1  如果要在绘图设备(一般为窗口部件)上绘图，只需创建一个QPainter,再将指针传到该设备中。

例如：

void MyWidget::paintEvent(QPaintEvent *event)

{

QPainter painter(this);

}

2  常用的初始化：画笔、画刷、字体

画笔：用来画线和边缘。它包含颜色、宽度、线性、拐点风格以及连线风格。

画刷：用来填充几何图形的图案。它一般由颜色和风格组成，但同时也可以是纹理(一个不断重复的图像)或者是一个渐变。

字体：用来绘制文字。字体有很多属性，包括字体族和磅值大小。

5.具体的实例

通过建立一个画图面板来了解Qpainter是怎样绘制图形的，其中包含两个类，画图的区域PainterArea类和主窗口mainWindow类

(1)实现PainterArea类

//paintarea.h

#ifndef PAINTAREA_H

#define PAINTAREA_H

#include

#include

#include

class PaintArea : public QWidget

{

Q_OBJECT

public:

enum Shape{Line,Rectangle,RoundRect,Ellipse,Polygon,Polyline,Points,Arc,Path,Text,

Pixmap};

PaintArea(QWidget * parent=0);

void setShape(Shape); //设置形状

void setPen(QPen); //设置画笔

void setBrush(QBrush); //设置画刷

void setFillRule(Qt::FillRule);//设置填充模式

void paintEvent(QPaintEvent *);//重画事件

private:

Shape shape;

QPen pen;

QBrush brush;

Qt::FillRule fillRule;

};

#endif // PAINTAREA_H

//paintarea.cpp

#include "paintarea.h"

#include

PaintArea::PaintArea(QWidget *parent)

:QWidget(parent)

{

setPalette(QPalette(Qt::white)); //设置背景颜色

setAutoFillBackground(true);//设置自动填充背景色

setMinimumSize(400,400);//设置窗口最下大小

}

void PaintArea::setShape(Shape s) //update()更新窗口部件

{

shape=s;

update();

}

void PaintArea::setPen(QPen p)

{

pen=p;

update();

}

void PaintArea::setBrush(QBrush b)

{

brush=b;

update();

}

void PaintArea::setFillRule(Qt::FillRule rule)

{

fillRule=rule;

update();

}

//重画事件

void PaintArea::paintEvent(QPaintEvent *)

{

QPainter p(this);

p.setPen(pen);

p.setBrush(brush);

QRect rect(100,100,250,200);//构造一个矩形

static const QPoint points[4]={

QPoint(100,100),

QPoint(200,150),

QPoint(300,250),

QPoint(150,300)

};//确定Points的四个点的坐标

int startAngle=60*16;

int spanAngle=180*16; //为绘制曲线设置参数变量

QPainterPath path; //QPainterPath为Qpainter类提供了一个存储容器，里面包含了画的内容和画的顺序，

path.moveTo(50,150); //当前位置移动到坐标50,150

path.lineTo(350,150); //当前位置开始画直线，终点位置坐标350,150

path.lineTo(100,325);

path.lineTo(200,50);

path.lineTo(300,325);

path.lineTo(50,150);

path.setFillRule(fillRule); //设置填充模式

switch(shape)

{

case Line: //直线

p.drawLine(rect.topLeft(),rect.bottomRight()); //绘制直线。起点为矩形左上点，终点为矩形右下点

break;

case Rectangle: //长方形

p.drawRect(rect);

break;

case RoundRect: //圆角方形

p.drawRoundRect(rect);

break;

case Ellipse: //椭圆形

p.drawEllipse(rect);

break;

case Polygon: //多边形

p.drawPolygon(points,4); //绘制4个顶点多边形

break;

case Polyline: //多边线

p.drawPolyline(points,4);

break;

case Points: //点

p.drawPoints(points,4);

break;

case Arc: //弧

p.drawArc(rect,startAngle,spanAngle); //后面两个参数分别为 起始角与跨度角

break;

case Path: //绘制之前已经画好的路径

p.drawPath(path);

break;

case Text: //文字

p.drawText(rect,Qt::AlignCenter,tr("Hello Qt!"));

break;

case Pixmap: //图片

p.drawPixmap(150,150,QPixmap("1.png"));//绘制一个图像

break;

default:

break;

