Rotate Image Using Cgcontextdrawimage

Rotate image using CGContextDrawImage

The thing to remember about coordinate transformations—well, one of the things to remember—is that you are not manipulating objects, like the Transform command in a graphics editor; you are manipulating space itself.

Imagine that the device is suspended over a desk by a gooseneck arm, and is fixed in position. Coordinate transformations move the desk around (translation), and turn it one way or the other (rotation), and even squash and stretch it (scaling).

Another of the things to remember about coordinate transformations is that transformation is always relative to the origin. Imagine that your desk starts out with one of its corners—corresponding to a corner of your view—directly underneath the corner of where your view ends up on the screen. Translating moves the corner of the desk, and the rest of the desk with it, sliding it one way or another underneath the screen. Rotating turns the desk around that corner.

One more thing: Transformations affect the future, not the past. Drawing something and then trying to transform it won't work, because you don't transform what you've drawn, you transform the space you're going to draw into. So, we need to move the desk before we can place the image in the right spot.

(I mention that last part because you have a couple of transformation commands that are immediately reverted by your CGContextRestoreGState call. There is no drawing in between for them to affect.)

So, let's start with the unrotated rectangle of the image.

CGRect imageRect = { pointWhereYouWantTheImageCentered, doodad.size };

Now, CGContextDrawImage takes a rectangle, but, as you know, it's going to draw the image from the lower-left corner of that rectangle, not the center. (Hence this whole exercise.)

So, here's what you're going to do. At the end of this, you're going to draw the image not at that point shown above, but at the zero point—that is, on the very corner of the desk. (Not centered on the corner, but with the image's corner on the desk's corner.)

How will that work? It takes some set-up. You're going to have to move your desk.

First, you need to move your desk up and right until the origin corner of your desk is at the desired center point:

CGContextTranslateCTM(context, imageRect.origin.x, imageRect.origin.y);

Then you do the rotation (turning the desk around its origin corner):

CGContextRotateCTM(context, angleInRadians);

Then you move the desk back down and left by half of the image's width and height:

CGContextTranslateCTM(context, imageRect.size.width * -0.5, imageRect.size.height * -0.5);

And then, finally, place the image on the corner of the desk.

CGContextDrawImage(context, (CGRect){ CGPointZero, imageRect.size }, [doodad CGImage]);

With your desk so moved, the center of that rectangle lies directly under the point on the screen where you want the image centered, so the image is so centered.

Why is CGContextDrawImage rotating my image

It's a very easy question.

Because iOS system has 3 different Coordinate System.

UIKit － y axis direction is down
Core Graphics(Quartz) － y axis direction is up
OpenGL ES － y axis direction is up

The originalImage is create by UIKit and the target image is create by Core Graphics, so it should be upside-down.

If you want get the correct image, you can use:

UIImageView* imageV = [[UIImageView alloc] initWithFrame:CGRectMake(100,100, 100, 100)];
imageV.layer.borderColor = [UIColor redColor].CGColor;
imageV.layer.borderWidth = 1;
imageV.image = img;
imageV.layer.transform = CATransform3DRotate(imageV.layer.transform, M_PI, 1.0f, 0.0f, 0.0f);
[self.view addSubview:imageV];

Hope it can help you.

CGImage rotating when i draw it on CGContext

I solved the problem by rotating image in separate context each time it is taken:

- (void)drawRect:(CGRect)rect
{
  CGContextRef context = UIGraphicsGetCurrentContext();
  CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),CGImageGetHeight(image)), image);
  [lineColor setStroke];
  [currentPath stroke];
  if(panEnded)
  {
    if(image!=nil)
    {
      CFRelease(image);
    }
    image=nil;
    image=CGBitmapContextCreateImage(context);
    [self rotateCGImage];
    panEnded=false;
    currentPath=nil;
  }
}

