Windows C: LoadBitmap() function is not working - c

Question

I write simple windows c program to display the bitmap at the place where the left mouse button is pressed. At the first time when I click my left mouse button, the bitmap appears. But on the second time on words the bitmap is not getting displayed on the place where I made a left mouse click.
Here is my code.........
LRESULT CALLBACK myHandler(HWND hw, UINT m, UINT mextra, long co_ord)
{
HDC hdc, hmemdc;
PAINTSTRUCT ps;
HBITMAP hbmp;
RECT r;
HGDIOBJ holdbmp;
int x, y;
switch(m)
{
case WM_LBUTTONDOWN:
hdc = BeginPaint(hw,&ps);
hmemdc = CreateCompatibleDC(hdc);
hbmp = LoadBitmap(h, MAKEINTRESOURCE(IDB_BITMAP1));
holdbmp = SelectObject(hmemdc, hbmp);
x = LOWORD(co_ord);
y = HIWORD(co_ord);
BitBlt(hdc, x, y, 190, 220, hmemdc, 0, 0, SRCCOPY);
EndPaint(hw,&ps);
SelectObject(hmemdc, holdbmp);
DeleteObject(hbmp);
DeleteDC(hmemdc);
DeleteDC(hdc);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hw,m,mextra,co_ord);
}
return 0L;
}

Answer 1

The code is wrong about seven different ways from Sunday. Even after the changes you've made in response to WhozCraig's comments, it is still wrong.
For starters, the only place you are allowed to call BeginPaint and EndPaint is in response to a WM_PAINT message. You are trying to call these functions in response to a WM_LBUTTONDOWN message. That cannot work. What you'll want to do is trigger a WM_PAINT message from within your WM_LBUTTONDOWN message handler, which you can do by calling the InvalidateRect() function, passing your window handle and NULL for the rectangle to invalidate (to invalidate your entire window). Then, inside of the WM_PAINT message handler, you can call BeginPaint/EndPaint and do your drawing. If you want the drawing to be different depending on whether the left mouse button is down, you can either set a flag inside of the WM_LBUTTONDOWN message handler and test the value of that flag inside of your WM_PAINT message handler, or you can use something like GetKeyState to determine whether the mouse button is down (VK_LBUTTON).
You are also leaking GDI objects because you are not correctly releasing/destroying them. A bitmap that has been loaded with LoadBitmap needs to be destroyed by calling DeleteObject. (However, loading a bitmap repeatedly inside of a WM_PAINT message handler will lead to poor performance. Instead, prefer to load the bitmap a single time in response to the WM_CREATE message, cache its handle in a global or class-level variable, use it when necessary, and destroy the bitmap via that handle in response to the WM_DESTROY message.)
The LOWORD and HIWORD macros should never be used for extracting cursor coordinates. These are liable to return the wrong result on multiple monitor systems. Instead, you should use GET_X_LPARAM and GET_Y_LPARAM. This is specifically mentioned in the MSDN documentation for the WM_LBUTTONDOWN message. Always read the documentation for things you are unfamiliar with!
Finally, the signature for your window procedure is also completely wrong. I have no idea where you got that signature, but not only do you have non-standard parameter names that obscures the actual meaning of those arguments, but you have the wrong types. A window procedure looks like this:
LRESULT CALLBACK myHandler(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
...
}
It is extremely difficult to learn Windows API programming by just hacking around, especially if you aren't disciplined about reading the MSDN documentation. If you really want to learn it, consider purchasing a book, like Charles Petzold's classic Programming Windows, 5th edition (yes, you need the 5th edition, not a newer edition).