I am trying to implement drawing on the bitmap and using bitblt to transfer
it to the control graphics object in the paint event. It seems to draw on
the bitmap ok but doesn't get transferred to the control graphics object in
the paint event. Any help would be appreciated. Here is my code:
public class as mycontrol
Private 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 v_BackImage As Bitmap = New Bitmap(Me.Width, Me.Height,
Me.CreateGraphics)
Private gph As Graphics = Graphics.FromImage(v_BackImage)
'do some drawing on gph
Private Sub Panel_Paint(ByVal sender As Object, ByVal e As
System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
'Get Device contexts for Source and Memory Graphics Objects
Dim hdcSrc As IntPtr = gph.GetHdc
Dim hdcDest As IntPtr = e.Graphics.GetHdc
BitBlt(hdcDest, 0, 0, Me.Width, Me.Height, hdcSrc, Me.Width, Me.Height,
13369376)
'Clean Up
gph.ReleaseHdc(hdcSrc)
e.Graphics.ReleaseHdc(hdcDest)
end sub
end class
"Sean Hederman" wrote:
[color=blue]
> *May* not work. No guarantees one way or another. As for using
> CreateGraphics, it should only be used to get information about the graphics
> surface and not to paint on. Have a look at
>
http://www.bobpowell.net/creategraphics.htm for more details.
>
> Basically if you replace all your CreateGraphics with a bitmap Graphics
> creation, and your Paint to bitblt the Bitmap, you should be fine, and be
> able to keep your code pretty much as it is.
>
> "Dennis" <Dennis@discussions.microsoft.com> wrote in message
> news:5159530E-0F3B-494F-AC2A-F43679AA7EE8@microsoft.com...[color=green]
> > Let me ask you another question if you don't mind. I have a User Control
> > Class that inheiits from the Panel Class. When my control is instaniated,
> > I
> > create a graphics object (myGraphics as Graphics = new Me.CreateGrahics)
> > I
> > maintain this graphics object and draw on it to repaint parts of the
> > control
> > or all of the control which ever is required depending on what the user
> > does.
> > If the control is resized, I recreate myGraphics object in the sizechanged
> > event.
> >
> > If I understand you correctly, this will not work under future versions of
> > .net..is that correct.
> >
> > "Sean Hederman" wrote:
> >[color=darkred]
> >> "Dennis" <Dennis@discussions.microsoft.com> wrote in message
> >> news:5DB98450-9294-4083-AF91-D773A78E49E5@microsoft.com...
> >> > I'm curious as to where M'soft documents that future versions may use
> >> > double
> >> > buffering as the default? Can you cite a link or reference? It's very
> >> > convientent to use a class graphics variable to update only parts of
> >> > the
> >> > display without recalculating and re-displaying the entire control.
> >>
> >> They don't. There are two issues here. One is that if you ever decide to
> >> switch on double bufferring, then all your code outside of Paint could be
> >> rendered useless. The other is that there are no guarantees about the
> >> Graphics object outside Paint. Since there are no guarantees, using the
> >> Graphics object elsewhere *could* be invalidated by future versions of
> >> .NET.
> >> Using Graphics outside Paint, knowing that it wraps an HDC is breaking
> >> encapsulation.
> >>
> >> As to updating only parts of your display, there are two main approaches
> >> you
> >> could follow here:
> >> 1. Use the Invalidate() overrides to only invalidate the parts of your
> >> control you're interested in, and only paint those items within the
> >> Graphics.ClipRectangle.
> >> 2. Roll your own double-bufferring system. Create a Bitmap object with
> >> the
> >> same characteristics as your control, generate a Graphics object from
> >> that,
> >> and manipulate that where you see fit. In your Paint, just blit the
> >> Bitmap
> >> onto your Control.
> >>
> >> > "Sean Hederman" wrote:
> >> >
> >> >> If you need to store the effects of transformations, what you can do
> >> >> is
> >> >> have
> >> >> Matrix member variable that you store your transformations in. Apply
> >> >> the
> >> >> changes to the Matrix in your various procedures, and then apply the
> >> >> Matrix
> >> >> to the Graphics object in the Paint.
