weird if statement causing to shut timer - c++

Question

So I've been trying to figure the following:
LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
HDC hDC; // Display context handle
PAINTSTRUCT PaintSt; // Structure defining area to be drawn
RECT aRect; // A working rectangle
HPEN hPen; // A working pen
HBRUSH hBrush; // A working brush
switch(message)
{
case WM_TIMER:
switch(wParam)
{
case IDT_TIMER1:
redraw = true;
InvalidateRect(hWnd, NULL, TRUE);
case IDT_TIMER2:
if(keys[UP])
{
rect2.bottom -= 5;
rect2.top -= 5;
}
if(keys[DOWN])
{
rect2.bottom += 5;
rect2.top += 5;
}
if(keys[RIGHT])
{
rect2.left += 5;
rect2.right += 5;
}
if(keys[LEFT])
{
rect2.left -= 5;
rect2.right -= 5;
}
}
return 0;
case WM_PAINT:
//if(redraw)
{
redraw = false;
render_frame();
}
return 0;
case WM_KEYDOWN:
switch(wParam)
{
case VK_UP:
keys[UP] = true;
break;
case VK_DOWN:
keys[DOWN] = true;
break;
case VK_LEFT:
keys[LEFT] = true;
break;
case VK_RIGHT:
keys[RIGHT] = true;
break;
default:
break;
}
return 0;
case WM_KEYUP:
switch(wParam)
{
case VK_UP:
keys[UP] = false;
break;
case VK_DOWN:
keys[DOWN] = false;
break;
case VK_LEFT:
keys[LEFT] = false;
break;
case VK_RIGHT:
keys[RIGHT] = false;
break;
default:
break;
}
return 0;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
default:
return DefWindowProc(hWnd, message, wParam, lParam); // default message processing
}
}
So here's the problem: in the case WM_PAINT:, when I uncomment the if statement, the time stops ticking for some reason. I have no idea why and don't know how to correlate this with anything. So, if I uncomment it, it will not render nor it will it recieve information from the other timer (there are two timers). Please help me, and please don't laugh if it is silly.

Answer 1

The WM_TIMER message is a "low priority" message, it is only generated when nothing else needs to be done. The trouble with your WM_PAINT handler is that it doesn't paint the first time it is generated, immediately after creating the window. EndPaint() isn't called, Which leaves the "window is dirty" status bit turned on. Which immediately causes another WM_PAINT message to be generated. Which still won't paint because redraw isn't true. Etcetera, your app is burning 100% core on the WM_PAINT messages and never gets idle enough to allow a WM_TIMER message to be generated.
Simply remove the redraw test to fix your problem. Always draw when Windows asks for it. Or pass the message to DefWindowProc().

Answer 2

Handling WM_PAINT without drawing anything (assuming redraw stays false), and without even calling DefWindowProc is very unorthodox. Your app might even be alive without you noticing.
From the doc:
An application must call BeginPaint and EndPaint in response to
WM_PAINT messages, or pass the message to the DefWindowProc function
to validate the window. DefWindowProc validates the update region; it
can send the WM_ERASEBKGND message if the window background needs to
be erased.