ChartCtrl源码剖析之——CChartScrollBar类

CChartScrollBar类用来针对每个轴的数据进行滚动，将那些不在当前区域内的数据通过滚动展示出来。

CChartScrollBar类的头文件。

#pragma once
class CChartAxis;
class CChartScrollBar : public CScrollBar
{
public:
    CChartScrollBar(CChartAxis* pParentAxis);
    ~CChartScrollBar();
    void CreateScrollBar(const CRect& PlottingRect);
    void OnHScroll(UINT nSBCode, UINT nPos);
    void OnVScroll(UINT nSBCode, UINT nPos);
    void Refresh();
    void SetEnabled(bool bEnabled)  { m_bEnabled = bEnabled; }
    bool GetEnabled() const            { return m_bEnabled; }
    void SetAutoHide(bool bAutoHide)  { m_bAutoHide = bAutoHide; }
    bool GetAutoHide() const          { return m_bAutoHide; }
    void OnMouseEnter();
    void OnMouseLeave();
private:
    bool IsScrollInverted() const;
    void MoveAxisToPos(int PreviousPos, int CurPos);
    CChartAxis* m_pParentAxis;
    bool m_bEnabled;
    bool m_bAutoHide;
};

CChartScrollBar类的源文件。

#include "stdafx.h"
#include "ChartScrollBar.h"
#include "ChartAxis.h"
#include "ChartCtrl.h"
#include "math.h"
CChartScrollBar::CChartScrollBar(CChartAxis* pParentAxis)
: CScrollBar(), m_pParentAxis(pParentAxis), m_bEnabled(false),
   m_bAutoHide(true)
{
}
CChartScrollBar::~CChartScrollBar()
{
}
void CChartScrollBar::CreateScrollBar(const CRect& PlottingRect)
{
    CRect Temp = PlottingRect;
    Temp.top++; Temp.left++;
    DWORD dwStyle = SBS_HORZ | WS_CHILD;
    if (m_pParentAxis->IsHorizontal())
    {
        if (m_pParentAxis->m_bIsSecondary)
            dwStyle |= SBS_TOPALIGN;
        else
            dwStyle += SBS_BOTTOMALIGN;
    }
    else
    {
        if (m_pParentAxis->m_bIsSecondary)
            dwStyle |= SBS_VERT | SBS_RIGHTALIGN;
        else
            dwStyle += SBS_VERT | SBS_LEFTALIGN;
    }
    CScrollBar::Create(dwStyle, Temp, m_pParentAxis->m_pParent,100);
    SCROLLINFO info;
    info.cbSize = sizeof(SCROLLINFO);    
    info.fMask = SIF_ALL;     
    info.nMin = 1;     
    info.nMax = 1;
    info.nPage = 1;
    info.nPos = 1;   
    CScrollBar::SetScrollInfo(&info);
}
bool CChartScrollBar::IsScrollInverted() const
{
    bool bInverted = false;
    if (m_pParentAxis->IsInverted() && m_pParentAxis->m_bIsHorizontal)
        bInverted = true;
    if (!m_pParentAxis->IsInverted() && !m_pParentAxis->m_bIsHorizontal)
        bInverted = true;
    return bInverted;
}
void CChartScrollBar::Refresh()
{
    double AxisMin=0, AxisMax=0;
    double SeriesMin=0, SeriesMax=0;
    m_pParentAxis->GetMinMax(AxisMin,AxisMax);
    m_pParentAxis->GetSeriesMinMax(SeriesMin,SeriesMax);
    double dStep = 0;
    int iTotalSteps = 0;
    int iCurrentStep = 0;
    if (m_pParentAxis->IsLogarithmic())
    {
        // TODO: do something if the series has 0 in it
        dStep = pow(AxisMax/AxisMin,0.1);
        iTotalSteps = (int)ceil(log(SeriesMax/SeriesMin)/log(dStep));
        iCurrentStep = (int)(log(AxisMin/SeriesMin)/log(dStep));
    }
    else
    {
        dStep = (AxisMax - AxisMin) / 10.0;
        iTotalSteps = (int)ceil((SeriesMax - SeriesMin)/dStep);
        iCurrentStep = (int)(iTotalSteps * ((AxisMin - SeriesMin)/(SeriesMax-SeriesMin)));
    }
    SCROLLINFO info;
    info.cbSize = sizeof(SCROLLINFO);    
    info.fMask = SIF_ALL;     
    if ( (AxisMax-AxisMin) == 0 || (SeriesMax-SeriesMin)==0 )
    {
        info.nMin = 1;     
        info.nMax = 1;
        info.nPage = 1;
        info.nPos = 1;   
    }
    else
    {
        info.nMin = 1;     
        info.nMax = iTotalSteps;
        info.nPage = 10;
        info.nPos = iCurrentStep;   
        if (IsScrollInverted())
            info.nPos = iTotalSteps - 9 - iCurrentStep;
        else
            info.nPos = iCurrentStep;   
    }
    CScrollBar::SetScrollInfo(&info);
}
void CChartScrollBar::OnHScroll(UINT nSBCode, UINT nPos)
