In two-dimensional images, clipping is an essential requirement as it provides selective rendering of pixels within the boundaries of the selected frame area. Bitmap lets you clip the source image and load a part of the whole image through Clipper transformation.

The following image shows the clipping feature.

Complete the following steps to clip an image using Bitmap in code.

1. Add the following import statement.
   • Visual Basic
   • C#

   • Visual Basic

   Imports System.IO
   

   • C#

   using System.IO;
   

2. Initialize a rectangle and a point as global variables in Form1 class.
   • Visual Basic
   • C#

   • Visual Basic

   'Initialize variables
   Dim start As Point
   Dim selection As Rect
   Dim dragHelper As C1DragHelper
   

   • C#

   //Initialize variables
   Point start;
   Rect selection;
   C1DragHelper dragHelper;
   

3. Initialize a variable to control drag gestures and subscribe a drag event in the MainWindow constructor.
   • Visual Basic
   • C#

   • Visual Basic

   'Initialize drag helper for drag gestures
   dragHelper = New C1DragHelper(image)
   
   'Subscribe a drag event
   dragHelper.DragDelta += dragHelper_DragDelta()
   

   • C#

   //Initialize drag helper for drag gestures
   dragHelper = new C1DragHelper(image);     
         
   //Subscribe a drag event
   dragHelper.DragDelta += dragHelper_DragDelta;
   

4. Add the following code to apply clipper transformation.
   • Visual Basic
   • C#

   • Visual Basic

   'Transform method to apply transformation
   Private Sub ApplyTransform(t As BaseTransform)
       Dim newBitmap = bitmap.Transform(t)
       bitmap.Dispose()
       bitmap = newBitmap
       UpdateImage()
   End Sub
   
   'Event to apply clipper transformation on button click
   Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
       Dim cropRect = DirectCast(selection, RectD).Round()
       ApplyTransform(New Clipper(New ImageRect(cropRect)))
   End Sub
   

   • C#

   //Transform method to apply transformation
   void ApplyTransform(BaseTransform t)
   {
       var newBitmap = bitmap.Transform(t);
       bitmap.Dispose();
       bitmap = newBitmap;
       UpdateImage();
   }
   
   //Event to apply clipper transformation on button click
   private void Button_Click_1(object sender, RoutedEventArgs e)
   {
       var cropRect = ((RectD)selection).Round();
       ApplyTransform(new Clipper(new ImageRect(cropRect)));
   }
   

5. Add the following code to select a portion of the image to be clipped.
   • Visual Basic
   • C#

   • Visual Basic

   'Events to selection a portion of image
   Private Sub dragHelper_DragDelta(sender As Object, e As C1DragDeltaEventArgs)
       Dim pos = e.GetPosition(image)
       pos = New Point(Math.Max(0, Math.Min(pos.X, bitmap.PixelWidth)),
                       Math.Max(0, Math.Min(pos.Y, bitmap.PixelHeight)))
   
       selection = New Rect(Math.Round(Math.Min(start.X, pos.X)),
                            Math.Round(Math.Min(start.Y, pos.Y)),
                            Math.Round(Math.Abs(start.X - pos.X)),
                            Math.Round(Math.Abs(start.Y - pos.Y)))
   End Sub
   
   Private Sub image_MouseLeftButtonDown(sender As Object, e As MouseButtonEventArgs) _
       Handles image.MouseLeftButtonDown
       MyBase.OnMouseLeftButtonDown(e)
       Dim pos = e.GetPosition(image)
       start = New Point(Math.Max(0, Math.Min(pos.X, bitmap.PixelWidth)),
                         Math.Max(0, Math.Min(pos.Y, bitmap.PixelHeight)))
   End Sub
   
   Private Sub image_MouseLeftButtonUp(sender As Object, e As MouseButtonEventArgs) _
       Handles image.MouseLeftButtonUp
       MyBase.OnMouseLeftButtonUp(e)
       Dim pt = e.GetPosition(image)
       If Math.Abs(pt.X - start.X) < 4 AndAlso Math.Abs(pt.Y - start.Y) < 4 Then
           selection = New Rect(0, 0, bitmap.PixelWidth, bitmap.PixelHeight)
       End If
   End Sub
   

   • C#

   //Events to select a portion of image from the image
   private void image_MouseLeftButtonDown(object sender, 
       System.Windows.Input.MouseButtonEventArgs e)
   {
      base.OnMouseLeftButtonDown(e);
       var pos = e.GetPosition(image);
       start = new Point(
       Math.Max(0, Math.Min(pos.X, bitmap.PixelWidth)),
       Math.Max(0, Math.Min(pos.Y, bitmap.PixelHeight)));
   }
   
   private void image_MouseLeftButtonUp(object sender, 
       System.Windows.Input.MouseButtonEventArgs e)
   {
       base.OnMouseLeftButtonUp(e);
       var pt = e.GetPosition(image);
       if (Math.Abs(pt.X - start.X) < 4 && Math.Abs(pt.Y - start.Y) < 4)
       {
           selection = new Rect(0, 0, bitmap.PixelWidth, bitmap.PixelHeight);
       }
   }
   
   void dragHelper_DragDelta(object sender, C1DragDeltaEventArgs e)
   {
       var pos = e.GetPosition(image);
       pos = new Point(Math.Max(0, Math.Min(pos.X, bitmap.PixelWidth)),
           Math.Max(0, Math.Min(pos.Y, bitmap.PixelHeight)));
   
       selection = new Rect(
           Math.Round(Math.Min(start.X, pos.X)),
           Math.Round(Math.Min(start.Y, pos.Y)),
           Math.Round(Math.Abs(start.X - pos.X)),
           Math.Round(Math.Abs(start.Y - pos.Y)));
   }
   

6. Press F5 to run the application and click 'Load Image' button to load an image.
7. Select a portion of the image through mouse and click 'Clip Image' button to crop the selected portion.