Hi,
I've got a routine that fetches a bitmap from a COM server and converts it
into a .NET format bitmap. The original DIB surface is 24 bit. When
blitting this bitmap to a window, the speed is pretty good when the window
is around 1/4 the size of the screen, but if I go maximise the window, it
slows to a crawl (relative crawl). Anyway, I've read some blogs about how
to increase the speed, including using GDI instead of GDI+, DirectDraw or
DirectX but am not sure what the best way to proceed would be. I don't want
the weight of DirectX or DD just to render a bitmap to a window. Any ideas?
btw: I also read that using 32bpp instead of 24bpp would be considerably
faster with .NET GDI+, but am not sure how to do the conversion. The way I
get the bitmap from the DIB is shown below (also code gained from around the
net and modified for my own uses). I'm not sure if creating a new 32 bit
surface and blitting the 24 bit one to that will do here to convert it, i.e.
there must be a better way. Any ideas?
''' <summary>
''' Convert a DIB format bitmap into a .NET bitmap.
''' </summary>
''' <param name="theDIB"></param>
''' <returns></returns>
''' <remarks></remarks>
Public Shared Function ToBitmap(ByVal theDIB As IntPtr) As Bitmap
Dim theImage As Bitmap = Nothing
Dim theStream As MemoryStream = Nothing
Dim fh As New BITMAPFILEHEADE R
Dim bmiTyp As Type = GetType(BITMAPI NFOHEADER)
Try
' Check and "parse" the bitmap header.
Dim bmi As BITMAPINFOHEADE R =
DirectCast(Mars hal.PtrToStruct ure(theDIB, bmiTyp), BITMAPINFOHEADE R)
If bmi.biSizeImage = 0 Then
bmi.biSizeImage = ((((bmi.biWidth * bmi.biBitCount) + 31) And
(Not 31)) >3) * Math.Abs(bmi.bi Height)
End If
If ((bmi.biClrUsed = 0) And (bmi.biBitCount < 16)) Then
bmi.biClrUsed = 1 << bmi.biBitCount
End If
Dim fhSize As Integer = Marshal.SizeOf( GetType(BITMAPF ILEHEADER))
Dim dibSize As Integer = bmi.biSize + (bmi.biClrUsed * 4) +
bmi.biSizeImage
Dim chars() As Char = {"B"c, "M"c}
fh.Type = chars
fh.Size = fhSize + dibSize
fh.OffBits = fhSize + bmi.biSize + (bmi.biClrUsed * 4)
' serialise the bitmap into a memory stream.
Dim theData(fh.Size ) As Byte
If Not ToBytes(fh, theData) Then
Throw New Exception("Fail ed to serialize into structure.")
End If
Marshal.Copy(th eDIB, theData, fhSize, dibSize)
theStream = New MemoryStream(th eData)
theImage = New Bitmap(theStrea m)
Catch Ex As Exception
If Not theImage Is Nothing Then
theImage.Dispos e()
theImage = Nothing
End If
Finally
' Release objects.
If Not theStream Is Nothing Then
theStream.Close ()
theStream = Nothing
End If
End Try
Return theImage
End Function
''' <summary>
''' Serialize an object into a set of bytes.
''' </summary>
''' <param name="theObject "></param>
''' <param name="theData"> </param>
''' <returns></returns>
''' <remarks></remarks>
Private Shared Function ToBytes(ByVal theObject As Object, ByVal theData As
Byte()) As Boolean
Dim theHandle As GCHandle
Dim theBuffer As IntPtr
Try
Dim theSize As Integer = Marshal.SizeOf( theObject)
If (theSize theData.Length) Then
Throw New ArgumentExcepti on("Buffer too small ", " byte()
theData. ")
End If
theHandle = GCHandle.Alloc( theData, GCHandleType.Pi nned)
theBuffer = theHandle.AddrO fPinnedObject()
Marshal.Structu reToPtr(theObje ct, theBuffer, False)
Return True
Catch ex As Exception
Return False
Finally
' Release
If theHandle.IsAll ocated Then
theHandle.Free( )
End If
End Try
End Function