{
    int MinPos;
    int MaxPos;
    int PreviousPos = CScrollBar::GetScrollPos();
    CScrollBar::GetScrollRange(&MinPos, &MaxPos);
    int CurPos = PreviousPos;
    bool bUpdate = true;
    switch (nSBCode)
    {
    case SB_LEFT:      
        CurPos = 0;
        break;
    case SB_RIGHT:      
        CurPos = MaxPos;
        break;
    case SB_ENDSCROLL:  
        bUpdate = false;
        break;
    case SB_LINELEFT:  
        if (CurPos > MinPos)
            CurPos--;
        break;
    case SB_LINERIGHT:   
        if (CurPos < MaxPos-9)
            CurPos++;
        break;
    case SB_PAGELEFT:    
        if (CurPos > MinPos)
            CurPos = max(MinPos, CurPos - 10);
        break;
    case SB_PAGERIGHT:     
        if (CurPos < MaxPos-9)
            CurPos = min(MaxPos, CurPos + 10);
        break;
    case SB_THUMBPOSITION:
            CurPos = nPos;
        break;
    case SB_THUMBTRACK:   
            CurPos = nPos;
        break;
    }
    if (bUpdate)
    {
        // Set the new position of the thumb (scroll box).
        CScrollBar::SetScrollPos(CurPos);
        MoveAxisToPos(PreviousPos,CurPos);
    }
}
void CChartScrollBar::OnVScroll(UINT nSBCode, UINT nPos)
{
    int MinPos;
    int MaxPos;
    int PreviousPos = CScrollBar::GetScrollPos();
    CScrollBar::GetScrollRange(&MinPos, &MaxPos);
    int CurPos = PreviousPos;
    bool bUpdate = true;
    switch (nSBCode)
    {
    case SB_BOTTOM:      
        CurPos = MaxPos;
        break;
    case SB_TOP:      
        CurPos = 0;
        break;
    case SB_ENDSCROLL:   
        bUpdate = false;
        break;
    case SB_LINEDOWN:  
        if (CurPos < MaxPos-9)
            CurPos++;
        break;
    case SB_LINEUP:   
        if (CurPos > MinPos)
            CurPos--;
        break;
    case SB_PAGEUP:    
        if (CurPos > MinPos)
            CurPos = max(MinPos, CurPos - 10);
        break;
    case SB_PAGEDOWN:     
        if (CurPos < MaxPos-9)
            CurPos = min(MaxPos, CurPos + 10);
        break;
    case SB_THUMBPOSITION:
        CurPos = nPos;
        break;
    case SB_THUMBTRACK:   
        CurPos = nPos;
        break;
    }
    if (bUpdate)
    {
        // Set the new position of the thumb (scroll box).
        CScrollBar::SetScrollPos(CurPos);
        MoveAxisToPos(PreviousPos,CurPos);
    }
}
void CChartScrollBar::MoveAxisToPos(int PreviousPos, int CurPos)
{
    double AxisMin=0, AxisMax=0;
    double SeriesMin=0, SeriesMax=0;
    m_pParentAxis->GetMinMax(AxisMin,AxisMax);
    m_pParentAxis->GetSeriesMinMax(SeriesMin,SeriesMax);
    if (m_pParentAxis->IsLogarithmic())
    {
        double dStep = pow(AxisMax/AxisMin,0.1);
        double dFactor = pow(dStep,(CurPos - PreviousPos));
        if (IsScrollInverted())
            m_pParentAxis->SetZoomMinMax(AxisMin/dFactor,AxisMax/dFactor);
        else
            m_pParentAxis->SetZoomMinMax(AxisMin*dFactor,AxisMax*dFactor);
    }
    else
    {
        double dStep = (AxisMax - AxisMin) / 10.0;
        double dOffset = (CurPos - PreviousPos) * dStep;
        if (IsScrollInverted())
            m_pParentAxis->SetZoomMinMax(AxisMin-dOffset,AxisMax-dOffset);
        else
            m_pParentAxis->SetZoomMinMax(AxisMin+dOffset,AxisMax+dOffset);
    }
}
void CChartScrollBar::OnMouseEnter()
{
    if (m_bEnabled && m_bAutoHide)
        ShowWindow(SW_SHOW);
}
void CChartScrollBar::OnMouseLeave()
{
    if (m_bEnabled && m_bAutoHide)
        ShowWindow(SW_HIDE);
}

这份源码一开始读的时候在info.nPage产生了理解偏差，再一次读的时候又在这个地方纠结了很久，现在把这个参数的意义再捋一遍，它的英文解释如下：

nPage 

Specifies the page size. A scroll bar uses this value to determine the appropriate size of the proportional scroll box. 

该值表示页尺寸，同时表示比例滚动框的大小。将这个理解清楚之后，后面OnHScroll函数和OnVScroll函数里面的加减10与加减9就相对比较好理解。