Python QGraphicsView中的PyQt位置已移动

我想用PyQt画一个棋盘。因此，我使用的是QtGui.qmain窗口。在qmain窗口中，我放置一个QtGui.QGridLayout，并在网格中添加一个QtGui.QGraphicsView作为中心小部件。QGraphicsView应将棋盘与64个棋盘以及作为QtGui.QGraphicsItem的棋子放在一起

我实现了这个，但现在我的定位有问题。似乎所有事物的位置都被一定量的移动或偏移，而且这个量似乎取决于QGraphicsItem的位置。瓷砖彼此不相邻，但它们之间的空间大小与瓷砖相同。当我拖放一个工件时（我已经覆盖了函数，因为我想对移动工件进行一些调整：即使鼠标离开棋盘，也要将它们放在棋盘上，即使在拐角处抓住工件，也要将其居中放置在光标下方），看起来工件移动的距离是原来的两倍

我制作了gui的屏幕截图来说明问题。在第二幅图中，我开始在左上角拖动并标记鼠标和工件的位置。光标和工件之间的距离随光标位置而变化。

这是源代码，请看一下并帮助我：

棋盘

import sys
from board import *

class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.initUI()


    def initUI(self):
        grid = QtGui.QGridLayout()
        grid.setColumnStretch(1,1)
        grid.setRowStretch(1,1)

        self.board = Board()
        grid.addWidget(self.board)

        mainWidget = QtGui.QWidget()
        mainWidget.setLayout(grid)
        self.setCentralWidget(mainWidget)

        self.setGeometry(200, 200, 800, 600)
        self.setWindowTitle('ChessBoard')
        self.show()

def main():
    app = QtGui.QApplication(sys.argv)
    m = MainWindow()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

board.py

from PyQt4 import QtGui, QtCore, QtSvg

SQHT = 60
WHITE, BLACK = COLORS = range(2)
LIGHT_COL = QtGui.QColor(220,225,235)
DARK_COL = QtGui.QColor(130,150,180)

class Board(QtGui.QGraphicsView):
    def __init__(self):
        super(Board, self).__init__(None)
        self.scene = QtGui.QGraphicsScene(self)
        self.setScene(self.scene)

        self.svg = '<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!-- Creator: CorelDRAW --> <svg    xmlns:dc="http://purl.org/dc/elements/1.1/"    xmlns:cc="http://web.resource.org/cc/"    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"    xmlns:svg="http://www.w3.org/2000/svg"    xmlns="http://www.w3.org/2000/svg"    xmlns:xlink="http://www.w3.org/1999/xlink"    xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"    xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"    xml:space="preserve"    width="50mm"    height="50mm"    shape-rendering="geometricPrecision"    text-rendering="geometricPrecision"    image-rendering="optimizeQuality"    fill-rule="evenodd"    clip-rule="evenodd"    viewBox="0 0 50 50"    id="svg2"    sodipodi:version="0.32"    inkscape:version="0.45"    sodipodi:docname="bn.svg"    sodipodi:docbase="/home/fkling/2/v0.1.2reduced/PieceThemes/Merida"    inkscape:output_extension="org.inkscape.output.svg.inkscape"    sodipodi:modified="true"><metadata    id="metadata13"><rdf:RDF><cc:Work        rdf:about=""><dc:format>image/svg+xml</dc:format><dc:type          rdf:resource="http://purl.org/dc/dcmitype/StillImage" /></cc:Work></rdf:RDF></metadata><defs    id="defs11"><linearGradient      inkscape:collect="always"      id="linearGradient2165"><stop        style="stop-color:#ffffff;stop-opacity:1;"        offset="0"        id="stop2167" /><stop        style="stop-color:#ffffff;stop-opacity:0;"        offset="1"        id="stop2169" /></linearGradient><linearGradient      inkscape:collect="always"      xlink:href="#linearGradient2165"      id="linearGradient2171"      x1="21.253071"      y1="37.59214"      x2="77.641281"      y2="37.469292"      gradientUnits="userSpaceOnUse" /></defs><sodipodi:namedview    inkscape:window-height="625"    inkscape:window-width="944"    inkscape:pageshadow="2"    inkscape:pageopacity="0.0"    guidetolerance="10.0"    gridtolerance="10.0"    objecttolerance="10.0"    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        self.pieces = []
        self.bRect = QtCore.QRectF(0,0,8*SQHT,8*SQHT)
        self.RANKS = 8
        self.FILES = 8

        self.setRenderHints(
            QtGui.QPainter.Antialiasing | QtGui.QPainter.TextAntialiasing | QtGui.QPainter.SmoothPixmapTransform)
        self.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.setDragMode(self.NoDrag)
        self.setInteractive(True)
        self.setTransformationAnchor(self.NoAnchor)
        self.scene.setItemIndexMethod(self.scene.NoIndex)
        self.setMouseTracking(True)
        self.setAlignment(QtCore.Qt.AlignTop | QtCore.Qt.AlignLeft)


