QT 2D绘图

缺乏、安全感 2022-03-26 07:41 334阅读 0赞

### 文章目录 ###

*  基础知识
 *  基本绘制和填充
 *  绘制文字
 *   *  代码
     *  效果
 *  绘制路径
 *   *  代码
     *  效果
 *  绘制图像
 *   *  四种常见的绘制图像的方法
     *  代码
     *  效果
     *  双缓冲绘图
     *   *  效果显示

# 基础知识 #

*  主要的三个类
    
     *  QPainter
        
         *  QWidget
         *  QPixmap
         *  QPicture
         *  QPrinter
         *  QOpenGLPaintDevice
     *  QPainterDevice
     *  QPainterEngine

**三者关系图**

QPainter

QPainEngine

QPaintDevice

# 基本绘制和填充 #

绘图系统由QPainter完成具体的绘制操作，QPainter可以绘制一切想要的图形，QPainter可以在继承自QPainterDevice类的任何对象上进行绘制操作

[Qt 之图形（QPainter 的基本绘图） 看这里][Qt _QPainter _]

# 绘制文字 #

可参考[Qt 之图形（绘制文本）][Qt]

## 代码 ##

QPainter painter(this);
    	QRectF rect(10.0, 10.0, 380.0, 280.0);
    	painter.setPen(Qt::red);
    	painter.drawRect(rect);
    	painter.setPen(Qt::blue);
    	painter.setPen(Qt::blue);
    	painter.drawText(rect, Qt::AlignHCenter, QStringLiteral("你好"));
    	painter.drawText(rect, Qt::AlignLeft, QStringLiteral("左对齐"));
    	painter.drawText(rect, Qt::AlignRight, QStringLiteral("右对齐"));
    	painter.drawText(rect, Qt::AlignVCenter, QStringLiteral("中间左侧对齐"));
    	painter.drawText(rect, Qt::AlignBottom, QStringLiteral("底部对齐"));
    	painter.drawText(rect, Qt::AlignCenter, QStringLiteral("中间对齐"));
    	painter.drawText(rect, Qt::AlignBottom | Qt::AlignRight, QStringLiteral("底部 | 右侧对齐"));

## 效果 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70]

# 绘制路径 #

详细看这里[Qt 之图形（QPainterPath）][Qt _QPainterPath]

## 代码 ##

QPainter painter(this);
    	painter.setRenderHint(QPainter::Antialiasing);
    	painter.setPen(Qt::red);
    	QPainterPath path;
    	path.moveTo(50, 250);
    	path.lineTo(50, 230);
    	path.cubicTo(QPointF(105, 40), QPointF(115, 80), QPointF(120, 60));
    	path.lineTo(130, 130);
    	path.addEllipse(QPoint(130, 130), 30, 30);
    	painter.setBrush(Qt::red);
    	painter.drawPath(path);
    	
    	path.translate(200, 0);
    	painter.setPen(Qt::darkBlue);
    	painter.drawPath(path);

## 效果 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70 1]

# 绘制图像 #

## 四种常见的绘制图像的方法 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70 2]

## 代码 ##

QPainter painter;
    	//绘制image
    	QImage image(100, 100, QImage::Format_ARGB32);
    	painter.begin(&image);
    	painter.setPen(QPen(Qt::green, 3));
    	painter.setBrush(Qt::yellow);
    	painter.drawRect(10, 10, 60, 60);
    	painter.drawText(10, 10, 60, 60, Qt::AlignCenter, QStringLiteral("QImage"));
    	painter.setBrush(QColor(0, 0, 0, 100));
    	painter.drawRect(50, 50, 40, 40);
    	painter.end();
    
    	//绘制pixmap
    	QPixmap pix(100, 100);
    	painter.begin(&pix);
    	painter.setPen(QPen(Qt::green, 3));
    	painter.setBrush(Qt::yellow);
    	painter.drawRect(10, 10, 60, 60);
    	painter.drawText(10, 10, 60, 60, Qt::AlignCenter, QStringLiteral("QPixmap"));
    	painter.setBrush(QColor(0, 0, 0, 100));
    	painter.drawRect(50, 50, 40, 40);
    	painter.end();
    
