Objective-C - 在 UIImageView 内旋转图像而不丢失图像的比例

Question

我想创建一个按钮，可以多次旋转UIImageView 中的图像。之后，我必须将其发送到外部 API。我不需要松开比例（如图片中所示）

Image after rotatation Image before rotation

我尝试了两种选择

选项 1：我放松了比例

    (UIImage *)imageRotatedByDegrees:(UIImage*)oldImage deg:(CGFloat)degrees
{
    // calculate the size of the rotated view's containing box for our drawing space
    UIView *rotatedViewBox = [[UIView alloc]      initWithFrame:CGRectMake(0,0,oldImage.size.width, oldImage.size.height)];
    CGAffineTransform t = CGAffineTransformMakeRotation(degrees * M_PI / 180);
    rotatedViewBox.transform = t;
    CGSize rotatedSize = rotatedViewBox.frame.size;
    // Create the bitmap context
    UIGraphicsBeginImageContext(rotatedSize);
    CGContextRef bitmap = UIGraphicsGetCurrentContext();

    // Move the origin to the middle of the image so we will rotate and scale around the center.
    CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);

    //   // Rotate the image context
    CGContextRotateCTM(bitmap, (degrees * M_PI / 180));

    // Now, draw the rotated/scaled image into the context
    CGContextScaleCTM(bitmap, 1.0, -1.0);
    CGContextDrawImage(bitmap, CGRectMake(-oldImage.size.width / 2, -oldImage.size.height / 2, oldImage.size.width, oldImage.size.height), [oldImage CGImage]);

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

选项 2：

(UIImage*)upsideDownBunny:(CGFloat)radians withImage:(UIImage*)testImage {

    __block CGImageRef cgImg;
    __block CGSize imgSize;
    __block UIImageOrientation orientation;
    dispatch_block_t createStartImgBlock = ^(void) {
        // UIImages should only be accessed from the main thread

        UIImage *img =testImage;
        imgSize = [img size]; // this size will be pre rotated
        orientation = [img imageOrientation];
        cgImg = CGImageRetain([img CGImage]); // this data is not rotated
    };
    if([NSThread isMainThread]) {
        createStartImgBlock();
    } else {
        dispatch_sync(dispatch_get_main_queue(), createStartImgBlock);
    }
    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
    // in iOS4+ you can let the context allocate memory by passing NULL
    CGContextRef context = CGBitmapContextCreate( NULL,
                                                 imgSize.width,
                                                 imgSize.height,
                                                 8,
                                                 imgSize.width * 4,
                                                 colorspace,
                                                 kCGImageAlphaPremultipliedLast);
    // rotate so the image respects the original UIImage's orientation
    switch (orientation) {
        case UIImageOrientationDown:
            CGContextTranslateCTM(context, imgSize.width, imgSize.height);
            CGContextRotateCTM(context, -radians);
            break;
        case UIImageOrientationLeft:
            CGContextTranslateCTM(context, 0.0, imgSize.height);
            CGContextRotateCTM(context, 3.0 * -radians / 2.0);
            break;
        case UIImageOrientationRight:
            CGContextTranslateCTM(context,imgSize.width, 0.0);
            CGContextRotateCTM(context, -radians / 2.0);
            break;
        default:
            // there are mirrored modes possible
            // but they aren't generated by the iPhone's camera
            break;
    }
    // rotate the image upside down

    CGContextTranslateCTM(context, +(imgSize.width * 0.5f), +(imgSize.height * 0.5f));
    CGContextRotateCTM(context, -radians);
    //CGContextDrawImage( context, CGRectMake(0.0, 0.0, imgSize.width, imgSize.height), cgImg );
    CGContextDrawImage(context, (CGRect){.origin.x = -imgSize.width* 0.9f , .origin.y = -imgSize.width* 0.5f , .size.width = imgSize.width, .size.height = imgSize.width}, cgImg);
    // grab the new rotated image
    CGContextFlush(context);
    CGImageRef newCgImg = CGBitmapContextCreateImage(context);
    __block UIImage *newImage;
    dispatch_block_t createRotatedImgBlock = ^(void) {
        // UIImages should only be accessed from the main thread
        newImage = [UIImage imageWithCGImage:newCgImg];
    };
    if([NSThread isMainThread]) {
        createRotatedImgBlock();
    } else {
        dispatch_sync(dispatch_get_main_queue(), createRotatedImgBlock);
    }
    CGColorSpaceRelease(colorspace);
    CGImageRelease(newCgImg);
    CGContextRelease(context);
    return newImage;
}

它适用于图像的旋转，但每次旋转图像和视图都会缩小。

有人可以帮助我吗？

Answer 1

如果你想为旋转设置动画，你可以使用 Core Animation。这不会改变图像本身，只是在屏幕上旋转它。

CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
rotationAnimation.toValue = [NSNumber numberWithFloat:M_PI * 2.0];
rotationAnimation.duration = duration;
rotationAnimation.cumulative = YES;
rotationAnimation.repeatCount = numRotations;
[self.imgviewRotate.layer addAnimation:animation forKey:@"animation"];