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Creating a Picture Panning Control in .NET

Thursday Aug 9th 2018 by Hannes DuPreez

Explore a very simple technique to accomplish a panning effect with your images.

Introduction

A frequent question on developer forums is how to do image panning in .NET. This article aims to show you a very simple way to accomplish panning with your images.

What Is Panning?

When you pan an image, you use the mouse to move to invisible parts of the image. In other words, you drag left on a picture and the right part of the image, that wasn't visible, becomes visible; when you drag upwards, the bottom part of the image becomes visible. Obviously, this same effect can be accomplished by using scrollbars where you scroll in the appropriate direction to see the parts of the image that is not visible.

Our Project

You will not be creating a very large project today. In fact, it will be a small project, yet very powerful. You will create a panning User Control which can be used in other projects.

Open Visual Studio and create either a Visual Basic or C# Windows Forms Application. You may name it anything you desire; just remember that my object names may differ from yours. Once your project has finished loading, add a User Control. Do this by selecting: Project-> Add User Control. Add the following controls and design it as follows:

ucPan User Control Size 760; 570
pnlPan Panel BorderStyle FixedSingle
    Dock Fill
    Size 746; 537
picPan PictureBox BorderStyle Fixed3D
    Size 700; 504
    Image Any Large Picture

Design
Figure 1: Design

I have included a picture of a giraffe surrounded by trees. I took it in the Kruger National Park (so beautiful) earlier this year, on holiday in the most beautiful province in South Africa: Mpumalanga.

Code

Declare a Point variable to keep track of where the Mouse button was initially clicked:

C#

   private Point pntStart = new Point();

VB.NET

   Private pntStart As New Point

Add the following code to the User Control's Load event:

C#

   private void ucPan_Load(object sender, EventArgs e)
   {

      pnlPan.AutoScroll = true;

      picPan.SizeMode = PictureBoxSizeMode.AutoSize;

   }

VB.NET

   Private Sub ucPan_Load(sender As Object, e As EventArgs) _
         Handles Me.Load

      pnlPan.AutoScroll = True

      picPan.SizeMode = PictureBoxSizeMode.AutoSize

   End Sub

In the Load event, you simply set the AutoScroll property of the Panel to true and the Picturebox's SizeMode to AutoSize. This means that the Picturebox will grow or shrink depending on the size of the supplied image.

Add the MouseDown event for the PictureBox:

C#

   private void picPan_MouseDown(object sender, MouseEventArgs e)
   {

      pntStart = new Point(e.X, e.Y);

   }

VB.NET

   Private Sub picPan_MouseDown(sender As Object, e As _
         MouseEventArgs) Handles picPan.MouseDown

      pntStart = New Point(e.X, e.Y)

   End Sub

This simply holds the initial starting point. Now, add the MouseMove event:

C#

   private void picPan_MouseMove(object sender, MouseEventArgs e)
   {

      if (e.Button == System.Windows.Forms.MouseButtons.Left)
      {
         int X = (pntStart.X - e.X);
         int Y = (pntStart.Y - e.Y);

         pnlPan.AutoScrollPosition =
            new Point((X - pnlPan.AutoScrollPosition.X),
            (Y - pnlPan.AutoScrollPosition.Y));
      }

   }

VB.NET

   Private Sub picPan_MouseMove(sender As Object, e As _
         MouseEventArgs) Handles picPan.MouseMove

      If e.Button = Windows.Forms.MouseButtons.Left Then

         Dim X As Integer = (pntStart.X - e.X)
         Dim Y As Integer = (pntStart.Y - e.Y)

         pnlPan.AutoScrollPosition =
         New Point((X - pnlPan.AutoScrollPosition.X), _
            (Y - pnlPan.AutoScrollPosition.Y))
      End If
   End Sub

In the MouseMove event, you simply shift the image up to where the button was clicked down in the MouseDown event.

Build your project. After your project is built successfully, your User Control will be ready to use. But first, you must add it from the Toolbox onto your form, as shown in Figure 2.

User Control inside the Toolbox
Figure 2: User Control inside the Toolbox

After you have added the User Control to your form, you can run your project. It will work as shown in Figure 3:

Running with borders displayed
Figure 3: Running with borders displayed

If you want to eliminate the borders, add the following code in Form1.

C#

   protected override void DefWndProc(ref Message m)
   {
      if (m.Msg != 131)
      base.DefWndProc(ref m);
   }

VB.NET

   Protected Overrides Sub DefWndProc(ByRef m As Message)

      If m.Msg <> 131 Then

         MyBase.DefWndProc(m)

      End If

This overrides the DefWndProc system function to send a message to hide the borders. Figure 4 shows the result.

Running without borders
Figure 4: Running without borders

Conclusion

Playing with pictures is fun. I hope you have enjoyed today's article and that you have learned from it.

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