Hi there,

I have a little problem with double buffering. I can easily implement a
buffering routine to prevent flicker but unfortunately this requires
rasterizing any meta files that I am drawing. For example, firstly I would
create a bitmap object of the correct size then acquire the graphics
context, when drawing the metafile into the bitmap it becomes rasterized,
and this process introduces some artifcating on certain metafiles. I can
completely remove this artifacting by drawing directly into the graphics
object, but this is not double buffered correctly, even with the style set
on the control.

Any ideas on how I would do this one? Thanks loads in advance!!

--
Nick Pateman

---------------------------------------------------------------
Please do not reply directly to me, but the entire newsgroup.
Any views expressed above are my own
Without predjudice

You could create a memory context(HDC)
that is compatible with your device and then
create a Graphics object from that hdc.

Use DrawImage to draw the metafile to the memory
device context and then use BitBlt to transfer the
metafile from memory to the screen.

This is the same method for double buffering a bitmap.

Converting the metafile to a bitmap first and double buffering
the bitmap is overkill.




"Nick" <nospam (AT) altavente (DOT) com> wrote

Hi Michael,

Thanks, I shall try this tommorrow...

Nick.

"Michael Phillips, Jr." <mphillips53 (AT) nospam (DOT) jun0.c0m> wrote

Hi Michael,

Im doing as suggested but unfortunately nothing appears, I'm just
getting a black area, this is my code,


Private Declare Function CreateCompatibleDC Lib "gdi32" Alias
"CreateCompatibleDC" (ByVal iHDC As IntPtr) As IntPtr
Private Declare Function GetDC Lib "user32" Alias "GetDC" (ByVal iHWND
As IntPtr) As IntPtr
Private Declare Function ReleaseDC Lib "user32" Alias "ReleaseDC" (ByVal
iHWND As IntPtr, ByVal iHDC As IntPtr) As Integer
Private Declare Function BitBlt Lib "gdi32" Alias "BitBlt" (ByVal
iDestDC As IntPtr, ByVal iDestX As Integer, ByVal iDestY As Integer, ByVal
iDestWidth As Integer, ByVal iDestHeight As Integer, ByVal iSrcDC As IntPtr,
ByVal iSrcX As Integer, ByVal iSrcY As Integer, ByVal iOp As Integer) As
Integer

Private Const SRCCOPY As Long = &HCC0020

Private pImgMetaFile As Image = Nothing
Private cIPrBufferHDC As IntPtr = IntPtr.Zero
Private cGraBuffer As Graphics = Nothing

Private Sub setup()
pImgMetaFile = Image.FromFile(Application.ExecutablePath.Substrin g(0,
Application.ExecutablePath.LastIndexOf("\") + 1) & "test.emf")

'//Create a compatible DC
Dim pIPrMyDC As IntPtr = GetDC(picBuffered.Handle)
cIPrBufferHDC = CreateCompatibleDC(pIPrMyDC)
Call ReleaseDC(Me.Handle, pIPrMyDC)

'//Acquire a graphics object
cGraBuffer = Graphics.FromHdc(cIPrBufferHDC)
End Sub

Private Sub picBuffered_Paint(ByVal sender As Object, ByVal e As
System.Windows.Forms.PaintEventArgs) Handles picBuffered.Paint
Call cGraBuffer.Clear(Me.BackColor)
Call cGraBuffer.DrawImage(pImgMetaFile, 0, 0, picBuffered.Width,
picBuffered.Height)
Dim pIntCurY As Integer
For pIntCurY = 0 To picBuffered.Height Step 10
Call cGraBuffer.DrawString("Double buffered...", Me.Font, New
SolidBrush(Color.Black), 0, pIntCurY)
Next

Dim pIPrDestHDC As IntPtr = e.Graphics.GetHdc()
Call BitBlt(pIPrDestHDC, 0, 0, picBuffered.Width, picBuffered.Height,
cIPrBufferHDC, 0, 0, SRCCOPY).ToString()
Call e.Graphics.ReleaseHdc(pIPrDestHDC)
End Sub

I've done this using a normal picturebox to draw onto, rather than the
object I had created in the other example. Nothing is being drawn though?

When setting up...

1. Getting the DC from the picture box
2. Creating a comparible DC from the DC acquired in step 1
3. Releasing the DC acquired in step 1
4. Creating a graphics object from the DC created in step 2

When drawing...

1. Drawing to the graphics object acquired in Step 4 when setting up
2. Getting the DC of the picture box
3. Blitting the DC created in step 2 when setting up to the DC acquired
in step 2
4. Releasing the DC acquired in step 2

I've had problems with BitBlt in the past with it not actually drawing
anything, is my declaration correct??

Nick.

"Michael Phillips, Jr." <mphillips53 (AT) nospam (DOT) jun0.c0m> wrote

Where I mentioned a black area appearing in the last past ignore that, it's
the backcolor of the control. I can get a red rectangle to flicker during
resizing if I use the FillRect API...

"Nick" <nospam (AT) altavente (DOT) com> wrote

.... I can get the "flickering rectangle" to "fixate" by calling the graphics
objects GetHDC method rather than the API, so I can draw fine to it with
everything except BitBlt.

Nick.

"Nick" <nospam (AT) altavente (DOT) com> wrote

Hi again,

I presume that the reason nothing is appearing is because I have not
called CreateCompatibleBitmap()? I've just tried it with that and although
the image is not appearing correctly, I'm getting something appearing.

So that basically leads me back to were I started, if I need to create a
bitmap object object for this buffer then how was my previous method
overkill? I understand that DrawImage of GDI is faster because it uses
hardware acceleration but in principal the GDI method is exactly the same.

Is it actually possible to perform double buffering with Metafiles in
..NET?

Nick.

"Nick" <nospam (AT) altavente (DOT) com> wrote

Ignore me, this is doing my head in, I'm not even sure I know what I'm
asking now. Double buffering has been performed correctly as the
artifacting has disappeared which is what my original problem was! Thanks
for your help!!

For other peoples reference you need to use CreateCompatibleBitmap after you
call CreateCompatibleDC. Thanks again and sorry for rambling!

Nick.

"Nick" <nospam (AT) altavente (DOT) com> wrote

Ignore me, this is doing my head in, I'm not even sure I know what I'm
asking now. Double buffering has been performed correctly as the
artifacting has disappeared which is what my original problem was! Thanks
for your help!!

For other peoples reference you need to use CreateCompatibleBitmap after you
call CreateCompatibleDC. Thanks again and sorry for rambling!

Nick.

"Nick" <nospam (AT) altavente (DOT) com> wrote