一、效果图
二、原理
- 因为QPainter只能绘制水平的矩形，而现在想要绘制旋转来一定角度的矩形，就需要使用QPainter的旋转功能了。使用到的函数分别如下：
- painter.translate(x1, y1);//把参数(x1, y1)指定的点移动到绘图区的左上角（绘图原点），使得目标绘制坐标成为坐标系的原点(0,0)
- painter.rotate(angle); //以坐标原点为中点，旋转参数指定角度，范围是[-180,180]
- painter.resetTransform();//恢复translate和rotate对painter作的修改
- 实现绘制旋转指定角度的矩形的原理：先把坐标系从指定度数的角度旋转到0度，然后在旋转后的坐标系中画一个水平的矩形，然后在旋转回去。就实现了指定角度的矩形绘制；
- 举例：比如以绘图区域中心为中点，绘制一个负45度的矩形。
painter.resetTransform();先重置参数
painter.translate(this-\>width()/2, this-\>height()/2);//把画图区域中心点作为坐标系原点
painter.rotate(-45);//从目标角度逆时针旋转到0du，
QRect rect;
rect.setX(0 - radius);//注意现在虽然是从(0,0)点绘制，但实际会在translate的参数指定的位置画出
rect.setY(0 - radius);
rect.setHeight(radius*2);
rect.setWidth(distance);
painter.fillRect(rect, QBrush(QColor(146, 251, 91, 128)));//绘制矩形
painter.resetTransform();//重置参数
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三、源代码
因为源代码很少，就直接贴在下面了
anglerectview.h
#ifndef ANGLERECTVIEW_H
#define ANGLERECTVIEW_H
#include <QWidget>
#include <QMouseEvent>
#include <QWheelEvent>
#include <QPoint>
#include <QList>
#include <QMenu>
#include <QApplication>
class AngleRectView : public QWidget
{
Q_OBJECT
public:
explicit AngleRectView(QWidget *parent);
~AngleRectView() override;
enum MoveDirection {
Up,
UpRight,
Right,
DownRight,
Down,
DownLeft,
Left,
UpLeft
};
protected:
void paintEvent(QPaintEvent *event) override;
void mouseMoveEvent(QMouseEvent *event) override;
private:
double CalcDistance(const QPoint& pt1, const QPoint& pt2);
int GetAngleOfCurrentAngleRotateToZoroAngleByDirection(int direction);
void DrawRegionBlock(QPainter &painter, int x1, int y1, int x2, int y2,
double step_width, int derection);
int CalcMoveDirection(int x1, int y1, int x2, int y2);
private:
QPoint mouse_current_move_pos_;
};
#endif // ANGLERECTVIEW_H
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anglerectview.cpp
#include "anglerectview.h"
#include <QPainter>
#include <QtMath>
#include <qmath.h>
AngleRectView::AngleRectView(QWidget *parent)
: QWidget(parent)
{
setMouseTracking(true);
}
AngleRectView::~AngleRectView()
{
}
void AngleRectView::paintEvent(QPaintEvent *event) {
Q_UNUSED(event)
QPainter painter(this);
//draw bg
QRect frame_rect = this->rect();
painter.fillRect(frame_rect, QBrush(QColor(54, 54, 54)));
int x1 = frame_rect.width()/2;
int y1 = frame_rect.height()/2;
int x2 = mouse_current_move_pos_.x();
int y2 = mouse_current_move_pos_.y();
int derection = CalcMoveDirection(x1, y1, x2, y2);
DrawRegionBlock(painter, x1, y1, x2, y2, 50, derection);
}
void AngleRectView::mouseMoveEvent(QMouseEvent *event) {
Q_UNUSED(event)
mouse_current_move_pos_ = event->pos();
update();
}
void AngleRectView::DrawRegionBlock(QPainter &painter, int x1, int y1, int x2, int y2,
double step_width, int derection) {
int radius = qRound(step_width / 5);
if(radius > 2) {
int distance = static_cast<int>(CalcDistance(QPoint(x1, y1), QPoint(x2, y2)));
distance += radius;
QRect rect;
painter.resetTransform();
int angle = GetAngleOfCurrentAngleRotateToZoroAngleByDirection(derection);
painter.translate(x1, y1);//trans 0,0 to x1, y1
painter.rotate(angle); //rotate to angle 0
rect.setX(0 - radius);
rect.setY(0 - radius);
rect.setHeight(radius*2);
rect.setWidth(distance);
painter.fillRect(rect, QBrush(QColor(146, 251, 91, 128)));
//draw outline
QPen backup_temp_pen = painter.pen();
painter.setPen(Qt::white);
painter.drawLine(rect.left(), rect.top(), rect.right(), rect.top());
painter.drawLine(rect.left(), rect.bottom(), rect.right(), rect.bottom());
painter.drawLine(rect.left(), rect.top(), rect.left(), rect.bottom());
painter.setPen(backup_temp_pen);
painter.resetTransform();
}
}
double AngleRectView::CalcDistance(const QPoint& pt1, const QPoint& pt2) {
return qSqrt(double(qPow(pt2.x() - pt1.x(), 2) + qPow(pt2.y() - pt1.y(), 2) ));
}
int AngleRectView::GetAngleOfCurrentAngleRotateToZoroAngleByDirection(int direction) {
switch (direction) {
case Right: { return 0;}
case DownRight:{ return 45;}
case Down:{ return 90; }
case DownLeft:{ return 135; }
case Left:{ return 180; }
case UpLeft:{ return -135; }
case Up:{ return -90; }
case UpRight:{ return -45; }
}
return 0;
}
int AngleRectView::CalcMoveDirection(int x1, int y1, int x2, int y2) {
double rr = qAtan2(y2 - y1, x2 - x1);
int angle = static_cast<int>(180/M_PI * rr);
if(angle > 0) {
angle = 360 - angle;
} else {
angle = angle * -1;
}
if(angle >= 23 && angle < 68) {
return UpRight;
} else if(angle >= 68 && angle < 113) {
return Up;
} else if(angle >= 113 && angle < 158) {
return UpLeft;
} else if(angle >= 158 && angle < 203) {
return Left;
} else if(angle >= 203 && angle < 248) {
return DownLeft;
} else if(angle >= 248 && angle < 293) {
return Down;
} else if(angle >= 293 && angle < 338) {
return DownRight;
} else if((angle >= 338 && angle < 360) ||
(angle >= 0 && angle < 23)) {
return Right;
}
return 0;
}
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在QtCreater中新建窗口应用程序，在主窗口的构造函数添加如下代码
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QHBoxLayout>
#include "./views/anglerectview/anglerectview.h"
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
//以下为手工添加的布局AngleRectView控件的代码
QHBoxLayout *center_layout = new QHBoxLayout(ui->centralwidget);
AngleRectView *angle_rect_view = new AngleRectView(ui->centralwidget);
angle_rect_view->setObjectName(QString::fromUtf8("angle_rect_view"));
center_layout->addWidget(angle_rect_view);
}
MainWindow::~MainWindow()
{
delete ui;
}
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