效果图:

                                            

可以实现打开图片，在打开的图片上画图，可以保存图片，以及橡皮擦，画笔调大调粗换色功能。

代码:

XImage.h:

#ifndef __XIMAGE__H__
#define __XIMAGE__H__
#include "qwidget.h"
#include
#include
#include
#include
class XImage :
public QWidget
{
Q_OBJECT
public:
XImage(QWidget* parent=NULL);
~XImage();
void paintEvent(QPaintEvent* ev) override;
void mouseMoveEvent(QMouseEvent* ev) override;
void mouseReleaseEvent(QMouseEvent* ev) override;
public slots:
void Open();
void SetPen(int size,QColor col);
void SetErase(int size);
void Save();
private:
QImage src;
QPoint mpos;
QPen pen;
QImage img;
};
#endif

XImage.cpp:

#include "XImage.h"
#include
#include "ui_XPS.h"
#include
XImage::XImage(QWidget* parent):QWidget(parent){}

void XImage::Open()
{
QString filename = QFileDialog::getOpenFileName(this, QStringLiteral("打开图片"),
"",QStringLiteral("支持格式(*.png *.jpg)"));
if (filename.isNull())return;
if (!src.load(filename))return;
mpos = QPoint();
img = src.copy();
update();
}

void XImage::mouseMoveEvent(QMouseEvent* ev)
{
QPainter painter(&img);
painter.setPen(pen);
if (mpos.isNull()) mpos = ev->pos();
painter.drawLine(QLine(mpos,ev->pos()));
mpos = ev->pos();
update();
}

void XImage::SetPen(int size, QColor col)
{
pen.setWidth(size);
pen.setColor(col);
pen.setCapStyle(Qt::RoundCap);
pen.setJoinStyle(Qt::RoundJoin);
}

void XImage::mouseReleaseEvent(QMouseEvent* ev)
{
mpos = QPoint();
}

void XImage::paintEvent(QPaintEvent* ev)
{
QPainter painter(this);
painter.drawImage(0,0,img);
}

void XImage::SetErase(int size)
{
pen.setWidth(size);
pen.setBrush(src);
}

void XImage::Save()
{
QString filename = QFileDialog::getSaveFileName(this, QStringLiteral("打开图片"),
"", QStringLiteral("支持格式(*.png *.jpg)"));
if (filename.isNull())return;
if (!src.save(filename))return;
}

XImage::~XImage(){}

XSP.h:

#ifndef __XPS__H__
#define __XPS__H__

#include
#include "ui_XPS.h"
#include
class XPS : public QMainWindow
{
Q_OBJECT

public:
XPS(QWidget *parent = Q_NULLPTR);
public slots:
void SetPen();
void SetColor();
void SetErase();
void Save();
private:
Ui::XPSClass ui;
QColor col;
};
#endif

XSH.cpp:

#include "XPS.h"
#include
#include
XPS::XPS(QWidget *parent)
: QMainWindow(parent)
{
ui.setupUi(this);

connect(ui.openaction,SIGNAL(triggered()),ui.Image,SLOT(Open()));  
connect(ui.saveaction,SIGNAL(triggered()),ui.Image,SLOT(Save()));  
col = QColor(250,0,0);  
SetPen();

QButtonGroup\* group = new QButtonGroup(this);  
group->addButton(ui.penButton);  
group->addButton(ui.eraseButton);  
group->setExclusive(true);  

}

void XPS::SetPen()
{
ui.Image->SetPen(ui.pensize->value(),col);
ui.penButton->setChecked(true);
}

void XPS::SetColor()
{
col = QColorDialog::getColor(Qt::red, this);
QString sty = QString("background-color:rgba(%1,%2,%3,%4)")
.arg(col.red()).arg(col.green()).arg(col.blue()).arg(col.alpha());
ui.colorButton->setStyleSheet(sty);
SetPen();
}

void XPS::SetErase()
{
ui.Image->SetErase(ui.pensize->value());
ui.eraseButton->setChecked(true);
}

void XPS::Save()
{
ui.Image->Save();
ui.statusBar->showMessage(QStringLiteral("保存结束"), 5000);
}

main.cpp:

#include "XPS.h"
#include

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

ui界面部分:

测试环境：vs2015

可能出现的问题:

要包含该目录: