WhatColor Program - shows the color under the cursor

Introduction

Here's a little program I wrote that shows the color under the cursor as well as the cursor's position. It's useful for grabbing colors from websites or pictures.

The Code

It's in Win32 C. I compile it with gcc under Dev-C++. In order to get it to compile on MSVC++ (which I've had for only two days and it seems a lot more complicated!) I had to set these project properties:

Code:

Configuration Properties:
    General
      Character Set: "Not Set"
    C/C++
      Precompiled Headers
         Create/Use Precompiled Header: "Not Using Precompiled Headers"

The C code, resource.rc, and icon are in the attachment. The C code is also here for your perusal.

Code:

// WhatColor.c
// Shows the position and color of the point under the cursor.
// To use, click on the window and drag the cursor around the screen.
// Dbl-click to close (or single-click on notification-area icon).

#include <windows.h>

#define SIZEX 92
#define SIZEY 42
#define POSX   0
#define POSY   0
#define COLOR_BACK RGB(0,0,0)
#define COLOR_FORE RGB(0,200,200)
#define ID_TASKBAR_ICON 1
#define MYWM_NOTIFYICON WM_USER

LRESULT CALLBACK windowProc (HWND hwnd, UINT msg, WPARAM wp, LPARAM lp)
{
    static HDC hdcDisp;
    static int x, y;
    static COLORREF color;

    switch (msg) {

    case WM_CREATE:
        hdcDisp = CreateDC ("DISPLAY", NULL, NULL, NULL);
        break;

    case WM_PAINT:
        {
        HDC hdc;
        PAINTSTRUCT ps;
        char txt[32];

        hdc = BeginPaint (hwnd, &ps);
        SetBkColor (hdc, COLOR_BACK);
        SetTextColor (hdc, COLOR_FORE);
        TextOut (hdc, 5, 5, txt, wsprintf (txt, "(%d, %d)", x, y));
        TextOut (hdc, 5, 23, txt, wsprintf (txt, "%02x %02x %02x",
            GetRValue (color), GetGValue (color), GetBValue (color)));
        EndPaint (hwnd, &ps);
        }
        break;

    case WM_LBUTTONDOWN:
        SetCapture (hwnd);
        SendMessage (hwnd, WM_MOUSEMOVE, wp, lp);
        break;

    case WM_MOUSEMOVE:
        if (GetCapture() != hwnd) break;
        // The extra stuff here is to make it work properly
        // when the window is not positioned at 0,0.
        x = POSX + (SHORT) LOWORD (lp);
        y = POSY + (SHORT) HIWORD (lp);
        color = GetPixel (hdcDisp, x, y);
        InvalidateRect (hwnd, NULL, TRUE);
        break;

    case WM_LBUTTONUP:
        ReleaseCapture();
        break;

    case MYWM_NOTIFYICON:
        switch (wp) {
        case ID_TASKBAR_ICON:
             switch (lp) {
             // Reacting to the button-down message seems to pass
             // the button-up to the next icon (after closing this one)
             // so instead, react to the button-up message.
             case WM_LBUTTONUP:
                  PostMessage (hwnd, WM_DESTROY, 0, 0);
                  break;
             }
             break;
        }
        break;

    case WM_LBUTTONDBLCLK:
    case WM_DESTROY:
        DeleteDC (hdcDisp);
        PostQuitMessage (0);
        break;

    default:
        return DefWindowProc (hwnd, msg, wp, lp);
    }
    return 0;
}

BOOL taskbarAddIcon (HWND hwnd, UINT id, HICON hicon)
{
    NOTIFYICONDATA nid = { sizeof (NOTIFYICONDATA) };
    nid.hWnd   = hwnd;
    nid.uID    = id;
    nid.uFlags = NIF_MESSAGE | NIF_ICON;
    nid.hIcon  = hicon;
    nid.uCallbackMessage = MYWM_NOTIFYICON;
    return Shell_NotifyIcon (NIM_ADD, &nid);
}

BOOL taskbarDeleteIcon (HWND hwnd, UINT id)
{
    NOTIFYICONDATA nid = { sizeof (NOTIFYICONDATA) };
    nid.hWnd   = hwnd;
    nid.uID    = id;
    return Shell_NotifyIcon (NIM_DELETE, &nid);
}

void registerWindow (HINSTANCE hinst, char *appName,
                     HBRUSH hbrBackground, WNDPROC wndproc)
{
    WNDCLASSEX wc    = { sizeof (wc) };
    wc.style         = CS_DBLCLKS;
    wc.lpfnWndProc   = wndproc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hinst;
    wc.hIcon         = LoadIcon (hinst, appName);
    wc.hCursor       = LoadCursor (NULL, IDC_ARROW);
    wc.hbrBackground = hbrBackground;
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = appName;
    wc.hIconSm       = LoadIcon (hinst, appName);
    RegisterClassEx (&wc);
}

int WINAPI WinMain (HINSTANCE hinst, HINSTANCE unused, PSTR cmd, int show)
{
    char *appName = "WhatColor";
    MSG msg;
    HWND hwnd;
    HBRUSH hbrBackground;
    HICON hIcon;

    hbrBackground = (HBRUSH) CreateSolidBrush (COLOR_BACK);
    registerWindow (hinst, appName, hbrBackground, windowProc);

    // Create invisible parent to keep the actual window out of the taskbar.
    hwnd = CreateWindow (appName, 0, 0, 0, 0, 0, 0, 0, 0, hinst, 0);
    hwnd = CreateWindow (appName, appName, WS_POPUP|WS_VISIBLE,
                POSX, POSY, SIZEX, SIZEY, hwnd, // The invisible parent
                0, hinst, 0);

    hIcon = (HICON) LoadImage (hinst, appName, IMAGE_ICON,
                               16, 16, LR_DEFAULTCOLOR);
    taskbarAddIcon (hwnd, ID_TASKBAR_ICON, hIcon);
    DestroyIcon (hIcon);

    while (GetMessage (&msg, 0, 0, 0))
        DispatchMessage (&msg);

    taskbarDeleteIcon (hwnd, ID_TASKBAR_ICON);
    DeleteObject (hbrBackground);
    return msg.wParam;
}