如何通过在它们之间画线来连接两个 QGraphicsItem（使用鼠标）
How to connect two QGraphicsItem by drawing line between them (using mouse)
我在场景中有一些自定义物品。我想允许用户使用鼠标连接这两个项目。我检查了 问题中的答案，但没有规定让用户连接两点。 （另请注意，物品必须是可移动的）
这是我想要的演示：
我想要两个椭圆之间的连接如上图
我能知道怎么做吗？
为此，您可能必须通过继承 QGraphicsScene 并覆盖鼠标事件来实现自己的场景 class。
这是您可以改进的代码：
import sys
from PyQt5 import QtWidgets, QtCore, QtGui
class CustomItem(QtWidgets.QGraphicsItem):
def __init__(self, pointONLeft=False, *args, **kwargs):
super().__init__(*args, **kwargs)
self.ellipseOnLeft = pointONLeft
self.point = None
self.endPoint =None
self.isStart = None
self.line = None
self.setAcceptHoverEvents(True)
self.setFlag(self.ItemIsMovable)
self.setFlag(self.ItemSendsGeometryChanges)
def addLine(self, line, ispoint):
if not self.line:
self.line = line
self.isStart = ispoint
def itemChange(self, change, value):
if change == self.ItemPositionChange and self.scene():
self.moveLineToCenter(value)
return super(CustomItem, self).itemChange(change, value)
def moveLineToCenter(self, newPos): # moves line to center of the ellipse
if self.line:
if self.ellipseOnLeft:
xOffset = QtCore.QRectF(-5, 30, 10, 10).x() + 5
yOffset = QtCore.QRectF(-5, 30, 10, 10).y() + 5
else:
xOffset = QtCore.QRectF(95, 30, 10, 10).x() + 5
yOffset = QtCore.QRectF(95, 30, 10, 10).y() + 5
newCenterPos = QtCore.QPointF(newPos.x() + xOffset, newPos.y() + yOffset)
p1 = newCenterPos if self.isStart else self.line.line().p1()
p2 = self.line.line().p2() if self.isStart else newCenterPos
self.line.setLine(QtCore.QLineF(p1, p2))
def containsPoint(self, pos): # checks whether the mouse is inside the ellipse
x = self.mapToScene(QtCore.QRectF(-5, 30, 10, 10).adjusted(-0.5, 0.5, 0.5, 0.5)).containsPoint(pos, QtCore.Qt.OddEvenFill) or \
self.mapToScene(QtCore.QRectF(95, 30, 10, 10).adjusted(0.5, 0.5, 0.5, 0.5)).containsPoint(pos,
QtCore.Qt.OddEvenFill)
return x
def boundingRect(self):
return QtCore.QRectF(-5, 0, 110, 110)
def paint(self, painter, option, widget):
pen = QtGui.QPen(QtCore.Qt.red)
pen.setWidth(2)
painter.setPen(pen)
painter.setBrush(QtGui.QBrush(QtGui.QColor(31, 176, 224)))
painter.drawRoundedRect(QtCore.QRectF(0, 0, 100, 100), 4, 4)
painter.setBrush(QtGui.QBrush(QtGui.QColor(214, 13, 36)))
if self.ellipseOnLeft: # draws ellipse on left
painter.drawEllipse(QtCore.QRectF(-5, 30, 10, 10))
else: # draws ellipse on right
painter.drawEllipse(QtCore.QRectF(95, 30, 10, 10))
# ------------------------Scene Class ----------------------------------- #
class Scene(QtWidgets.QGraphicsScene):
def __init__(self):
super(Scene, self).__init__()
self.startPoint = None
self.endPoint = None
self.line = None
self.graphics_line = None
self.item1 = None
self.item2 = None
def mousePressEvent(self, event):
self.line = None
self.graphics_line = None
