QPainterPath（组合路径，路径运动）

组合路径

void ComplicatedPathWidget::paintEvent(QPaintEvent *) {    QPainter painter(this);    painter.setRenderHint(QPainter::Antialiasing);    QPainterPath path;    path.lineTo(100, 0);    path.cubicTo(200, 0, 100, 50, 200, 100); // 贝塞尔曲线    path.closeSubpath(); // 画一条线到路径的第一个点，闭合路径    path.addRect(50, 50, 50, 50); // 加一个矩形    QPainterPath path2;    path2.addEllipse(80, 30, 50, 50);    path = path.subtracted(path2); // 扣掉圆    painter.translate(20, 20);    painter.setBrush(Qt::lightGray);    painter.drawPath(path);    painter.setBrush(Qt::NoBrush);    painter.drawRect(path.boundingRect());}

沿路径运动

QPainterPath::pointAtPercent(qreal t) 是一个很有用的函数，t 的值为 [0, 1.0]，可以取得路径上任意一点的坐标，在动画一节里会使用这个函数来实现动画的插值函数，让物体沿着任意的路径运动，这里没有用 Qt 的动画框架实现了让物体沿着任意的路径运动

#ifndef ANIMATIONALONGPATHWIDGET_H#define ANIMATIONALONGPATHWIDGET_H#include <QWidget>#include <QPainterPath>class AnimationAlongPathWidget : public QWidget {    Q_OBJECTpublic:    explicit AnimationAlongPathWidget(QWidget *parent = 0);    ~AnimationAlongPathWidget();protected:    void timerEvent(QTimerEvent *event) Q_DECL_OVERRIDE;    void paintEvent(QPaintEvent *event) Q_DECL_OVERRIDE;private:    QPainterPath path;    float percent;    float step;    int timerId;};#endif // ANIMATIONALONGPATHWIDGET_H

#include "AnimationAlongPathWidget.h"#include <QPainter>#include <QtGlobal>#include <QTimerEvent>AnimationAlongPathWidget::AnimationAlongPathWidget(QWidget *parent) : QWidget(parent) {    step = 0.02;    percent = 0;    // 构造一个任意的曲线    path.cubicTo(50, 0, 30, 100, 100, 100);    path.cubicTo(150, 100, 250, 0, 200, 100);    path.cubicTo(150, 100, 250, 0, 300, 140);    path.quadTo(150, 310, 150, 100);    // 启动定时器    timerId = startTimer(60);}AnimationAlongPathWidget::~AnimationAlongPathWidget() {}void AnimationAlongPathWidget::timerEvent(QTimerEvent *event) {    // 不停的更新 percent 的值，刷新界面，实现动画效果    if (event->timerId() == timerId) {        percent += step;        if (percent < 0 || percent > 1) {            step = -step; // 运动方向取反            percent = qMin(percent, 1.0F);            percent = qMax(percent, 0.0F);        }        update();    }}void AnimationAlongPathWidget::paintEvent(QPaintEvent *) {    QPainter painter(this);    painter.setRenderHint(QPainter::Antialiasing);    painter.translate(20, 20);    painter.drawPath(path);    painter.setBrush(Qt::red);    painter.drawEllipse(path.pointAtPercent(percent), 4, 4);}