Setting color and font attribute for individual items

Like any other window, you can set the font of the tree view control. This

font is applied to all the item labels. Similarly, all the labels are of

the same color. Although the next version of the tree view control will

allow the ownerdraw style, for now you have to implement it yourself. Since

the tree view control does not have any support for individual item color

or font, we have to implement this as an after effect. In plain terms,

we draw the labels to our liking after the control has already painted

the control window.

There are some constraints that have to be adhered to. Since the tree
view control computes the height of the items ( all items have the same
height ) based on the window font, if we change the font size we can only
decrease it so that the text does not overlap with the other labels. Also,
the tree view control, automatically manages the horizontal scrollbar,
so it is better to maintain the width of the label.

 

Step 1: Add member variable to track font and color

Since the control has no support for item font or color, we have to track

this information within our program. We use a CMap object to associate

these properties with the tree items. The map will contain information

for only those items that we explicitly change. We define a nested structure

that is used with the CMap object, to hold the color and the font information.

protected:
	struct Color_Font
	{
		COLORREF color;
		LOGFONT  logfont;
	};
	CMap< void*, void*, Color_Font, Color_Font& > m_mapColorFont ;

Step 2: Add helper functions to get/set font and color

Define the helper functions to get or set the item font or color. To set

the font, we actually pass the logfont rather than a font handle. Also

note that we have defined a pair of functions to get and set the bold attribute.

There are two reasons for providing a separate function for the bold attribute

although we can use the font function. The first reason is that the tree

view control directly supports setting an item to bold. Secondly, using

the built in support also maintains the proper setting for the horizontal

scrollbar.

void CTreeCtrlX::SetItemFont(HTREEITEM hItem, LOGFONT& logfont)
{
	Color_Font cf;
	if( !m_mapColorFont.Lookup( hItem, cf ) )
		cf.color = (COLORREF)-1;
	cf.logfont = logfont;
	m_mapColorFont[hItem] = cf;
}

void CTreeCtrlX::SetItemBold(HTREEITEM hItem, BOOL bBold)
{
	SetItemState( hItem, bBold ? TVIS_BOLD: 0, TVIS_BOLD );
}

void CTreeCtrlX::SetItemColor(HTREEITEM hItem, COLORREF color)
{
	Color_Font cf;
	if( !m_mapColorFont.Lookup( hItem, cf ) )
		cf.logfont.lfFaceName[0] = '\0';
	cf.color = color;
	m_mapColorFont[hItem] = cf;
}

BOOL CTreeCtrlX::GetItemFont(HTREEITEM hItem, LOGFONT * plogfont)
{
	Color_Font cf;
	if( !m_mapColorFont.Lookup( hItem, cf ) )
		return FALSE;
	if( cf.logfont.lfFaceName[0] == '\0' ) 
		return FALSE;
	*plogfont = cf.logfont;
	return TRUE;

}

BOOL CTreeCtrlX::GetItemBold(HTREEITEM hItem)
{
	return GetItemState( hItem, TVIS_BOLD ) & TVIS_BOLD;
}

COLORREF CTreeCtrlX::GetItemColor(HTREEITEM hItem)
{
	// Returns (COLORREF)-1 if color was not set
	Color_Font cf;
	if( !m_mapColorFont.Lookup( hItem, cf ) )
		return (COLORREF)-1;
	return cf.color;

}

Step 3: Add WM_PAINT handler

In this function we first let the control update a memory device context. We then redraw the visible labels using the user defined attributes. We let the control handle the highlighting of items, so before we update a label we make sure that it is not selected or drophilited. Also, if the items font or color attributes were not changed, we don’t need to redraw it. Once all the updates are ready in the memory device context, we blit it to the actual device context.

In the first implementation, I let the control directly draw on the screen and then redrew the items that had a different font or color. This caused a visible flicker as the items got updated a second time. To overcome this we use a memory device context for all the updates and finally we copy this to the main device context. After creating a compatible DC, we add a compatible bitmap to the memory DC and set the clip region to be the same as the paint DC.

After the default window procedure for the control has updated the device context, we scan through all the visible items and update the items that have a user defined color or font.

void CTreeCtrlX::OnPaint()
{
	CPaintDC dc(this);

	// Create a memory DC compatible with the paint DC
	CDC memDC;
	memDC.CreateCompatibleDC( &dc );

	CRect rcClip, rcClient;
	dc.GetClipBox( &rcClip );
	GetClientRect(&rcClient);

	// Select a compatible bitmap into the memory DC
	CBitmap bitmap;
	bitmap.CreateCompatibleBitmap( &dc, rcClient.Width(), rcClient.Height() );
	memDC.SelectObject( &bitmap );

	// Set clip region to be same as that in paint DC
	CRgn rgn;
	rgn.CreateRectRgnIndirect( &rcClip );
	memDC.SelectClipRgn(&rgn);
	rgn.DeleteObject();



	// First let the control do its default drawing.
	CWnd::DefWindowProc( WM_PAINT, (WPARAM)memDC.m_hDC, 0 );


	HTREEITEM hItem = GetFirstVisibleItem();

	int n = GetVisibleCount()+1;
	while( hItem && n--)
	{
		CRect rect;

		// Do not meddle with selected items or drop highlighted items
		UINT selflag = TVIS_DROPHILITED | TVIS_SELECTED;
		Color_Font cf;

		if ( !(GetItemState( hItem, selflag ) & selflag )
			&& m_mapColorFont.Lookup( hItem, cf ))
		{
			CFont *pFontDC;
			CFont fontDC;
			LOGFONT logfont;

			if( cf.logfont.lfFaceName[0] != '\0' )
			{
				logfont = cf.logfont;
			}
			else
			{
				// No font specified, so use window font
				CFont *pFont = GetFont();
				pFont->GetLogFont( &logfont );
			}

			if( GetItemBold( hItem ) )
				logfont.lfWeight = 700;
			fontDC.CreateFontIndirect( &logfont );
			pFontDC = memDC.SelectObject( &fontDC );

			if( cf.color != (COLORREF)-1 )
				memDC.SetTextColor( cf.color );

			CString sItem = GetItemText( hItem );

			GetItemRect( hItem, &rect, TRUE );
			memDC.SetBkColor( GetSysColor( COLOR_WINDOW ) );
			memDC.TextOut( rect.left+2, rect.top+1, sItem );

			memDC.SelectObject( pFontDC );
		}
		hItem = GetNextVisibleItem( hItem );
	}


	dc.BitBlt( rcClip.left, rcClip.top, rcClip.Width(), rcClip.Height(), &memDC,
				rcClip.left, rcClip.top, SRCCOPY );
}

Step 4: Go ahead and change the item font or color

Here are some examples.

	// Change the item color to red
	SetItemColor( hItem, RGB(255,0,0));

	// Change the item to italicized font and underlined
	LOGFONT logfont;
	CFont *pFont = GetFont();
	pFont->GetLogFont( &logfont );
	logfont.lfItalic = TRUE;
	logfont.lfUnderline = TRUE;
	SetItemFont(hti, logfont );