self.item1 = None
self.item2 = None
self.startPoint = None
self.endPoint = None
if self.itemAt(event.scenePos(), QtGui.QTransform()) and isinstance(self.itemAt(event.scenePos(),
QtGui.QTransform()), CustomItem):
self.item1 = self.itemAt(event.scenePos(), QtGui.QTransform())
self.checkPoint1(event.scenePos())
if self.startPoint:
self.line = QtCore.QLineF(self.startPoint, self.endPoint)
self.graphics_line = self.addLine(self.line)
self.update_path()
super(Scene, self).mousePressEvent(event)
def mouseMoveEvent(self, event):
if event.buttons() & QtCore.Qt.LeftButton and self.startPoint:
self.endPoint = event.scenePos()
self.update_path()
super(Scene, self).mouseMoveEvent(event)
def filterCollidingItems(self, items): # filters out all the colliding items and returns only instances of CustomItem
return [x for x in items if isinstance(x, CustomItem) and x != self.item1]
def mouseReleaseEvent(self, event):
if self.graphics_line:
self.checkPoint2(event.scenePos())
self.update_path()
if self.item2 and not self.item1.line and not self.item2.line:
self.item1.addLine(self.graphics_line, True)
self.item2.addLine(self.graphics_line, False)
else:
if self.graphics_line:
self.removeItem(self.graphics_line)
super(Scene, self).mouseReleaseEvent(event)
def checkPoint1(self, pos):
if self.item1.containsPoint(pos):
self.item1.setFlag(self.item1.ItemIsMovable, False)
self.startPoint = self.endPoint = pos
else:
self.item1.setFlag(self.item1.ItemIsMovable, True)
def checkPoint2(self, pos):
item_lst = self.filterCollidingItems(self.graphics_line.collidingItems())
contains = False
if not item_lst: # checks if there are any items in the list
return
for self.item2 in item_lst:
if self.item2.containsPoint(pos):
contains = True
self.endPoint = pos
break
if not contains:
self.item2 = None
def update_path(self):
if self.startPoint and self.endPoint:
self.line.setP2(self.endPoint)
self.graphics_line.setLine(self.line)
def main():
app = QtWidgets.QApplication(sys.argv)
scene = Scene()
item1 = CustomItem(True)
scene.addItem(item1)
item2 = CustomItem()
scene.addItem(item2)
view = QtWidgets.QGraphicsView(scene)
view.setViewportUpdateMode(view.FullViewportUpdate)
view.setMouseTracking(True)
view.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
上面代码的解释：
我通过继承QGraphicsItem 制作了自己的自定义Item。 pointONLeft=False是检查椭圆要画在哪一边。如果 pointONLeft=True，那么您在问题图像中看到的红色圆圈将绘制在左侧。
addLine、itemChange和moveLineToCenter方法取自。我建议您在继续之前仔细阅读该答案。
CustomItem里面的containsPoint方法检查鼠标是否在圆圈内。此方法将从自定义 Scene 访问，如果鼠标在圆圈内，它将通过使用 CustomiItem.setFlag(CustomItem.ItemIsMovable, False).
禁用移动
为了画线，我使用 PyQt 提供的 QLineF。如果你想知道如何通过拖动画一条直线，我建议你参考。虽然解释是针对 qpainterpath 的，但同样适用于此处。
collidingItems()是QGraphicsItem提供的方法。它 returns 所有碰撞的项目，包括线本身。因此，我创建了 filterCollidingItems 以仅过滤掉属于 CustomItem.
