BitBlt not updating WM_PAINT in Windows C++ API - c++

Question

I have the following function to draw a loaded bitmap to a window.
void OnPaint(HWND hwnd) {
PAINTSTRUCT ps;
HDC hdc;
BITMAP bitmap;
HDC hdcMem;
HGDIOBJ oldBitmap;
hdc = BeginPaint(hwnd, &ps);
hdcMem = CreateCompatibleDC(hdc);
HBITMAP bmp = mainBitmap;
oldBitmap = SelectObject(hdcMem, mainBitmap);
GetObject(bmp, sizeof(bitmap), &bitmap);
x += 64;
RECT rect;
rect.left = x;
rect.top = 0;
rect.right = x+64;
rect.bottom = 64;
HBITMAP hBmp = CreateCompatibleBitmap(
hdc, // Handle to a device context
rect.right - rect.left, // Bitmap width
rect.bottom - rect.top // Bitmap height
);
BitBlt(
hdc, // Destination rectangle context handle
0, // Destination rectangle x-coordinate
0, // Destination rectangle y-coordinate
rect.right - rect.left, // Destination rectangle width
rect.bottom - rect.top, // Destination rectangle height
hdcMem, // A handle to the source device context
rect.left, // Source rectangle x-coordinate
rect.top, // Source rectangle y-coordinate
SRCCOPY // Raster-operation code
);
SelectObject(hdcMem, oldBitmap);
DeleteDC(hdcMem);
EndPaint(hwnd, &ps);
}
And I have the following image loaded into HBITMAP mainBitmap:
The image is drawn when the window opens successfully, and I see the first icon in the sprite bitmap (yellow grapple hook), but my issue is, when I press 'C' to re-paint the window, the image does not change to the next icon in the sprite image.
Things I Know
On initialization, x = 64;
Every time I press 'C', paint is called. (Confirmed in Visual
Studio Debugger)
x is incremented by 64 each time OnPaint is called.
Why is the graphic not changing?
Here is my WindowsProc function to handle the WM_PAINT message:
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
switch (uMsg) {
HANDLE_MSG(hwnd, WM_PAINT, OnPaint);
}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

Answer 1

Try to call function InvalidateRect() to update region.