如何繪製一條從鼠標到PyQt5中某一點的直線？

Question

這裏是我的代碼：

import sys 
from PyQt5.QtWidgets import (QApplication, QLabel, QWidget) 
from PyQt5.QtGui import QPainter, QColor, QPen 
from PyQt5.QtCore import Qt 

class MouseTracker(QWidget): 
    distance_from_center = 0 
    def __init__(self): 
     super().__init__() 
     self.initUI() 
     self.setMouseTracking(True) 

    def initUI(self): 
     self.setGeometry(200, 200, 1000, 500) 
     self.setWindowTitle('Mouse Tracker') 
     self.label = QLabel(self) 
     self.label.resize(500, 40) 
     self.show() 

    def mouseMoveEvent(self, event): 
     distance_from_center = round(((event.y() - 250)**2 + (event.x() - 500)**2)**0.5) 
     self.label.setText('Coordinates: (%d : %d)' % (event.x(), event.y()) + "Distance from center: " + str(distance_from_center))  

     q = QPainter() #Painting the line 
     q.begin(self) 
     q.drawLine(event.x(), event.y(), 250, 500) 
     q.end() 

    def drawPoints(self, qp, x, y): 
     qp.setPen(Qt.red) 
     qp.drawPoint(x, y) 

app = QApplication(sys.argv) 
ex = MouseTracker() 
sys.exit(app.exec_()) 

我試圖做的是用油漆從鼠標到窗口小部件的中間位置的簡單線這樣的：

 q = QPainter() #Painting the line 
     q.begin(self) 
     q.drawLine(event.x(), event.y(), 250, 500) 
     q.end() 

但是，當我運行它，沒有線是可見的。我需要做什麼？

Answer 1

您必須執行功能QPaintEvent，在此功能中您必須畫線，此外必須調用功能update()來更新圖紙。

import sys 
from PyQt5.QtWidgets import (QApplication, QLabel, QWidget) 
from PyQt5.QtGui import QPainter, QColor, QPen 
from PyQt5.QtCore import Qt 

class MouseTracker(QWidget): 
    distance_from_center = 0 
    def __init__(self): 
     super().__init__() 
     self.initUI() 
     self.setMouseTracking(True) 

    def initUI(self): 
     self.setGeometry(200, 200, 1000, 500) 
     self.setWindowTitle('Mouse Tracker') 
     self.label = QLabel(self) 
     self.label.resize(500, 40) 
     self.show() 
     self.pos = None 

    def mouseMoveEvent(self, event): 
     distance_from_center = round(((event.y() - 250)**2 + (event.x() - 500)**2)**0.5) 
     self.label.setText('Coordinates: (%d : %d)' % (event.x(), event.y()) + "Distance from center: " + str(distance_from_center))  
     self.pos = event.pos() 
     self.update() 

    def paintEvent(self, event): 
     if self.pos: 
      q = QPainter(self) 
      q.drawLine(self.pos.x(), self.pos.y(), 250, 500) 


app = QApplication(sys.argv) 
ex = MouseTracker() 
sys.exit(app.exec_()) 

輸出：

Answer 2

您只能使用一個QPainter的paintEvent方法內。所以解決的一個方法是在類中記錄x和y座標並更新根部件。然後調用paintEvent，您將看到該行。

例如

import sys 
from PyQt5.QtWidgets import QApplication, QLabel, QWidget 
from PyQt5.QtGui import QPainter 
from PyQt5.QtCore import Qt 

class MouseTracker(QWidget): 
    distance_from_center = 0 
    def __init__(self): 
     super().__init__() 
     self.initUI() 
     self.setMouseTracking(True) 
     self.x = -1 
     self.y = -1 

    def initUI(self): 
     self.setGeometry(200, 200, 1000, 500) 
     self.setWindowTitle('Mouse Tracker') 
     self.label = QLabel(self) 
     self.label.resize(500, 40) 
     self.show() 

    def paintEvent(self, e): 

     if not (self.x == -1 or self.y == -1): 
      q = QPainter() #Painting the line 

      q.begin(self) 

      q.drawLine(self.x, self.y, 250, 500) 
      q.end() 

    def mouseMoveEvent(self, event): 
     distance_from_center = round(((event.y() - 250)**2 + (event.x() - 500)**2)**0.5) 
     self.label.setText('Coordinates: (%d : %d)' % (event.x(), event.y()) + "Distance from center: " + str(distance_from_center)) 

     self.x = event.x() 
     self.y = event.y() 

     self.update() 

    def drawPoints(self, qp, x, y): 
     qp.setPen(Qt.red) 
     qp.drawPoint(x, y) 

app = QApplication(sys.argv) 
ex = MouseTracker() 
sys.exit(app.exec_()) 

我不知道如何self.x和self.y將初始設置。 -1和paintEvent中的支票感覺有點不好意思，但至少它是油漆。