实例的项目
（另外，请注意 collidingItems() returns 以相反的顺序插入冲突项，即如果首先插入 CustomItem1，然后插入 CustomItem，那么如果该行发生碰撞，第二个项目将首先返回。因此，如果两个项目彼此重叠并且行发生碰撞，那么最后插入的项目将变为 item2 您可以通过更改 z value)
来更改此设置
读者可以在评论中提出建议或疑问。如果你有更好的答案，欢迎留言。
虽然解决方案 很好，但我想提供一个略有不同的概念来增加一些好处：
- 改进了对象结构和控制；
- 更可靠的碰撞检测；
- 通过使其更符合对象，绘画略有简化；
- 更好的可读性（主要是通过使用更少的变量和函数）；
- 更清晰的连接创建（线“捕捉”到控制点）；
- 可以在两侧都有控制点（也可以防止同一侧的连接）并删除已经存在的连接（通过再次“连接”相同的点）；
- 多个控制点之间的连接；
- 它不再是 ;-)
想法是控制点是 actual QGraphicsItem 对象 (QGraphicsEllipseItem) 和 CustomItem 的 children。
这不仅简化了绘画，还改进了对象碰撞检测和管理：不需要复杂的函数来绘制新线，并创建一个绘制在 around 其 pos 通过获取目标 scenePos() 确保我们已经知道该行的目标；这也使得检测鼠标光标是否确实在控制点内变得更加容易。
请注意，出于简化原因，我将一些属性设置为 class 成员。如果要为更高级或自定义的控件创建项目的子class，则应将这些参数创建为实例属性；在这种情况下，您可能更愿意继承自 QGraphicsRectItem：即使您仍然需要重写绘画以绘制圆角矩形，它也可以更轻松地设置其属性（钢笔、画笔和矩形）甚至更改它们在运行时运行，因此您只需要在 paint() 中访问这些属性，同时还确保在 Qt 需要时正确调用更新。
from PyQt5 import QtCore, QtGui, QtWidgets
class Connection(QtWidgets.QGraphicsLineItem):
def __init__(self, start, p2):
super().__init__()
self.start = start
self.end = None
self._line = QtCore.QLineF(start.scenePos(), p2)
self.setLine(self._line)
def controlPoints(self):
return self.start, self.end
def setP2(self, p2):
self._line.setP2(p2)
self.setLine(self._line)
def setStart(self, start):
self.start = start
self.updateLine()
def setEnd(self, end):
self.end = end
self.updateLine(end)
def updateLine(self, source):
if source == self.start:
self._line.setP1(source.scenePos())
else:
self._line.setP2(source.scenePos())
self.setLine(self._line)
class ControlPoint(QtWidgets.QGraphicsEllipseItem):
def __init__(self, parent, onLeft):
super().__init__(-5, -5, 10, 10, parent)
self.onLeft = onLeft
self.lines = []
# this flag **must** be set after creating self.lines!
self.setFlags(self.ItemSendsScenePositionChanges)
def addLine(self, lineItem):
for existing in self.lines:
if existing.controlPoints() == lineItem.controlPoints():
# another line with the same control points already exists
return False
self.lines.append(lineItem)
return True
def removeLine(self, lineItem):
for existing in self.lines:
if existing.controlPoints() == lineItem.controlPoints():
self.scene().removeItem(existing)
self.lines.remove(existing)
return True
return False
def itemChange(self, change, value):
for line in self.lines:
line.updateLine(self)
return super().itemChange(change, value)
class CustomItem(QtWidgets.QGraphicsItem):
pen = QtGui.QPen(QtCore.Qt.red, 2)
brush = QtGui.QBrush(QtGui.QColor(31, 176, 224))
controlBrush = QtGui.QBrush(QtGui.QColor(214, 13, 36))
rect = QtCore.QRectF(0, 0, 100, 100)
def __init__(self, left=False, right=False, *args, **kwargs):
super().__init__(*args, **kwargs)
self.setFlags(self.ItemIsMovable)
self.controls = []
for onLeft, create in enumerate((right, left)):
if create:
control = ControlPoint(self, onLeft)
self.controls.append(control)
control.setPen(self.pen)
control.setBrush(self.controlBrush)
if onLeft:
control.setX(100)
control.setY(35)
def boundingRect(self):
adjust = self.pen.width() / 2
return self.rect.adjusted(-adjust, -adjust, adjust, adjust)
def paint(self, painter, option, widget=None):
painter.save()
painter.setPen(self.pen)
painter.setBrush(self.brush)
painter.drawRoundedRect(self.rect, 4, 4)
painter.restore()
class Scene(QtWidgets.QGraphicsScene):
startItem = newConnection = None
def controlPointAt(self, pos):
mask = QtGui.QPainterPath()
mask.setFillRule(QtCore.Qt.WindingFill)
for item in self.items(pos):
if mask.contains(pos):
# ignore objects hidden by others
return
if isinstance(item, ControlPoint):
return item
if not isinstance(item, Connection):
