1、概述
源码放在文章末尾

该项目实现了可交互的动画验证码控件，趣味性十足：

字符变换动画
噪音动画
可拖动交互

项目demo演示如下所示：

项目部分代码如下所示：

#ifndef CAPTCHAMOVABLELABEL_H
#define CAPTCHAMOVABLELABEL_H

#include <QLabel>
#include <QTime>
#include <QPropertyAnimation>
#include <QDebug>
#include <QMouseEvent>
#include <QPainter>
#include <QPainterPath>
#include <QApplication>
#include <QGraphicsDropShadowEffect>
#include <cmath>
#include <QTimer>

#define CAPTCHA_REFRESH_DURATION 300 // 刷新的动画时长
#define CAPTCHA_CHAR_ANGLE_MAX 20 // 最大旋转角：20°
#define CAPTCHA_SHADOW_BLUR_MAX 80 // 最大的阴影模糊半径

class CaptchaMovableLabel : public QLabel
{
    Q_OBJECT
    Q_PROPERTY(int refreshProgress READ getRefreshProgress WRITE setRefreshProgress)
    Q_PROPERTY(int pressProgress READ getPressProgress WRITE setPressProgress)
public:
    CaptchaMovableLabel(QWidget* parent);

    void setAngle(int angle);
    void setColor(QColor color);
    void setText(QString ch);
    void startRefreshAnimation();
    void setMoveBorder(QRect rect);

    QString text();

protected:
    void paintEvent(QPaintEvent *) override;
    void mousePressEvent(QMouseEvent *ev) override;
    void mouseMoveEvent(QMouseEvent *ev) override;
    void mouseReleaseEvent(QMouseEvent *ev) override;

private:
    void startPressAnimation(int end);
    void setRefreshProgress(int g);
    int getRefreshProgress();
    inline bool isNoAni();
    void setPressProgress(int g);
    int getPressProgress();

private slots:
    void slotMovePos();

private:
    QPoint press_pos;
    bool dragging =  false;
    bool moved = false;
    QGraphicsDropShadowEffect effect;

    QString ch;
    QColor color;
    int angle = 0;
    int refreshProgress = 100;

    QString prevCh;
    QColor prevColor;
    int prevAngle = 0;
    QString prevChar;

    int pressProgress = 0;

    bool inited = false;
    QTimer movingTimer;
    int moveR, moveG, moveB;
};

#endif // CAPTCHAMOVABLELABEL_H

#include "captchamovablelabel.h"


CaptchaMovableLabel::CaptchaMovableLabel(QWidget *parent) : QLabel(parent)
{
    effect.setOffset(0, 0);
//    effect.setBlurRadius(8);
    setGraphicsEffect(&effect);

    movingTimer.setInterval(30);
    movingTimer.setSingleShot(false);
    connect(&movingTimer, SIGNAL(timeout()), this, SLOT(slotMovePos()));
}

void CaptchaMovableLabel::setAngle(int angle)
{
    this->prevAngle = this->angle;
    this->angle = angle;
}

void CaptchaMovableLabel::setColor(QColor color)
{
    this->prevColor = this->color;
    this->color = color;

    moveR = qrand() % 5;
    moveG = qrand() % 5;
    moveB = qrand() % 5;
    movingTimer.start();
}

void CaptchaMovableLabel::setText(QString text)
{
    this->prevCh = this->ch;
    this->ch = text;

    // 计算合适的高度
    QFontMetrics fm(this->font());
    double w = fm.horizontalAdvance(text)+2;
    double h = fm.height();

    const double PI = 3.141592;
    int xieHalf = sqrt(w*w/4+h*h/4); // 斜边的一半
    double a = atan(w/h) + CAPTCHA_CHAR_ANGLE_MAX * PI / 180; // 最大的倾斜角度
    int w2 = xieHalf * sin(a) * 2;

    a = atan(w/h) - CAPTCHA_CHAR_ANGLE_MAX * PI / 180;
    int h2 = xieHalf * cos(a) * 2;

    resize(w2, h2);
}

void CaptchaMovableLabel::startRefreshAnimation()
{
    if (!inited) // 第一次，直接显示，取消动画
    {
        inited = true;
        return ;
    }

    QPropertyAnimation* ani = new QPropertyAnimation(this, "refreshProgress");
    ani->setStartValue(0);
    ani->setEndValue(100);
    ani->setDuration(qrand() % (CAPTCHA_REFRESH_DURATION / 3) + CAPTCHA_REFRESH_DURATION / 3);
    ani->start();
    connect(ani, SIGNAL(finished()), ani, SLOT(deleteLater()));
    connect(ani, SIGNAL(finished()), &movingTimer, SLOT(start()));
}

