自绘TTrackBar

.h文件

class PACKAGE ttrackBar11 : public TTrackBar
{
private:
    TCanvas *m_pCanvas;
protected:
    void __fastcall CrnNotify(TWMNotify &Message);
    void __fastcall CrnCustomDraw(TWMNotify &Message);
    BEGIN_MESSAGE_MAP
        VCL_MESSAGE_HANDLER(CN_NOTIFY, TWMNotify, CrnNotify);
    END_MESSAGE_MAP(TWinControl);
public:
    __fastcall ttrackBar11(TComponent* Owner);
    __fastcall ~ttrackBar11();
__published:
};

.cpp文件

static inline void ValidCtrCheck(ttrackBar11 *)
{
    new ttrackBar11(NULL);
}
//---------------------------------------------------------------------------
__fastcall ttrackBar11::ttrackBar11(TComponent* Owner)
    : TTrackBar(Owner)
{
    m_pCanvas = new TCanvas;
}

__fastcall ttrackBar11::~ttrackBar11()
{
    delete m_pCanvas;
}
//---------------------------------------------------------------------------
namespace Trackbar11
{
    void __fastcall PACKAGE Register()
    {
        TComponentClass classes[1] = {__classid(ttrackBar11)};
        RegisterComponents("Samples", classes, 0);
    }
}
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
void __fastcall ttrackBar11::CrnNotify(TWMNotify &Message)
{
    LPNMCUSTOMDRAW lpDraw = (LPNMCUSTOMDRAW)Message.NMHdr;

    if(lpDraw->hdr.code == NM_CUSTOMDRAW)
    {
        try
        {
            m_pCanvas->Lock();
            m_pCanvas->Handle = lpDraw->hdc;
            if(!(lpDraw->dwDrawStage & CDDS_ITEM))
                Message.Result = CDRF_NOTIFYITEMDRAW;
            else
                CrnCustomDraw(Message);
        }
        __finally
        {
            m_pCanvas->Handle = NULL;
            m_pCanvas->Unlock();
        }
    }
}
//---------------------------------------------------------------------------
void __fastcall ttrackBar11::CrnCustomDraw(TWMNotify &Message)
{
    LPNMCUSTOMDRAW lpDraw = (LPNMCUSTOMDRAW)Message.NMHdr;

    // 63 63 72 75 6E 2E 63 6F 6D
    if(!(lpDraw->dwDrawStage & CDDS_PREPAINT))
        return;

    TRect rct = lpDraw->rc;

    if(lpDraw->dwItemSpec == TBCD_THUMB) // 绘制滑块
    {
        m_pCanvas->Brush->Color = clRed;
        m_pCanvas->FillRect(rct);

        Frame3D(m_pCanvas, rct, clWhite, clGray, 1);
    }
    else if(lpDraw->dwItemSpec == TBCD_CHANNEL)
    {
        // ccrun注：可以自己搞个图片贴上去，效果更好
        //m_pCanvas->CopyRect(rct, Form1->Image1->Canvas, Form1->Image1->ClientRect);

        m_pCanvas->Brush->Color = clSkyBlue;
        m_pCanvas->FillRect(rct);

        char cc[] = {0x63, 0x63, 0x72, 0x75, 0x6E, 0x00 }; // a joke - -#
        String strCaption = String().sprintf("%s TrackBar", cc);

        int nLeftOffset = (rct.Width() - m_pCanvas->TextWidth(strCaption)) / 2;
        int nTopOffset = (rct.Height() - m_pCanvas->TextHeight(strCaption)) / 2;

        m_pCanvas->Font->Color = clBlue;
        m_pCanvas->Font->Name = "宋体";
        m_pCanvas->Font->Size = 9;

        m_pCanvas->TextRect(rct, rct.Left + nLeftOffset, rct.Top + nTopOffset, strCaption);

        DrawEdge(m_pCanvas->Handle, &rct, EDGE_SUNKEN, BF_RECT);
    }

    // 如果是绘制刻度就交给系统默认的处理
    Message.Result = (lpDraw->dwItemSpec == TBCD_TICS)?
            CDRF_DODEFAULT: CDRF_SKIPDEFAULT;
}