Qt实现矩形大小任意缩放的示例代码

#ifndef POINTBUTTON_H
#define POINTBUTTON_H
#include <QPushButton>
#include <QWidget>
#include <QMouseEvent>

class PointButton : public QPushButton
{
public:
    PointButton(QWidget *parent);
    ~PointButton();

public:
    bool isPressed;                                 // 用来判断用户是否正按在拖曳按钮上

protected:
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);

private:
    void setQss();                                  // 设置拖曳按钮样式

private:
    float startX;                                   // 用来移动拖曳按钮
    float startY;
};

#endif // POINTBUTTON_H

#include "point_button.h"
#include <QString>
#include "window.h"

PointButton::PointButton(QWidget *parent): QPushButton(parent) {
    this->resize(10, 10);
    this->isPressed = false;
    this->setQss();
}

PointButton::~PointButton() {

}

void PointButton::setQss() {
    QString qss = "QPushButton {\n"
                  "border-radius: 5px;\n"
                  "border: 1px solid black;"
                  "background-color: rgb(255, 255, 255);\n"
                  "}\n"
                  "QPushButton:hover {\n"
                  "border-width: 2px;\n"
                  "}";

    this->setStyleSheet(qss);
}

void PointButton::mousePressEvent(QMouseEvent *event) {
    QPushButton::mousePressEvent(event);
    this->startX = event->x();
    this->startY = event->y();
    this->isPressed = true;
}

void PointButton::mouseMoveEvent(QMouseEvent *event) {
    QPushButton::mouseMoveEvent(event);
    float disX = event->x() - this->startX;
    float disY = event->y() - this->startY;
    this->move(this->x()+disX, this->y()+disY);
    Window *parent = (Window*) this->parent();
    parent->changeSize();
}

void PointButton::mouseReleaseEvent(QMouseEvent *event) {
    QPushButton::mouseReleaseEvent(event);
    this->isPressed = false;
}

#ifndef WINDOW_H
#define WINDOW_H

#include <QWidget>
#include <QPaintEvent>
#include <QMouseEvent>
#include <QPen>

#include "point_button.h"

class Window : public QWidget
{
    Q_OBJECT

public:
    Window(QWidget *parent = nullptr);
    ~Window();
    void changeSize();                              // 改变矩形尺寸
    void hideCornerBtns();                          // 隐藏边角拖曳按钮
    void showCornerBtns();                          // 设置边角拖曳按钮位置并显示

protected:
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void paintEvent(QPaintEvent *event);

private:
    int x1;                                         // x1和y1是矩形左上角坐标
    int y1;
    int x2;                                         // x2和y2是矩形右下角坐标
    int y2;

    QPen pen;

    PointButton *topLeftBtn;
    PointButton *topRightBtn;
    PointButton *bottomLeftBtn;
    PointButton *bottomRightBtn;
};
#endif // WINDOW_H

#include "window.h"
#include <Qt>
#include <QPainter>
#include <QDebug>


Window::Window(QWidget *parent): QWidget(parent) {
    this->pen = QPen(Qt::black);
    this->topLeftBtn = new PointButton(this);
    this->topRightBtn = new PointButton(this);
    this->bottomLeftBtn = new PointButton(this);
    this->bottomRightBtn = new PointButton(this);

    this->x1 = float(NULL);
    this->y1 = float(NULL);
    this->x2 = float(NULL);
    this->y2 = float(NULL);
    this->hideCornerBtns();
}

Window::~Window() {

}

void Window::mousePressEvent(QMouseEvent *event) {
    QWidget::mousePressEvent(event);
    this->x1 = float(NULL);
    this->y1 = float(NULL);
    this->x2 = float(NULL);
    this->y2 = float(NULL);
    this->hideCornerBtns();

    this->x1 = event->x();
    this->y1 = event->y();
    this->update();

}

void Window::mouseMoveEvent(QMouseEvent *event) {
    QWidget::mouseMoveEvent(event);

    if (this->topLeftBtn->isPressed || this->topRightBtn->isPressed ||
        this->bottomLeftBtn->isPressed || this->bottomRightBtn->isPressed)
        return;

    this->x2 = event->x();
    this->y2 = event->y();
    this->update();
}

void Window::paintEvent(QPaintEvent *event) {
    QWidget::paintEvent(event);

    if (this->x1==float(NULL) || this->y1==float(NULL) || this->x2==float(NULL) || this->y2==float(NULL)) {
        return;
    }

    QPainter painter(this);
    painter.setPen(this->pen);
    int width = this->x2 - this->x1;
    int height = this->y2 - this->y1;
    painter.drawRect(this->x1, this->y1, width, height);

    this->showCornerBtns();
}

void Window::hideCornerBtns() {
    this->topLeftBtn->hide();
    this->topRightBtn->hide();
    this->bottomLeftBtn->hide();
    this->bottomRightBtn->hide();
}

void Window::showCornerBtns() {
    int halfWidth = int(this->topLeftBtn->width() / 2);
    int halfHeight = int(this->topLeftBtn->height() / 2);
    this->topLeftBtn->move(this->x1-halfWidth, this->y1-halfHeight);
    this->topRightBtn->move(this->x2-halfWidth, this->y1-halfHeight);
    this->bottomLeftBtn->move(this->x1-halfWidth, this->y2-halfHeight);
    this->bottomRightBtn->move(this->x2-halfWidth, this->y2-halfHeight);

    this->topLeftBtn->show();
    this->topRightBtn->show();
    this->bottomLeftBtn->show();
    this->bottomRightBtn->show();
}

void Window::changeSize() {
    if (this->topLeftBtn->isPressed) {
        this->x1 = int(this->topLeftBtn->x() + this->topLeftBtn->width()/2);
        this->y1 = int(this->topLeftBtn->y() + this->topLeftBtn->height()/2);
    }
    else if (this->topRightBtn->isPressed) {
        this->x2 = int(this->topRightBtn->x() + this->topRightBtn->width()/2);
        this->y1 = int(this->topRightBtn->y() + this->topRightBtn->height()/2);
    }
    else if (this->bottomLeftBtn->isPressed) {
        this->x1 = int(this->bottomLeftBtn->x() + this->bottomLeftBtn->width()/2);
        this->y2 = int(this->bottomLeftBtn->y() + this->bottomLeftBtn->height()/2);
    }
    else if (this->bottomRightBtn->isPressed) {
        this->x2 = int(this->bottomRightBtn->x() + this->bottomRightBtn->width()/2);
        this->y2 = int(this->bottomRightBtn->y() + this->bottomRightBtn->height()/2);
    }
    this->update();
}

#include "window.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Window w;
    w.show();
    return a.exec();
}