Bitmap not being painted in Win32 C++

Question

I have a window using Win32 and in the message handler I have a case for WM_PAINT, so that a bitmap is drawn in the window. However on running the bitmap is not drawn, is there something I am missing? Do I need to manually send the WM_PAINT message?

Here is the code I have: http://pastebin.com/bi48LB0U

and this is the WM_PAINT case:

case WM_PAINT:
    hDC = BeginPaint(hwnd, &ps);
    bmp = LoadBitmap(hInst, L"C:\\example.bmp");
    memDCExercising = CreateCompatibleDC(hDC);
    SelectObject(memDCExercising, bmp);
    BitBlt(hDC, 100, 100, 500, 500, memDCExercising, 0, 0, SRCCOPY);
    DeleteDC(memDCExercising);
    DeleteObject(bmp);
    EndPaint(hwnd, &ps);
    break;

Doomed to fail, LoadBitmap() takes the resource ID, not a path name. You need LoadImage() instead. And yes, always check winapi return values, assert() at a minimum. — Hans Passant, Jun 19 '15 at 09:28
[LoadBitmap](https://msdn.microsoft.com/en-us/library/dd145033.aspx): *"A pointer to a null-terminated string that contains the **name of the bitmap resource** to be loaded. Alternatively, this parameter can consist of the **resource identifier** in the low-order word and zero in the high-order word."* — IInspectable, Jun 19 '15 at 09:29
You're asking the wrong question: There is no way to create a resource ID for an file residing on disk. Resource IDs are available for resources compiled into a binary image only. If you want to load a file from disk, use [LoadImage](https://msdn.microsoft.com/en-us/library/ms648045.aspx) instead. — IInspectable, Jun 19 '15 at 09:31
You really truly do not want to load an image from disk in `WM_PAINT`. That can be called a lot. Load it once and hold on to the HBITMAP. — David Heffernan, Jun 19 '15 at 09:31
I have it working from loading the resource once. Would I be able to modify the resource and reload it at runtime? My program wants to be able to display the original image and a modified image... — Pottsiex5, Jun 19 '15 at 09:45
You do not seem to understand what the term [Resources](https://msdn.microsoft.com/en-us/library/ff468900.aspx) refers to, when used with Windows binaries. — IInspectable, Jun 19 '15 at 09:47
On a side note, you are leaking the `HBITMAP` returned by `SelectObject()`. You need to save and restore it before calling `DeleteDC()`: `HBITMAP oldBmp = (HBITMAP) SelectObject(memDCExercising, bmp); ... SelectObject(memDCExercising, oldBmp); DelectDC(memDCExercising);` — Remy Lebeau, Jun 20 '15 at 08:45

score 1 · Accepted Answer · answered Jun 19 '15 at 09:40

Your bitmap doesn't show, because your call to LoadBitmap returns NULL, due to an invalid lpBitmapName argument. From the documentation for LoadBitmap:

lpBitmapName [in]: A pointer to a null-terminated string that contains the name of the bitmap resource to be loaded. Alternatively, this parameter can consist of the resource identifier in the low-order word and zero in the high-order word. The MAKEINTRESOURCE macro can be used to create this value.

In other words: LoadBitmap can only load bitmaps from Resources of type RT_BITMAP (or predefined bitmaps provided by the system). If you need to load a bitmap from disk, use LoadImage instead.

If you need to load image data other than plain bitmap files, consider using the Windows Imaging Component.

Bitmap not being painted in Win32 C++

1 Answers1