mask.addPath(item.shape().translated(item.scenePos()))
def mousePressEvent(self, event):
if event.button() == QtCore.Qt.LeftButton:
item = self.controlPointAt(event.scenePos())
if item:
self.startItem = item
self.newConnection = Connection(item, event.scenePos())
self.addItem(self.newConnection)
return
super().mousePressEvent(event)
def mouseMoveEvent(self, event):
if self.newConnection:
item = self.controlPointAt(event.scenePos())
if (item and item != self.startItem and
self.startItem.onLeft != item.onLeft):
p2 = item.scenePos()
else:
p2 = event.scenePos()
self.newConnection.setP2(p2)
return
super().mouseMoveEvent(event)
def mouseReleaseEvent(self, event):
if self.newConnection:
item = self.controlPointAt(event.scenePos())
if item and item != self.startItem:
self.newConnection.setEnd(item)
if self.startItem.addLine(self.newConnection):
item.addLine(self.newConnection)
else:
# delete the connection if it exists; remove the following
# line if this feature is not required
self.startItem.removeLine(self.newConnection)
self.removeItem(self.newConnection)
else:
self.removeItem(self.newConnection)
self.startItem = self.newConnection = None
super().mouseReleaseEvent(event)
def main():
import sys
app = QtWidgets.QApplication(sys.argv)
scene = Scene()
scene.addItem(CustomItem(left=True))
scene.addItem(CustomItem(left=True))
scene.addItem(CustomItem(right=True))
scene.addItem(CustomItem(right=True))
view = QtWidgets.QGraphicsView(scene)
view.setRenderHints(QtGui.QPainter.Antialiasing)
view.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
一个小建议：我发现您有总是在 paint 方法中创建对象的习惯，即使这些值通常是“硬编码”的； Graphics View 框架最重要的方面之一是它的性能，python 显然会部分降低性能，因此如果您有在运行时保持不变的属性（矩形、钢笔、画笔），通常最好使它们更“静态”，至少作为实例属性，以尽可能简化绘画。
我在场景中有一些自定义物品。我想允许用户使用鼠标连接这两个项目。我检查了
这是我想要的演示：
我想要两个椭圆之间的连接如上图
我能知道怎么做吗？
为此，您可能必须通过继承 QGraphicsScene 并覆盖鼠标事件来实现自己的场景 class。
这是您可以改进的代码：
import sys
from PyQt5 import QtWidgets, QtCore, QtGui
class CustomItem(QtWidgets.QGraphicsItem):
def __init__(self, pointONLeft=False, *args, **kwargs):
super().__init__(*args, **kwargs)
self.ellipseOnLeft = pointONLeft
self.point = None
self.endPoint =None
self.isStart = None
self.line = None
self.setAcceptHoverEvents(True)
self.setFlag(self.ItemIsMovable)
self.setFlag(self.ItemSendsGeometryChanges)
def addLine(self, line, ispoint):
if not self.line:
self.line = line
self.isStart = ispoint
def itemChange(self, change, value):
if change == self.ItemPositionChange and self.scene():
self.moveLineToCenter(value)
return super(CustomItem, self).itemChange(change, value)
def moveLineToCenter(self, newPos): # moves line to center of the ellipse
if self.line:
if self.ellipseOnLeft:
xOffset = QtCore.QRectF(-5, 30, 10, 10).x() + 5
yOffset = QtCore.QRectF(-5, 30, 10, 10).y() + 5
else:
xOffset = QtCore.QRectF(95, 30, 10, 10).x() + 5
yOffset = QtCore.QRectF(95, 30, 10, 10).y() + 5
newCenterPos = QtCore.QPointF(newPos.x() + xOffset, newPos.y() + yOffset)
p1 = newCenterPos if self.isStart else self.line.line().p1()
p2 = self.line.line().p2() if self.isStart else newCenterPos
self.line.setLine(QtCore.QLineF(p1, p2))
def containsPoint(self, pos): # checks whether the mouse is inside the ellipse
x = self.mapToScene(QtCore.QRectF(-5, 30, 10, 10).adjusted(-0.5, 0.5, 0.5, 0.5)).containsPoint(pos, QtCore.Qt.OddEvenFill) or \
self.mapToScene(QtCore.QRectF(95, 30, 10, 10).adjusted(0.5, 0.5, 0.5, 0.5)).containsPoint(pos,
QtCore.Qt.OddEvenFill)
return x
def boundingRect(self):
return QtCore.QRectF(-5, 0, 110, 110)
def paint(self, painter, option, widget):
