Graphics

11-Jan-09 9:14

Regards
I have a problem. I cant get to refresh an image the second time it should be displayed. I am using gdi+ function Graphics::DrawImage. The image displays correctly but the second time (in a loop) the function is called the image isn't refreshed. Instead the image stays (on screen) as the first time it was drawn. I know that the image (bitmap) is changed between the two calls for DrawImage function because, when I do something with the window the image is drawn to, (like resizing it, minimizing etc.), the image is refreshed, but if I do nothing the image stays as it is the first time DrawImage draws it. I am changing image's pixels in another function named Render(), that is called before DrawImage.
Is there another function that draws image on screen, or is there a clear screen function. (I tried with graphics.Clear(color) function but after it the screen is filled with the color 'color' and again it it stays like that indefinitely)
The bitmap is created in memory and isn't read from the disk (although it's the same thing once it is in memory).
Here is part of the code which is called continously (in a loop):

void Prikaz(HDC hdc){
    Graphics graphics(hdc);
    Render();
    Bitmap FrameBuffer((BITMAPINFO*) &((*BMPSlika).InfoHeader), (*BMPSlika).PixelData);
    graphics.DrawImage(&FrameBuffer,0,0);
}

BMPSlika is a pointer to the bitmap image structure.

Re: GDI+ refresh image (C++) [modified]

Tim Craig11-Jan-09 17:03

Tim Craig

11-Jan-09 17:03

It's not clear what you're using as a framework for the rest of your application, but I think you might be missing the "invalidate" call on the window after you draw to it to get it refreshed.

"Republicans are the party that says government doesn't work and then they get elected and prove it." -- P.J. O'Rourke

Valdyr11-Jan-09 23:25

11-Jan-09 23:25

I'm using .net framework, and i don't have invalidate function. is there an equivalent in .net?
I'm using MFC in standard windows libraries, in VS 2008, (VC++ 2008).

modified on Monday, January 12, 2009 11:19 AM

Tim Craig12-Jan-09 9:53

Tim Craig

12-Jan-09 9:53

I don't use .Net so I can't speak definitively about it but a quick search of MSDN.Microsoft.com shows that most .Net windows have an Invalidate function.

Um, you just confused me since you modifed your post. If you're using MFC, you have an Invalidate on your View class. Earlier, you said you didn't have MFC which would be true if you were using VS 2008 Express.

"Republicans are the party that says government doesn't work and then they get elected and prove it." -- P.J. O'Rourke

Valdyr12-Jan-09 13:46

Re: GDI+ refresh image (C++) [modified]

12-Jan-09 13:46

uff sorry about that...
i searched through the project settings and found out that it is using MFC standard windows libraries... before that I hurriedly concluded, since I can't use invalidate function and I've not fount an mfc90.dll (in VS2008), that I dont have MFC... D'Oh! | :doh:

Valdyr13-Jan-09 1:46

13-Jan-09 1:46

there is a problem and I cant use invalidate, i'll work on that. in the meanwhile here is WndProc procedure, it might bee something here that prevents image being refreshed. I think some of the variables in PAINTSTRUCT ps, HWND hWnd, and HDC hdc are not properly set for the image to be refreshed; (firstly I think it has something to do with PAINTSTRUCT);

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, 
   WPARAM wParam, LPARAM lParam){
   PAINTSTRUCT  ps;
   HDC		hdc;

   switch(message){
   case WM_PAINT:
	 hdc = BeginPaint(hWnd, &ps);
	 Prikaz(hdc);
      return 0;
   case WM_DESTROY:
      PostQuitMessage(0);
	  SnimiBitmap();
      return 0;
   default:
      return DefWindowProc(hWnd, message, wParam, lParam);
   }
}

this is WndProc process, in case it can solve my problem. I think there is something with this WM_PAINT case, it is called only when I resize, minimize, move it offscreen OR when i hold mouse pointer over the (display) window.
In first three situations when I resize, minimize, or move offscreen, the image does get refreshed, (the WM_PAINT case is executed and in it the Prikaz(hdc) iz executed which displays new image)
In the fourth situation, when I hold a mouse pointer over the display window, the WM_PAINT case is switched and the Prikaz(hdc) does get executed (including all the functions in Prikaz(hdc)), but the image doesn't get refreshed...? D'Oh! | :doh:

