window painting background

Ok, I have a simple app that can draw lines and shapes, etc..

It draws to the screen DC and to a frame buffer memory DC which I use to keep track of what has been drawn.

Now, to the problem.. when the screen is redrawn (when my window proc handles WM_PAINT) it redraws everything correctly, except for some reason the background is black (when it should be white).

It is redrawn using a simple BitBlt from the memory to the screen.

I'll post some code if its really needed, but I would think someone could figure this out without it.

Thanks for any advice.

Realy need some code.

Are you creating compatible bitmaps in both HDC's of the right size?

What flag are you using for the type of drawing (last param in BitBlt() )? use SRCCOPY

Are you painting the bmp's white at any stage?

Are you BitBlt() ing the screen dc to the frame buffer before calling for a WP_PAINT?

Use this to paint the buffer white.

Code:

---

BitBlt(hdcBuffer, 0, 0, iWidth, iHeight, hdcBuffer, 0, 0, WHITENESS);

---

Yes, I have bitmaps on both side..
Yes, i'm using SRCCOPY.
I don't know what you mean by painting the bitmaps white... this is a simple painting app, so you can choose any color of brush if thats what you mean.. but besides for that, no.
Yes, before the call to WM_PAINT there is a call to BitBlt to copy the screen to the memory DC.

I'm not sure how to do the code formatting thing.. but here is what I have in WM_PAINT:

else if(Message==WM_PAINT)
{
PAINTSTRUCT psStruct;
hDc=BeginPaint(hwnd,&psStruct);

BitBlt(hDc,0,0,nWidth,nHeight,hDcMem,0,0,SRCCOPY);

EndPaint(hwnd,&psStruct);
return 0;
}

hDc is just my screen DC, and hDcMem is obviously my frame buffer (mem). nWidth and nHeight were gathered using GetDeviceCaps.

Everything is displayed properly.. just the background is black, so i'm not sure what would cause that. I'm new to doing GDI stuff so its possible I just missed something.

Hope that helps some..
As usual, any help is appreciated

When the bitmaps are created using a call to
CreateCompatibleBitmap() or similar they contain an image full of rubbish, random values in each pixcell.

Mine have blackish distortion in them at start so I paint them white (or another colour). They need to be 'initialised', you would not use a variable without first initialising its contents.

The bitmap was created at the same size as nWidth, nHeight?



http://www.cprogramming.com/cboard/s...threadid=10866
has a zip of a graphing program (not working) with a functioning frame buffer system. (graphfix.zip not graph.zip)

Try adding that WHITENESS line right at the start fo drawing a graph and see if it helps.

K.. I think i've got it covered now.

See, the image was fine besides for it starting out black.. so like you said, I now just fill it white when its created.. and then the problem is pretty much gone.

I guess I just assumed the image would automatically be white or transparent.

Thanks for the help. :)