#include <windows.h>

#define ID_TIMER 1

void FindWindowSize(int*, int*);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow) 
{
    static TCHAR     szAppName[] = TEXT("WhatClr"); 
    HWND             hwnd; 
    int              cxWindow, cyWindow;
    MSG              msg; 
    WNDCLASS         wndclass;

    wndclass.style          = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc    = WndProc;
    wndclass.cbClsExtra     = 0;
    wndclass.cbWndExtra     = 0;
    wndclass.hInstance      = hInstance;
    wndclass.hIcon          = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground  = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName   = NULL;
    wndclass.lpszClassName  = szAppName;

    if(!RegisterClass(&wndclass)) {
        MessageBox(NULL, TEXT("This program requires Windows NT !"), szAppName, MB_ICONERROR);
        return 0;
    }

    FindWindowSize(&cxWindow, &cyWindow);
    
    hwnd = CreateWindow(szAppName, TEXT("What Color"),
                        WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_BORDER,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        cxWindow, cyWindow,
                        NULL, NULL, hInstance, NULL);

    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);

    while(GetMessage(&msg, NULL, 0, 0))
    { 
        TranslateMessage(&msg); 
        DispatchMessage(&msg); 
    }
    return msg.wParam;
}

void FindWindowSize(int* pcxWindow, int* pcyWindow)
{
    HDC           hdcScreen;
    TEXTMETRIC    tm;
    
    hdcScreen = CreateIC(TEXT("DISPLAY"), NULL, NULL, NULL);
    GetTextMetrics(hdcScreen, &tm);
    DeleteDC(hdcScreen);
    
    *pcxWindow = 2*GetSystemMetrics(SM_CXBORDER)+12*tm.tmAveCharWidth;
    *pcyWindow = 2*GetSystemMetrics(SM_CYBORDER)+GetSystemMetrics(SM_CYCAPTION)+2*tm.tmHeight;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) 
{
    static COLORREF     cr, crLast;
    static HDC          hdcScreen;
    HDC                 hdc;
    PAINTSTRUCT         ps;
    POINT               pt;
    RECT                rc;
    TCHAR               szBuffer[16];
    
    switch(message) 
    {
    case WM_CREATE:
        hdcScreen = CreateDC(TEXT("DISPLAY"), NULL, NULL, NULL);
        SetTimer(hwnd, ID_TIMER, 100, NULL);
        return 0;
    
    case WM_TIMER:
        GetCursorPos(&pt);
        cr = GetPixel(hdcScreen, pt.x, pt.y);
        SetPixel(hdcScreen, pt.x, pt.y, 0);
        
        if(cr!=crLast)
        {
            crLast = cr;
            InvalidateRect(hwnd, NULL, FALSE);
        }
        return 0;
    
    case WM_PAINT:
        hdc = BeginPaint(hwnd, &ps);
        GetClientRect(hwnd, &rc);
        wsprintf(szBuffer, TEXT("  %02X %02X %02X  "),
                    GetRValue(cr), GetGValue(cr), GetBValue(cr));
        DrawText(hdc, szBuffer, -1, &rc, DT_SINGLELINE|DT_CENTER|DT_VCENTER);
        EndPaint(hwnd, &ps);
        return 0;
        
    case WM_DESTROY: 
        DeleteDC(hdcScreen);
        KillTimer(hwnd, ID_TIMER);
        PostQuitMessage(0);
        return 0;            
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}