[VB6 and API] - Convert a hdc to long variable

[joaquim]

i build 1 function for convert hdc to long variable:

Public Function ConvertPicturetoLong(PicControl As PictureBox) As Long
    Dim mdc As Long
    Dim mBMP As Long
    mdc = CreateCompatibleDC(PicControl.hDC)
    mBMP = CreateCompatibleBitmap(PicControl.hDC, PicControl.ScaleWidth, PicControl.ScaleHeight)
    SelectObject mdc, mBMP
    ConvertPicturetoLong = mBMP
    DeleteObject mBMP
    DeleteDC mdc
End Function

but i belive that isn't work, because when i do:

dim s as long
 s = ConvertPicturetoLong(PicAnimation(PicAnimation.Count - 1))
        PicAnimation(PicAnimation.Count - 1).Picture = Nothing
        Debug.Print BitBlt(PicAnimation(PicAnimation.Count - 1), 0, 0, UserControl.Width, UserControl.Height, s, 0, 0, vbSrcCopy)

because the bitblt() give me 0(zero). what isn't right?

[LaVolpe]

In your function, you create a bitmap and select it into a dc, then delete the bitmap and the dc before the function exits. The bitmap is destroyed.
Besides, the variable you are returning did reference a Bitmap not an hDC. And you are using the return value as the source hDC parameter in the BitBlt call. BitBlt requires hDC handles not bitmap handles.

You are using your function to return an hDC for a BitBlt call, I think this is more correct

Public Function ConvertPicturetoLong(PicControl As PictureBox) As Long
      ConvertPicturetoLong = PicControl.hDC
End Function

But you don't need a function, you can reference the picturebox directly.

[joaquim]

In your function, you create a bitmap and select it into a dc, then delete the bitmap and the dc before the function exits. The bitmap is destroyed.
Besides, the variable you are returning did reference a Bitmap not an hDC. And you are using the return value as the source hDC parameter in the BitBlt call. BitBlt requires hDC handles not bitmap handles.

You are using your function to return an hDC for a BitBlt call, I think this is more correct

Public Function ConvertPicturetoLong(PicControl As PictureBox) As Long
      ConvertPicturetoLong = PicControl.hDC
End Function

But you don't need a function, you can reference the picturebox directly.

i lose the image before use the bitblt()

......
Dim s As Long
        picGraphicsEffects.Picture = UserControl.Image
        UserControl.Picture = Nothing
        Load PicAnimation(PicAnimation.Count)
        PrintWindow Extender.Container.hwnd, PicAnimation(PicAnimation.Count - 1).hDC, 0
        PicAnimation(PicAnimation.Count - 1).Refresh
        PicAnimation(PicAnimation.Count - 1).Picture = PicAnimation(PicAnimation.Count - 1).Image
        s = PicAnimation(PicAnimation.Count - 1).hDC
        PicAnimation(PicAnimation.Count - 1).Picture = Nothing
        BitBlt PicAnimation(PicAnimation.Count - 1).hDC, 0, 0, UserControl.Width, UserControl.Height, s, Extender.Left, Extender.Top, vbSrcCopy ' has you see i use the variable long, but without sucess:(
        PicAnimation(PicAnimation.Count - 1).Refresh
        PicAnimation(PicAnimation.Count - 1).Picture = PicAnimation(PicAnimation.Count - 1).Image
        TransparentAlphaBlendDIB picGraphicsEffects, PicAnimation(PicAnimation.Count - 1), CLng(m_Opacy), picGraphicsEffects.Point(0, 0)
        UserControl.Picture = PicAnimation(PicAnimation.Count - 1).Image
        Unload PicAnimation(PicAnimation.Count - 1)
................

why?

[LaVolpe]

If the picturebox does not have AutoRedraw=True and is hidden/not visible, you should get just black I would think.
If the picturebox does have AutoRedraw=True and the size is smaller than what you are trying to Blt, you will get only the size of the picturebox, the rest should be black I would think

Now, if PicAnimation(picAnimation.Count-1).AutoRedraw=False, then this is a problem...

        PrintWindow Extender.Container.hwnd, PicAnimation(PicAnimation.Count - 1).hDC, 0
        PicAnimation(PicAnimation.Count - 1).Refresh ' << erased without AutoRedraw=True

If the above isn't the problem, I'm sure this is part of it too

        PicAnimation(PicAnimation.Count - 1).Picture = PicAnimation(PicAnimation.Count - 1).Image
        s = PicAnimation(PicAnimation.Count - 1).hDC
        PicAnimation(PicAnimation.Count - 1).Picture = Nothing ' << erased DC
        ' ^^ if the AutoRedraw = True, the hDC changed, therefore s points to a destroyed hDC

It is never safe to cache a VB hDC since VB can change it whenever it wants. Try this example
-- add a picturebox to a form & paste this code. Run project & click the picturebox.
See the results. You may be surprised

Private Sub Picture1_Click()
    Picture1.AutoRedraw = True
    Picture1.PaintPicture Me.Icon, 0, 0
    Debug.Print "hDC before setting picture to image: "; Picture1.hDC
    Set Picture1.Picture = Picture1.Image
    Debug.Print "hDC after setting picture to image: "; Picture1.hDC
    Set Picture1.Picture = Nothing
    Debug.Print "hDC after setting picture1.picture=nothing: "; Picture1.hDC
End Sub

[joaquim]

If the picturebox does not have AutoRedraw=True and is hidden/not visible, you should get just black I would think.
If the picturebox does have AutoRedraw=True and the size is smaller than what you are trying to Blt, you will get only the size of the picturebox, the rest should be black I would think

Now, if PicAnimation(picAnimation.Count-1).AutoRedraw=False, then this is a problem...

        PrintWindow Extender.Container.hwnd, PicAnimation(PicAnimation.Count - 1).hDC, 0
        PicAnimation(PicAnimation.Count - 1).Refresh ' << erased without AutoRedraw=True

If the above isn't the problem, I'm sure this is part of it too

        PicAnimation(PicAnimation.Count - 1).Picture = PicAnimation(PicAnimation.Count - 1).Image
        s = PicAnimation(PicAnimation.Count - 1).hDC
        PicAnimation(PicAnimation.Count - 1).Picture = Nothing ' << erased DC
        ' ^^ if the AutoRedraw = True, the hDC changed, therefore s points to a destroyed hDC

It is never safe to cache a VB hDC since VB can change it whenever it wants. Try this example
-- add a picturebox to a form & paste this code. Run project & click the picturebox.
See the results. You may be surprised

Private Sub Picture1_Click()
    Picture1.AutoRedraw = True
    Picture1.PaintPicture Me.Icon, 0, 0
    Debug.Print "hDC before setting picture to image: "; Picture1.hDC
    Set Picture1.Picture = Picture1.Image
    Debug.Print "hDC after setting picture to image: "; Picture1.hDC
    Set Picture1.Picture = Nothing
    Debug.Print "hDC after setting picture1.picture=nothing: "; Picture1.hDC
End Sub

yes... the 3 values are diffent...
Can i put here my code by steps(because the real problem isn't with the post title)?
and yes the autoredraw is true and the scalemode is in pixels. and they are hidden.