯齿，但貌似没用
CGContextSetShouldAntialias(mainViewContentContext, true);
// Create CGImageRef of the main view bitmap content, and then
// release that bitmap context
CGImageRef mainViewContentBitmapContext = CGBitmapContextCreateImage(mainViewContentContext);
CGContextRelease(mainViewContentContext);
// convert the finished resized image to a UIImage
UIImage *theImage = [UIImage imageWithCGImage:mainViewContentBitmapContext];
// image is retained by the property setting above, so we can
// release the original
CGImageRelease(mainViewContentBitmapContext);
return theImage;
}
首先处理新生的画图范围
CGRect rect;
if (MaskImage.size.height>1000.0||MaskImage.size.width>1000.0)
{
rect = CGRectMake(0,
0,
MaskImage.size.width,
MaskImage.size.height);
}else{
rect = CGRectMake(0,
0,
MaskImage.size.width * 4.0,
MaskImage.size.height * 4.0);
}
然后我们需要把原图和遮罩图转换为像素位图
CGImageRef imageRef = CGImageCreateWithImageInRect([Backimage CGImage], rect);
UIImage *cutIMG = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
//遮罩图
CGImageRef maskImage = MaskImage.CGImage;
//原图
CGImageRef originImage = cutIMG.CGImage;
然后需要定义一个图形上下文与色彩空间
CGImageRef originImage = cutIMG.CGImage;
CGContextRef mainViewContentContext;
CGColorSpaceRef colorSpace;
colorSpace = CGColorSpaceCreateDeviceRGB();
// create a bitmap graphics context the size of the image
mainViewContentContext = CGBitmapContextCreate (NULL,
rect.size.width,
rect.size.height,
8,
0,
colorSpace,
kCGImageAlphaPremultipliedLast);
// free the rgb colorspace
CGColorSpaceRelease(colorSpace);
接下来是把原图和遮罩图的像素位图画到画布上
CGContextClipToMask(mainViewContentContext,
CGRectMake(0,
0,
rect.size.width,
rect.size.height),
maskImage);
CGContextDrawImage(mainViewContentContext,
CGRectMake(0,
0,
rect.size.width,
rect.size.height),
originImage);
CGContextSetAllowsAntialiasing(mainViewContentContext, true);//说是抗锯齿，但貌似没用
CGContextSetShouldAntialias(mainViewContentContext, true);
// Create CGImageRef of the main view bitmap content, and then
// release that bitmap context
CGImageRef mainViewContentBitmapContext = CGBitmapContextCreateImage(mainViewContentContext);
CGContextRelease(mainViewContentContext);
注意要手动去释放已创建的指针。
最后是把合成后的像素位图转换为一般的图片
UIImage *theImage = [UIImage imageWithCGImage:mainViewContentBitmapContext];
CGImageRelease(mainViewContentBitmapContext);
除此之外还有一种方式，也是官方文档提到的
遮罩方法二
关键代码
+(UIImage *)creatImageWithBackimage:(UIImage *)Backimage andMaskImage:(UIImage *)MaskImage
{
CGImageRef maskImage = MaskImage.CGImage;
// CGImageRef bgimage = BgImage.CGImage;
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskImage), CGImageGetHeight(maskImage), CGImageGetBitsPerComponent(maskImage), CGImageGetBitsPerPixel(maskImage), CGImageGetBytesPerRow(maskImage), CGImageGetDataProvider(maskImage),NULL, false);
CGImageRef imageWithAlpha = Backimage.CGImage;
CGImageRef masked = CGImageCreateWithMask(imageWithAlpha, mask);
UIImage * newimage = [UIImage imageWithCGImage:masked];
// CGImageRelease(maskImage);
// CGImageRelease(imageWithAlpha);
CGImageRelease(masked);
return newimage;
}
从这里看的出来，相对而言简短很多。
这里使用到的关键是
CGImageMaskCreate(size_t width, size_t height,size_t bitsPerComponent, size_t bitsPerPixel, size_t bytesPerRow， CGDataProviderRef provider, const CGFloat decode[], bool shouldInterpolate)
sizt_t：是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，这是个枚举
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
后面设置遮罩图的透明通道
CGImageRef imageWithAlpha = Backimage.CGImage;
CGImageRef masked = CGImageCreateWithMask(imageWithAlpha, mask);
UIImage * newimage = [UIImage imageWithCGImage:masked];
// CGImageRelease(maskImage);
// CGImageRelease(imageWithAlpha);
CGImageRelease(masked);
PS：第二种方法和第一种的效果是相反的。