Qt笔记——绘图(QBitmap,QPixmap,QImage,QPicture)

• QPainter绘图
  • 重写绘图事件，虚函数
  • 如果窗口绘图，必须放在绘图事件里实现
  • 绘图事件内部自动调用，窗口需要重绘的时候，状态改变
• 绘图设备（QPixmap，QImage，QBitmap，QPicture）
• QPixmap图片背景透明，针对屏幕进行优化了，和平台相关，不能对图片进行修改
• QImage 和平台无关，可以对图片进行修改，在线程中绘图
• QPicture 保存绘图 的状态（二进制文件）
• pixmap.save("../pixmap.png"); 保存图片
• setWindowFlags(Qt::FramelessWindowHint | windowFlags());去除边框
• setAttribute(Qt::WA_TranslucentBackground);设置透明

QPainter

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

protected:
    void paintEvent(QPaintEvent *event);

private slots:
    void on_pushButton_clicked();

private:
    Ui::Widget *ui;
    int x=0;
};

#endif // WIDGET_H

#include "widget.h"
#include "ui_widget.h"
#include <QPainter>
#include <QPen>
#include <QBrush>
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
}

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

void Widget::paintEvent(QPaintEvent *event)
{
    //QPainter p(this);
    QPainter p;//创建画家对象
    p.begin(this);//指定当前窗口为绘图设备
    //画背景图
    //p.drawPixmap(0,0, width(), height(), QPixmap("../Image/bk.png"));
    //p.drawPixmap(rect(),QPixmap("../Image/bk.png"));

    //定义画笔
    QPen pen;
    pen.setWidth(5);//设置线宽
    pen.setColor(QColor(124,123,0));//rgb
    pen.setStyle(Qt::DashDotDotLine);

    QBrush brush;
    brush.setColor(Qt::red);
    brush.setStyle(Qt::Dense1Pattern);

    //p.setPen(pen);
    p.setBrush(brush);
    //画直线
    p.drawLine(50,50,150,50);
    p.drawLine(50, 50,50,150 );

    //画矩形
    p.drawRect(x,150,100,50);

    p.drawEllipse(QPoint(150,150),25,50);

    p.drawPixmap(x,180,80,80,QPixmap("../Image/face.png"));

    p.end();
}

void Widget::on_pushButton_clicked()
{
    x += 20;
    if(x>width())
    {
        x = 0;
    }
    update();
}

　QBitmap

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

protected:
    void paintEvent(QPaintEvent *event);

private:
    Ui::Widget *ui;
};

#endif // WIDGET_H

#include "widget.h"
#include "ui_widget.h"
#include <QPainter>
#include <QBitmap>
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
}

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

void Widget::paintEvent(QPaintEvent *event)
{
    QPainter p(this);
    //QPixmap图片背景透明
    p.drawPixmap(0,0,QPixmap("../Image/butterfly.png"));
    //QBitmap
    p.drawPixmap(200,0, QBitmap("../Image/butterfly.png"));
    //QPixmap 图片背景白色
    QPixmap pixmap;
    pixmap.load("../Image/butterfly1.png");

}

　QPixmap

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

private:
    Ui::Widget *ui;
};

#endif // WIDGET_H

#include "widget.h"
#include "ui_widget.h"
#include <QPainter>
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    QPixmap pixmap(400, 300);
    QPainter p(&pixmap);
    p.fillRect(0,0,400,300,QBrush(Qt::white));

    pixmap.fill(Qt::white);
    p.drawPixmap(0,0,80,80,QPixmap("../Image/face.png"));

    //保存图片
    pixmap.save("../pixmap.png");
}

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

　QImage

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

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);

    QImage image(400,300,QImage::Format_ARGB32);
    QPainter p;
    p.begin(&image);

    p.drawLine(50,50,100,100);

    for(int i=0;i<50;i++)
    {
        for(int j=0;j<50;j++)
        {
            image.setPixel(QPoint(i,j),qRgb(0,255,0));

        }
    }
    p.end();

    image.save("../image.png");
}

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

QPicture

#include "widget.h"
#include "ui_widget.h"
#include <QPainter>
#include <QPicture>
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    QPicture picture;
    QPainter p;
    p.begin(&picture);
    p.drawLine(50,50,100,100);
    p.end();

    picture.save("../picture.png");
}

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

void Widget::paintEvent(QPaintEvent *event)
{
//    QPicture pic;
//    pic.load("../picture.png");
    QPainter p(this);
//    p.drawPicture(0,0,pic);

    QPixmap pixmap;
    pixmap.load("../Image/face.png");
    QImage tempImage = pixmap.toImage();
    p.drawImage(0,0, tempImage);

    QImage image;
    image.load("../Image/face.png");
    QPixmap tempPixmap = QPixmap::fromImage(image);
}　　

窗口透明

#include "widget.h"
#include "ui_widget.h"
#include <QPainter>
#include <QMouseEvent>
#include <QDebug>
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    setWindowFlags(Qt::FramelessWindowHint | windowFlags());

    setAttribute(Qt::WA_TranslucentBackground);
}

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

void Widget::paintEvent(QPaintEvent *event)
{
    QPainter p(this);
    p.drawLine(50,50,100,100);
}

void Widget::mousePressEvent(QMouseEvent *event)
{
    if(event->button() == Qt::RightButton)
    {
     close();
     qDebug()<<"close";
    }
    else if(event->button() == Qt::LeftButton)
    {
        p = event->globalPos() - this->frameGeometry().topLeft();
        qDebug()<<"left";
    }
}

void Widget::mouseMoveEvent(QMouseEvent *event)
{
    if(event->button() & Qt::LeftButton)
    {
            move(event->globalPos()-p);
    }
}

原文地址：https://www.cnblogs.com/dalanjing/p/8724876.html