Delay icon loading and create grayscale version

Src/Merge2.rc

@@ -12,7 +12,6 @@
 // remains consistent on all systems.
 
 IDR_MAINFRAME           ICON                    "res\\Merge.ico"
-IDR_MAINFRAME_ICON_GRAY ICON                    "res\\Merge_gray.ico"
 IDR_MERGEPROJECT        ICON                    "res\\MergeProject.ico"
 IDR_MERGEDOCTYPE        ICON                    "res\\MergeDoc.ico"
 IDR_DIRDOCTYPE          ICON                    "res\\MergeDir.ico"

Src/TitleBarHelper.cpp

@@ -23,14 +23,14 @@ CTitleBarHelper::CTitleBarHelper()
 	, m_bMouseTracking(false)
 	, m_nTrackingButton(-1)
 	, m_nHitTest(HTNOWHERE)
+	, m_icon(nullptr)
+	, m_icon_gray(nullptr)
 {
 }
 
 void CTitleBarHelper::Init(CWnd *pWnd)
 {
 	m_pWnd = pWnd;
-	m_icon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
-	m_icon_gray = AfxGetApp()->LoadIcon(IDR_MAINFRAME_ICON_GRAY);
 }
 
 int CTitleBarHelper::GetTopMargin() const
@@ -40,6 +40,7 @@ int CTitleBarHelper::GetTopMargin() const
 
 void CTitleBarHelper::DrawIcon(CWnd* pWnd, CDC& dc, bool active)
 {
+	DelayLoadIcon(pWnd);
 	HICON hIcon = active ? m_icon : m_icon_gray;
 	if (hIcon == nullptr)
 		return;
@@ -334,3 +335,61 @@ void CTitleBarHelper::ReloadAccentColor()
 {
 	CAccentColor::Get().Reload();
 }
+
+HICON CTitleBarHelper::CreateGrayIcon(HICON hIcon)
+{
+    ICONINFO iconInfo;
+    GetIconInfo(hIcon, &iconInfo);
+
+    BITMAP bitmap;
+    GetObject(iconInfo.hbmColor, sizeof(BITMAP), &bitmap);
+    const int width = bitmap.bmWidth;
+    const int height = bitmap.bmHeight;
+    const int pixsize = width * height;
+
+    BITMAPINFO bmi;
+    ZeroMemory(&bmi, sizeof(BITMAPINFO));
+    bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
+    bmi.bmiHeader.biWidth = width;
+    bmi.bmiHeader.biHeight = height;
+    bmi.bmiHeader.biPlanes = 1;
+    bmi.bmiHeader.biBitCount = 32;
+    bmi.bmiHeader.biCompression = BI_RGB;
+
+    RGBQUAD* pixels = new RGBQUAD[pixsize];
+    HDC hdc = GetDC(NULL);
+    GetDIBits(hdc, iconInfo.hbmColor, 0, height, pixels, &bmi, DIB_RGB_COLORS);
+
+    for (int i = 0; i < pixsize; i++)
+    {
+        BYTE gray = (BYTE)(0.3 * pixels[i].rgbRed + 0.59 * pixels[i].rgbGreen + 0.11 * pixels[i].rgbBlue);
+        pixels[i].rgbRed = gray;
+        pixels[i].rgbGreen = gray;
+        pixels[i].rgbBlue = gray;
+    }
+
+    HBITMAP hbmGray = CreateCompatibleBitmap(hdc, width, height);
+    SetDIBits(hdc, hbmGray, 0, height, pixels, &bmi, DIB_RGB_COLORS);
+
+    ICONINFO grayIconInfo = iconInfo;
+    grayIconInfo.hbmColor = hbmGray;
+    HICON hGrayIcon = CreateIconIndirect(&grayIconInfo);
+
+    DeleteObject(iconInfo.hbmColor);
+    DeleteObject(iconInfo.hbmMask);
+    DeleteObject(hbmGray);
+    ReleaseDC(NULL, hdc);
+    delete[] pixels;
+
+    return hGrayIcon;
+}
+
+void CTitleBarHelper::DelayLoadIcon(CWnd* pWnd)
+{
+	if (m_icon && m_icon_gray)
+		return;
+	m_icon = (HICON)pWnd->SendMessage(WM_GETICON, ICON_SMALL2, 0);
+	if (m_icon == nullptr)
+		m_icon = (HICON)GetClassLongPtr(pWnd->m_hWnd, GCLP_HICONSM);
+	m_icon_gray = (m_icon == nullptr) ? nullptr : CreateGrayIcon(m_icon);
+}

Src/TitleBarHelper.h

@@ -41,6 +41,8 @@ class CTitleBarHelper {
 
 	void ShowSysMenu(CPoint point);
 	COLORREF GetIntermediateColor(COLORREF a, COLORREF b, float ratio);
+	HICON CreateGrayIcon(HICON hIcon);
+	void DelayLoadIcon(CWnd* pWnd);
 
 	CWnd* m_pWnd;
 	CSize m_size;

Src/resource.h

@@ -30,7 +30,6 @@
 #define IDR_POPUP_PLUGIN_COMMAND_LINE_MENU 126
 #define IDR_POPUP_PLUGIN_ADD_MENU       127
 #define IDR_POPUP_DIRVIEW_COMPAREMETHOD 128
-#define IDR_MAINFRAME_ICON_GRAY         129
 #define IDD_ABOUTBOX                    200
 #define IDD_OPEN                        202
 #define IDD_SAVECLOSING                 203