simple screen capture demo based Qt

simple-qt-screen-capture.cpp

#include <QApplication>
#include <QPainter>
#include <QWidget>
#include <QKeyEvent>
#include <QRect>
#include <QPoint>
#include <QImage>
#include <QCursor>
#include <QClipboard>

enum Status {
  Explore = 0,
  Capturing,
  Captured
};

class DemoWidget : public QWidget {

public:
  explicit DemoWidget(QImage *img) {
    setMouseTracking(true);
    this->screenImg = img;
  }
  void paintEvent(QPaintEvent *event) override {
    QPainter painter(this);

    painter.drawImage(QRect(QPoint(0, 0), this->size()),
                      *this->screenImg);

    if (status == Explore) {
      return;
    }
    if (status == Capturing) {
      painter.setPen(QPen(Qt::red));
      int w = abs(currX - startX);
      int h = abs(currY - startY);
      int left = startX < currX ? startX : currX;
      int top = startY < currY ? startY : currY;
      painter.drawRect(left, top, w, h);
      return;
    }
    if (status == Captured) {
      painter.setPen(QPen(Qt::blue));
      painter.drawRect(capturedRect);
      return;
    }
  }
protected:
  void mousePressEvent(QMouseEvent *event) override {
    switch (status) {
      case Explore: {
        status = Capturing; // 进入Capturing
        startX = event->pos().x();
        startY = event->pos().y();
        currX = startX;
        currY = startY;
        break;
      }
      default:break;  // 其余状态都不关心
    }
    this->update();
  }
  void mouseReleaseEvent(QMouseEvent *event) override {
    switch (status) {
      case Capturing: {
        // 进入Captured态
        status = Captured;
        // 保存区域
        int w = abs(currX - startX);
        int h = abs(currY - startY);
        int left = startX < currX ? startX : currX;
        int top = startY < currY ? startY : currY;
        capturedRect = QRect(left, top, w, h);
        break;
      }
      default: break;
    }
    this->update();
  }
  void mouseMoveEvent(QMouseEvent *event) override {
    switch (status) {
      case Capturing: {
        auto pos = event->pos();
        currX = pos.x();
        currY = pos.y();
        break;
      }
      default:break;
    }
    this->update();
  }
  void keyPressEvent(QKeyEvent *event) override {
    if (event->key() == Qt::Key_Return && status == Captured) {
      // 1. 获取捕获的图像区域
      auto picRealSize = screenImg->size();
      auto winSize = this->size();
      int realRectX = capturedRect.x() * picRealSize.width() / winSize.width();
      int realRectY = capturedRect.y() * picRealSize.height() / winSize.height();
      int realRectW =
          capturedRect.width() * picRealSize.width() / winSize.width();
      int realRectH =
          capturedRect.height() * picRealSize.height() / winSize.height();
      QRect imgRect(realRectX, realRectY, realRectW, realRectH);
      // 2. 从保存的屏幕图像中获取指定区域的图像数据
      auto copiedImg = this->screenImg->copy(imgRect);
      // 3. 将图像数据写入到操作系统粘贴板
      QClipboard *clipboard = QGuiApplication::clipboard();
      clipboard->setImage(copiedImg);
      // 4. 回到Explore
      status = Explore;
      return;
    }
    if (event->key() == Qt::Key_Escape) {
      status = Explore;
    }
    this->update();
  }
private:
  int startX = 0, startY = 0;
  int currX = 0, currY = 0;
  QRect capturedRect;
  Status status = Explore;
  QImage *screenImg;
};

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

  QScreen *screen = QApplication::screenAt(QCursor().pos());
  QImage screenImg = screen->grabWindow(0).toImage();

  DemoWidget w(&screenImg);
  w.resize(400, 300);
  w.show();
  return QApplication::exec();
}