        self.drawBoard()

        self._drawPiece(0, 0, WHITE, self.svg)

        for piece in self.pieces:
            piece.setMovable(True)


    def isLight(self, row, col):
        return (row % 2) == (col % 2)

    def drawBoard(self):
        for col in range(self.FILES):
            for row in range(self.RANKS):
                BTile(self, row, col, LIGHT_COL if self.isLight(row, col) else DARK_COL)

    def _drawPiece(self, row, col, color, piece):
        BPiece(self, row, col, color, piece)

    def getBRect(self):
        return self.bRect


class BoardElement(QtGui.QGraphicsItem):
    #TODO make abstract - how can I do this and keep inheritance from QGraphicsItem?
    def __init__(self, board, row, col):
        super(BoardElement, self).__init__(None)
        self.board = board
        x, y = self._rowCol2Pos(row, col)
        self.setPos(x,y)
        board.scene.addItem(self)

    def _rowCol2Pos(self, row, col):
        x = col * SQHT
        y = row * SQHT
        return x, y

    def _updatePos(self, x, y):
        self.setPos(x,y)
        self.board.scene.update()

    def _getXYOnBoardCentered(self, mx, my):
        rect = self.board.getBRect()
        dh = int(SQHT/2)
        left = mx - dh
        right = mx + dh
        top = my - dh
        bottom = my + dh
        if left < rect.left():
            x = rect.left()
        elif right > rect.right():
            x = rect.right() - SQHT
        else:
            x = mx - dh
        if top < rect.top():
            y = rect.top()
        elif bottom > rect.bottom():
            y = rect.bottom() - SQHT
        else:
            y = my - dh
        return x,y

    def _getXYOnBoard(self, mx, my):
        rect = self.board.getBRect()
        dh = int(SQHT/2)
        left = mx - dh
        right = mx + dh
        top = my - dh
        bottom = my + dh
        if left < rect.left():
            x = rect.left()
        elif right > rect.right():
            x = rect.right() - SQHT
        else:
            x = mx
        if top < rect.top():
            y = rect.top()
        elif bottom > rect.bottom():
            y = rect.bottom() - SQHT
        else:
            y = my
        return x,y


class BTile(BoardElement):
    def __init__(self, board, row, col, sqColor):
        super(BTile, self).__init__(board, row, col)
        self.sqColor = sqColor
        x, y = self._rowCol2Pos(row, col)
        self.bRect = QtCore.QRectF(x, y, SQHT, SQHT)

    def boundingRect(self):
        return self.bRect

    def paint(self, painter, option, widget):
        painter.setPen(self.sqColor)
        painter.setBrush(self.sqColor)
        painter.drawRect(self.bRect)


class BPiece(BoardElement):
    def __init__(self, board, row, col, color, piece):
        super(BPiece, self).__init__(board, row, col)
        self.color = color
        self.piece = piece
        self.svg = piece
        self.pixmap = QtSvg.QSvgRenderer(QtCore.QByteArray(self.svg))
        self._updateBRect()
        self.movable = False
        self.setAcceptHoverEvents(True)
        self.setZValue(2)
        x, y = self._rowCol2Pos(row, col)
        self.setPos(x,y)
        board.pieces.append(self)

    def _updateBRect(self):
        self.bRect = QtCore.QRectF(self.pos().x(), self.pos().y(), SQHT, SQHT)

    def boundingRect(self):
        self._updateBRect()
        return self.bRect

    def paint(self, painter, option, widget):
        self._updateBRect()
        self.pixmap.render(painter, self.bRect)

    def setMovable(self, movable):
        self.movable = movable
        self.setFlag(QtGui.QGraphicsItem.ItemIsMovable, self.movable)

    def hoverMoveEvent(self, event):
        if self.movable:
            self.setCursor(QtCore.Qt.OpenHandCursor)
            self.setFocus()

    def mousePressEvent(self, event):
        QtGui.QGraphicsItem.mousePressEvent(self, event)
        self.setCursor(QtCore.Qt.ClosedHandCursor)
        self.setZValue(3)

    def mouseMoveEvent(self, event):
        pos = event.scenePos()
        x,y = self._getXYOnBoardCentered(pos.x(), pos.y())
        self._updatePos(x,y)

    def mouseReleaseEvent(self, event):
        self.setZValue(2)
        p = event.pos()
        bx,by = self._getXYOnBoard(p.x(), p.y())
        x = (bx // SQHT) * SQHT
        y = (by // SQHT) * SQHT
        self._updatePos(x,y)