    	//绘制bitmap
    	QBitmap bit(100, 100);
    	painter.begin(&bit);
    	painter.setPen(QPen(Qt::green, 3));
    	painter.setBrush(Qt::yellow);
    	painter.drawRect(10, 10, 60, 60);
    	painter.drawText(10, 10, 60, 60, Qt::AlignCenter, QStringLiteral("QBitmap"));
    	painter.setBrush(QColor(0, 0, 0, 100));
    	painter.drawRect(50, 50, 40, 40);
    	painter.end();
    
    	//绘制picture
    	QPicture picture;
    	painter.begin(&picture);
    	painter.setPen(QPen(Qt::green, 3));
    	painter.setBrush(Qt::yellow);
    	painter.drawRect(10, 10, 60, 60);
    	painter.drawText(10, 10, 60, 60, Qt::AlignCenter, QStringLiteral("QPicture"));
    	painter.setBrush(QColor(0, 0, 0, 100));
    	painter.drawRect(50, 50, 40, 40);
    	painter.end();
    
    
    	painter.begin(this);
    	painter.drawImage(50, 20, image);
    	painter.drawPixmap(200, 20, pix);
    	painter.drawPixmap(50, 170, bit);
    	painter.drawPicture(200, 170, picture);

## 效果 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70 4]

## 双缓冲绘图 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70 5]\#\#\# 代码  
在头文件加入

private:
    	QPixmap pix;
    	QPixmap tempPix;
    	QPoint startPoint;
    	QPoint endPoint;
    
    	//是否正在绘图的标志
    	bool isDrawing;
    
    protected:
    	void mousePressEvent(QMouseEvent *event);
    	void mouseMoveEvent(QMouseEvent *event);
    	void mouseReleaseEvent(QMouseEvent *event);
    	void paintEvent(QPaintEvent *event);

在cpp文件加入

void ch10_4_1::mousePressEvent(QMouseEvent *event)
    {
    	if (event->button() == Qt::LeftButton)
    	{
    		startPoint = event->pos();
    		isDrawing = true;
    	}
    }
    
    void ch10_4_1::mouseMoveEvent(QMouseEvent *event)
    {
    	if (event->button() & Qt::LeftButton){
    		endPoint = event->pos();
    		tempPix = pix;
    		update();
    	}
    }
    
    void ch10_4_1::mouseReleaseEvent(QMouseEvent *event)
    {
    	if (event->button() == Qt::LeftButton){
    		endPoint = event->pos();
    		isDrawing = false;
    		update();
    	}
    }
    
    void ch10_4_1::paintEvent(QPaintEvent *event)
    {
    	int x = startPoint.x();
    	int y = startPoint.y();
    	int width = endPoint.x() - x;
    	int height = endPoint.y() - y;
    	QPainter painter;
    	painter.begin(&tempPix);
    	painter.drawRect(x, y, width, height);
    	painter.end();
    	painter.begin(this);
    	painter.drawPixmap(0, 0, tempPix);
    	if (! isDrawing)
    	{
    		pix = tempPix;
    	}
    }

其中的ch10\_4\_1为类名

**这里先在临时缓冲区进行绘图，然后将其绘制到界面上，最后判断是否已经完成绘图，如果是，则将临时缓冲区内容复制到缓冲区中，这样就完成了整个矩形的绘制**

如果想实现Windows桌面上的拖动鼠标出现的橡皮筋选择框，可以使用QRubberBand类来实现橡皮筋线。

### 效果显示 ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70 6]

[Qt _QPainter _]: https://blog.csdn.net/liang19890820/article/details/51154216
[Qt]: https://blog.csdn.net/liang19890820/article/details/51227894
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[Qt _QPainterPath]: https://blog.csdn.net/liang19890820/article/details/51393152
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70 1]: /images/20220326/b349beddd8d64e10947bfb91aa9aa04f.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N0eTk0NQ_size_16_color_FFFFFF_t_70 6]: /images/20220326/1384a8a81e394b41957deab11f8d2cea.png