-(void)rotateCGImage
{
  UIGraphicsBeginImageContext(CGSizeMake(CGImageGetWidth(image), CGImageGetHeight(image)));
  CGContextRef context = UIGraphicsGetCurrentContext();
  CGContextDrawImage(context, CGRectMake(0 , 0, CGImageGetWidth(image), CGImageGetHeight(image)), image);

  CGContextRotateCTM (context, radians(90));
  if(image!=nil)
  {
    CFRelease(image);
  }
  image=nil;
  image=CGBitmapContextCreateImage(context);

}

cgcontext rotate rectangle

Rotation is about the context's origin, which is the same point that rectangles are relative to. If you imagine a sheet of graph paper in the background, you can see what's going on more clearly:

The line is the “bottom” (y=0) of your window/view/layer/context. Of course, you can draw below the bottom if you want, and if your context is transformed the right way, you might even be able to see it.

Anyway, I'm assuming that what you want to do is rotate the rectangle in place, relative to an unrotated world, not rotate the world and everything in it.

The only way to rotate anything is to rotate the world, so that's how you need to do it:

1. Save the graphics state.

2. Translate the origin to the point where you want to draw the rectangle. (You probably want to translate to its center point, not the rectangle's origin.)

   

3. Rotate the context.

   

4. Draw the rectangle centered on the origin. In other words, your rectangle's origin point should be negative half its width and negative half its height (i.e., (CGPoint){ width / -2.0, height / -2.0 })—don't use the origin it had before, because you already used that in the translate step.

   

5. Restore the gstate so that future drawing isn't rotated.

How use CGContextDrawImage in Swift 3?

In Swift 3, many functions for CGContext are imported as an instance method of CGContext, the property name CGImage has renamed to cgImage. And CGRectMake is removed.

Try this:

    bitmap!.draw(cgImage!, in: CGRect(x: -size.width / 2, y: -size.height / 2, width: size.width, height: size.height))

(Hope ! would be safe for your usage.)

func draw(CGImage, in: CGRect, byTiling: Bool)

Rotate Newly Created iOS Image 90 Degrees Prior to Saving as PNG

I finally got this to work using one of the answers on this post: How to Rotate a UIImage 90 degrees?

I used this method:

- (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;
}

And then called it like this:

//Rotate it
UIImage *rotatedImage = [self imageRotatedByDegrees:signatureImage deg:90];

Thanks, everyone.

CGContextDrawImage draws image upside down when passed UIImage.CGImage

Instead of

CGContextDrawImage(context, CGRectMake(0, 0, 145, 15), image.CGImage);

Use

[image drawInRect:CGRectMake(0, 0, 145, 15)];

In the middle of your begin/end CGcontext methods.

This will draw the image with the correct orientation into your current image context - I'm pretty sure this has something to do with the UIImage holding onto knowledge of the orientation while the CGContextDrawImage method gets the underlying raw image data with no understanding of orientation.

Rotating a CGImage

-(UIImage*) rotate:(UIImage*) src andOrientation:(UIImageOrientation)orientation
{
    UIGraphicsBeginImageContext(src.size);

    CGContextRef context=(UIGraphicsGetCurrentContext());

    if (orientation == UIImageOrientationRight) {
        CGContextRotateCTM (context, 90/180*M_PI) ;
    } else if (orientation == UIImageOrientationLeft) {
        CGContextRotateCTM (context, -90/180*M_PI);
    } else if (orientation == UIImageOrientationDown) {
        // NOTHING
    } else if (orientation == UIImageOrientationUp) {
        CGContextRotateCTM (context, 90/180*M_PI);
    }

    [src drawAtPoint:CGPointMake(0, 0)];
    UIImage *img=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;

}

use this one .. it works perfect ! Just make sure you use this function when you are picking images from UIImagePicker:

example:

UIImage *image;
image = [self rotate:image andOrientation:image.imageOrientation];

Make sure to use this function in place where you pick photos from documents directory.

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