> >> >>
> >> >> As for why you shouldn't store the Graphics object, there's no
> >> >> guarantee
> >> >> that the Graphics object has any meaning outside the Paint event. For
> >> >> example, when double bufferring is enabled, then the Graphics object
> >> >> being
> >> >> passed to your Paint relates to a GraphicsBuffer object rather than
> >> >> the
> >> >> actual drawing surface. More importantly, the next time Paint is
> >> >> invoked,
> >> >> you're given a different GraphicsBuffer object. Thus, painting on your
> >> >> stored Graphics object will not result in the painting being on the
> >> >> drawing
> >> >> surface. In addition, since there's no guarantee, future versions of
> >> >> .NET
> >> >> may break your code even if you don't use double buffering.
> >> >>
> >> >> "Sanjay" <sanjays.singh@gmail.com> wrote in message
> >> >> news:ed5OJEkJFHA.3196@TK2MSFTNGP15.phx.gbl...
> >> >> > Hi Hederman,
> >> >> > thanks for your reply.
> >> >> > But our's is a different requirement.We do all our drawing in units
> >> >> > of
> >> >> > mils(0.001 inch).And so we are doing a lot of transformations
> >> >> > to/from supported units to/from mils here and there.If I put all the
> >> >> > transformations in the paint,It will really be messy.Anyway it is
> >> >> > not
> >> >> > possible with the current implementations.
> >> >> >
> >> >> > Also could u plz make me clear as to why r u against making in a
> >> >> > data
> >> >> > member.
> >> >> >
> >> >> > I will be thankful to u for the same
> >> >> >
> >> >> > thanking u
> >> >> > sanjay
> >> >> >
> >> >> > ----- Original Message -----
> >> >> > From: "Sean Hederman" <usemy@blogentry.com>
> >> >> > Newsgroups:
> >> >> > microsoft.public.dotnet.framework,microsoft.public .dotnet.framework.drawing,
> >> >> > microsoft.public.dotnet.framework.windowsforms,mic rosoft.public.dotnet.gener
> >> >> > al,microsoft.public.dotnet.languages.vb
> >> >> > Sent: Friday, March 11, 2005 6:10 PM
> >> >> > Subject: Re: Should I store Graphics object ?
> >> >> >
> >> >> >
> >> >> >> You should definately not store the graphics object. All the code
> >> >> >> using
> >> >> >> Graphics should ideally be encapsulated within the Paint/OnPaint
> >> >> > procedures.
> >> >> >>
> >> >> >> "Sanjay" <sanjays.singh@gmail.com> wrote in message
> >> >> >> news:eSmneajJFHA.3196@TK2MSFTNGP15.phx.gbl...
> >> >> >> > hi,
> >> >> >> >
> >> >> >> > We are currently porting our project from VB6 to VB .NET.
> >> >> >> >
> >> >> >> > Earlier we used to make scale transformations on objects like
> >> >> >> > pictureBox
> >> >> > ,
> >> >> >> > forms etc.Now Such transformations are made on the graphics
> >> >> >> > object
> >> >> >> > of
> >> >> > the
> >> >> >> > form/pictureBox.
> >> >> >> >
> >> >> >> > Should It be better if make a graphics object from my pictureBox
> >> >> >> > in
> >> >> >> > load
> >> >> >> > event handler of the form and store it as member variable of the
> >> >> >> > form ,
> >> >> >> > make
> >> >> >> > transformations as and when required(we really require such
> >> >> >> > transformations
> >> >> >> > from mils to pixels.). And finally I can dispose it when the form
> >> >> >> > is
> >> >> >> > disposed.
> >> >> >> >
> >> >> >> > But I have read somewhere that Graphics object should never be
> >> >> >> > stored
> >> >> >> > as
> >> >> >> > member varibale of a class.And so I am really confused as to what
> >> >> >> > should
> >> >> > I
> >> >> >> > do ?
> >> >> >> >
> >> >> >> > Plz help me regarding this..
> >> >> >> >
> >> >> >> > sanjay
> >> >> >>
> >> >> >>
> >> >> >
> >> >> >
> >> >>
> >> >>
> >> >>
> >>
> >>
> >>[/color][/color]
>
>
>[/color]
