bitblt flickering problem

[mookie0001]

Hi everyone,

I am trying to smoothly scroll a VERY large image across a form. Unfortunately, I am getting very bad flickering problems. One helpful person recommended that I blit only the screen size instead of the entire picture. Unfortunately, I followed a tutorial to get this far and do not quite understand how I would go about doing this. Can someone give me a few pointers on this, or recommend other ways to stop the flickering (code snippets would be helpful). Thanks in advance!

-Chris


Here is my current source code:

Dim gameboard_image As New Bitmap("e:\hugePicture.jpg&quot

'Create the target graphics and get an hDC from it
Dim formGraphics As Graphics = Me.CreateGraphics()
Dim targethDC As IntPtr = formGraphics.GetHdc()

'Create an offscreen dc and select our bitmap in to it
Dim offscreenhDC As IntPtr = CreateCompatibleDC(targethDC)
Dim oldObject As IntPtr = SelectObject(offscreenhDC, gameboard_image.GetHbitmap())


Private Sub form2_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint

BitBlt(targethDC, m_dragOffset.X, m_dragOffset.Y, gameboard_image.Width, gameboard_image.Height, offscreenhDC, 0, 0, SRCCOPY)

End Sub

 

[T0AD]

Hi Chris,

Try "double buffering", (at least I think that's what it's called!) It's very similar to what you've got above.

You need to create an off-screen DC the size of your drawing surface (let's say, the form) and blit your image to that in it's starting position. (don't forget the SelectObject, etc - but it looks like you're OK with all that stuff)

1. Blit the whole thing to your form's DC.
2. Clear the off-screen DC.
3. Blit the image to your off-screen DC in the next position.
4. Blit the whole thing to your form's DC, again. Etc, etc.

It should appear flickerless - let me know if you want me to stick some code together for you.

Hope it helps,
Pete