How to zoom in a Picturebox with scrollwheel in vb.net

问题:

I'm using a set of graphics overlays to draw an image inside a picturebox control using the graphics object. I have placed the Picturebox inside a Panel and set the Panel to autoscroll. What I need to know how to do now is use the Mouse scroll wheel to blow up the size of the picture in small increments while maintaining the quality of the image drawn. Anyone know how to do this?

When I update with Abdias Software code below, the picture starts out smaller when Sizemode property of picturebox is set to StretchImage. I have a pan feature with the mouse that might be interfering with keeping this code from working properly. Any Ideas? What could be keeping this from working properly?

SOLVED

This code worked much better for me than any of the two below:

Private Sub PictureBox_MouseWheel(sender As System.Object,                              e As MouseEventArgs) Handles PictureBox1.MouseWheel     If e.Delta  0 Then         If e.Delta  2000 Then Exit Sub 'maximum 2000?         End If          PictureBox1.Width += CInt(PictureBox1.Width * e.Delta / 1000)         PictureBox1.Height += CInt(PictureBox1.Height * e.Delta / 1000)     End If  End Sub 

回答1:

You can try this code. It assumes there exist a Panel1 and PictureBox1 on the form (PictureBox1 inside the Panel1 with Panel1.AutoScroll = True) with an image set on the PictureBox.

The code doesn't calculate center point of the zoom, but you can use the e.Location (or e.X/e.Y) for that.

Update - here is the new code that is (should be) more robust than the previous (see bottom):

Public Class Form1      Private _originalSize As Size = Nothing     Private _scale As Single = 1     Private _scaleDelta As Single = 0.0005      Private Sub Form_MouseWheel(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseWheel          'if very sensitive mouse, change 0.00005 to something even smaller            _scaleDelta = Math.Sqrt(PictureBox1.Width * PictureBox1.Height) * 0.00005          If e.Delta  0 Then             _scale += _scaleDelta         End If          If e.Delta  0 Then _         PictureBox1.Size = New Size(CInt(Math.Round(_originalSize.Width * _scale)), _                                     CInt(Math.Round(_originalSize.Height * _scale)))      End Sub      Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load         PictureBox1.SizeMode = PictureBoxSizeMode.StretchImage          'init this from here or a method depending on your needs         If PictureBox1.Image IsNot Nothing Then             PictureBox1.Size = Panel1.Size             _originalSize = Panel1.Size         End If      End Sub  End Class 

Old code - works, but is unstable on large changes probably due to rounding errors in Scale():

Public Class Form1      Private _scale As New SizeF(1, 1)     Private _scaleDelta As New SizeF(0.01, 0.01) '1% for each wheel tick      Private Sub Form_MouseWheel(sender As System.Object,                                  e As MouseEventArgs) Handles Me.MouseWheel 'count incrementally          _scale.Height = 1         _scale.Width = 1          If e.Delta  0 Then             _scale -= _scaleDelta         End If          If e.Delta  0 Then _         PictureBox1.Scale(_scale)      End Sub      Private Sub Form1_Load(sender As System.Object,                             e As EventArgs) Handles MyBase.Load          PictureBox1.SizeMode = PictureBoxSizeMode.StretchImage          'init picturebox size = image size         If PictureBox1.Image IsNot Nothing Then             PictureBox1.Scale(New SizeF(1, 1))             PictureBox1.Size = PictureBox1.Image.Size         End If      End Sub  End Class 

回答2:

basically, you need an image viewer. I used this before: http://cyotek.com/blog/creating-a-scrollable-and-zoomable-image-viewer-in-csharp-part-4

it works great. however, it is an user control.

for picturebox, you need create graphics from the image, and then interpolation it. here is an example: http://www.dotnetcurry.com/ShowArticle.aspx?ID=196

I did not check this one, but looks like will work.

回答3:

I noticed that there's an undesirable effect with the StretchImage SizeMode that ignores the image ratio. I just added a width and height ratio variable to include in the "zoom" algorithm. See _ratWidth and _ratHeight in code below.

Public Class Form1  Private _originalSize As Size = Nothing Private _scale As Single = 1 Private _scaleDelta As Single = 0.0005 Private _ratWidth, _ratHeight As Double  Private Sub Form_MouseWheel(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseWheel      'if very sensitive mouse, change 0.00005 to something even smaller        _scaleDelta = Math.Sqrt(PictureBox1.Width * PictureBox1.Height) * 0.00005      If e.Delta  0 Then         _scale += _scaleDelta     End If      If e.Delta  0 Then _     PictureBox1.Size = New Size(CInt(Math.Round((_originalSize.Width * _ratWidth) * _scale)), _                                 CInt(Math.Round((_originalSize.Height * _ratHeight) * _scale)))  End Sub  Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load     PictureBox1.SizeMode = PictureBoxSizeMode.StretchImage      'init this from here or a method depending on your needs     If PictureBox1.Image IsNot Nothing Then         _ratWidth = PictureBox1.Image.Width / PictureBox1.Image.Height         _ratHeight = PirctureBox1.Image.Height / PictureBox1.Image.Width         PictureBox1.Size = Panel1.Size         _originalSize = Panel1.Size     End If End Sub End Class 

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