}

}

//前面的椭圆形、直线、长方形、圆角矩形，弧 都是利用矩形为骨架构成的，具体如何构成参照介绍中的绘制函数中的图。

(2)实现主窗口类MainWidget

//mainwindow.h头文件

#ifndef MAINWINDOW_H

#define MAINWINDOW_H

#include

#include

#include

#include

#include

#include

#include

class MainWindow : public QWidget

{

Q_OBJECT

public:

MainWindow(QWidget *parent = 0);

~MainWindow();

private:

PaintArea *paintArea;

QLabel *shapelabel;//形状

QComboBox *shapeComboBox;

QLabel *penWidthLable;//画笔宽度

QSpinBox *penWidthSpinBox;

QLabel *penColorLabel;//画笔颜色

QFrame *penColorFrame;

QPushButton *penColorbtn;//画笔颜色按钮

QLabel *penStyleLabel;

QComboBox *penStyleComboBox;//画笔风格

QLabel *penCapLabel;

QComboBox *penCapComboBox;

QLabel *penJoinLabel;

QComboBox *penJoinComboBox;

QLabel *fillLabel;

QComboBox *fillComboBox;

QLabel *brushStyleLabel;

QComboBox *brushStyleComboBox;

QLabel *brushColorlabel;

QFrame *brushColorFrame;

QPushButton *brushColorbtn;

QGridLayout *settingLayout;

protected slots:

void ShowShape(int);

void ShowPenWidth(int);

void ShowPenColor();

void ShowPenStyle(int);

void ShowPenCap(int);

void ShowPenJoin(int);

void ShowFill();

void ShowBrushColor();

void ShowBrush(int);

};

#endif // MAINWINDOW_H

//mainwindow.cpp

#include"mainwindow.h"

#include "paintarea.h"

#include

MainWindow::MainWindow(QWidget *parent)

: QWidget(parent)

{

paintArea=new PaintArea;

shapelabel=new QLabel("形状："); //形状选择下拉列表框

shapeComboBox=new QComboBox;

shapeComboBox->addItem(tr("Line"),PaintArea::Line);

shapeComboBox->addItem(tr("RoundRect"),PaintArea::RoundRect);

shapeComboBox->addItem(tr("Ellipse"),PaintArea::Ellipse);

shapeComboBox->addItem(tr("Polygon"),PaintArea::Polygon);

shapeComboBox->addItem(tr("Polyline"),PaintArea::Polyline);

shapeComboBox->addItem(tr("Points"),PaintArea::Points);

shapeComboBox->addItem(tr("Arc"),PaintArea::Arc);

shapeComboBox->addItem(tr("Rectangle"),PaintArea::Rectangle);

shapeComboBox->addItem(tr("Path"),PaintArea::Path);

shapeComboBox->addItem(tr("Text"),PaintArea::Text);

shapeComboBox->addItem(tr("Pixmap"),PaintArea::Pixmap);

connect(shapeComboBox,SIGNAL(activated(int)),this,SLOT(ShowShape(int)));

penColorLabel=new QLabel("画笔颜色："); //画笔颜色选择控件

penColorFrame=new QFrame;

penColorFrame->setFrameStyle(QFrame::Panel|QFrame::Sunken);//Panel - QFrame画一个平板使内容看起来凸起或者凹陷,

