Question

我正在使用混合模式目标输出来触摸图像。我成功地做到了这一点。

实际上我通过触摸减少alpha，所以我也可以设置力量现在我的问题是关于用触摸重绘图像的擦除部分（即我想用强度拉回图像或者想要将alpha设置得更暗）。为此，我正在备份原始图像，然后我裁剪了触摸部分并将其与图像合并。但问题在于它的吸引力超过应有的水平。

请注意，绘制重叠时，重绘过程会使图像比原始图像更暗（需要设置上限）。那么我怎样才能避免在我已经绘制图像的位置重绘，以避免原始图像变暗。

我还附上了代码。

// Code to erase an image  


        UIGraphicsBeginImageContext(self._overlayImage.image.size);
        CGRect rect =CGRectMake(0, 0, self._overlayImage.image.size.width, self._overlayImage.image.size.height) ;
        CGContextRef context = UIGraphicsGetCurrentContext();
        CGImageRef imageRef=self._overlayImage.image.CGImage;

        if (imageRef) {
            // Restore the screen that was previously saved
            CGContextTranslateCTM(context, 0, rect.size.height);
            CGContextScaleCTM(context, 1.0, -1.0);

            CGContextDrawImage(context, rect, imageRef);
            //CGImageRelease(imageRef);

            CGContextTranslateCTM(context, 0, rect.size.height);
            CGContextScaleCTM(context, 1.0, -1.0);
        }

        // Erase the background -- raise the alpha to clear more away with eash swipe
        //  [[UIImage imageNamed:@"eraser222.png"] drawAtPoint:point blendMode:kCGBlendModeDestinationOut alpha:.2];
        [ [UIImage imageNamed:@"eraser222.png"] drawInRect:CGRectMake(newPoint.x-self.imgOrignal.size.width*2*radius/self._overlayImage.bounds.size.width, newPoint.y-self.imgOrignal.size.height*2*radius/self._overlayImage.bounds.size.height, self.imgOrignal.size.width*2*radius/self._overlayImage.bounds.size.width, self.imgOrignal.size.height*2*radius/self._overlayImage.bounds.size.height) blendMode:kCGBlendModeDestinationOut alpha:strength/3];

        self._overlayImage.image=UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();


// code to draw an image

 UIImage *cropped = [self imageByCropping:self.imgOrignal toRect:CGRectMake(newPoint.x-self.imgOrignal.size.width*2*radius/self._overlayImage.bounds.size.width, newPoint.y-self.imgOrignal.size.height*2*radius/self._overlayImage.bounds.size.height, self.imgOrignal.size.width*2*radius/self._overlayImage.bounds.size.width, self.imgOrignal.size.height*2*radius/self._overlayImage.bounds.size.height)];
 UIGraphicsBeginImageContext(self._overlayImage.image.size);
        CGRect rect =CGRectMake(0, 0, self._overlayImage.image.size.width, self._overlayImage.image.size.height) ;
        CGContextRef context = UIGraphicsGetCurrentContext();
        CGImageRef imageRef=self._overlayImage.image.CGImage;

        if (imageRef) {
            // Restore the screen that was previously saved
            CGContextTranslateCTM(context, 0, rect.size.height);
            CGContextScaleCTM(context, 1.0, -1.0);

            CGContextDrawImage(context, rect, imageRef);
            //CGImageRelease(imageRef);

            CGContextTranslateCTM(context, 0, rect.size.height);
            CGContextScaleCTM(context, 1.0, -1.0);
        }




        [ cropped drawInRect:CGRectMake(newPoint.x-self.imgOrignal.size.width*2*radius/self._overlayImage.bounds.size.width, newPoint.y-self.imgOrignal.size.height*2*radius/self._overlayImage.bounds.size.height, self.imgOrignal.size.width*2*radius/self._overlayImage.bounds.size.width, self.imgOrignal.size.height*2*radius/self._overlayImage.bounds.size.height) blendMode:kCGBlendModeNormal alpha:strength];



        cropped= [UIImage imageWithData:UIImagePNGRepresentation(cropped)];


        UIImage *finalimage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();


        self._overlayImage.image=finalimage;

Answer 1

我知道在这里为时已晚，但我已达成一个解决方案，我想在此分享，因为它可以帮助有需要的人。无法删除和重绘相同的图像。所以我研究了两张图片。一张原始图像和第二张图片是零。第二个图像用于绘制用户触摸屏幕的路径。从此创建了一个新的上下文，绘制了原始图像，然后用kCGBlendModeDestinationOut混合模式绘制了路径图像。它是kCGBlendModeDestinationOut这个方法的主要英雄。主要任务是使用kCGBlendModeDestinationOut混合模式完成的。因此获得所需的效果。查看我的博客here。

如何重新绘制在iphone中移动的触摸图像

1 个答案: