Implementing Scrollbars: Step 3

At the end of the Color.CPP file, add the new local function, CalcClientMetrics, which interprets the WM_SIZE message's client area parameters.

Parameters:  HWND hWnd                  Window handle 
int *nClientWidth          Width in and width out 
int *nClientHeight         Height in and height out 
int *nRightBarThickness    Resulting thickness of the Y scrollbar 
int *nBottomBarThickness   Resulting thickness of the X scrollbar 
ProtoType:  Color.h 
Notes:      Use this function to interpret the client area width and 
height parameters from the WM_SIZE message. The incoming 
parameters attempt to give us the correct client area, excluding 
scrollbars. But, because while processing this message we 
show or hide the scrollbars, the incoming parameters often are 
not correct. Therefore, we must get the true client area 
dimensions, including scrollbars, and get the thickness of 
scrollbars. The caller can then make its own decisions about 
the size of the client area. 
void CalcClientMetrics (HWND hWnd, 
int *nClientWidth, 
int *nClientHeight, 
int *nRightBarThickness, 
int *nBottomBarThickness) 
   DWORD dwStyle, dwVersion; 
   int cxClient, cyClient, cxScroll, cyScroll; 
   /* Initialize local variables */ 
   cxClient = *nClientWidth; 
   cyClient = *nClientHeight; 
   cxScroll = GetSystemMetrics(SM_CXVSCROLL); 
   cyScroll = GetSystemMetrics(SM_CYHSCROLL); 
   dwStyle = GetWindowLong(hWnd, GWL_STYLE); 
   /* Adjust for the difference in how newer WIN32 versions report 
   scrollbar thickness when there is a window border */ 
   dwVersion = GetVersion(); 
   if (LOBYTE(LOWORD(dwVersion)) >= 4) 
      cxScroll += GetSystemMetrics(SM_CXBORDER); 
      cyScroll += GetSystemMetrics(SM_CYBORDER); 
   /* If there is a window border, subtract it from the scrollbar thickness */ 
   if (dwStyle & WS_BORDER) 
      cxScroll -= GetSystemMetrics(SM_CXBORDER); 
      cyScroll -= GetSystemMetrics(SM_CYBORDER); 
   /* Add the scrollbar thickness to the client area */ 
   if (dwStyle & WS_VSCROLL) 
      cxClient += cxScroll; 
   if (dwStyle & WS_HSCROLL) 
      cyClient += cyScroll; 
   /* Update the caller's variables */ 
   *nClientWidth = cxClient; 
   *nClientHeight = cyClient; 
   *nRightBarThickness = cxScroll; 
   *nBottomBarThickness = cyScroll; 

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