this leads me to conclusion that, in situation when the mouse is over the display window, something is not "properly" set in this line, (since the Prikaz(hdc) uses argument hdc):
hdc = BeginPaint(hWnd, &ps);
I have seen the variables in ps (which is an PAINTSTRUCT structure), the hWnd (which is of HWND type) and hdc (HDC type (:lol))... In each situation they hold different values except for ps.fErase, ps.fIncUpdate, ps.fRestore. they are allways set to value 0;
there is allso ps.rgbReserved which is an pointer to an array of bytes but i'll examine it more closely.
if anyone knows about PAINTSTRUCT structure or hWnd and hdc, what is wrong with them when the image doesn't get refreshed, please let me know. in meanwhile I will try something with ps.rgbReserved, and try to get invalidate() function to include in my code, (this has something to do with .NET namespaces to do i think)....

Mark Salsbery13-Jan-09 6:38

13-Jan-09 6:38

You mentioned something about a loop in your first post - where is this loop and
what is it (supposed to be) doing?

WM_PAINT is posted to your window's message queue by the system. The parameters are
not in your control, nor are they wrong, nor should you be trying to send/post a WM_PAINT
message yourself.

Window rendering has been the same since the beginning of Windows....the problem is in YOUR code,
not some problem in MFC (which you're not using apparently), .NET (which you're not using apparently),
or the system.

void Prikaz(HDC hdc){
    Graphics graphics(hdc);
    Render();
    Bitmap FrameBuffer((BITMAPINFO*) &((*BMPSlika).InfoHeader), (*BMPSlika).PixelData);
    graphics.DrawImage(&FrameBuffer,0,0);
}

This code has nothing to do with WM_PAINT or Invalidatexxxx() functions. The bitmap will be rendered
immediately if the HDC and the Bitmap are valid.

According to your comments, your WM_PAINT handling code is working fine, so where else are
you calling this from and how are you obtaining the HDC?

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Valdyr13-Jan-09 9:07

13-Jan-09 9:07

Read the message please.

Mark Salsbery wrote:
You mentioned something about a loop in your first post - where is this loop and
what is it (supposed to be) doing?

for "loop" i meant calling the Prikaz() function over again (that was in first post)

Mark Salsbery wrote:
WM_PAINT is posted to your window's message queue by the system. The parameters are
not in your control, nor are they wrong, nor should you be trying to send/post a WM_PAINT
message yourself.

i'm not trying to change the message to constantly switch to WM_PAINT case, nor I said the parameters are whong (READ THE MESSAGES and then answer them if you wish to)

Mark Salsbery wrote:

Window rendering has been the same since the beginning of Windows....the problem is in YOUR code,
not some problem in MFC (which you're not using apparently), .NET (which you're not using apparently),
or the system.

the problem IS in my code (that's why I asked for help in the first place) , and there IS a problem with my .NET config in my VS.

Mark Salsbery wrote:
This code has nothing to do with WM_PAINT or Invalidatexxxx() functions. The bitmap will be rendered
immediately if the HDC and the Bitmap are valid.

that code is called when the WM_PAINT message is set.
the bitmap is rendered (correctly), but only the first time the WM_PAINT is called. the WM_PAINT is called (in my program) only when i do something with the window the image is displayed in, like resizing, minimizing, holding a mouse pointer over the window.....
in the first two situations, when i resize it or minimize (and maximize ofc) the image that is displayed gets updated... (my image in the program is constantly changed in the Render() function)
in the last situation when i hold a mouse pointer over the window the WM_PAINT case gets executed, and whit it the Prikaz function, but then the image doesnt get updated.
I was asking for a way to constantly update the image when WM_PAINT is switched.

Mark Salsbery wrote:
According to your comments, your WM_PAINT handling code is working fine, so where else are
you calling this from and how are you obtaining the HDC?

i dont understand you, i'm not calling it from anywhere else in my code.

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, 
   WPARAM wParam, LPARAM lParam){
   PAINTSTRUCT  ps;
   HDC			hdc;
   switch(message){
   case WM_PAINT:
	 hdc = BeginPaint(hWnd, &ps);	 
	 Prikaz(hdc, hWnd);
      return 0;
   case WM_DESTROY:
      PostQuitMessage(0);
	  SnimiBitmap();
      return 0;
   default:
      return DefWindowProc(hWnd, message, wParam, lParam);
   }

i'm geting it with the BeginPaint

Mark Salsbery13-Jan-09 9:27

13-Jan-09 9:27

OK I've gone through your posts....there's so much contradicting information it
makes it really hard to follow Smile | :)

From all I can see, you are not using .NET and you're not using MFC.

