Getting a Qt Widget to update a mouse event inside a Qt form made with Qt Designer

Question

I have made a custom QGraphicsView that I'm adding as a widget into an app form I made using Qt Designer. Everything appears to be working including the mouse clicks. The method that does the drawing gets called but I'm having trouble getting to actually repaint on the screen. I tried creating a copy of the paintEvent method and calling in the mouseEvent method. I also tried calling the paintEvent directly. I Can't seem to get it to repaint with the mouseEvent. Here is the code:

import sys
from PySide2 import QtCore, QtGui, QtWidgets
from PyQt5.QtWidgets import QFileDialog
from PySide2.QtUiTools import QUiLoader
from PySide2.QtWidgets import QApplication, QPushButton, QLineEdit, QAction, QSlider
from PySide2.QtWidgets import QListWidget, QTabWidget, QGraphicsView, QGraphicsScene
from PySide2.QtWidgets import QSpinBox, QWidget, QDialog, QVBoxLayout
from PySide2.QtGui import QPixmap, QImage, QMatrix, QPainter, QColor
from PySide2.QtGui import QMouseEvent, QCursor, QPaintEvent
from PySide2.QtCore import QFile, QObject, SIGNAL

import cv2
import numpy as np
import math

class Display_Pixels(QGraphicsView):

    def __init__(self, parent=None):
        QGraphicsView.__init__(self, parent=parent)
        #super().__init__()
        self.initUI()
        self.img = cv2.imread('roi.jpg')

    def initUI(self):      
        #self.setGeometry(100, 100, 450, 450)
        #self.setWindowTitle('By Pixel')
        #self.setMouseTracking(True)
        #self.show()
        res = 40 
        self.grid = np.array([ [-1] * res  for n in range(res)]) # list comprehension
        #print(self.grid.shape)


    def paintEvent(self, e):
        qp = QPainter()
        qp.begin(self.viewport())
        self.drawRectangles(qp)
        qp.end()

    def mousePaintEvent(self):
        qp = QPainter()
        qp.begin(self.viewport())
        self.drawRectangles(qp)
        qp.end()

    def drawRectangles(self, qp, w = 20):
        print("Drawing")
        mode = 0
        x,y = 0,0 # starting position
        lr = 20
        hr = 35
        col = QColor(0, 0, 0)
        col.setNamedColor('#d4d4d4')
        qp.setPen(col)
        #print(self.img.shape)

        for g_row, img_row in zip(self.grid, self.img):
            #print(img_row.shape)
            for g_col, img_col in zip(g_row, img_row):
                r, g, b = (img_col[0], img_col[1], img_col[2])
                #print(r,g,b)

                if g_col == 1:
                    if mode == 0:
                        r = int(math.log(r+1)*lr)
                        g = int(math.log(g+1)*hr)
                        b = int(math.log(b+1)*lr)
                    elif mode == 1:
                        if r+50 <= 220: r = r+50
                        if g+80 <= 255: g = g+80
                        if b+50 <= 220: b = b+50
                    else:
                        if r+70 <= 220: r = r+70
                        if g+140 <= 255: g = g+140
                        if b+70 <= 220: b = b+70

                    qp.setBrush(QColor(r, g, b))
                    qp.drawRect(x, y, w, w)
                else:
                    qp.setBrush(QColor(r, g, b))
                    qp.drawRect(x, y, w, w)

                #qp.setBrush(QColor(200, 0, 0))
                #qp.drawRect(x, y, w, w)
                x = x + w  # move right
            y = y + w # move down
            x = 0 # rest to left edge


    def mousePressEvent(self, QMouseEvent):
        w = 16.0

        #print("MOUSE:")
        #print('(', int(QMouseEvent.x()/w), ', ', int(QMouseEvent.y()/w), ')')
        #print (QMouseEvent.pos())
        x = float(QMouseEvent.x())
        y = float(QMouseEvent.y())
        self.grid[int(y/w)][int(x/w)] = -1 * self.grid[int(y/w)][int(x/w)]
        #print(img[int(y/w), int(x/w), :])
        self.paintEvent(QPaintEvent)
        #self.mousePaintEvent()
        self.update()
        self.repaint()      

if __name__ == '__main__':
    app = QApplication.instance()
    if app is None: 
        app = QApplication(sys.argv)
    px = Display_Pixels()
    px.show()
    sys.exit(app.exec_())

Answer 1

You should not call the paintEvent method directly, creating a method with a similar name will not magically be called. You have to call the update() method of the viewport() .

def mousePressEvent(self, event):
    w = 16.0
    x = int(event.x()*1.0/w)
    y = int(event.y()*1.0/w)
    s1, s2 = self.grid.shape
    # verify
    if 0 <= y < s1 and 0 <= x < s2:
        self.grid[x][y] = -self.grid[x][y]
        self.viewport().update()