如何将网格坐标转换回（x，y）？

Question

I am creating a game in PyQt5 where the user can click inside a grid to form squares. If the user chooses four grid spaces that form a square, the corners are connected with lines. My code currently looks like this:

import sys
from PyQt5.QtGui import QPainter, QColo, QPen, QBrush
from PyQt5.QtCore import Qt, QRect, QPoint
from PyQt5.QtWidgets import QWidget, QApplication

CELL_COUNT = 8
CELL_SIZE = 50
GRID_ORIGINX = 150
GRID_ORIGINY = 150
W_WIDTH = 700
W_HEIGHT = 700

class TribeSquares(QWidget):

def __init__(self):
    super().__init__()
    self.setGeometry(300, 300, W_WIDTH, W_HEIGHT)
    a = ''
    self.__board = [[a,a,a,a,a,a,a,a],[a,a,a,a,a,a,a,a],[a,a,a,a,a,a,a,a],[a,a,a,a,a,a,a,a],[a,a,a,a,a,a,a,a],[a,a,a,a,a,a,a,a],[a,a,a,a,a,a,a,a],[a,a,a,a,a,a,a,a]]
    self.__row = None
    self.__col = None
    self.__clicked0 = []
    self.show()

First, I converted (x,y) coordinates to grid coordinates.

def mousePressEvent(self, event):
    self.__x = event.x()
    self.__y = event.y()
    self.__row = (event.y() - GRID_ORIGINY) // CELL_SIZE
    self.__col = (event.x() - GRID_ORIGINX) // CELL_SIZE
    row = self.__row
    col = self.__col
    self.update()

For another method, I want to convert (row,col) back to (x,y). I tried reversing the process and doing it like this:

def cell2coord(self, row, col):
    return ((row * CELL_SIZE) + GRID_ORIGINX, (col * CELL_SIZE) + GRID_ORIGINY)

Next, in the paintEvent, I try to call the method I created.

def paintEvent(self, event):
    qp = QPainter()
    qp.begin(self)
    for r in range(CELL_COUNT):
        for c in range(CELL_COUNT):
            qp.setPen(QPen(Qt.black, 1))
            qp.drawRect(CELL_SIZE * c + GRID_ORIGINX, CELL_SIZE * r + GRID_ORIGINY, CELL_SIZE, CELL_SIZE)
            if (r, c) in self.__clicked0:
                qp.setPen(QPen(QColor(40, 85, 66), 1))
                qp.setBrush(QColor(40, 85, 66))
                qp.drawRect(CELL_SIZE * c + GRID_ORIGINX + 7.5, CELL_SIZE * r + GRID_ORIGINY + 7.5, 35, 35)
                qp.setBrush(QColor(237, 237, 237))
            elif (r, c) in self.__clicked1:
                qp.setPen(QPen(QColor(231, 181, 71), 1))
                qp.setBrush(QColor(231, 181, 71))
                qp.drawRect(CELL_SIZE * c + GRID_ORIGINX + 7.5, CELL_SIZE * r + GRID_ORIGINY + 7.5, 35, 35)
                qp.setBrush(QColor(237, 237, 237))
    for (r, c) in self.__clicked0:
        x,y = self.cell2coord(r,c)
        x2,y2 = self.cell2coord(self.__row, self.__col)
        if r == self.__row or c == self.__col:
            qp.setPen(QPen(QColor(40, 85, 66), 5))
            qp.drawLine(x, y, x2, y2)
    for (r, c) in self.__clicked1:
        if r == self.__row or c == self.__col:
            qp.setPen(QPen(QColor(231, 181, 71), 5))
            qp.drawLine(x, y, x2, y2)
    qp.end()

if __name__ == '__main__':
  app = QApplication(sys.argv)
  ex = TribeSquares()
  sys.exit(app.exec_())

But it didn't work. The lines are not showing up in the right spot and connecting the squares created by user clicks in the grid. What can I do?

Answer 1

Just as you have built the rectangles to paint in the paintEvent method, you could do it to get the QRect , and then use its center() method, and then get its coordinates.

def cell2coord(self, row, col):
    center_pos = QRect(CELL_SIZE * c + GRID_ORIGINX, CELL_SIZE * r + GRID_ORIGINY, CELL_SIZE, CELL_SIZE).center()
    return center_pos.x(), center_pos.y()