pen = QtGui.QPen(QtCore.Qt.red)
pen.setWidth(2)
painter.setPen(pen)
painter.setBrush(QtGui.QBrush(QtGui.QColor(31, 176, 224)))
painter.drawRoundedRect(QtCore.QRectF(0, 0, 100, 100), 4, 4)
painter.setBrush(QtGui.QBrush(QtGui.QColor(214, 13, 36)))
if self.ellipseOnLeft: # draws ellipse on left
painter.drawEllipse(QtCore.QRectF(-5, 30, 10, 10))
else: # draws ellipse on right
painter.drawEllipse(QtCore.QRectF(95, 30, 10, 10))
# ------------------------Scene Class ----------------------------------- #
class Scene(QtWidgets.QGraphicsScene):
def __init__(self):
super(Scene, self).__init__()
self.startPoint = None
self.endPoint = None
self.line = None
self.graphics_line = None
self.item1 = None
self.item2 = None
def mousePressEvent(self, event):
self.line = None
self.graphics_line = None
self.item1 = None
self.item2 = None
self.startPoint = None
self.endPoint = None
if self.itemAt(event.scenePos(), QtGui.QTransform()) and isinstance(self.itemAt(event.scenePos(),
QtGui.QTransform()), CustomItem):
self.item1 = self.itemAt(event.scenePos(), QtGui.QTransform())
self.checkPoint1(event.scenePos())
if self.startPoint:
self.line = QtCore.QLineF(self.startPoint, self.endPoint)
self.graphics_line = self.addLine(self.line)
self.update_path()
super(Scene, self).mousePressEvent(event)
def mouseMoveEvent(self, event):
if event.buttons() & QtCore.Qt.LeftButton and self.startPoint:
self.endPoint = event.scenePos()
self.update_path()
super(Scene, self).mouseMoveEvent(event)
def filterCollidingItems(self, items): # filters out all the colliding items and returns only instances of CustomItem
return [x for x in items if isinstance(x, CustomItem) and x != self.item1]
def mouseReleaseEvent(self, event):
if self.graphics_line:
self.checkPoint2(event.scenePos())
self.update_path()
if self.item2 and not self.item1.line and not self.item2.line:
self.item1.addLine(self.graphics_line, True)
self.item2.addLine(self.graphics_line, False)
else:
if self.graphics_line:
self.removeItem(self.graphics_line)
super(Scene, self).mouseReleaseEvent(event)
def checkPoint1(self, pos):
if self.item1.containsPoint(pos):
self.item1.setFlag(self.item1.ItemIsMovable, False)
self.startPoint = self.endPoint = pos
else:
self.item1.setFlag(self.item1.ItemIsMovable, True)
def checkPoint2(self, pos):
item_lst = self.filterCollidingItems(self.graphics_line.collidingItems())
contains = False
if not item_lst: # checks if there are any items in the list
return
for self.item2 in item_lst:
if self.item2.containsPoint(pos):
contains = True
self.endPoint = pos
break
if not contains:
self.item2 = None
def update_path(self):
if self.startPoint and self.endPoint:
self.line.setP2(self.endPoint)
self.graphics_line.setLine(self.line)
def main():
app = QtWidgets.QApplication(sys.argv)
scene = Scene()
item1 = CustomItem(True)
scene.addItem(item1)
item2 = CustomItem()
scene.addItem(item2)
view = QtWidgets.QGraphicsView(scene)
view.setViewportUpdateMode(view.FullViewportUpdate)
view.setMouseTracking(True)
view.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
上面代码的解释：
我通过继承QGraphicsItem 制作了自己的自定义Item。 pointONLeft=False是检查椭圆要画在哪一边。如果 pointONLeft=True，那么您在问题图像中看到的红色圆圈将绘制在左侧。
addLine、itemChange和moveLineToCenter方法取自
禁用移动CustomItem里面的containsPoint方法检查鼠标是否在圆圈内。此方法将从自定义Scene访问，如果鼠标在圆圈内，它将通过使用CustomiItem.setFlag(CustomItem.ItemIsMovable, False).为了画线，我使用 PyQt 提供的
QLineF。如果你想知道如何通过拖动画一条直线，我建议你参考qpainterpath的，但同样适用于此处。
实例的项目collidingItems()是QGraphicsItem提供的方法。它 returns 所有碰撞的项目，包括线本身。因此，我创建了filterCollidingItems以仅过滤掉属于CustomItem.
