使用Qt5+CMake实现图片的区域选择（附源码）

近期研发涉及到了图片的区域选择，找来一些资料一直不能很满意，所以自己实现了一个。

实现步骤如下。源码可以点击ImageAOI获取。

Gitee clone: ImageAOI.

如下资料来自源码的README。

---

ImageAOI (XLabel): AOI Selection Based on Qt5

Dependency

Qt >= 5.0

Usage

• Double click to trigger the selector
• Mouse scrolling t zoom in/out
  
  

Reference (Appreciation)

ImageCropper

---

本工具的实现灵感来自ImageCropper。部分源码也做了参考，在此表示非常感。

实现功能如上面图片所示，方面，快捷。操作起来很有快感。

实现步骤

1. 创建一个基于QLabel的类XLabel。

注意需要引用#include <QLabel>。此段代码主要在xlabel.h文件中。

class XLabel : public QLabel
{
    Q_OBJECT  

public:
    explicit XLabel(QWidget* parent = Q_NULLPTR, Qt::WindowFlags f = Qt::WindowFlags());
    ~XLabel();

}

注意 ·Q_OBJECT·必须不能忘记，否则无法顺利生成。

2. 加入所必须的一些临时变量。

image是图片本身，需要载入。scale为缩放变量。selection_mode是用来决定是否显示区域的变量，双击图片区域激活或取消显示。

private:
	QImage image;
	float scale;

	// area selection
	bool selection_mode;
	QRectF croppingRect;

	bool mouse_pressed;
	QPoint start_mouse_pos;
	QRectF last_static_rect;
	CursorPosition cursor_pos;

3. 加入图片的鼠标事件和绘图事件函数。

函数主要继承自QWidget。只有捕获到事件，才能顺利操作。

protected:
	virtual void mousePressEvent(QMouseEvent* event);

	virtual void mouseMoveEvent(QMouseEvent* event);

	virtual void mouseReleaseEvent(QMouseEvent* event);

    virtual void wheelEvent(QWheelEvent* e);

	// double click
	virtual void mouseDoubleClickEvent(QMouseEvent *event);

	void paintEvent(QPaintEvent* _event) override;

4. 实现事件函数。

这里分为两部分，鼠标事件用于更新变量。绘图事件中变量的基础上，完成绘制和渲染。

• 鼠标事件如下

void XLabel::mousePressEvent(QMouseEvent* event)
{
	if (Qt::LeftButton == event->button())
	{
		mouse_pressed = true;
		start_mouse_pos = originPoint(event->pos());
		last_static_rect = croppingRect;
	}

	updateCursorIcon(originPoint(event->pos()));
}

void XLabel::mouseMoveEvent(QMouseEvent* event)
{
	auto origin_p = originPoint(event->pos());

	if (!mouse_pressed)
	{
		cursor_pos = cursorPosition(croppingRect, origin_p);

		updateCursorIcon(origin_p);
	}
	else if (cursor_pos != CursorPositionUndefined)
	{
		QPointF mouseDelta;
		mouseDelta.setX(origin_p.x() - start_mouse_pos.x());
		mouseDelta.setY(origin_p.y() - start_mouse_pos.y());

		int dx = WIDGET_MINIMUM_SIZE.width() / 2;
		int dy = WIDGET_MINIMUM_SIZE.height() / 2;
		//
		if (cursor_pos != CursorPositionMiddle)
		{
			QRectF newGeometry =
				calculateGeometry(
					last_static_rect,
					cursor_pos,
					mouseDelta);

			if (!newGeometry.isNull())
			{

				// boudary check
				if (newGeometry.x() < image.width() - dx && newGeometry.y () < image.height() - dy
					&& newGeometry.width() + newGeometry.x() > dx
					&& newGeometry.height() + newGeometry.y() > dy)
				{
					if (newGeometry.width() >= WIDGET_MINIMUM_SIZE.width() && newGeometry.height() >= WIDGET_MINIMUM_SIZE.height())
					{
						croppingRect = newGeometry;
					}
				}

			}
		}
		else
		{
			auto new_pt = last_static_rect.topLeft() + mouseDelta;
			if (new_pt.x() < image.width() - dx && new_pt.y() < image.height() - dy
				&& croppingRect.width() + new_pt.x() > dx
				&& croppingRect.height() + new_pt.y() > dy)
			{
				croppingRect.moveTo(last_static_rect.topLeft() + mouseDelta);
			}
		}

		update();

	}

}

void XLabel::mouseReleaseEvent(QMouseEvent* event)
{
	mouse_pressed = false;
	updateCursorIcon(originPoint(event->pos()));

	// single-click signal
    //emit clicked(int(0.5 + event->x()/scale), int(0.5+event->y()/scale));
	printf("[ %d, %d] \n", (int)event->x(), (int)event->y());
}

void XLabel::wheelEvent(QWheelEvent * e)
{
	int numDegrees = e->delta() / 8;
	int numSteps = numDegrees / 15;

	float k = numDegrees > 0 ? 1.09 : 0.90;

	k = k *scale;

	setScale(k );

