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Asked: 2026-05-26T15:09:27+00:00

In Win32 do the co-ordinates returned by GET_X_PARAM and GET_Y_PARAM calls start from 0

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In Win32 do the co-ordinates returned by GET_X_PARAM and GET_Y_PARAM calls start from 0 or from 1?
If I have a screen with resolution 640X480 then what values do I get? Are they from 0 to 639 and 0 to 479? Or 1 to 640 and 1 to 480?

extern "C" LRESULT CALLBACK WindowProc (HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)  
{  
      Switch(message)  
      {  
            case WM_MOUSEMOVE:              
                  iXPosition = GET_X_LPARAM(lParam);   
                  iYPosition = GET_Y_LPARAM(lParam);  
      }  
}
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1 Answer

  1. Editorial Team

    For WM_MOUSEMOVE, the coordinates are relative to the window’s client area, not the screen – see MSDN. Given that, the points start at 0,0 for the top-left corner of the window’s client area.

    Also note that if you do use an API that returns screen-based mouse coordinates, like GetCursorPos, you can get negative values back on a multi-monitor system: 0,0 is the top-left of the primary monitor, which could have a secondary monitor set above or to the left of it; so the actual desktop could ‘start’ at a negative or other non-0,0 value. (GetSystemMetrics(SM_XVIRTUALSCREEN) will return the left edge, for example.)

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