How to: Rotate, Reflect, and Skew Images

You can rotate, reflect, and skew an image by specifying destination points for the upper-left, upper-right, and lower-left corners of the original image. The three destination points determine an affine transformation that maps the original rectangular image to a parallelogram.

Example

For example, suppose the original image is a rectangle with upper-left corner at (0, 0), upper-right corner at (100, 0), and lower-left corner at (0, 50). Now suppose you map those three points to destination points as follows.

Original point	Destination point
Upper-left (0, 0)	(200, 20)
Upper-right (100, 0)	(110, 100)
Lower-left (0, 50)	(250, 30)

The following illustration shows the original image and the image mapped to the parallelogram. The original image has been skewed, reflected, rotated, and translated. The x-axis along the top edge of the original image is mapped to the line that runs through (200, 20) and (110, 100). The y-axis along the left edge of the original image is mapped to the line that runs through (200, 20) and (250, 30).

The following illustration shows a similar transformation applied to a photographic image.

The following illustration shows a similar transformation applied to a metafile.

The following example produces the images shown in the first illustration.

        ' New Point(200, 20)  = destination for upper-left point of original
        ' New Point(110, 100) = destination for upper-right point of original
        ' New Point(250, 30)  = destination for lower-left point of original
        Dim destinationPoints As Point() = { _
            New Point(200, 20), _
            New Point(110, 100), _
            New Point(250, 30)}

        Dim image As New Bitmap("Stripes.bmp")

        ' Draw the image unaltered with its upper-left corner at (0, 0).
        e.Graphics.DrawImage(image, 0, 0)

        ' Draw the image mapped to the parallelogram.
        e.Graphics.DrawImage(image, destinationPoints)

    Point[] destinationPoints = {
new Point(200, 20),   // destination for upper-left point of 
                      // original
new Point(110, 100),  // destination for upper-right point of 
                      // original
new Point(250, 30)};  // destination for lower-left point of 
    // original

    Image image = new Bitmap("Stripes.bmp");

    // Draw the image unaltered with its upper-left corner at (0, 0).
    e.Graphics.DrawImage(image, 0, 0);

    // Draw the image mapped to the parallelogram.
    e.Graphics.DrawImage(image, destinationPoints);

Compiling the Code

The preceding example is designed for use with Windows Forms, and it requires PaintEventArgs e, which is a parameter of the Paint event handler. Make sure to replace Stripes.bmp with the path to an image that is valid on your system.

See Also

Other Resources

Working with Images, Bitmaps, Icons, and Metafiles