在 QWidget python GUI 上画一个圆圈

Question

我想画一个圆而不是点这是 class ，它在小部件的任何位置的按下事件上绘制红点我想画一个圆圈（空心圆圈）作为轮廓而不是隐藏部分图片的实心圆圈

     import sys
    from PyQt5.QtWidgets import *
    from PyQt5.QtCore import *
    from PyQt5.QtGui import *

        class Canvas(QWidget):

            def __init__(self, photo, *args, **kwargs):
                super().__init__(*

args, **kwargs)
            self.image = QImage(photo)
            self.setFixedSize(self.image.width(), self.image.height())

        def mousePressEvent(self, event):
            if event.button() == Qt.LeftButton:
                qp = QPainter(self.image)
                qp.setRenderHint(QPainter.Antialiasing)
                qp.setPen(QPen(Qt.red, 5))
                qp.setBrush(Qt.red)
                qp.drawPoint(event.pos())
                self.update()

        def paintEvent(self, event):
            qp = QPainter(self)
            rect = event.rect()
            qp.drawImage(rect, self.image, rect)


    class MainWindow(QMainWindow):

        def __init__(self):
            super().__init__()
            w = QWidget()
            self.setCentralWidget(w)
            grid = QGridLayout(w)
            grid.addWidget(Canvas('photo.jpeg'))

    if __name__ == '__main__':
        app = QApplication(sys.argv)
        gui = MainWindow()
        gui.show()
        sys.exit(app.exec_())

Answer 1

我相信这就是你想要做的。

在这种情况下，您需要利用哪个绘图设备传递给 QPainter。在 mousePressEvent 和 mouseMoveEvent 期间使用 QPainter(self) 因此任何绘制的内容只会持续到下一次更新。然后在mouseReleaseEvent满意圆的大小后，可以在QImage上用QPainter(self.image)画画永久画圆

import sys
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *

class Canvas(QWidget):

    def __init__(self, photo, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.image = QImage(photo)
        self.setFixedSize(self.image.width(), self.image.height())
        self.pressed = self.moving = False
        self.revisions = []

    def mousePressEvent(self, event):
        if event.button() == Qt.LeftButton:
            self.pressed = True
            self.center = event.pos()
            self.update()

    def mouseMoveEvent(self, event):
        if event.buttons() & Qt.LeftButton:
            self.moving = True
            r = (event.pos().x() - self.center.x()) ** 2 + (event.pos().y() - self.center.y()) ** 2
            self.radius = r ** 0.5
            self.update()

    def mouseReleaseEvent(self, event):
        if event.button() == Qt.LeftButton:
            self.revisions.append(self.image.copy())
            qp = QPainter(self.image)
            self.draw_circle(qp) if self.moving else self.draw_point(qp)
            self.pressed = self.moving = False
            self.update()

    def paintEvent(self, event):
        qp = QPainter(self)
        rect = event.rect()
        qp.drawImage(rect, self.image, rect)
        if self.moving:
            self.draw_circle(qp)
        elif self.pressed:
            self.draw_point(qp)

    def draw_point(self, qp):
        qp.setPen(QPen(Qt.black, 5))
        qp.drawPoint(self.center)

    def draw_circle(self, qp):
        qp.setRenderHint(QPainter.Antialiasing)
        qp.setPen(QPen(Qt.black, 3, Qt.DashLine))
        qp.drawEllipse(self.center, self.radius, self.radius)

    def undo(self):
        if self.revisions:
            self.image = self.revisions.pop()
            self.update()

    def reset(self):
        if self.revisions:
            self.image = self.revisions[0]
            self.revisions.clear()
            self.update()


class MainWindow(QMainWindow):

    def __init__(self):
        super().__init__()
        w = QWidget()
        self.setCentralWidget(w)
        canvas = Canvas('photo.png')
        grid = QGridLayout(w)
        grid.addWidget(canvas)
        QShortcut(QKeySequence('Ctrl+Z'), self, canvas.undo)
        QShortcut(QKeySequence('Ctrl+R'), self, canvas.reset)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    gui = MainWindow()
    gui.show()
    sys.exit(app.exec_())

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