//QFrame::Sunken - 框架和内容看起来凹陷

penColorFrame->setAutoFillBackground(true);

penColorFrame->setPalette(QPalette(Qt::blue));//设置默认颜色为蓝色

penColorbtn=new QPushButton;

connect(penColorbtn,SIGNAL(clicked()),this,SLOT(ShowPenColor()));

penWidthLable=new QLabel("画笔宽度：");//画笔宽度选择控件

penWidthSpinBox=new QSpinBox;

penWidthSpinBox->setRange(0,20);//设置字宽滑块的取值范围

connect(penWidthSpinBox,SIGNAL(valueChanged(int)),this,SLOT(ShowPenWidth(int)));

penStyleLabel=new QLabel; //画笔风格选择下拉列表框

penStyleComboBox=new QComboBox;

penStyleComboBox->addItem(tr("SolidLine"),Qt::SolidLine);

penStyleComboBox->addItem(tr("DashLine"),Qt::DashLine);

penStyleComboBox->addItem(tr("DotLine"),Qt::DotLine);

penStyleComboBox->addItem(tr("DashDotLine"),Qt::DashDotLine);

penStyleComboBox->addItem(tr("DashDotDotLine"),Qt::DashDotDotLine);

penStyleComboBox->addItem(tr("CustomDashLine"),Qt::CustomDashLine);//这段如果报错，可以把addItem后面的参数置换为int类的数字

connect(penStyleComboBox,SIGNAL(activated(int)),this,SLOT(ShowPenStyle(int)));

penCapLabel=new QLabel; //画顶端风格选择下拉列表框

penCapComboBox=new QComboBox;

penCapComboBox->addItem(tr("SquareCap"),Qt::SquareCap);

penCapComboBox->addItem(tr("FlatCap"),Qt::FlatCap);

penCapComboBox->addItem(tr("RoundCap"),Qt::RoundCap);

connect(penCapComboBox,SIGNAL(activated(int)),this,SLOT(ShowPenCap(int)));

penJoinLabel=new QLabel;//画笔连接点风格选择下拉列表框

penJoinComboBox=new QComboBox;

penJoinComboBox->addItem(tr("BevelJoin"),Qt::BevelJoin);

penJoinComboBox->addItem(tr("MiterJoin"),Qt::MiterJoin);

penJoinComboBox->addItem(tr("RoundJoin"),Qt::RoundJoin);

fillLabel=new QLabel;//填充模式选择下拉列表框

fillComboBox=new QComboBox;

fillComboBox->addItem(tr("Odd Even"),Qt::OddEvenFill);

fillComboBox->addItem(tr("Winding"),Qt::WindingFill);

connect(fillComboBox,SIGNAL(activated(int)),this,SLOT(ShowFill()));

brushColorlabel=new QLabel;//画刷风格选择下拉列表框

brushColorFrame=new QFrame;

brushColorbtn=new QPushButton;

brushColorFrame->setFrameStyle(QFrame::Panel|QFrame::Sunken);

brushColorFrame->setAutoFillBackground(true);

brushColorFrame->setPalette(QPalette(Qt::green));

connect(brushColorbtn,SIGNAL(clicked()),this,SLOT(ShowBrushColor()));

brushStyleLabel=new QLabel; //画刷风格选择下拉列表框

brushStyleComboBox=new QComboBox;

brushStyleComboBox->addItem(tr("SolidPattern"),1);

brushStyleComboBox->addItem(tr("Dense1Pattern"),2);

brushStyleComboBox->addItem(tr("Dense2Pattern"),3);

brushStyleComboBox->addItem(tr("Dense3Pattern"),4);

brushStyleComboBox->addItem(tr("Dense4Pattern"),5);

brushStyleComboBox->addItem(tr("Dense5Pattern"),6);

brushStyleComboBox->addItem(tr("Dense6Pattern"),7);

brushStyleComboBox->addItem(tr("Dense7Pattern"),8);

brushStyleComboBox->addItem(tr("HorPattern"),9);

brushStyleComboBox->addItem(tr("VerPattern"),10);

brushStyleComboBox->addItem(tr("CrossPattern"),11);

