旋转图像上下文 (CGContextRotateCTM) 导致其变为空白。为什么?

发布于 2024-11-07 05:18:43 字数 542 浏览 0 评论 0原文

#define radians(degrees) (degrees * M_PI/180)

UIImage *rotate(UIImage *image) {
  CGSize size = image.size;;

  UIGraphicsBeginImageContext(size);
  CGContextRef context = UIGraphicsGetCurrentContext();

  // If this is commented out, image is returned as it is.
  CGContextRotateCTM (context, radians(90));

  [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
  UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();

  return newImage;
}

会不会还有什么问题?没主意了。

#define radians(degrees) (degrees * M_PI/180)

UIImage *rotate(UIImage *image) {
  CGSize size = image.size;;

  UIGraphicsBeginImageContext(size);
  CGContextRef context = UIGraphicsGetCurrentContext();

  // If this is commented out, image is returned as it is.
  CGContextRotateCTM (context, radians(90));

  [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
  UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();

  return newImage;
}

Could something else be wrong? Out of ideas.

如果你对这篇内容有疑问,欢迎到本站社区发帖提问 参与讨论,获取更多帮助,或者扫码二维码加入 Web 技术交流群。

扫码二维码加入Web技术交流群

发布评论

需要 登录 才能够评论, 你可以免费 注册 一个本站的账号。

评论(5

時窥 2024-11-14 05:18:43

问题是你的上下文正在围绕(0,0)(即左上角)旋转。如果绕左上角旋转 90 度,则所有绘图都将超出上下文范围。您需要一个两步变换将上下文的原点移动到中间,然后旋转。此外,您还需要以移动/旋转的原点为中心绘制图像,如下所示:

CGContextTranslateCTM( context, 0.5f * size.width, 0.5f * size.height ) ;
CGContextRotateCTM( context, radians( 90 ) ) ;

[ image drawInRect:(CGRect){ { -size.width * 0.5f, -size.height * 0.5f }, size } ] ;

HTH

The problem is your context is being rotated around (0,0) which is the top left corner. If you rotate 90 degrees around the top left corner, all your drawing will occur out of the bounds of the context. You need a 2-step transform to move the origin of the context to it's middle, and THEN rotate. Also you need to draw your image centered around the moved/rotated origin, like this:

CGContextTranslateCTM( context, 0.5f * size.width, 0.5f * size.height ) ;
CGContextRotateCTM( context, radians( 90 ) ) ;

[ image drawInRect:(CGRect){ { -size.width * 0.5f, -size.height * 0.5f }, size } ] ;

HTH

请远离我 2024-11-14 05:18:43

我尝试遵循代码,它有效,从 http://www.catamount.com/blog/1015/uiimage-extensions-for-cutting-scaling-and-rotating-uiimages/

+ (UIImage *)rotateImage:(UIImage*)src byRadian:(CGFloat)radian
{
    // calculate the size of the rotated view's containing box for our drawing space
    //UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0, src.size.width, src.size.height)];
    //CGAffineTransform t = CGAffineTransformMakeRotation(radian);
    //rotatedViewBox.transform = t;
    //CGSize rotatedSize = rotatedViewBox.frame.size;
    CGRect rect = CGRectApplyAffineTransform(CGRectMake(0,0, src.size.width, src.size.height), CGAffineTransformMakeRotation(radian));
    CGSize rotatedSize = rect.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, radian);

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

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

I try followed code, it works, get from http://www.catamount.com/blog/1015/uiimage-extensions-for-cutting-scaling-and-rotating-uiimages/

+ (UIImage *)rotateImage:(UIImage*)src byRadian:(CGFloat)radian
{
    // calculate the size of the rotated view's containing box for our drawing space
    //UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0, src.size.width, src.size.height)];
    //CGAffineTransform t = CGAffineTransformMakeRotation(radian);
    //rotatedViewBox.transform = t;
    //CGSize rotatedSize = rotatedViewBox.frame.size;
    CGRect rect = CGRectApplyAffineTransform(CGRectMake(0,0, src.size.width, src.size.height), CGAffineTransformMakeRotation(radian));
    CGSize rotatedSize = rect.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, radian);

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

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}
溺ぐ爱和你が 2024-11-14 05:18:43

如果您不想更改所有原点和大小,请移动中心,旋转并再次将中心更改为角,如下所示:

CGContextTranslateCTM( context, 0.5f * size.width, 0.5f * size.height ) ;
CGContextRotateCTM(上下文,弧度(90));
CGContextTranslateCTM( context, -0.5f * size.width, -0.5f * size.height ) ;

然后像这样正常绘制:

[image drawInRect:CGRectMake(0, 0, size.width, size.高度)];

If you don't want to change all the origins and sizes, move the center, rotate and change the center to corner again like this:

CGContextTranslateCTM( context, 0.5f * size.width, 0.5f * size.height ) ;
CGContextRotateCTM( context, radians( 90 ) ) ;
CGContextTranslateCTM( context, -0.5f * size.width, -0.5f * size.height ) ;

Then draw normally like this:

