GDI+ Double Buffering: backbuffer dual-colored monochrome

Question

I am trying to build a very simple graphical app using C++, windows api and GDI+. When first trying to build the app, heavy flickering was introduced, so this code tries to use double buffering, but fails. hdcBuf is the backbuffer.

When trying to draw something to the backbuffer using GDI+ Graphics::DrawCachedBitmap the bitmap is drawn dual-colored in black and white.

LoadBitmapRes creates a CachedBitmap from the EXE resources; this function works with single buffering.

Is there anything wrong in the code? Thanks in advance!

Global:

CachedBitmap* fish;
HDC hdc;
HDC hdcBuf;
HBITMAP hbmpBuf;
Graphics* gfxBuf;

WM_CREATE:

hdc = GetDC(hwnd);
hdcBuf = CreateCompatibleDC(hdc);
hbmpBuf = CreateCompatibleBitmap(hdcBuf, 640, 480);
SelectObject(hdcBuf, hbmpBuf);
gfxBuf = Graphics::FromHDC(hdcBuf); 
fish = LoadBitmapRes(gfxBuf, MAKEINTRESOURCE(FISH2), "SPRITE");

WM_PAINT:

HDC temp = BeginPaint(hwnd, &ps);
gfxBuf->DrawCachedBitmap(fish, x, y);
BitBlt(temp, 0, 0, 640, 480, hdcBuf, 0, 0, SRCCOPY);
EndPaint(hwnd, &ps);

Yes - with any error it would return NULL but it doesn't, and it works singly buffered — user10F64D4, Aug 13 '13 at 00:13
Hmm. I don't see any obvious errors but I would check the results of each API function call. — 500 - Internal Server Error, Aug 13 '13 at 00:31
Update: Apparently everything is painted in monochrome black and white — user10F64D4, Aug 13 '13 at 00:38

IInspectable · Accepted Answer · 2013-08-13T13:10:03.607

5

When creating a memory DC using CreateCompatibleDC its display surface is exactly one monochrome pixel wide and one monochrome pixel high. Consequently when calling CreateCompatibleBitmap on this memory DC a monochrome bitmap is created.

Since the bitmap selected into a memory DC controls the color characteristics, you have to make sure that it matches the DC you are eventually using to display the contents of the memory DC. To do so you should pass the destination DC to CreateCompatibleBitmap.

Corrected code:

hdc = GetDC(hwnd);
hdcBuf = CreateCompatibleDC(hdc);
hbmpBuf = CreateCompatibleBitmap(hdc, 640, 480); // uses source DC
SelectObject(hdcBuf, hbmpBuf);

edited Aug 13 '13 at 13:10

answered Aug 13 '13 at 12:56

IInspectable

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@user Unrelated to your question I would place this code in the [`WM_SIZE`](http://msdn.microsoft.com/en-us/library/windows/desktop/ms632646.aspx) handler. If you have a fixed size window you will still get a `WM_SIZE` message when the window is created. If it is resizable your code is already prepared, and you only need to update the width/height parameters in your `BitBlt` call. – IInspectable Aug 13 '13 at 13:29

GDI+ Double Buffering: backbuffer dual-colored monochrome

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