QString CaptchaMovableLabel::text()
{
    return ch;
}

void CaptchaMovableLabel::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setFont(this->font());
    painter.setRenderHint(QPainter::SmoothPixmapTransform);

    int w2 = width()/2, h2 = height()/2;
    painter.translate(w2, h2); // 平移到中心，绕中心点旋转

    if (isNoAni()) // 不在动画中，直接绘制
    {
        painter.setPen(color);
        painter.rotate(angle);
        painter.drawText(QRect(-w2, -h2, width(), height()), Qt::AlignCenter, ch);
        return ;
    }

    // 动画里面，前后渐变替换
    double newProp = refreshProgress / 100.0;
    double oldProp = 1.0 - newProp;

    double a = prevAngle * oldProp + angle * newProp + 0.5;
    painter.save();
    painter.rotate(a);

    QColor c = prevColor;
    c.setAlpha(c.alpha() * oldProp); // 旧文字渐渐消失
    painter.setPen(c);
    painter.drawText(QRect(-w2,-h2,width(),height()), Qt::AlignCenter, prevCh);

    c = this->color;
    c.setAlpha(c.alpha() * newProp); // 新文字渐渐显示
    painter.setPen(c);
    painter.drawText(QRect(-w2, -h2, width(), height()), Qt::AlignCenter, ch);
    painter.restore();
}

void CaptchaMovableLabel::mousePressEvent(QMouseEvent *ev)
{
    if (ev->button() == Qt::LeftButton)
    {
        // 开始拖拽
        press_pos = ev->pos();
        dragging = true;
        moved = false;
        this->raise();
        movingTimer.stop();

        startPressAnimation(200);

        return ev->accept();
    }
    QLabel::mousePressEvent(ev);
}

void CaptchaMovableLabel::mouseMoveEvent(QMouseEvent *ev)
{
    if (dragging && ev->buttons() & Qt::LeftButton)
    {
        if (!moved && (ev->pos() - press_pos).manhattanLength() < QApplication::startDragDistance())
        {
            return QLabel::mouseMoveEvent(ev); // 还没到这时候
        }
        moved = true;
        move(this->pos() + ev->pos() - press_pos);
        ev->accept();
        return ;
    }
    QLabel::mouseMoveEvent(ev);
}

void CaptchaMovableLabel::mouseReleaseEvent(QMouseEvent *ev)
{
    if (dragging)
    {
        // 结束拖拽
        dragging = false;
        movingTimer.start();

        startPressAnimation(0);
    }
    if (moved)
        return ev->accept();
    QLabel::mouseReleaseEvent(ev);
}

void CaptchaMovableLabel::startPressAnimation(int end)
{
    QPropertyAnimation* ani = new QPropertyAnimation(this, "pressProgress");
    ani->setStartValue(pressProgress);
    ani->setEndValue(end);
    ani->setDuration(CAPTCHA_REFRESH_DURATION << 1);
    ani->start();
    connect(ani, SIGNAL(finished()), ani, SLOT(deleteLater()));
}

void CaptchaMovableLabel::setRefreshProgress(int g)
{
    this->refreshProgress = g;
    update();
}

int CaptchaMovableLabel::getRefreshProgress()
{
    return refreshProgress;
}

bool CaptchaMovableLabel::isNoAni()
{
    return refreshProgress == 100;
}

void CaptchaMovableLabel::setPressProgress(int g)
{
    this->pressProgress = g;
    double off = g / 100;
    effect.setBlurRadius(g / 20.0);
    effect.setOffset(-off, off);
}

int CaptchaMovableLabel::getPressProgress()
{
    return pressProgress;
}

void CaptchaMovableLabel::slotMovePos()
{
    if (refreshProgress < 100)
        return ;

    int val = color.red() + moveR;
    if ( val > 255)
    {
        val = 255;
        moveR = - qrand() % 5;
    }
    else if (val < 0)
    {
        val = 0;
        moveR = - qrand() % 5;
    }
    color.setRed(val);

    val = color.green() + moveG;
    if ( val > 255)
    {
        val = 255;
        moveG = - qrand() % 5;
    }
    else if (val < 0)
    {
        val = 0;
        moveG = - qrand() % 5;
    }
    color.setGreen(val);

    val = color.blue() + moveB;
    if ( val > 255)
    {
        val = 255;
        moveB = - qrand() % 5;
    }
    else if (val < 0)
    {
        val = 0;
        moveB = - qrand() % 5;
    }
    color.setBlue(val);
}

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