brushStyleComboBox->addItem(tr("BDiagPattern"),12);

brushStyleComboBox->addItem(tr("FDiagPattern"),13);

brushStyleComboBox->addItem(tr("DiagCrossPattern"),14);

brushStyleComboBox->addItem(tr("LinearGradientPattern"),15);

brushStyleComboBox->addItem(tr("ConicalGradientPattern"),16);

brushStyleComboBox->addItem(tr("RadialGradientPattern"),17);

brushStyleComboBox->addItem(tr("TexturePattern"),24);

connect(brushStyleComboBox,SIGNAL(activated(int)),this,SLOT(ShowBrush(int)));

settingLayout=new QGridLayout;//画板布局

settingLayout->addWidget(shapelabel,0,0);

settingLayout->addWidget(shapeComboBox,0,1);

settingLayout->addWidget(penColorLabel,0,2);

settingLayout->addWidget(penColorFrame,0,3);

settingLayout->addWidget(penColorbtn,0,4);

settingLayout->addWidget(penWidthLable,1,0);

settingLayout->addWidget(penWidthSpinBox,1,1);

settingLayout->addWidget(penStyleLabel,1,2);

settingLayout->addWidget(penStyleComboBox,1,3);

settingLayout->addWidget(penCapLabel,2,0);

settingLayout->addWidget(penCapComboBox,2,1);

settingLayout->addWidget(penJoinLabel,2,2);

settingLayout->addWidget(penJoinComboBox,2,3);

settingLayout->addWidget(fillLabel,3,0);

settingLayout->addWidget(fillComboBox,3,1);

settingLayout->addWidget(brushColorlabel,3,2);

settingLayout->addWidget(brushColorFrame,3,3);

settingLayout->addWidget(brushColorbtn,3,4);

settingLayout->addWidget(brushStyleLabel,4,0);

settingLayout->addWidget(brushStyleComboBox,4,1);

QVBoxLayout *mainLayout=new QVBoxLayout(this);

mainLayout->addLayout(settingLayout);

mainLayout->addWidget(paintArea);

ShowShape(shapeComboBox->currentIndex());

}

//以下就是各种槽函数了

void MainWindow::ShowShape(int value)

{

PaintArea::Shape shape=PaintArea::Shape(shapeComboBox->itemData(value,Qt::UserRole).toInt());

paintArea->setShape(shape);

}

void MainWindow::ShowPenWidth(int value)//画笔宽度

{

QColor color=penColorFrame->palette().color(QPalette::Window);

Qt::PenStyle style=Qt::PenStyle(penStyleComboBox->itemData(penStyleComboBox->currentIndex(),Qt::UserRole).toInt());

Qt::PenCapStyle cap=Qt::PenCapStyle(penCapComboBox->itemData(penCapComboBox->currentIndex(),Qt::UserRole).toInt());

Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(penJoinComboBox->currentIndex(),Qt::UserRole).toInt());

paintArea->setPen(QPen(color,value,style,cap,join));

}

void MainWindow::ShowPenColor()//画笔颜色

{

QColor color=QColorDialog::getColor(Qt::blue);

penColorFrame->setPalette(QPalette(color));

int value=penWidthSpinBox->value();

Qt::PenStyle style=Qt::PenStyle(penStyleComboBox->itemData(penStyleComboBox->currentIndex(),Qt::UserRole).toInt());

Qt::PenCapStyle cap=Qt::PenCapStyle(penCapComboBox->itemData(penCapComboBox->currentIndex(),Qt::UserRole).toInt());

Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(penJoinComboBox->currentIndex(),Qt::UserRole).toInt());

paintArea->setPen(QPen(color,value,style,cap,join));

}

void MainWindow::ShowPenStyle(int styleValue)//画笔风格

{

QColor color=penColorFrame->palette().color(QPalette::Window);

int value=penWidthSpinBox->value();