从PyQt4导入QtGui、QtCore、QtSvg
SQHT=60
白色、黑色=颜色=范围（2）
灯光颜色=QtGui.QColor（220225235）
暗颜色=QtGui.QColor（130150180）
课程板（QtGui.QGraphicsView）：
定义初始化（自）：
超级（板，自身）。\uuuuu初始\uuuuuuu（无）
self.scene=QtGui.qgraphicscene（self）
self.setScene（self.scene）
self.svg='image/svg+xml'
self.pieces=[]
self.bRect=QtCore.QRectF（0,0,8*SQHT，8*SQHT）
self.RANKS=8
self.FILES=8
self.setrenderints(
QtGui.QPainter.Antialiasing | QtGui.QPainter.TextAntialiasing | QtGui.QPainter.SmoothPixmapTransform）
self.setVerticalScrollBarPolicy（QtCore.Qt.ScrollBarAlwaysOff）
self.setHorizontalScrollBarPolicy（QtCore.Qt.ScrollBarAlwaysOff）
self.setDragMode（self.NoDrag）
self.setInteractive（True）
self.setTransformationAnchor（self.NoAnchor）
self.scene.setItemIndexMethod（self.scene.NoIndex）
self.setMouseTracking（True）
self.setAlignment（QtCore.Qt.AlignTop | QtCore.Qt.AlignLeft）
自动绘图板（）
self.\u绘图件（0，0，白色，self.svg）
对于一件一件的self.pieces：
件。可移动（真）
def isLight（自身、行、列）：
返回（行%2）==（列%2）
def牵引板（自）：
对于范围内的列（self.FILES）：
对于范围内的行（self.RANKS）：
b文件（自身、行、列、亮\u如果自身为亮（行、列）、否则为暗\u列）
def_抽件（自身、行、列、颜色、件）：
B件（自身、行、列、颜色、件）
def getBRect（自我）：
返回self.bRect
类BoardElement（QtGui.QGraphicsItem）：
#TODO make abstract-如何做到这一点并保留QGraphicsItem的继承？
定义初始值（自身、板、行、列）：
super（BoardElement，self）。\uuuuu init\uuuuuuu（无）
self.board=board
x、 y=自我。_行COL2POS（行，列）
自我设定位置（x，y）
board.scene.addItem（自我）
def_RowCol2PO（自身、行、列）：
x=col*SQHT
y=行*SQHT
返回x，y
def_updatePos（self，x，y）：
自我设定位置（x，y）
self.board.scene.update（）
def_getXYOnBoardCentered（self、mx、my）：
rect=self.board.getBRect（）
dh=int（SQHT/2）
左=mx-dh
右=mx+dh
top=my-dh
底部=我的+dh
如果左rect.right（）
x=rect.right（）-SQHT
其他：
x=mx-dh
如果toprect.bottom（）：
y=rect.bottom（）-SQHT
其他：
y=my-dh
返回x，y
def_getXYOnBoard（自我、mx、我的）：
rect=self.board.getBRect（）
dh=int（SQHT/2）
左=mx-dh
右=mx+dh
top=my-dh
底部=我的+dh
如果左rect.right（）
x=rect.right（）-SQHT
其他：
x=mx
如果toprect.bottom（）：
y=rect.bottom（）-SQHT
其他：
y=我的
返回x，y
B类文件（BoardElement）：
def _u初始（自身、板、行、列、sqColor）：
超级（b文件，自我）。\uuuu初始\uuuuuuuuuuuuuuuu（板，行，列）
self.sqColor=sqColor
x、 y=自我。_行COL2POS（行，列）
self.bRect=QtCore.QRectF（x，y，SQHT，SQHT）
def boundingRect（自）：
返回self.bRect
def绘制（自绘制、绘制、选项、小部件）：
painter.setPen（self.sqColor）
画家。挫折（self.sqColor）
画家drawRect（self.bRect）
B类零件（板件）：
定义初始（自身、板、行、列、颜色、块）：
超级（b块，自我）。\u初始（板，行，列）
self.color=颜色
self.piece=piece
self.svg=piece
self.pixmap=QtSvg.qsvgrender（QtCore.QByteArray（self.svg））
self.\u updateBRect（）
self.movable=False
self.setAcceptHoverEvents（True）
自我设置值（2）
x、 y=自我。_行COL2POS（行，列）
自我设定位置（x，y）
board.pieces.append（自我）
def_updateBRect（自）：
self.bRect=QtCore.QRectF（self.pos（）.x（），self.pos（）.y（），SQHT，SQHT）
def boundingRect（自）：
self.\u updateBRect（）
返回self.bRect
def绘制（自绘制、绘制、选项、小部件）：
self.\u updateBRect（）
self.pixmap.render（画家，self.bRect）
def设置可移动（自身，可移动）：
self.m