Here's some code I use to copy part of a bitmap image to the ClipRectangle
passed for repainting. Note that v_BackImage is my background bitmap I
defined as a private variable in my overall class.
Private Sub me_Paint(ByVal sender As Object, ByVal e As
System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
Dim hdcControl As IntPtr = e.Graphics.GetHdc
Dim hdcBitmapDC As IntPtr = gph.GetHdc
Dim hdcBitmapHandle As IntPtr = v_BackImage.GetHbitmap 'This takes
up 85% of time
SelectObject(hdcBitmapDC, hdcBitmapHandle)
BitBlt(hdcControl, e.ClipRectangle.X, e.ClipRectangle.Y,
e.ClipRectangle.Width, e.ClipRectangle.Height, hdcBitmapDC,
e.ClipRectangle.X, e.ClipRectangle.Y, &HCC0020)
DeleteObject(hdcBitmapHandle)
gph.ReleaseHdc(hdcBitmapDC)
e.Graphics.ReleaseHdc(hdcControl)
exit sub
'**** Explaination of above *********
' BitBlt copies the graphic data to a Device Context. A Device
Context is a data structure maintained by GDI. A device context is
'associated with a particular display device, such as a printer or
video display. For a video display, a device context is usually
'associated with a particular window on the display, but it can also
be an offscreen display.
'What you do, is create a Device Context and then associate a Bitmap
with the Device Context ( with SelectObject ). Then you
' draw to the Device Context ( using BitBlt ) to alter the Bitmap.
You can't use GDI functions to directly draw to a bitmap.
'After using a Device Context, you need to clean stuff up ( release
and delete ) or else the device context stays locked and
' other attempts to draw again will fail. Also not cleaning up will
result in memory leaks.
--
Dennis in Houston
"James Westgate" wrote:
> Hi,
>
> You need to create a compatible device context. See my post on the 19th of
> July under Graphics.DrawIMage uses More memory
>
> James
>
> --
> Create interactive diagrams and flowcharts with ERM Diagram at
> http://www.crainiate.net
>
> Take the ERM Tour at http://www.flowchartcontrol.com
>
>
> "DraguVaso" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > Hi,
> >
> > In the override of the Paint-method of a DataGridTextBoxColumn I want to
> > show an image with BitBlt, to see what I can gain there on performance.
> > The problem is: It doesn't show me the image in the DataGrid-Cell's, but a
> > black background...
> >
> > Does anybody has any idea what I am doing wrong?
> >
> > Thanks a lot in advance,
> >
> > Pieter
> >
> >
> > Declare Auto Function BitBlt Lib "GDI32.DLL" ( _
> > ByVal hdcDest As IntPtr, _
> > ByVal nXDest As Integer, _
> > ByVal nYDest As Integer, _
> > ByVal nWidth As Integer, _
> > ByVal nHeight As Integer, _
> > ByVal hdcSrc As IntPtr, _
> > ByVal nXSrc As Integer, _
> > ByVal nYSrc As Integer, _
> > ByVal dwRop As Int32) As Boolean
> > Private Const SRCCOPY As Integer = &HCC0020
> >
> > Protected Overloads Overrides Sub Paint(ByVal g As Graphics, ByVal
> > bounds As Rectangle, ByVal source As CurrencyManager, ByVal rowNum As
> > Integer, ByVal backBrush As Brush, ByVal foreBrush As Brush, ByVal
> > alignToRight As Boolean)
> > Dim rectB As New Rectangle
> > rectB = bounds
> > rectB.Width = rectB.Width + 1
> > Dim g3 As Graphics
> > g3 = Graphics.FromImage(fe.BackgroundImage)
> > 'fe.BackgroundImage is a bitmap I read from a stream (PixelFormat =
> > Format32bppPArgb)
> > Dim HDC1 As IntPtr = g.GetHdc
> > Dim HDC2 As IntPtr = g3.GetHdc
> > Me.BitBlt(HDC1, 0, 0, rectB.Width, rectB.Height, HDC2, 0,
> > 0,
> > SRCCOPY)
> > g.ReleaseHdc(HDC1)
> > g3.ReleaseHdc(HDC2)
> > ...
> >
> >
>
>
>
Similar Threads
