C# Image/PictureBox Rotations

Introduction

I was working on an Etch A Sketch like program and made a knob image and wanted to simply rotate it as the user hit the arrow keys. I found many sources online, but none that got it done just how I wanted (see links below in References section). I then decided since I figured it out and got it all working why not make a simple demo with source that others could use.

Background

Loading an image from a dialogue prompt
Creating bitmaps, image/draw updates, and Graphic manipulation

Using the Code

There is a class called Utilities in the Utilities.cs file that contains the functions for rotating an image from the center or given an offset to rotate from.

Here is the main rotation function RotateImage:

/// <summary>
/// Creates a new Image containing the same image only rotated
/// </summary>
/// <param name=""image"">The <see cref=""System.Drawing.Image"/"> to rotate
/// <param name=""offset"">The position to rotate from.
/// <param name=""angle"">The amount to rotate the image, clockwise, in degrees
/// <returns>A new <see cref=""System.Drawing.Bitmap"/"> of the same size rotated.</see>
/// <exception cref=""System.ArgumentNullException"">Thrown if <see cref=""image"/"> 
/// is null.</see>
public static Bitmap RotateImage(Image image, PointF offset, float angle)
{
    if (image == null)
        throw new ArgumentNullException("image");
        
    //create a new empty bitmap to hold rotated image
    Bitmap rotatedBmp = new Bitmap(image.Width, image.Height);
    rotatedBmp.SetResolution(image.HorizontalResolution, image.VerticalResolution);
    
    //make a graphics object from the empty bitmap
    Graphics g = Graphics.FromImage(rotatedBmp);
    
    //Put the rotation point in the center of the image
    g.TranslateTransform(offset.X, offset.Y);
    
    //rotate the image
    g.RotateTransform(angle);
    
    //move the image back
    g.TranslateTransform(-offset.X, -offset.Y);
    
    //draw passed in image onto graphics object
    g.DrawImage(image, new PointF(0, 0));
    
    return rotatedBmp;
}

And here is how it is used:

//Load an image in from a file
Image image = new Bitmap("Picture.png");
//Set our picture box to that image
pictureBox.Image = (Bitmap)image.Clone();

//Store our old image so we can delete it
Image oldImage = pictureBox.Image;
//Pass in our original image and return a new image rotated 35 degrees right
pictureBox.Image = Utilities.RotateImage(image, 35);
if (oldImage != null)
{
    oldImage.Dispose();
}

Points of Interest

Graphics are very powerful and allow you to do image manipulation really easily. For instance, this code could easily be modified to scale instead. I may added to this with more utilities like that.