（另外，请注意 collidingItems() returns 以相反的顺序插入冲突项，即如果首先插入 CustomItem1，然后插入 CustomItem，那么如果该行发生碰撞，第二个项目将首先返回。因此，如果两个项目彼此重叠并且行发生碰撞，那么最后插入的项目将变为 item2 您可以通过更改 z value)
读者可以在评论中提出建议或疑问。如果你有更好的答案，欢迎留言。
虽然解决方案
- 改进了对象结构和控制；
- 更可靠的碰撞检测；
- 通过使其更符合对象，绘画略有简化；
- 更好的可读性（主要是通过使用更少的变量和函数）；
- 更清晰的连接创建（线“捕捉”到控制点）；
- 可以在两侧都有控制点（也可以防止同一侧的连接）并删除已经存在的连接（通过再次“连接”相同的点）；
- 多个控制点之间的连接；
- 它不再是 ;-)
想法是控制点是 actual QGraphicsItem 对象 (QGraphicsEllipseItem) 和 CustomItem 的 children。
这不仅简化了绘画，还改进了对象碰撞检测和管理：不需要复杂的函数来绘制新线，并创建一个绘制在 around 其 pos 通过获取目标 scenePos() 确保我们已经知道该行的目标；这也使得检测鼠标光标是否确实在控制点内变得更加容易。
请注意，出于简化原因，我将一些属性设置为 class 成员。如果要为更高级或自定义的控件创建项目的子class，则应将这些参数创建为实例属性；在这种情况下，您可能更愿意继承自 QGraphicsRectItem：即使您仍然需要重写绘画以绘制圆角矩形，它也可以更轻松地设置其属性（钢笔、画笔和矩形）甚至更改它们在运行时运行，因此您只需要在 paint() 中访问这些属性，同时还确保在 Qt 需要时正确调用更新。
from PyQt5 import QtCore, QtGui, QtWidgets
class Connection(QtWidgets.QGraphicsLineItem):
def __init__(self, start, p2):
super().__init__()
self.start = start
self.end = None
self._line = QtCore.QLineF(start.scenePos(), p2)
self.setLine(self._line)
def controlPoints(self):
return self.start, self.end
def setP2(self, p2):
self._line.setP2(p2)
self.setLine(self._line)
def setStart(self, start):
self.start = start
self.updateLine()
def setEnd(self, end):
self.end = end
self.updateLine(end)
def updateLine(self, source):
if source == self.start:
self._line.setP1(source.scenePos())
else:
self._line.setP2(source.scenePos())
self.setLine(self._line)
class ControlPoint(QtWidgets.QGraphicsEllipseItem):
def __init__(self, parent, onLeft):
super().__init__(-5, -5, 10, 10, parent)
self.onLeft = onLeft
self.lines = []
