Qt中QPainter与坐标的使用

目录

• 一、坐标系统与坐标变换
• 示例
• 二、可缩放图形

一、坐标系统与坐标变换

坐标系统

QPainter坐标变换相关函数

示例

绘制五角星

船舰widget窗口，只重载paintEvent函数

#include "widget.h"
#include "ui_widget.h"
#include <QPalette>
#include <QPainter>
#include <cmath>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    setPalette(QPalette(Qt::white));
    setAutoFillBackground(true);
    resize(600,300);
}

Widget::~Widget()
{
    delete ui;
}

void Widget::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);
    QPainter painter(this);
    QPen pen;                                      //笔
    pen.setStyle(Qt::SolidLine);
    painter.setPen(pen);
    painter.setRenderHint(QPainter::Antialiasing); //抗锯齿

    QBrush brush;                                  //刷子
    brush.setColor(Qt::yellow);
    brush.setStyle(Qt::SolidPattern);
    painter.setBrush(brush);

    //qreal deg = 3.141592*2/5;
    qreal deg = (360/5)*3.141592/180;
    qreal R=100;
    QPoint points[5] = {
        QPoint(R,0),
        QPoint(R*std::cos(deg),-R*std::sin(deg)),
        QPoint(R*std::cos(2*deg),-R*std::sin(2*deg)),
        QPoint(R*std::cos(3*deg),-R*std::sin(3*deg)),
        QPoint(R*std::cos(4*deg),-R*std::sin(4*deg)),
    };
    QPainterPath starPath;

    starPath.moveTo(points[3]);
    starPath.lineTo(points[1]);
    starPath.lineTo(points[4]);
    starPath.lineTo(points[2]);
    starPath.lineTo(points[0]);
    starPath.closeSubpath();

    QFont font;
    font.setPointSize(12);
    starPath.addText(points[0], font, "0");
    starPath.addText(points[1], font, "1");
    starPath.addText(points[2], font, "2");
    starPath.addText(points[3], font, "3");
    starPath.addText(points[4], font, "4");

    painter.setFont(font);
    painter.save();                  //保存
    painter.translate(100,120);
    painter.drawPath(starPath);
    painter.drawText(0,0,"S1");

    painter.restore();              //恢复
    painter.translate(300,120);
    painter.rotate(90);
    painter.scale(0.7,0.7);
    painter.drawPath(starPath);
    painter.drawText(0,0,"S2");

    painter.resetTransform();
    painter.translate(500,120);
    painter.rotate(-90);
    painter.scale(1.05,1.05);
    painter.drawPath(starPath);
    painter.drawText(0,0,"S3");
}

二、可缩放图形

视口: 绘图设备的任意一个矩形区域的物理坐标，可以只选取物理坐标的一个矩形区域用
于绘图。视口默认情况下等于绘图设备的整个矩形区。
窗口: 对应于视口的矩形区域，只不过是用逻辑坐标定义的坐标系，窗口坐标的中心在矩
形中心。
使用窗口坐标绘制，不用管实际的物理大小

#include "widget.h"
#include "ui_widget.h"
#include <QPalette>
#include <QPainter>
#include <QLinearGradient>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    setPalette(QPalette(Qt::white));
    setAutoFillBackground(true);
    resize(300,300);
}

Widget::~Widget()
{
    delete ui;
}

void Widget::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    int W = QWidget::width();
    int H = QWidget::height();

    int side = qMin(W,H);
    QRect rect((W-side)/2,(H-side)/2, side,side);  //视口大小
    painter.drawRect(rect);
    painter.setViewport(rect);
    painter.setWindow(-100,-100,200,200);

    QLinearGradient linerGradient(0,0,100,0);     // 渐变
    linerGradient.setColorAt(0,Qt::yellow);
    linerGradient.setColorAt(1,Qt::green);
    linerGradient.setSpread(QGradient::PadSpread); //发散

    painter.setCompositionMode(QPainter::RasterOp_NotSourceXorDestination);
    painter.setBrush(linerGradient);
    for (size_t i=0; i<36; i++) {
        painter.drawEllipse(QPoint(50,0),50,50);
        painter.rotate(10);
    }
}

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