Qt_QLabel文字滚动 滚动字幕

1.实现效果

做了两种实现方式，蓝色边框是字符滚动，红色边框是像素滚动，显然像素滚动要更顺滑些。

2.简述

实现思路1
准备足够显示满宽的字符，每次删除最左边的一个字符，不够显示的时候，在后边追加字符。

实现思路2
画一个宽度是Label宽度+文本宽度的文本框，从x=0开始，每次将文本框的起始位置减1。当一个完整文本宽度被减完之后，重新从x=0开始画。

实现1

#include "CRollLabel.h"
#include 
#include 
CRollLabel::CRollLabel(QWidget *parent)
    : QLabel(parent)
{
    this->startTimer(300);
}

void CRollLabel::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event)
    if(0 == m_nCharWidth)
        return ;

    QPainter painter(this);
    m_strDrawText = m_strText.mid(m_nCurrentIndex);
    while((m_strDrawText.size() * m_nCharWidth) <= width()){
        m_strDrawText += m_strText + " ";
    }
    painter.drawText(rect(),alignment(),m_strDrawText);
}

void CRollLabel::timerEvent(QTimerEvent *event)
{
    Q_UNUSED(event)

    m_strText = text();
    if(!m_strText.isEmpty()){
        int nSumWidth = fontMetrics().width(m_strText);
        m_nCharWidth = nSumWidth/m_strText.size();
    }

    m_nCurrentIndex++;
    if(m_nCurrentIndex > m_strText.size()){
        m_nCurrentIndex = 0;
    }

    update();
}

----------------------------------------以上是源文件，以下是头文件
#ifndef CROLLLABEL_H
#define CROLLLABEL_H

#include 
#include 

class CRollLabel : public QLabel
{
    Q_OBJECT
public:
    explicit CRollLabel(QWidget *parent = nullptr);

public:
    void setInterVal(int nInterVal){startTimer(nInterVal);}
protected:
    void paintEvent(QPaintEvent *event);
    void timerEvent(QTimerEvent *event);
private:
    int m_nCharWidth = 0;
    int m_nCurrentIndex = 0;
    QString m_strText;
    QString m_strDrawText;
};

#endif // CROLLLABEL_H

实现2

#include "CScrollLabel.h"
#include 
#include 

CScrollLabel::CScrollLabel(QWidget *parent) : QLabel(parent)
{
    this->startTimer(100);
}


void CScrollLabel::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event)
    QPainter painter(this);
    QRectF rectText = rect();
    rectText.setWidth(width() + m_nTextWidth);
    rectText.setX(-m_nCurrentIndex);
    painter.drawText(rectText,alignment(),m_strDrawText);
}

void CScrollLabel::timerEvent(QTimerEvent *event)
{
    Q_UNUSED(event)
    if(text().isEmpty())
        return ;

    if(m_strText != text()){
        m_strText = text();
        m_nCurrentIndex = 0;
        m_nTextWidth = fontMetrics().width(m_strText);
    }

    while(fontMetrics().width(m_strDrawText) < width() + m_nTextWidth){
        m_strDrawText += text();
    }

    m_nCurrentIndex++;
    if(m_nCurrentIndex == m_nTextWidth){
        m_nCurrentIndex = 0;
    }

    update();
}

----------------------------------------以上是源文件，以下是头文件

#ifndef CSCROLLLABEL_H
#define CSCROLLLABEL_H

#include 
#include 

class CScrollLabel : public QLabel
{
    Q_OBJECT
public:
    explicit CScrollLabel(QWidget *parent = nullptr);

public:
    void setInterVal(int nInterVal){startTimer(nInterVal);}
protected:
    void paintEvent(QPaintEvent *event);
    void timerEvent(QTimerEvent *event);
private:
    int m_nCharWidth = 0;
    int m_nCurrentIndex = 0;        //文本起始x点
    int m_nTextWidth = 0;
    QString m_strText;
    QString m_strDrawText;
};

#endif // CSCROLLLABEL_H