# this flag **must** be set after creating self.lines!
self.setFlags(self.ItemSendsScenePositionChanges)
def addLine(self, lineItem):
for existing in self.lines:
if existing.controlPoints() == lineItem.controlPoints():
# another line with the same control points already exists
return False
self.lines.append(lineItem)
return True
def removeLine(self, lineItem):
for existing in self.lines:
if existing.controlPoints() == lineItem.controlPoints():
self.scene().removeItem(existing)
self.lines.remove(existing)
return True
return False
def itemChange(self, change, value):
for line in self.lines:
line.updateLine(self)
return super().itemChange(change, value)
class CustomItem(QtWidgets.QGraphicsItem):
pen = QtGui.QPen(QtCore.Qt.red, 2)
brush = QtGui.QBrush(QtGui.QColor(31, 176, 224))
controlBrush = QtGui.QBrush(QtGui.QColor(214, 13, 36))
rect = QtCore.QRectF(0, 0, 100, 100)
def __init__(self, left=False, right=False, *args, **kwargs):
super().__init__(*args, **kwargs)
self.setFlags(self.ItemIsMovable)
self.controls = []
for onLeft, create in enumerate((right, left)):
if create:
control = ControlPoint(self, onLeft)
self.controls.append(control)
control.setPen(self.pen)
control.setBrush(self.controlBrush)
if onLeft:
control.setX(100)
control.setY(35)
def boundingRect(self):
adjust = self.pen.width() / 2
return self.rect.adjusted(-adjust, -adjust, adjust, adjust)
def paint(self, painter, option, widget=None):
painter.save()
painter.setPen(self.pen)
painter.setBrush(self.brush)
painter.drawRoundedRect(self.rect, 4, 4)
painter.restore()
class Scene(QtWidgets.QGraphicsScene):
startItem = newConnection = None
def controlPointAt(self, pos):
mask = QtGui.QPainterPath()
mask.setFillRule(QtCore.Qt.WindingFill)
for item in self.items(pos):
if mask.contains(pos):
# ignore objects hidden by others
return
if isinstance(item, ControlPoint):
return item
if not isinstance(item, Connection):
mask.addPath(item.shape().translated(item.scenePos()))
def mousePressEvent(self, event):
if event.button() == QtCore.Qt.LeftButton:
item = self.controlPointAt(event.scenePos())
if item:
self.startItem = item
self.newConnection = Connection(item, event.scenePos())
self.addItem(self.newConnection)
return
super().mousePressEvent(event)
def mouseMoveEvent(self, event):
if self.newConnection:
item = self.controlPointAt(event.scenePos())
if (item and item != self.startItem and
self.startItem.onLeft != item.onLeft):
p2 = item.scenePos()
else:
p2 = event.scenePos()
self.newConnection.setP2(p2)
return
super().mouseMoveEvent(event)
def mouseReleaseEvent(self, event):
if self.newConnection:
item = self.controlPointAt(event.scenePos())
if item and item != self.startItem:
self.newConnection.setEnd(item)
if self.startItem.addLine(self.newConnection):
item.addLine(self.newConnection)
else:
# delete the connection if it exists; remove the following
# line if this feature is not required
self.startItem.removeLine(self.newConnection)
self.removeItem(self.newConnection)
else:
self.removeItem(self.newConnection)
self.startItem = self.newConnection = None
super().mouseReleaseEvent(event)
def main():
import sys
app = QtWidgets.QApplication(sys.argv)
scene = Scene()
scene.addItem(CustomItem(left=True))
scene.addItem(CustomItem(left=True))
scene.addItem(CustomItem(right=True))
scene.addItem(CustomItem(right=True))
view = QtWidgets.QGraphicsView(scene)
view.setRenderHints(QtGui.QPainter.Antialiasing)
view.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
一个小建议：我发现您有总是在 paint 方法中创建对象的习惯，即使这些值通常是“硬编码”的； Graphics View 框架最重要的方面之一是它的性能，python 显然会部分降低性能，因此如果您有在运行时保持不变的属性（矩形、钢笔、画笔），通常最好使它们更“静态”，至少作为实例属性，以尽可能简化绘画。