QPainters 同步背后的机制

Question

上下文

我有一个自定义小部件，它应该制作点移动的动画以制作一种加载小部件。为了实现这个目标，我开始使用 QPainter 和 QVariantAnimation 对象，它们似乎是完成这项工作的不错工具。问题是我认为我在绘图时初始化的QPainters相互冲突。

技术

为了实现这一点，我初始化了多个 QVariantAnimation，它发出信号 .valueChanged() 我连接到一个函数 update()，它应该启动 painEvent()，如文档中所写

A paint event is a request to repaint all or part of a widget. It can happen for one of the following reasons:repaint() or update() was invoked, the widget was obscured and has now been uncovered, or many other reasons.

由于我在不同的时间启动不同的动画，我想 update() 被调用了很多次，从而干扰了另一个已经在工作的 QPainter。但是，正如我在文档中所读，

When update() is called several times or the window system sends several paint events, Qt merges these events into one event with a larger region.

但它没有指定 QPainter 具有相同区域的任何 ID，这就是我认为它崩溃的原因。它记录如下消息：

QBackingStore::endPaint() called with active painter on backingstore paint device

最小工作示例

from PyQt5.QtWidgets import QApplication, QWidget, QVBoxLayout, QDialog, QPushButton
from PyQt5.QtCore import Qt, pyqtSlot, QVariantAnimation, QVariant, QTimer
from PyQt5.QtGui import QColor, QPainter, QBrush
import time

class Dialog(QDialog):
    def __init__(self, *args, **kwargs):
        QDialog.__init__(self, *args, **kwargs)
        self.resize(500, 500)
        self.setLayout(QVBoxLayout())
        self.button = QPushButton()
        self.layout().addWidget(self.button)
        self.paintWidget = PaintWidget()
        self.layout().addWidget(self.paintWidget)
        self.button.clicked.connect(self.paintWidget.startPainting)
        self.button.clicked.connect(self.reverse)

    def reverse(self):
        if self.paintWidget.isMoving:
            self.paintWidget.stopPainting()

class PaintWidget(QWidget):
    def __init__(self):
        super(PaintWidget, self).__init__()
        self.dotRadius = 10
        self.dotColor = QColor(255, 100, 100)
        self.numberOfDots = 3

        self.isMoving = False

        self.animation = []
        self.createAnimation()

        self.dotPosition = [[0, 0], [0, 0], [0, 0]]

    def startPainting(self):
        for i in range(self.numberOfDots):
            self.animation[i].start()
            time.sleep(200)
        self.isActive = True

    def createAnimation(self):
        for i in range(self.numberOfDots):
            self.animation.append(QVariantAnimation(self, startValue=0, endValue=500, duration=3000))
            self.animation[i].valueChanged.connect(self.updatePosition)

    @pyqtSlot(QVariant)
    def updatePosition(self, position):
        self.dotPosition = [position, 0]
        self.update()

    def paintEvent(self, event):
        painter = QPainter(self)
        painter.fillRect(self.rect(), Qt.transparent)
        painter.setRenderHint(QPainter.Antialiasing, True)
        painter.setPen(Qt.NoPen)

        for i in range(self.numberOfDots):
            painter.save()
            painter.translate(0, 0)
            position = (self.dotPosition[i][0], self.dotPosition[i][1])
            color = self.dotColor
            painter.setBrush(QBrush(color, Qt.SolidPattern))
            painter.drawEllipse(position[0], position[1], self.dotRadius, self.dotRadius)
            painter.restore()


if __name__ == '__main__':
    import sys
    app = QApplication(sys.argv)
    dial = Dialog()
    dial.show()
    sys.exit(app.exec_())

结果

我知道目前这段代码不起作用，因为我无法检索更新了哪个点的动画，但我认为这里的主要问题是画家之间的干扰。 因此，谁能告诉我为什么会发生这种情况并指出一个可能的解决方案？另外，为了知道更新的点并选择好的位置，我真的不确定该怎么做。

Answer 1

您的代码存在以下错误：

切勿在主 GUI 线程中使用 time.sleep()，因为它会阻止生成应用程序冻结的事件循环。
变量 dotPosition 必须存储您要替换它的所有位置，在 updatePosition 方法中只有一个位置。
如果要存储位置而不是列表，则应使用 QPoint，使用列表也不错，但使用 QPoint 可使代码更具可读性。
不要在不必要的情况下使用 painter.save() 和 painter.restore()，也不要使用 painter.translate()。

综合以上，解决方案如下：

from functools import partial
from PyQt5 import QtCore, QtGui, QtWidgets


class Dialog(QtWidgets.QDialog):
    def __init__(self, *args, **kwargs):
        super(Dialog, self).__init__(*args, **kwargs)
        self.resize(500, 500)

        self.button = QtWidgets.QPushButton()
        self.paintWidget = PaintWidget()

        self.button.clicked.connect(self.paintWidget.startPainting)

        lay = QtWidgets.QVBoxLayout(self)
        lay.addWidget(self.button)
        lay.addWidget(self.paintWidget)


class PaintWidget(QtWidgets.QWidget):
    def __init__(self):
        super(PaintWidget, self).__init__()
        self.dotRadius = 10
        self.dotColor = QtGui.QColor(255, 100, 100)

        self.animations = []

        self.dotPosition = [
            QtCore.QPoint(0, 0),
            QtCore.QPoint(0, 0),
            QtCore.QPoint(0, 0),
        ]

        self.createAnimation()

    def startPainting(self):
        for i, animation in enumerate(self.animations):
            QtCore.QTimer.singleShot(i * 200, animation.start)

    def createAnimation(self):
        for i, _ in enumerate(self.dotPosition):
            wrapper = partial(self.updatePosition, i)
            animation = QtCore.QVariantAnimation(
                self,
                startValue=0,
                endValue=500,
                duration=3000,
                valueChanged=wrapper,
            )
            self.animations.append(animation)

    @QtCore.pyqtSlot(int, QtCore.QVariant)
    def updatePosition(self, i, position):
        self.dotPosition[i] = QtCore.QPoint(position, 0)
        self.update()

    def paintEvent(self, event):
        painter = QtGui.QPainter(self)
        painter.fillRect(self.rect(), QtCore.Qt.transparent)
        painter.setRenderHint(QtGui.QPainter.Antialiasing, True)
        painter.setPen(QtCore.Qt.NoPen)
        painter.setBrush(
            QtGui.QBrush(self.dotColor, QtCore.Qt.SolidPattern)
        )

        for position in self.dotPosition:    
            painter.drawEllipse(position, self.dotRadius, self.dotRadius)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    dial = Dialog()
    dial.show()
    sys.exit(app.exec_())

QPainters 同步背后的机制

Mechanics behind the synchronisation of QPainters

python

pyqt

qpainter

pyqt5

qvariantanimation

上下文

技术

最小工作示例

结果