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OnPaint over controls

I have a form with several controls. I would like to paint *over* several
controls (mainly GroupBoxes and Labels). But, Everywhere I try to perform
painting, I end up "behind" the controls. I need a device context for the
entire form, that I can render to *after* all the controls have been
painted.

Suggestions?
Thanks
DanB
Nov 17 '05 #1
4 13118
You can get a Graphics object for each of the controls seperately by calling CreateGraphics() on each of them.
You can hide the controls by calling Hide() and just paint normally.

Unfortunately, I don't think there is a way to obtain a device context that will draw over a child control, however, there is a
class style that can be used to set the control's device context to that of the parent's. Form and Control do not set this flag so
you'd have to implement your own container using NativeWindow. Probably not worth the effort.

Maybe, you can try to prevent the controls from refreshing by overriding the WndProc method and preventing any paint messages from
being sent to the child controls. I'm not sure if this can be done, but it might not help since Windows will probably "remember"
the last bitmap used for each control and overwrite your form's context anyway.

If simply hiding the controls isn't good enough (if you need to do alpha blending or overwrite non-client area, etc. and keep the
controls visible) then I would suggest you create "smart" implementations of the controls on the form so that they can render as
appropriate for their clipping region.

GL

--
Dave Sexton
dave@www..jwaonline..com
-----------------------------------------------------------------------
"Dan Baker" <dbmail> wrote in message news:OM**************@TK2MSFTNGP15.phx.gbl...
I have a form with several controls. I would like to paint *over* several controls (mainly GroupBoxes and Labels). But, Everywhere
I try to perform painting, I end up "behind" the controls. I need a device context for the entire form, that I can render to
*after* all the controls have been painted.

Suggestions?
Thanks
DanB

Nov 17 '05 #2
This is completely erroneous and will cause nothing but pain.

You must NEVER paint on a control after obtaining it's Graphics object using
CreateGraphics. See the GDI+ FAQ #1 most asked question for details.

You can use interop to obtain the desktop window and draw directly on that.
This will enable pixels to be forced onto any control but can cause a few
problems for clean refreshes.

The best method is to use a seperate layered window control with per-pixel
alpha to create a semi-transparent window that sits on top of all others on
the form.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.

"Dave" <NO*********@dotcomdatasolutions.com> wrote in message
news:eg**************@TK2MSFTNGP09.phx.gbl...
You can get a Graphics object for each of the controls seperately by
calling CreateGraphics() on each of them.
You can hide the controls by calling Hide() and just paint normally.

Unfortunately, I don't think there is a way to obtain a device context
that will draw over a child control, however, there is a class style that
can be used to set the control's device context to that of the parent's.
Form and Control do not set this flag so you'd have to implement your own
container using NativeWindow. Probably not worth the effort.

Maybe, you can try to prevent the controls from refreshing by overriding
the WndProc method and preventing any paint messages from being sent to
the child controls. I'm not sure if this can be done, but it might not
help since Windows will probably "remember" the last bitmap used for each
control and overwrite your form's context anyway.

If simply hiding the controls isn't good enough (if you need to do alpha
blending or overwrite non-client area, etc. and keep the controls visible)
then I would suggest you create "smart" implementations of the controls on
the form so that they can render as appropriate for their clipping region.

GL

--
Dave Sexton
dave@www..jwaonline..com
-----------------------------------------------------------------------
"Dan Baker" <dbmail> wrote in message
news:OM**************@TK2MSFTNGP15.phx.gbl...
I have a form with several controls. I would like to paint *over* several
controls (mainly GroupBoxes and Labels). But, Everywhere I try to perform
painting, I end up "behind" the controls. I need a device context for the
entire form, that I can render to *after* all the controls have been
painted.

Suggestions?
Thanks
DanB


Nov 17 '05 #3
Your solution sounds good. I'm trying to animate over the controls (like a
bouncing arrow, pointing into a list of items). All controls are static, and
don't have any user-interaction, so the refresh shouldn't be a problem.
I've done this before in MFC without problems.

I would like to perform the animation in a timer routine. Is there any way
of getting a Graphics object in the timer routine that will allow me to
paint on this semi-transparent window you are describing?

DanB
"Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message
news:e4**************@TK2MSFTNGP12.phx.gbl...
This is completely erroneous and will cause nothing but pain.

You must NEVER paint on a control after obtaining it's Graphics object
using CreateGraphics. See the GDI+ FAQ #1 most asked question for details.

You can use interop to obtain the desktop window and draw directly on
that. This will enable pixels to be forced onto any control but can cause
a few problems for clean refreshes.

The best method is to use a seperate layered window control with per-pixel
alpha to create a semi-transparent window that sits on top of all others
on the form.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.

