Re: transparent marquee text above bitmap

"AliR \(VC++ MVP\)" <AliR@online.nospam>
Mon, 14 Apr 2008 15:33:08 -0500
Here is one version:

#pragma once

// CMarqeeText
class CMarqeeText : public CStatic

   virtual ~CMarqeeText();

   void SetScrollingText(CString Text,CString FontName,int FontSize);

   virtual BOOL PreCreateWindow(CREATESTRUCT& cs);
   virtual void PreSubclassWindow();
   virtual void DrawItem(LPDRAWITEMSTRUCT /*lpDrawItemStruct*/);

   afx_msg void OnTimer(UINT nIDEvent);
   afx_msg BOOL OnEraseBkgnd(CDC* pDC);

   CString m_Text;
   long m_Offset;
   int m_TextExtent;
   CBitmap m_Bmp;
   CFont m_Font;

// MarqeeText.cpp : implementation file

#include "stdafx.h"
#include "MarqeeText.h"

// CMarqeeText

: m_Offset(0)



// CMarqeeText message handlers
void CMarqeeText::SetScrollingText(CString Text,CString FontName,int
   m_Text = Text;
   CRect Rect;
   m_Offset = -Rect.Width();

   CDC *pDC = GetDC();
   CSize Size = pDC->GetTextExtent(m_Text);
   m_TextExtent =;




void CMarqeeText::OnTimer(UINT nIDEvent)
   if (m_Offset > m_TextExtent)
      CRect Rect;
      m_Offset = -Rect.Width();


BOOL CMarqeeText::PreCreateWindow(CREATESTRUCT& cs)
   return CStatic::PreCreateWindow(cs);

void CMarqeeText::PreSubclassWindow()

void CMarqeeText::DrawItem(LPDRAWITEMSTRUCT lpDIS)
   CDC dc;

   CRect Rect;

   CRgn Rgn;

   CDC MemDC;

   CBitmap Bmp;

   CDC MemDC2;

   CBitmap *pOldBmp = MemDC2.SelectObject(&m_Bmp);

   CRect TextRect = Rect;



BOOL CMarqeeText::OnEraseBkgnd(CDC* pDC)
   if (m_Bmp.GetSafeHandle() == NULL)
      CRect Rect;
      CWnd *pParent = GetParent();
      pParent->ScreenToClient(&Rect); //convert our corrdinates to our

      //copy what's on the parents at this point
      CDC *pDC = pParent->GetDC();
      CDC MemDC;
      CBitmap *pOldBmp = MemDC.SelectObject(&m_Bmp);

   return TRUE;

"AliR (VC++ MVP)" <AliR@online.nospam> wrote in message

I'm not really sure what it is that you are trying to do in the PaintBk
method. Specially the line

   CClientDC clDC(GetParent());

But there are a couple of approaches:
One is to take a snapshot of the background before you paint the static
control for the first time. And you use that in your paint method later
The other is to invalidate the parent window just under the control before
each time you paint.

  CRect Rect;

Both method involve setting the background mode to transparent and setting
the brush to hollow brush in =WM_CTRLCOLOR.

If you want to post more meaningful code then, maybe we can help a little

"fiversen" <> wrote in message


I want to draw a marquee text above a bitmap.

If the background of the text has a solid color:
void COTextMarq::DrawItem( lpDraw..)
  HDC hdc = lpDraw->hDC;
  BITMAP hBit = ::CreateCompatibleBitmap(
hdc, // handle to DC
w, // width of bitmap, in pixels
h); // height of bitmap, in pixels

  HDC hdcM = ::CreateCompatibleDC(hdc);
  ::SelectObject(hdcM, hBit);

  //fill background in hdcM
  //draw text in hdcM

  ::BitBlt(hdc, x, y, w, h, hdcM, 0, 0, SRCCOPY);

To draw transparent,
I take clear bitmap and clear dc and draw the clear background
(I take it from an example):
void COTextMarq::PaintBk(CDC* pDC)
   CClientDC clDC(GetParent());
   CRect rect;
   CRect rect1;



   if (IsWindowVisible())
if (m_dcBk.m_hDC == NULL)
    m_bmpBk.CreateCompatibleBitmap(&clDC, rect.Width(),
    m_pbmpOldBk = m_dcBk.SelectObject(&m_bmpBk);
    m_dcBk.BitBlt(0, 0, rect.Width(), rect.Height(), &clDC,
rect1.left,, SRCCOPY);
} // if
pDC->BitBlt(0, 0, rect.Width(), rect.Height(), &m_dcBk, 0, 0,

I call PaintBk in the first part of the DrawItem() function.

this is a little bit slowly and flicker a little bit.

So - I want to opitmize it:

- to draw into m_dcBk in DrawItem(),
then the background is not clear before the new Painting.

Is there a propper way ?

Thanks Frank Iversen

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