My first scrollbar

This is a discussion on My first scrollbar within the Windows Programming forums, part of the Platform Specific Boards category; I have been reading Prosise's MFC book and am trying to get my first scrollbar working in a ruler application ...

  1. #1
    IAmRegistered
    Guest

    My first scrollbar

    I have been reading Prosise's MFC book and am trying to get my first scrollbar working in a ruler application but have encountered a couple of problems. Firstly when the scrollbar is moved it snaps back to its original position although this only occurs in debug builds strangely. The second problme is that it doesnt redraw properly leaving the numbers out of place or not there at all

    I'd appreciate it if someone could take a look at my code for me

    Code:
    //app.h
    
    #ifndef APP_H
    #define APP_H
    
    #include <afxwin.h>
    
    class RulerApp : public CWinApp
    {
    public:
    	virtual BOOL InitInstance( );
    };
    
    
    class RulerWin :public CFrameWnd
    {
    public:
    	RulerWin( );
    	afx_msg void OnPaint( );
    	afx_msg void OnSize( UINT nType, int cx, int cy );
    	afx_msg void OnHScroll( UINT nSBCode, UINT nPos, CScrollBar* pScrollBar );
    
    protected:
    	DECLARE_MESSAGE_MAP( )
    
    private:
    	int horzScrollPos;
    	int horzPageSize;
    	int virtualWidth;
    
    };
    
    RulerApp app;
    
    
    
    #endif

    Code:
    //app.cpp
    
    #include "app.h"
    
    BOOL RulerApp::InitInstance( )
    {
    	m_pMainWnd = new RulerWin( );
    	m_pMainWnd->ShowWindow( m_nCmdShow );
    	m_pMainWnd->UpdateWindow( );
    
    	return TRUE;
    }
    
    
    BEGIN_MESSAGE_MAP( RulerWin, CFrameWnd )
    	ON_WM_PAINT( )
    	ON_WM_SIZE( )
    	ON_WM_HSCROLL( )
    END_MESSAGE_MAP( )
    
    
    RulerWin::RulerWin( )
    {
    	Create( NULL, _T("A strange ruler..."), WS_OVERLAPPEDWINDOW | WS_HSCROLL );
    	virtualWidth = 4000;
    }
    
    
    void RulerWin::OnPaint( )
    {
    	CPaintDC dc( this );
    
    	dc.SetWindowOrg( horzScrollPos, 0 );		//added to to ake
    
    	dc.SetMapMode( MM_LOMETRIC );
    
    	CBrush yellowBrush;
    	yellowBrush.CreateSolidBrush( RGB( 240, 240, 0 ) );
    
    	CRect ruler( 200, -700, 5000, -1150 );	//+ve up, +ve right
    
    	CBrush* oldBrush = dc.SelectObject( &yellowBrush );
    	dc.Rectangle( &ruler );
    	dc.SelectObject( oldBrush );
    
    	dc.SetBkMode( TRANSPARENT );
    	dc.SetTextAlign( TA_CENTER | TA_TOP );
    
    	int i;
    	for( i = 200; i <= 5000; i += 100 )
    	{
    		if( i != 200 )
    		{
    			char cm[ 3 ];
    			itoa( (i-200)/100, cm, 10 );
    			dc.TextOut( _T( i ), -1050, cm );
    		}
    
    		dc.MoveTo( i, -1100 );
    		dc.LineTo( i, -1150 );
    	}
    }
    
    
    void RulerWin::OnSize( UINT nType, int cx, int cy )
    {
    	CFrameWnd::OnSize( nType, cx, cy );
    
    	//ALL THE FOLLOWING STUFF SYNCRONISES THE THUMB SIZE AND WINDOW SIZE
    	int horzScrollMax = 0;
    	horzScrollPos = horzPageSize = 0;
    
    	if( cx < virtualWidth )		//screenwidth < workspace width
    	{
    		horzScrollMax = virtualWidth - 1;	//max scroll pos set to just less than workspace size
    		horzPageSize = cx;		//page size set to screen width
    		horzScrollPos = min( horzScrollPos, virtualWidth - horzPageSize - 1 );
    	}
    
    	SCROLLINFO si;
    
    	si.fMask = SIF_ALL;
    	si.nMin = 0;
    	si.nMax = horzScrollMax;
    	si.nPos = horzScrollPos;
    	si.nPage = horzPageSize;
    
    	SetScrollInfo( SB_HORZ, &si, TRUE );
    
    }
    
    
    void RulerWin::OnHScroll( UINT nSBCode, UINT nPos, CScrollBar* pScrollBar )
    {
    	int delta;
    	const int MOVEMENT = 10;
    
    	switch( nSBCode )
    	{
    	case SB_LINELEFT:
    		delta = -MOVEMENT;
    		break;
    
    	case SB_PAGELEFT:
    		delta = -horzPageSize;
    		break;
    
    	case SB_LINERIGHT:
    		delta = MOVEMENT;
    		break;
    
    	case SB_PAGERIGHT:
    		delta = horzPageSize;
    		break;
    
    	case SB_THUMBTRACK:
    		delta = (int)nPos - horzScrollPos;
    		break;
    
    	default:
    		break;
    	}
    
    	int scrollPos = horzScrollPos + delta;
    	int maxPos = virtualWidth - horzPageSize;
    
    	if( scrollPos < 0 )
    	{
    		delta = -horzScrollPos;
    	}
    	else if( scrollPos > maxPos )
    	{
    		delta = maxPos - horzScrollPos;
    	}
    
    	if( delta != 0 )
    	{
    		horzScrollPos += delta;
    		SetScrollPos( SB_HORZ, horzScrollPos, TRUE );
    		ScrollWindow( -delta, 0 );
    	}
    }
    tia

  2. #2
    Seeking motivation... endo's Avatar
    Join Date
    May 2002
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    537
    remembered my login now

    Still need help with this one though, its really put me off programming for a while
    Couldn't think of anything interesting, cool or funny - sorry.

  3. #3
    Registered User
    Join Date
    Jun 2003
    Posts
    245
    You don't seem to clearing the painting area before writing your updated text to it.

    Secondly, when pasting code containing colons and brackets, please tick the "Disable smilies in this post" - it makes your post more readable.

  4. #4
    Seeking motivation... endo's Avatar
    Join Date
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    537
    Dont think I'm being lazy, but what do you mean clear the painting area? Is there a CPaintDC function you had in mind?
    Couldn't think of anything interesting, cool or funny - sorry.

  5. #5
    Seeking motivation... endo's Avatar
    Join Date
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    537
    ok I now put an Invalidate( ) call in before I call ScrollWindow( ). This solves part of the problem but causes the screen to flash, so I'm sure this isnt the proper solution.

    The other part of the problem is the difference between the debug and release builds, whereby the debug build causes the scrollbar to snap back and the release build doesnt. The code is the same, why do I have such different results?
    Couldn't think of anything interesting, cool or funny - sorry.

  6. #6
    Seeking motivation... endo's Avatar
    Join Date
    May 2002
    Posts
    537
    Sorry to bump, but I'm still a little lost with this - I expected it to be a bit more simple when I looked at the literature...
    Couldn't think of anything interesting, cool or funny - sorry.

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