If your window redraws fine when you resize it, move it, or move another window over
and then off it, then your WM_PAINT handler code is working fine.

Here's the code I have so far:

void Prikaz(HDC hdc){
    Graphics graphics(hdc);
    Render();
    Bitmap FrameBuffer((BITMAPINFO*) &((*BMPSlika).InfoHeader), (*BMPSlika).PixelData);
    graphics.DrawImage(&FrameBuffer,0,0);
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, 
   WPARAM wParam, LPARAM lParam){
   PAINTSTRUCT  ps;
   HDC			hdc;
   switch(message){
   case WM_PAINT:
	 hdc = BeginPaint(hWnd, &ps);	 
	 Prikaz(hdc, hWnd);
      return 0;
   case WM_DESTROY:
      PostQuitMessage(0);
	  SnimiBitmap();
      return 0;
   default:
      return DefWindowProc(hWnd, message, wParam, lParam);
   }

Prikaz() is only called from the WM_PAINT handler code, correct?

How many places is Render() called from?

If you call an Invalidate function from Render() to force a repaint of
the window (or a portion of the window) then you'll have an infinite redraw
loop, which will really slow down your UI Smile | :)

So if you're calling Render() perhaps from another thread that is updating the bitmap,
then the code making the call to Render() should then call an invalidate function
like InvalidateRect() to tell the system it should send another WM_PAINT.

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Valdyr13-Jan-09 10:06

13-Jan-09 10:06

Yes, Prikaz is only called from the WM_PAINT handler code.
Render() is called only from Prikaz(), (that is a bit stupid, i could do completely without Prikaz())

In render() i'm just repainting the bitmap, and calling it from prikaz().

it's a problem i cant use invalidate, (someone refered to it in .net or mfc),

Mark Salsbery wrote:
call an invalidate function
like InvalidateRect() to tell the system it should send another WM_PAINT.

i need that function that tells the system to send another WM_PAINT, but as i have seen in some case when WM_PAINT handler is executed, (i mean on Prikaz() in WM_PAINT handler to be executed) the image on the screen doesn't get always updated (in some cases graphics.DrawImage() does update the image and in some cases it doesn't)... i was trying to see what causes DrawImage to redraw image and how to "simulate" that condition...
i'll use InvalidateRect() as you said, it must work...

modified on Tuesday, January 13, 2009 4:45 PM

Mark Salsbery13-Jan-09 18:53

13-Jan-09 18:53

Valdyr wrote:
it's a problem i cant use invalidate

Invalidate() is specific to MFC. You need to Use one of the Win32
Invalidate functions...InvalidateRect() or InvalidateRgn(). For an instant
repaint you can call UpdateWindow() right after the Invalidatexxx call.
There's also RedrawWindow(), which combines the Invalidate and UpdateWindow
into one call, with some extra flags for finer control.

Valdyr wrote:
i was trying to see what causes DrawImage to redraw image

In your case, it gets called any time you get a WM_PAINT message for your window,
since you aren't calling it anywhere else. You'll get WM_PAINT messages when an area
of the window is marked invalid, as described above, or by the system when you resize
the window larger (which invalidates the newly exposed part of the window) or move
another window off of your window.

So back to your code, if you're not getting desired results, the only place left is in
your Render() code.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Valdyr14-Jan-09 8:48

14-Jan-09 8:48

it works, thanks Big Grin | :-D

thats what i needed, InvalidateRect(), i didn't know about it in gdi.
now the image gets updated "on it's own"

Mark Salsbery14-Jan-09 8:59

14-Jan-09 8:59

Cool!

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Valdyr14-Jan-09 9:09

14-Jan-09 9:09

yeea

Tim Craig14-Jan-09 8:39

Tim Craig

14-Jan-09 8:39

Setup a timer and call your render code from that. In your render code call the proper invalidate function to get the WM_PAINT message sent. Just remember there's not much reason to set the timer faster than your monitor can refresh the frame or you be spending rendering cycles you won't see. This way you'll get an orderly, controllable stream of screen updates and rendering cycles.

"Republicans are the party that says government doesn't work and then they get elected and prove it." -- P.J. O'Rourke

Valdyr14-Jan-09 8:58

14-Jan-09 8:58

i'll do that,
my problem was that i wasn't using invalidate function (i didn't know about other invalidate functions, just about that that is in MFC)

Valdyr14-Jan-09 9:07