How can i draw interactively a line in QGraphicScene in PyQt5 - python-3.x

Question

I'm trying to draw a line interactively but I can't figure out how to do it. Anyone can help me?
I'm using PyQt5. I create a QGraphicsScene, I override mouse press event but when I try to draw the draw the it draw nothing.
Finally, I have another question. How can I snap this line to the grid?
import math
import sys
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
class neGraphicScene(QGraphicsScene):
_colorBackGround: str
_colorLightLines: str
_colorDarkLines: str
_penLight: QPen
_penDark: QPen
gridSize: int = 20
gridSquares: int = 5
isLineDrawing = False
def __init__(self, parent=None):
QGraphicsScene.__init__(self, QRectF(-1000, -1000, 2000, 2000), parent)
self.setSceneColor()
self.begin, self.destination = QPoint(), QPoint()
def setSceneColor(self, _lightLines="#2f2f2f", _darkLines="#292929", _background="#393939"):
self._colorBackGround = _background
self._colorLightLines = _lightLines
self._colorDarkLines = _darkLines
self._penLight = QPen(QColor(self._colorLightLines))
self._penLight.setWidth(1)
self._penDark = QPen(QColor(self._colorDarkLines))
self._penDark.setWidth(2)
self.setBackgroundBrush(QColor(self._colorBackGround))
def setGraphicScene(self, width, height):
self.setSceneRect(-width // 2, -height // 2, width, height)
def mouseDoubleClickEvent(self, event):
QGraphicsScene.mouseMoveEvent(self, event)
def mousePressEvent(self, event):
self.isLineDrawing = True
if event.buttons() & Qt.LeftButton:
print('Point 1')
self.begin = event.pos()
self.destination = self.begin
self.update()
def mouseMoveEvent(self, event):
if event.buttons() & Qt.LeftButton:
print('Point 2')
self.destination = event.pos()
self.update()
def mouseReleaseEvent(self, event):
self.isLineDrawing = False
print('Point 3')
def drawBackground(self, painter, rect):
super(neGraphicScene, self).drawBackground(painter, rect)
# self.drawBackgroundGrid(painter, rect)
if self.isLineDrawing:
if not self.begin.isNull() and not self.destination.isNull():
line = QLineF(self.begin, self.destination)
painter.setPen(Qt.red)
painter.drawLine(line)
This is the QGraphicsView and the QWidgetStuff to made the minimal example working properly:
class neGraphicView(QGraphicsView):
def __init__(self, graphicScene, parent=None):
super().__init__(parent)
# self._dragPos = QPoint(0, 0)
self.sharedGraphicScene = graphicScene
self.setScene(self.sharedGraphicScene)
self._mousePressed = False
self._isPanning = False
self.initUI()
def initUI(self):
self.setRenderHints(
QPainter.Antialiasing | QPainter.HighQualityAntialiasing |
QPainter.TextAntialiasing | QPainter.SmoothPixmapTransform)
self.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
self.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
self.setDragMode(QGraphicsView.RubberBandDrag)
class NodeEditorWindow(QWidget):
mainLayout: QVBoxLayout
mainGraphicsScene: neGraphicScene
view: neGraphicView
def __init__(self, parent=None):
super(NodeEditorWindow, self).__init__(parent)
self.initUI()
def initUI(self):
self.setGeometry(200, 200, 800, 600)
self.mainLayout = QVBoxLayout()
self.mainLayout.setContentsMargins(0, 0, 0, 0)
self.setLayout(self.mainLayout)
self.mainGraphicsScene = neGraphicScene()
self.view = neGraphicView(self.mainGraphicsScene, self)
self.mainLayout.addWidget(self.view)
self.setWindowTitle("Node Editor")
self.show()
if __name__ == '__main__':
app = QApplication(sys.argv)
app.setStyle("Fusion")
win = NodeEditorWindow()
win.show()
sys.exit(app.exec())
This is the grid function:
def drawBackgroundGrid(self, _painter, _rect):
# here we create our grid
_left = int(math.floor(_rect.left()))
_right = int(math.ceil(_rect.right()))
_top = int(math.floor(_rect.top()))
_bottom = int(math.ceil(_rect.bottom()))
first_left = _left - (_left % self.gridSize)
first_top = _top - (_top % self.gridSize)
try:
# compute all lines to be drawn
lightLines, darkLines = [], []
for x in range(first_left, _right, self.gridSize):
if x % (self.gridSize * self.gridSquares) != 0:
lightLines.append(QLineF(x, _top, x, _bottom))
else:
darkLines.append(QLineF(x, _top, x, _bottom))
for y in range(first_top, _bottom, self.gridSize):
if y % (self.gridSize * self.gridSquares) != 0:
lightLines.append(QLineF(_left, y, _right, y))
else:
darkLines.append(QLineF(_left, y, _right, y))
# draw the lines
_painter.setPen(self._penLight)
_painter.drawLines(*lightLines)
_painter.setPen(self._penDark)
_painter.drawLines(*darkLines)
except Exception as e:
# print(e)
pass