Persisting Graphics

[rbulph]

I've looked and I'm sure it must be on here somewhere, but I can't find it. How do I persist an image in VB.net? Say I wanted to show an image that joined up all the points that a mouse had moved to. I can draw in the Paint event, but this is the MouseMove event, so how do I handle that? How do I store the previous image before drawing the next line on it?

[snarfblam]

Instead of drawing to the window, you can draw to a bitmap and set the bitmap as the control's Image or BackGroundImage property, calling the Invalidate method to refresh the image.

[rbulph]

Instead of drawing to the window' date=' you can draw to a bitmap and set the bitmap as the control's Image or BackGroundImage property, calling the Invalidate method to refresh the image.[/quote']

 

Thanks. So how do I draw to the bitmap? It doesn't seem to have any graphics methods. Here's my code which doesn't work because the best I can do is draw to a Graphics object:

 

 

Public Class Form1
   Dim g As System.Drawing.Graphics
   Dim b As Bitmap

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

       g = Me.PictureBox1.CreateGraphics

       b = New Bitmap(Me.PictureBox1.Width, Me.PictureBox1.Height, g)

       Dim rt As New System.Drawing.RectangleF
       Dim pr As New System.Drawing.SizeF
       pr.Width = 20
       pr.Height = 40
       rt.Size = pr

       g.DrawEllipse(Pens.Black, rt)

       Me.PictureBox1.Invalidate()

   End Sub

   Private Sub PictureBox1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles PictureBox1.Paint

       Me.PictureBox1.Image = b

   End Sub
End Class

[snarfblam]

Use the Graphics.FromImage method to create a graphics object which can manipulate a bitmap.

[rbulph]

Use the Graphics.FromImage method to create a graphics object which can manipulate a bitmap.

I'm none the wiser. Where? And with what argument?

[jo0ls]

Dim g as Graphics = Graphics.FromImage(bitmapName)

[snarfblam]

[Vb]

'Create an image to persist

Dim MyBitmap As New Bitmap(MyPictureBox.Width, MyPictureBox.Height)

'Persist, Image. Goooood image.

MyPictureBox.Image = MyBitmap

'Now we can manipulate Image.

Dim MyGraphics As Graphics = Graphics.FromImage(MyBitmap)

[/code]

Chances are you will want the Graphics object, and maybe the Bitmap object, to be of class scope.

[rbulph]

[Vb]

'Create an image to persist

Dim MyBitmap As New Bitmap(MyPictureBox.Width, MyPictureBox.Height)

'Persist, Image. Goooood image.

MyPictureBox.Image = MyBitmap

'Now we can manipulate Image.

Dim MyGraphics As Graphics = Graphics.FromImage(MyBitmap)

[/code]

Chances are you will want the Graphics object, and maybe the Bitmap object, to be of class scope.

OK, thanks, seems to work.

 

What I was thinking was that I needed to just draw what I was drawing in the MouseMove event and avoid triggering the paint event of the PictureBox, because I thought this would lead to flickering. But your code does trigger that event and there is no flickering. If I use the picturebox's CreateGraphics method then this seems to work just as well.