Transparent desktop icons

Introduction

Several years ago, I downloaded a program called TransparentW that would make the text background of the desktop icons transparent. It was cool and made the desktop a whole lot prettier. What struck my fancy was the author's (Jay Guerette) comment about similar utilities asking for money considering how much time and code was involved.

I've used this utility on nearly all of the machines I've worked on and have never given it a second thought. Until today, that is. Curiosity got the best of me and I wanted to know just how much, or how little in this case, code was involved in accomplishing this task. Here are the relevant pieces of code. The first thing to do is find the listview window that owns the desktop icons.

Finding the right window

There are two ways of finding the correct window. One is a bit cleaner than the other, but I'll show both just for comparison purposes.

My first thought was to use GetDesktopWindow() to find the listview window, but the handle returned was not what I expected. I could, however, use it to enumerate all child windows of the desktop, stopping when the listview window was found.

BOOL CALLBACK EnumProc( HWND hWnd, LPARAM )
{
    TCHAR   szClass[128];

    GetClassName(hWnd, szClass, sizeof(szClass));
    if (lstrcmp(szClass, "SysListView32") == 0)
        return FALSE;

    return TRUE;
}
...
hWnd = GetDesktopWindow();
if (NULL != hWnd)
    EnumChildWindows(hWnd, EnumProc, 0);

It looks good, but the problem is that the desktop owns several listview windows.

BOOL CALLBACK EnumProc( HWND hWnd, LPARAM )
{
    TCHAR   szClass[128];

    GetClassName(hWnd, szClass, sizeof(szClass));
    if (lstrcmp(szClass, "SysListView32") == 0)
    {
        GetClassName(GetParent(hWnd), szClass, sizeof(szClass));
        if (lstrcmp(szClass, "SHELLDLL_DefView") == 0)
        {
            GetClassName(GetParent(GetParent(hWnd)), szClass, 
                   sizeof(szClass));
            if (lstrcmp(szClass, "Progman") == 0)
            {
                // we now have the window that is a child of
                // "SHELLDLL_DefView" and a grandchild of "Progman"
                return FALSE;
            }
        }
    }

    return TRUE;
}

Notice how the calls to GetParent() could get out of hand, or extra variables would be needed. The window handle can be saved in a global variable, or in the LPARAM parameter. The latter is done via:

*((HWND *) lParam) = hWnd;

assuming that EnumChildWindows() was called with a HWND* variable as the third parameter.

A slightly more elegant solution is to make a few calls to FindWindowEx(). This looks like:

hWnd = FindWindow("Progman", NULL);
// start with FindWindow() to get the initial hWnd

if (NULL != hWnd)
    hWnd = FindWindowEx(hWnd, NULL, "SHELLDLL_DefView", NULL);
if (NULL != hWnd)
    hWnd = FindWindowEx(hWnd, NULL, "SysListView32", NULL);

If you've never used Spy++ that ships with Visual Studio, this is a very good project to cut your teeth on. When you start the utility, open the Find Window dialog and select the Desktop, with the little crosshair. Notice that the window has no caption and the class is SysListView32. Click the OK button. In the ensuing Window Properties dialog, click the Windows tab. The listview control has a parent (click the handle) belonging to the SHELLDLL_DefView class. This window, in turn, has a parent (click the handle) belonging to the Progman class and has a Program Manager caption.

Making the change

Once the correct window handle of the listview control has been obtained, the background color can be changed. A check is done on the current background color to prevent an unnecessary change.

// if the window was found, ...
if (NULL != hWnd)
{
    COLORREF colorBackground = 
        ListView_GetTextBkColor(hWnd); // LVM_GETTEXTBKCOLOR
    if (0xffffffff != colorBackground)
    {
        ListView_SetTextBkColor(hWnd, 0xffffffff); // LVM_SETTEXTBKCOLOR

        // add the 'desktop' to the update region
        InvalidateRect(hWnd, NULL, TRUE);

        // paint the update regions
        UpdateWindow(hWnd);
    }
}

Now since the desktop window can be refreshed at any time (e.g., games), the background color will then be reverted back to its non-transparent state. One solution is to couple this code with a timer of some sort and re-check the background color periodically.

Notes

While this method works fine (for most folks), it is still considered a "hack", and thus a more preferred method was born. See here for details. I don't agree with their "These programs not only consume valuable memory and processing time..." statement, however. Their solution actually modifies an OS file. That's all well and good, but they claim it is against company policy to disclose which file(s) are altered. I was able to get the name of the file, however.

Enjoy!

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