Windows/C++ -- rendering icon to bitmap with transparency

Question

I am no expert in anything GDI. But I was given some code YEARS ago which has served me decently well. But, it's getting old ... and with new windows10 dark theme, it's showing it's flaws.

I am rendering a menu (in an explorer menu plugin). Here's the snippet of code used to generate the bitmap.

My goal, to convert this code to generate a bitmap with transparency of the icon preserved.

(the result HBITMAP ends up in pItem->m_hBitmap )

HICON hIcon;
if ( (iIndex >= 0) && (ExtractIconEx(iconDLLPath, iIndex, NULL, &hIcon, 1) != 0) )
{
    HDC hdc = CreateIC(L"DISPLAY", NULL, NULL, NULL);
    HDC hdcMem = CreateCompatibleDC(hdc);

    // XP demands 12x12, otherwise use 16x16
    int cx = GetSystemMetrics((m_bUseSmallerIcons) ? SM_CXMENUCHECK : SM_CXSMICON);
    int cy = GetSystemMetrics((m_bUseSmallerIcons) ? SM_CYMENUCHECK : SM_CYSMICON);
    pItem->m_hBitmap = CreateCompatibleBitmap(hdc, cx, cy);
    HBITMAP hBmOld = (HBITMAP) SelectObject(hdcMem, pItem->m_hBitmap);

    // DC:  paint entire mem dc COLOR_MENU so icon looks transparent
    // when painted into context menu having this background color
    HBRUSH hBrush = CreateSolidBrush(GetSysColor(COLOR_MENU));
    RECT rect;
    rect.left = 0;
    rect.top = 0;
    rect.right = cx;
    rect.bottom = cy;
    FillRect(hdcMem, &rect, hBrush);
    DeleteObject(hBrush);

    // Draw icon transparently, on top of the background color.  Transparent
    // areas will be the background color.
    DrawIconEx(hdcMem, 0, 0, hIcon, cx, cy, 0, 0, DI_NORMAL);

    // Cleanup
    SelectObject(hdcMem, hBmOld);
    DeleteDC(hdc);
    DeleteDC(hdcMem);

    DestroyIcon(hIcon);
}

I should remove the which draws the white background, but how do I put down a transparent background? Everything I've tried yields a black background.
* just removing the white "fill" * SetBkMode(TRANSPARENT) * using the theme code to get the menu color...

How do I go about making a proper bitmap with transparency?

DrawIconEx is probably doing its job with transparency. But the bitmap is not transparent. I don't know exactly what is going on here, you could draw on PNG file with transparency, or paint the bitmap using TransparentBlt... — Barmak Shemirani

Peter Weyzen Peter Weyzen · Accepted Answer · 2019-11-26T20:29:08

Ultimately, the answer is that I am doing nothing wrong. This menu is rendered as part of a menu constructed in a shell plugin using IContextMenu.

The answer - implement IContextMenu2. And in doing so, do an owner draw menu item.

Windows/C++ -- rendering icon to bitmap with transparency

1 Answers