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目录
Qt绘图基础
QPainter概述
QPainter是Qt中的核心绘图类，提供了高度抽象的2D绘图功能。它允许我们在各种设备上进行绘制，包括：
- 窗口部件(QWidget)
- 像素图(QPixmap)
- 图像(QImage)
基本工作流程
cpp
void Widget::paintEvent(QPaintEvent* event)
{
QPainter painter(this);
// 设置绘图属性
painter.setRenderHint(QPainter::Antialiasing);
// 进行绘制操作
painter.drawLine(0, 0, 100, 100);
}
绘图事件系统
paintEvent事件
paintEvent是Qt中处理绘制的核心事件，在以下情况会被触发：
- 窗口首次显示
- 窗口从最小化恢复
- 窗口被其他窗口遮挡后重新显示
- 调用update()或repaint()函数
重绘机制
cpp
class Widget : public QWidget
{
Q_OBJECT
public:
Widget(QWidget *parent = nullptr);
~Widget();
void paintEvent(QPaintEvent* event) override
{
QPainter painter(this);
// 绘制代码
}
void updateContent()
{
update(); // 请求重绘，异步
// repaint(); // 立即重绘，同步
}
private:
Ui::Widget *ui;
};文字绘制技术
基本文字绘制
cpp
class Widget : public QWidget
{
Q_OBJECT
public:
Widget(QWidget *parent = nullptr);
~Widget();
void paintEvent(QPaintEvent*) override
{
QPainter painter(this);
// 设置字体
QFont font("Arial", 20);
font.setBold(true);
painter.setFont(font);
// 设置颜色
painter.setPen(QColor(255, 0, 0));
// 绘制文本
painter.drawText(rect(), Qt::AlignCenter, "Hello Qt!");
}
private:
Ui::Widget *ui;
};
高级文字效果
cpp
void paintEvent(QPaintEvent*) override
{
QPainter painter(this);
// 文字阴影效果
QFont font("Times", 40);
painter.setFont(font);
// 绘制阴影
painter.setPen(QColor(0, 0, 0, 127));
painter.drawText(rect().adjusted(2, 2, 2, 2),
Qt::AlignCenter, "Shadow Text");
// 绘制主文本
painter.setPen(Qt::white);
painter.drawText(rect(), Qt::AlignCenter, "Shadow Text");
}
基本图形绘制
线条绘制
cpp
void paintEvent(QPaintEvent*) override
{
QPainter painter(this);
// 设置画笔
QPen pen(Qt::red, 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin);
painter.setPen(pen);
// 绘制各种线条
painter.drawLine(10, 10, 100, 100); // 直线
painter.drawArc(10, 120, 80, 80, 0, 180 * 16); // 圆弧
}
形状绘制
cpp
void paintEvent(QPaintEvent*) override
{
QPainter painter(this);
// 矩形
painter.fillRect(10, 10, 90, 60, Qt::blue);
// 圆形
painter.drawEllipse(120, 10, 90, 90);
// 多边形
QPolygon polygon;
polygon << QPoint(10,100) << QPoint(110,100)
<< QPoint(60,180);
painter.drawPolygon(polygon);
}
图片处理
基本图片绘制
cpp
void paintEvent(QPaintEvent*) override
{
QPainter painter(this);
QPixmap pixmap(":/images/example.png");
painter.drawPixmap(10, 10, pixmap);
}高级图片效果
cpp
void paintEvent(QPaintEvent*) override
{
QPainter painter(this);
QPixmap pixmap("C:\\Users\\Administrator\\Desktop\\图形界面-QT.png");
// 图片缩放
QPixmap scaled = pixmap.scaled(200, 200,
Qt::KeepAspectRatio,
Qt::SmoothTransformation);
// 添加圆形裁剪
QPainterPath path;
path.addEllipse(10, 10, 200, 200);
painter.setClipPath(path);
painter.drawPixmap(10, 10, scaled);
}
特效与动画
渐变效果
cpp
void paintEvent(QPaintEvent*) override
{
QPainter painter(this);
// 线性渐变
QLinearGradient gradient(0, 0, width(), height());
gradient.setColorAt(0, Qt::red);
gradient.setColorAt(1, Qt::blue);
painter.fillRect(rect(), gradient);
}
时钟绘制
cpp
class ClockWidget : public QWidget
{
Q_OBJECT
public:
explicit ClockWidget(QWidget *parent = nullptr) : QWidget(parent)
{
setFixedSize(400, 400);
QTimer *timer = new QTimer(this);
connect(timer, &QTimer::timeout, this, QOverload<>::of(&ClockWidget::update));
timer->start(1000);
}
protected:
void paintEvent(QPaintEvent *event) override
{
Q_UNUSED(event);
QPainter painter(this);
painter.setRenderHint(QPainter::Antialiasing);
painter.translate(width() / 2, height() / 2);
QTime currentTime = QTime::currentTime();
drawClockPlate(&painter);
drawHourHand(&painter, currentTime);
drawMinuteHand(&painter, currentTime);
drawSecondHand(&painter, currentTime);
drawCenterPoint(&painter);
}
private:
void drawClockPlate(QPainter *painter)
{
QPen pen(Qt::black);
pen.setWidth(2);
painter->setPen(pen);
painter->setBrush(Qt::white);
painter->drawEllipse(-180, -180, 360, 360);
for (int i = 0; i < 60; ++i) {
painter->save();
painter->rotate(6.0 * i);
if (i % 5 == 0) {
pen.setWidth(3);
painter->setPen(pen);
painter->drawLine(0, -160, 0, -145);
painter->save();
painter->rotate(-6.0 * i);
QFont font("Arial", 15, QFont::Bold);
painter->setFont(font);
int num = (i / 5 == 0) ? 12 : i / 5;
QRect textRect(-20, -190, 40, 40);
painter->drawText(textRect, Qt::AlignCenter, QString::number(num));
painter->restore();
} else {
pen.setWidth(1);
painter->setPen(pen);
painter->drawLine(0, -160, 0, -150);
}
painter->restore();
}
}
void drawHourHand(QPainter *painter, const QTime &time)
{
painter->save();
double angle = 30.0 * (time.hour() % 12) + 0.5 * time.minute();
painter->rotate(angle);
QPen pen(Qt::black, 4);
painter->setPen(pen);
painter->drawLine(0, 0, 0, -80);
painter->restore();
}
void drawMinuteHand(QPainter *painter, const QTime &time)
{
painter->save();
double angle = 6.0 * time.minute() + 0.1 * time.second();
painter->rotate(angle);
QPen pen(Qt::blue, 3);
painter->setPen(pen);
painter->drawLine(0, 0, 0, -120);
painter->restore();
}
void drawSecondHand(QPainter *painter, const QTime &time)
{
painter->save();
double angle = 6.0 * time.second();
painter->rotate(angle);
QPen pen(Qt::red, 2);
painter->setPen(pen);
painter->drawLine(0, 20, 0, -140);
painter->restore();
}
void drawCenterPoint(QPainter *painter)
{
painter->setPen(Qt::NoPen);
painter->setBrush(Qt::red);
painter->drawEllipse(-8, -8, 16, 16);
painter->setBrush(Qt::black);
painter->drawEllipse(-4, -4, 8, 8);
}
};