Manual rendering disappears

I'm trying to render a bitmap. The actual rendering seems to work fine, however since I'm rendering on top of another controls (a tab control to be precise) my own rendering doesn't show up. It's overwritten by the tab control's rendering. If I disable the default renderings my bitmap showsup but then , of course, the controls won't.

I did the default drawings first and then my own (I thought mine would overwrite theirs then, but nope...).

This is my WM_PAINT handler:

Code:

//Render
case WM_PAINT:
{
	//Render the normal windows
	DefWindowProc(Handle, Message, wParam, lParam);

	//Render the image (if neccessary)
	if(CurrentBitmap != NULL)
	{
		RenderImage();
	}
	return 0;
}

and my RenderImage function basically looks like this:

Code:

//Data
PAINTSTRUCT PaintStruct;
HDC SourceDevice;
HDC TargetDevice;

//Retrieves a target device
TargetDevice = BeginPaint(ImageFrame, &PaintStruct);
if(TargetDevice == NULL)
{
	return FALSE;
}

//Retrieves a source device
SourceDevice = CreateCompatibleDC(TargetDevice);
if(SourceDevice == NULL)
{
	EndPaint(ImageFrame, &PaintStruct);
	return FALSE;
}

//Select a handle to the bitmap object
if(!SelectObject(SourceDevice, CurrentBitmap))
{
	DeleteDC(SourceDevice);
	EndPaint(ImageFrame, &PaintStruct);
	return FALSE;
}

//Blits an image
if(!BitBlt(TargetDevice, 1, 1, ImageFrameWidth, ImageFrameHeight, SourceDevice, 0, 0, SRCCOPY))
{
	DeleteDC(SourceDevice);
	EndPaint(ImageFrame, &PaintStruct);
	return FALSE;
}

//Clean up
DeleteDC(SourceDevice);
EndPaint(ImageFrame, &PaintStruct);

Any suggestions?

Try invalidating the areas your bitmap will be updating prior to calling your Render function. BeginPaint validates the update region and this is presumably happening when the default, system painting of your window occurs. You may wish to track how the update region changes by using GetUpdateRect.

Don't know if any of that will help much, though.

Try using the TAB controls HDC

ie
hdc = GetDC(hTabCrtl);

and its client rect in the paint function

I suggest creating a compat HDC to hold your bmp when the TAB control is created, deleteing it when the TAB control is destroyed. As opposed to creating one every paint.

Unless using a .NET compiler this is a GDI resource leak

if(!SelectObject(SourceDevice, CurrentBitmap))

Ok, I retrieved the device from the tab control and moved the bitmap -> source device into the image loader. It works fine now, however if I want the image to be drawn immediately I have to invalidate the tab control and manually call WM_PAINT through SendMessage(MainWindow, WM_PAINT, NULL, NULL).

If I only invalidate the rect the image will only be drawn if I min/max it or move it outside the screen and back. Is this normal?

Anyway, it works so I shouldn't complain. It just seems weird to send a WM_PAINT message manually.

Originally posted by Magos
It works fine now, however if I want the image to be drawn immediately I have to invalidate the tab control and manually call WM_PAINT through SendMessage(MainWindow, WM_PAINT, NULL, NULL).....It just seems weird to send a WM_PAINT message manually.

UpdateWindow sends the WM_PAINT for you, if you prefer. RedrawWindow will do the invalidation/update in one fn call, given the right parameters.

to be picky

InvalidateRect() sends the paint msg

UpdateWindow() bypasses the msg que and processes the paint immediately

Picky's good - so long as you don't mind pedantic.

msdn for InvalidateRect:
The InvalidateRect function adds a rectangle to the specified window's update region.

msdn for UpdateWindow:
The UpdateWindow function updates the client area of the specified window by sending a WM_PAINT message to the window

Raise your pedantic to bordering on obsessive....

I suppose it shows the diversity of info, on the same function, available in MSDN

MFC
The UpdateWindow member function sends a WM_PAINT message directly, bypassing the application queue. If the update region is empty, WM_PAINT is not sent.

SDK
The UpdateWindow function updates the client area of the specified window by sending a WM_PAINT message to the window if the window's update region is not empty. The function sends a WM_PAINT message directly to the window procedure of the specified window, bypassing the application queue. If the update region is empty, no message is sent.