"Dave" <NO*********@dotcomdatasolutions.com> wrote in message
news:eg**************@TK2MSFTNGP09.phx.gbl...
You can get a Graphics object for each of the controls seperately by
calling CreateGraphics() on each of them.
You can hide the controls by calling Hide() and just paint normally.

Unfortunately, I don't think there is a way to obtain a device context
that will draw over a child control, however, there is a class style that
can be used to set the control's device context to that of the parent's.
Form and Control do not set this flag so you'd have to implement your own
container using NativeWindow. Probably not worth the effort.

Maybe, you can try to prevent the controls from refreshing by overriding
the WndProc method and preventing any paint messages from being sent to
the child controls. I'm not sure if this can be done, but it might not
help since Windows will probably "remember" the last bitmap used for each
control and overwrite your form's context anyway.

If simply hiding the controls isn't good enough (if you need to do alpha
blending or overwrite non-client area, etc. and keep the controls
visible) then I would suggest you create "smart" implementations of the
controls on the form so that they can render as appropriate for their
clipping region.

GL

--
Dave Sexton
dave@www..jwaonline..com
-----------------------------------------------------------------------
"Dan Baker" <dbmail> wrote in message
news:OM**************@TK2MSFTNGP15.phx.gbl...
I have a form with several controls. I would like to paint *over* several
controls (mainly GroupBoxes and Labels). But, Everywhere I try to perform
painting, I end up "behind" the controls. I need a device context for
the entire form, that I can render to *after* all the controls have been
painted.

Suggestions?
Thanks
DanB



Nov 17 '05 #4
I think Bob's suggesting that you create an overlaid window, that's transparent, and covers your entire form area.

You'd have to hook-up the events so that any changes to the underlying Form's location/bounds is reflected on the overlaying window.

If you use an overlaying Form you can use Windows API calls (or the CreateGraphics() method that Bob doesn't like) to obtain the
device context and draw at any time (including in a timer routine), or you can create a custom window implementation by deriving
from NativeWindow. Using the latter solution forces you to write most of the code using Interop.

Here's the reference I use for GDI coding:

http://msdn.microsoft.com/library/de...vcons_8x45.asp

GL
--
Dave Sexton
dave@www..jwaonline..com
-----------------------------------------------------------------------
"Dan Baker" <dbmail> wrote in message news:u6**************@TK2MSFTNGP10.phx.gbl...
Your solution sounds good. I'm trying to animate over the controls (like a bouncing arrow, pointing into a list of items). All
controls are static, and don't have any user-interaction, so the refresh shouldn't be a problem. I've done this before in MFC
without problems.

I would like to perform the animation in a timer routine. Is there any way of getting a Graphics object in the timer routine that
will allow me to paint on this semi-transparent window you are describing?

DanB
"Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message news:e4**************@TK2MSFTNGP12.phx.gbl...
This is completely erroneous and will cause nothing but pain.

You must NEVER paint on a control after obtaining it's Graphics object using CreateGraphics. See the GDI+ FAQ #1 most asked
question for details.

You can use interop to obtain the desktop window and draw directly on that. This will enable pixels to be forced onto any control
but can cause a few problems for clean refreshes.

The best method is to use a seperate layered window control with per-pixel alpha to create a semi-transparent window that sits on
top of all others on the form.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.

"Dave" <NO*********@dotcomdatasolutions.com> wrote in message news:eg**************@TK2MSFTNGP09.phx.gbl...
You can get a Graphics object for each of the controls seperately by calling CreateGraphics() on each of them.
You can hide the controls by calling Hide() and just paint normally.

Unfortunately, I don't think there is a way to obtain a device context that will draw over a child control, however, there is a
class style that can be used to set the control's device context to that of the parent's. Form and Control do not set this flag
so you'd have to implement your own container using NativeWindow. Probably not worth the effort.

Maybe, you can try to prevent the controls from refreshing by overriding the WndProc method and preventing any paint messages
from being sent to the child controls. I'm not sure if this can be done, but it might not help since Windows will probably
"remember" the last bitmap used for each control and overwrite your form's context anyway.

If simply hiding the controls isn't good enough (if you need to do alpha blending or overwrite non-client area, etc. and keep
the controls visible) then I would suggest you create "smart" implementations of the controls on the form so that they can
render as appropriate for their clipping region.

GL

--
Dave Sexton
dave@www..jwaonline..com
-----------------------------------------------------------------------
"Dan Baker" <dbmail> wrote in message news:OM**************@TK2MSFTNGP15.phx.gbl...
I have a form with several controls. I would like to paint *over* several controls (mainly GroupBoxes and Labels). But,
Everywhere I try to perform painting, I end up "behind" the controls. I need a device context for the entire form, that I can
render to *after* all the controls have been painted.

Suggestions?
Thanks
DanB



Nov 17 '05 #5

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