Qt::PenStyle style=Qt::PenStyle(penStyleComboBox->itemData(styleValue,Qt::UserRole).toInt());

Qt::PenCapStyle cap=Qt::PenCapStyle(penCapComboBox->itemData(penCapComboBox->currentIndex(),Qt::UserRole).toInt());

Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(penJoinComboBox->currentIndex(),Qt::UserRole).toInt());

paintArea->setPen(QPen(color,value,style,cap,join));

}

void MainWindow::ShowPenCap(int capValue)//顶端风格

{

QColor color=penColorFrame->palette().color(QPalette::Window);

int value=penWidthSpinBox->value();

Qt::PenStyle style=Qt::PenStyle(penStyleComboBox->itemData(penStyleComboBox->currentIndex(),Qt::UserRole).toInt());

Qt::PenCapStyle cap=Qt::PenCapStyle(penCapComboBox->itemData(capValue,Qt::UserRole).toInt());

Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(penJoinComboBox->currentIndex(),Qt::UserRole).toInt());

paintArea->setPen(QPen(color,value,style,cap,join));

}

void MainWindow::ShowPenJoin(int joinValue)//画笔连接点风格

{

QColor color=penColorFrame->palette().color(QPalette::Window);

int value=penWidthSpinBox->value();

Qt::PenStyle style=Qt::PenStyle(penStyleComboBox->itemData(penStyleComboBox->currentIndex(),Qt::UserRole).toInt());

Qt::PenCapStyle cap=Qt::PenCapStyle(penCapComboBox->itemData(penCapComboBox->currentIndex(),Qt::UserRole).toInt());

Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(joinValue,Qt::UserRole).toInt());

paintArea->setPen(QPen(color,value,style,cap,join));

}

void MainWindow::ShowFill()//填充模式

{

Qt::FillRule fill=Qt::FillRule(fillComboBox->itemData(fillComboBox->currentIndex(),Qt::UserRole).toInt());

paintArea->setFillRule(fill);

}

void MainWindow::ShowBrushColor()//画刷颜色

{

QColor color=QColorDialog::getColor(Qt::blue);

brushColorFrame->setPalette(QPalette(color));

ShowBrush(brushStyleComboBox->currentIndex());

}

void MainWindow::ShowBrush(int value)//画刷风格

{

QColor color=brushColorFrame->palette().color(QPalette::Window);//画刷当前的颜色

Qt::BrushStyle style=Qt::BrushStyle(brushStyleComboBox->itemData(value,Qt::UserRole).toInt());//获取用户选择的画刷风格

if(style==Qt::LinearGradientPattern)//线性渐变

{

QLinearGradient linearGradient(0,0,400,400);//线性渐变的起止点位置

linearGradient.setColorAt(0.0,Qt::white);//渐变比和渐变颜色

linearGradient.setColorAt(0.2,color);

linearGradient.setColorAt(1.0,Qt::black);

paintArea->setBrush(linearGradient);

}

else if(style==Qt::RadialGradientPattern)//圆形渐变

{

QRadialGradient radialGradient(200,200,150,150,100);//中心点，半径，焦点

radialGradient.setColorAt(0.0,Qt::white);

radialGradient.setColorAt(0.2,color);

radialGradient.setColorAt(1.0,Qt::black);

paintArea->setBrush(radialGradient);

}

else if(style==Qt::ConicalGradientPattern)//锥形渐变

{

QConicalGradient conicalGradient(200,200,30);

conicalGradient.setColorAt(0.0,Qt::white);

conicalGradient.setColorAt(0.2,color);

conicalGradient.setColorAt(1.0,Qt::black);

paintArea->setBrush(conicalGradient);

}

else if(style==Qt::TexturePattern)

{

paintArea->setBrush(QBrush(QPixmap("2.png")));

}

else

{

paintArea->setBrush(QBrush(color,style));

}

}

MainWindow::~MainWindow()

{

}