ios - 使用 UIGraphics 组合两个图像时遇到问题，图像位置不正确

Question

我正在尝试制作一个简单的应用程序，将相机叠加层与在 UIImagePicker 中拍摄的照片相结合。在这个例子中，我想将熊耳朵的叠加 View 与照片结合起来。

- (IBAction)pushTakePhoto:(id)sender {

    UIImagePickerController *picker = [[UIImagePickerController alloc] init];
    picker.delegate = self;
    picker.sourceType = UIImagePickerControllerSourceTypeCamera;
    picker.cameraDevice=UIImagePickerControllerCameraDeviceFront;

    //create overlay UIView
    UIImage *bearEars = [UIImage imageNamed:@"bearEars"];
    UIImageView *imageView = [[UIImageView alloc] initWithImage:bearEars];

    UIView *camerOverlayView = [[UIView alloc] initWithFrame:imageView.frame];
    [camerOverlayView addSubview:imageView];


    [picker setCameraOverlayView:camerOverlayView];

    [self presentViewController:picker animated:YES completion:NULL];


}

上面的代码创建了叠加层，效果很好。下面的代码结合了图像:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {

    UIImage *chosenImage = info[UIImagePickerControllerOriginalImage];

    //first we flip the image
    UIImage * flippedImage = [UIImage imageWithCGImage:chosenImage.CGImage scale:chosenImage.scale orientation:UIImageOrientationLeftMirrored];
    chosenImage=flippedImage;

    //now we need to add the ears


    //get pics
    UIImage *backgroundImage = chosenImage;
    UIImage *watermarkImage = [UIImage imageNamed:@"bearEars"];

    //start a workspace
    UIGraphicsBeginImageContext(backgroundImage.size);
    [backgroundImage drawInRect:CGRectMake(0, 0, backgroundImage.size.width, backgroundImage.size.height)];
    //position seems off for some reason
    [watermarkImage drawInRect:CGRectMake(0, 0, backgroundImage.size.width, backgroundImage.size.height)];
    UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    chosenImage=result;


    self.finalImageView.image = chosenImage;

    [picker dismissViewControllerAnimated:YES completion:NULL];

}

但是，当我合并图像时，bearEars 叠加层并未定位在 (0,0) 处，而是位于最终图像的中间。我不确定为什么会这样。我只是想让它像在相机 View 中一样覆盖图像。任何想法为什么会这样？谢谢

Answer 1

我认为图像居中，因为您在两个图像的 drawInRect 方法中使用相同的矩形大小。尝试将水印图像的大小从backgroundImage.size更改为watermarkImage.size:

[watermarkImage drawInRect:CGRectMake(0, 0, watermarkImage.size.width, watermarkImage.size.height)];

编辑:

要为水印图像设置正确的尺寸，您需要找到缩放尺寸 - 预览中的图像与最终图像的尺寸差异。您可以通过将backgroundImage的宽度除以self.view的宽度来做到这一点

CGFloat scale = backgroundImage.size.width / self.view.frame.size.width;

然后你可以在绘制watermarkImage时使用这个值:

[watermarkImage drawInRect:CGRectMake(0, 0, watermarkImage.size.width * scale, watermarkImage.size.height * scale)];

希望对您有所帮助。