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

心安伴我暖 2024-11-14 05:18:43

扩展 Nielsbot 的答案,我创建了以下代码片段。请注意,最好将其设为函数而不是代码片段,以防止“复制/粘贴编程”。我还没有做到这一点,所以请随意适应它。

代码片段:

// <Draw in frame with orientation>
UIImage* imageToDrawRotated = <#image#>;
float rotationAngle = <#angle#>;
CGRect drawFrame = CGRectMake(<#CGFloat x#>, <#CGFloat y#>, <#CGFloat width#>, <#CGFloat height#>);
CGContextTranslateCTM(UIGraphicsGetCurrentContext(), floor(drawFrame.origin.x + drawFrame.size.width/2), floor(drawFrame.origin.y + drawFrame.size.height/2));
CGContextRotateCTM(UIGraphicsGetCurrentContext(), rotationAngle);
[imageToDrawRotated drawInRect:CGRectMake(-floor(drawFrame.size.width/2), -floor(drawFrame.size.height/2), drawFrame.size.width, drawFrame.size.height)];
CGContextRotateCTM(UIGraphicsGetCurrentContext(), -rotationAngle);
CGContextTranslateCTM(UIGraphicsGetCurrentContext(), -floor(drawFrame.origin.x + drawFrame.size.width/2), -floor(drawFrame.origin.y + drawFrame.size.height/2));
// </Draw in frame with orientation>

另外,我欢迎有更好的方法将 CGContext 重置为其之前的状态。

Expanding on Nielsbot's answer, I created the following snippet. Note that this should preferably be made a function rather than a code snippet, to prevent 'copy/paste programming'. I didn't get to that yet, so feel free to adapt it.

Code snippet:

// <Draw in frame with orientation>
UIImage* imageToDrawRotated = <#image#>;
float rotationAngle = <#angle#>;
CGRect drawFrame = CGRectMake(<#CGFloat x#>, <#CGFloat y#>, <#CGFloat width#>, <#CGFloat height#>);
CGContextTranslateCTM(UIGraphicsGetCurrentContext(), floor(drawFrame.origin.x + drawFrame.size.width/2), floor(drawFrame.origin.y + drawFrame.size.height/2));
CGContextRotateCTM(UIGraphicsGetCurrentContext(), rotationAngle);
[imageToDrawRotated drawInRect:CGRectMake(-floor(drawFrame.size.width/2), -floor(drawFrame.size.height/2), drawFrame.size.width, drawFrame.size.height)];
CGContextRotateCTM(UIGraphicsGetCurrentContext(), -rotationAngle);
CGContextTranslateCTM(UIGraphicsGetCurrentContext(), -floor(drawFrame.origin.x + drawFrame.size.width/2), -floor(drawFrame.origin.y + drawFrame.size.height/2));
// </Draw in frame with orientation>

Also, I welcome a better way to reset the CGContext to its previous state.

走过海棠暮 2024-11-14 05:18:43

我喜欢 @lbsweek 的解决方案,但我有点担心只是为了转换而分配 UIView,而是尝试了下面的方法

- (UIImage *)rotateImage:(UIImage *)sourceImage byDegrees:(float)degrees
{
    CGFloat radian = degrees * (M_PI/ 180);
    CGRect contextRect = CGRectMake(0, 0, sourceImage.size.width, sourceImage.size.height);
    float newSide = MAX([sourceImage size].width, [sourceImage size].height);
    CGSize newSize =  CGSizeMake(newSide, newSide);
    UIGraphicsBeginImageContext(newSize);
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGPoint contextCenter = CGPointMake(CGRectGetMidX(contextRect), CGRectGetMidY(contextRect));
    CGContextTranslateCTM(ctx, contextCenter.x, contextCenter.y);
    CGContextRotateCTM(ctx, radian);
    CGContextTranslateCTM(ctx, -contextCenter.x, -contextCenter.y);
    [sourceImage drawInRect:contextRect];
    UIImage* rotatedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return rotatedImage;
}

I liked the solution by @lbsweek but I was bit worried about alloc ing UIView just for transform, instead I tried the below

- (UIImage *)rotateImage:(UIImage *)sourceImage byDegrees:(float)degrees
{
    CGFloat radian = degrees * (M_PI/ 180);
    CGRect contextRect = CGRectMake(0, 0, sourceImage.size.width, sourceImage.size.height);
    float newSide = MAX([sourceImage size].width, [sourceImage size].height);
    CGSize newSize =  CGSizeMake(newSide, newSide);
    UIGraphicsBeginImageContext(newSize);
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGPoint contextCenter = CGPointMake(CGRectGetMidX(contextRect), CGRectGetMidY(contextRect));
    CGContextTranslateCTM(ctx, contextCenter.x, contextCenter.y);
    CGContextRotateCTM(ctx, radian);
    CGContextTranslateCTM(ctx, -contextCenter.x, -contextCenter.y);
    [sourceImage drawInRect:contextRect];
    UIImage* rotatedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return rotatedImage;
}
~没有更多了~
我们使用 Cookies 和其他技术来定制您的体验包括您的登录状态等。通过阅读我们的 隐私政策 了解更多相关信息。 单击 接受 或继续使用网站,即表示您同意使用 Cookies 和您的相关数据。
原文