11

I'm trying to draw a rectangle on GUI created by PyQt5 by drag and drop. I managed to do that, but the rectangle is drawn when the mouse left key is released.

What I want to do is like this link:

  • When the mouse left button is pressed, start drawing the rectangle.
  • While dragging, adjust the rectangle shape with the mouse movement.
  • When the mouse left button is released, determine the rectangle shape.

How can I implement this? Thanks in advance.

Here's my code.

# -*- coding: utf-8 -*-

import sys
from PyQt5 import QtWidgets, QtCore
from PyQt5.QtGui import QPainter

class MyWidget(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        self.setGeometry(30,30,600,400)
        self.pos1 = [0,0]
        self.pos2 = [0,0]
        self.show()

    def paintEvent(self, event):
        width = self.pos2[0]-self.pos1[0]
        height = self.pos2[1] - self.pos1[1]     

        qp = QPainter()
        qp.begin(self)           
        qp.drawRect(self.pos1[0], self.pos1[1], width, height)        
        qp.end()

    def mousePressEvent(self, event):
        self.pos1[0], self.pos1[1] = event.pos().x(), event.pos().y()
        print("clicked")

    def mouseReleaseEvent(self, event):
        self.pos2[0], self.pos2[1] = event.pos().x(), event.pos().y()
        print("released")
        self.update()

if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    window = MyWidget()
    window.show()
    app.aboutToQuit.connect(app.deleteLater)
    sys.exit(app.exec_())
eyllanesc
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1 Answers1

14

You do not have to use the mouseReleaseEvent function, but the mouseMoveEvent function that is called each time the mouse is moved, and I have modified the code to make it simpler.

class MyWidget(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        self.setGeometry(30,30,600,400)
        self.begin = QtCore.QPoint()
        self.end = QtCore.QPoint()
        self.show()

    def paintEvent(self, event):
        qp = QtGui.QPainter(self)
        br = QtGui.QBrush(QtGui.QColor(100, 10, 10, 40))  
        qp.setBrush(br)   
        qp.drawRect(QtCore.QRect(self.begin, self.end))       

    def mousePressEvent(self, event):
        self.begin = event.pos()
        self.end = event.pos()
        self.update()

    def mouseMoveEvent(self, event):
        self.end = event.pos()
        self.update()

    def mouseReleaseEvent(self, event):
        self.begin = event.pos()
        self.end = event.pos()
        self.update()
eyllanesc
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  • Thank you for your answer and modifying my code. This is exactly what I've been looking for. – pothny3 Jun 10 '17 at 02:23
  • If I draw another rectangle previous rectangle vanishes. Why? – Mitesh Patel Nov 05 '19 at 12:37
  • Because PaintEvent blanks the canvas and draws precisely one line. If you want to keep the line and draw others you'll need to keep a list of lines that PaintEvent paints, adding to it with each drop. – holdenweb Feb 11 '23 at 10:47