我想从UIView创建一个UI
Image对象.视图不透明.
因为我正在使用以下代码：
因为我正在使用以下代码：
+ (UIImage *) imageWithView:(UIView *)view
{
UIGraphicsBeginImageContextWithOptions(view.bounds.size,view.opaque,[[UIScreen mainScreen] scale]);
[view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage * img = UIGraphicsGetimageFromCurrentimageContext(); UIGraphicsEndImageContext();
return img;
}
但由于某些原因,而不是透明的背景,我得到一个黑色背景的图像.
我已经尝试将UIGraphicsBeginImageContextWithOptions中的“opaque”参数设置为NO,但没有不同的结果.
任何建议？
(类似的问题CGContext transparency problem没有答案)
解决方法
我确定你创建这样的UIImage时不能定义透明度 – 你可以掩盖使用图像的UIImageView.
类似以下功能的类似操作可以实现：
// handles img masking operation
CGImageRef copyImageAndAddAlphaChannel(CGImageRef sourceImage) {
CGImageRef retVal = NULL;
size_t width = CGImageGetWidth(sourceImage);
size_t height = CGImageGetHeight(sourceImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef offscreenContext = CGBitmapContextCreate(NULL,width,height,8,colorSpace,kCGImageAlphaPremultipliedFirst);
if (offscreenContext != NULL) {
CGContextDrawImage(offscreenContext,CGRectMake(0,height),sourceImage);
retVal = CGBitmapContextCreateImage(offscreenContext);
CGContextRelease(offscreenContext);
}
CGColorSpaceRelease(colorSpace);
return retVal;
}
// png masks can mask png,gif or jpg...
- (UIImage*)maskImage:(UIImage *)image withMask:(UIImage *)maskImage
{
CGImageRef maskRef = maskImage.CGImage;
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),CGImageGetHeight(maskRef),CGImageGetBitsPerComponent(maskRef),CGImageGetBitsPerPixel(maskRef),CGImageGetBytesPerRow(maskRef),CGImageGetDataProvider(maskRef),NULL,false);
CGImageRef sourceImage = [image CGImage];
CGImageRef imageWithAlpha = sourceImage;
//add alpha channel for images that don't have one (ie GIF,JPEG,etc...)
//this however has a computational cost
if ((CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNone) || (CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNoneskipFirst))
{
imageWithAlpha = copyImageAndAddAlphaChannel(sourceImage);
}
CGImageRef masked = CGImageCreateWithMask(imageWithAlpha,mask);
CGImageRelease(mask);
//release imageWithAlpha if it was created by copyImageAndAddAlphaChannel
if (sourceImage != imageWithAlpha)
{
CGImageRelease(imageWithAlpha);
}
UIImage* retimage = [UIImage imageWithCGImage:masked];
CGImageRelease(masked);
return retimage;
}
你可以这样称呼：
UIImage *imgMasked = [self maskImage:[UIImage imageNamed:@"full_image.png"] withMask:[UIImage imageNamed:@"masked_image.png"]];
masked_image.png需要是一个alpha通道的图像,它将剪出你的黑色bg.