}

void XLabel::mouseDoubleClickEvent(QMouseEvent * event)
{

	selection_mode = !selection_mode;
	update();
}

• 绘图事件如下，核心的绘制都在此处。

void XLabel::paintEvent(QPaintEvent * _event)
{
	QLabel::paintEvent(_event);

	if (image.isNull()) return;
	int width = image.width();

	//printf("Selection: %d\n", (int)selection_mode);

	QPixmap rawImage = QPixmap::fromImage(image);
	QPainter widgetPainter;
	widgetPainter.begin(&rawImage);

	// Image boundary
	QRectF rect(2, 2, image.width()-4, image.height()-4);
	QPen pen0(Qt::darkRed);
	if (selection_mode)
	{
		pen0 = QPen(Qt::darkGreen);
	}
	pen0.setWidth(4);
	widgetPainter.setPen(pen0);
	widgetPainter.drawRect(rect);

	if (selection_mode)
	{
		if (croppingRect.isNull()) {
			const int width = image.width() / 2  - 4;
			const int height = image.height() / 2 - 4;
			croppingRect.setSize(QSize(width, height));

			float x = (image.width() - croppingRect.width()) / 2-2;
			float y = (image.height() - croppingRect.height()) / 2-2;
			croppingRect.moveTo(x, y);
		}

		//qDebug() << "H: " << croppingRect.height();

		// 1. bg color
		widgetPainter.setBrush(QBrush(QColor(0, 0x6f, 0, 120)));
		QPen pen;
		pen.setColor(Qt::yellow);
		pen.setWidth(2);
		widgetPainter.setPen(pen);

		widgetPainter.drawRect(croppingRect);
		// pos
		widgetPainter.setPen(Qt::red);
		QFont font;
		font.setPointSize(croppingRect.width() >240 ? 16 : 10);
		widgetPainter.setFont(font);
		auto tl = croppingRect.topLeft();
		widgetPainter.drawText(QPoint(tl.x() + 6, tl.y() + 24), QString("(%1, %2, %3, %4)").arg(croppingRect.x()).arg(croppingRect.y())\
			.arg(croppingRect.width()).arg(croppingRect.height()));

		// 2. corner boxes
		{
			widgetPainter.setPen(Qt::green);
			widgetPainter.setBrush(QBrush(Qt::white));
			const int edgelen = 8;

			// Вспомогательные X координаты
			int leftXCoord = croppingRect.left() - edgelen/2+1;
			int centerXCoord = croppingRect.center().x() - edgelen / 2;
			int rightXCoord = croppingRect.right() - edgelen / 2+1;
			// Вспомогательные Y координаты
			int topYCoord = croppingRect.top() - edgelen / 2+1;
			int middleYCoord = croppingRect.center().y() - edgelen / 2;
			int bottomYCoord = croppingRect.bottom() - edgelen / 2+1;
			//
			const QSize pointSize(edgelen, edgelen);
			//
			QVector<QRect> points;
			points
				// левая сторона
				<< QRect(QPoint(leftXCoord, topYCoord), pointSize)
				<< QRect(QPoint(leftXCoord, middleYCoord), pointSize)
				<< QRect(QPoint(leftXCoord, bottomYCoord), pointSize)
				// центр
				<< QRect(QPoint(centerXCoord, topYCoord), pointSize)
				<< QRect(QPoint(centerXCoord, middleYCoord), pointSize)
				<< QRect(QPoint(centerXCoord, bottomYCoord), pointSize)
				// правая сторона
				<< QRect(QPoint(rightXCoord, topYCoord), pointSize)
				<< QRect(QPoint(rightXCoord, middleYCoord), pointSize)
				<< QRect(QPoint(rightXCoord, bottomYCoord), pointSize);
			//
			widgetPainter.drawRects(points);
		}

		// 3. center dash lines
		{
			QPen dashPen(Qt::white);
			dashPen.setStyle(Qt::DashLine);
			widgetPainter.setPen(dashPen); 

			widgetPainter.drawLine(
				QPoint(croppingRect.center().x(), croppingRect.top()),
				QPoint(croppingRect.center().x(), croppingRect.bottom()));
			// ... горизонтальная
			widgetPainter.drawLine(
				QPoint(croppingRect.left(), croppingRect.center().y()),
				QPoint(croppingRect.right(), croppingRect.center().y()));
		}

	}

	widgetPainter.end();
	this->setPixmap(rawImage.scaledToWidth(scale*width)); 

}

4. 实现主函数，完成一个界面，测试此类是否可行。

实现一个最简单的QLabel，完成显示，并加入XLabel显示到界面上，完成鼠标拖动测试。

#include <QApplication>
#include <QDialog>
#include <QVBoxLayout>
#include <QLabel>

#include "src/xlabel.h"

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	QDialog wgt;
	wgt.setMouseTracking(true);
	QVBoxLayout* layout = new QVBoxLayout(&wgt);
	wgt.setLayout(layout);

	auto xlabel = new XLabel(&wgt);
	layout->addWidget(xlabel);
	layout->addStretch();

	QImage img("../logo_s.png");
	xlabel->setImageMap(img);

	wgt.resize(640, 480);
	wgt.show();

	return a.exec();
}

完整代码可访问ImageAOI。

Gitee clone: ImageAOI.