PyQT4 GUI Update

Question

I have a PyQT GUI code which takes user input (angle) from a spinbox and updates the compass object on the GUI at that specified angle. I want to update the compass object from inside the code instead of spinbox using a for-loop(0 to 360), with some delay in between, to make a clock-like motion. Please suggest some way to achieve that.

Current code:

import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *


#>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
class CompassWidget(QWidget):

    angleChanged = pyqtSignal(float)

    def __init__(self, parent = None):

        QWidget.__init__(self, parent)

        self._angle = 0.0
        self._margins = 10
        self._pointText = {0: "N", 45: "NE", 90: "E", 135: "SE", 180: "S",
                           225: "SW", 270: "W", 315: "NW"}               

    def paintEvent(self, event):

        painter = QPainter()
        painter.begin(self)
        painter.setRenderHint(QPainter.Antialiasing)

        painter.fillRect(event.rect(), self.palette().brush(QPalette.Window))
        self.drawMarkings(painter)
        self.drawNeedle(painter)

        painter.end()

    def drawMarkings(self, painter):

        painter.save()
        painter.translate(self.width()/2, self.height()/2)
        scale = min((self.width() - self._margins)/120.0,
                    (self.height() - self._margins)/120.0)
        painter.scale(scale, scale)

        font = QFont(self.font())
        font.setPixelSize(10)
        metrics = QFontMetricsF(font)

        painter.setFont(font)
        painter.setPen(self.palette().color(QPalette.Shadow))

        i = 0
        while i < 360:
            if i % 45 == 0:
                painter.drawLine(0, -40, 0, -50)
                painter.drawText(-metrics.width(self._pointText[i])/2.0, -52,self._pointText[i])
            else:
                painter.drawLine(0, -45, 0, -50)
            painter.rotate(1)
            i += 1

        painter.restore()

    def drawNeedle(self, painter):

        painter.save()
        painter.translate(self.width()/2, self.height()/2)
        painter.rotate(self._angle)
        scale = min((self.width() - self._margins)/120.0,
                    (self.height() - self._margins)/120.0)
        painter.scale(scale, scale)

        painter.setPen(QPen(Qt.NoPen))
        painter.setBrush(self.palette().brush(QPalette.Shadow))

        painter.drawPolygon(
            QPolygon([QPoint(-10, 0), QPoint(0, -45), QPoint(10, 0),
                      QPoint(0, 45), QPoint(-10, 0)])
            )

        painter.setBrush(self.palette().brush(QPalette.Highlight))

        painter.drawPolygon(
            QPolygon([QPoint(-5, -25), QPoint(0, -45), QPoint(5, -25),
                      QPoint(0, -30), QPoint(-5, -25)])
            )

        painter.restore()

    def sizeHint(self):

        return QSize(600, 600)

    def angle(self):
        return self._angle

    @pyqtSlot(float)
    def setAngle(self, angle):

        if angle != self._angle:
            self._angle = angle
            self.angleChanged.emit(angle)
            self.update()

    angle = pyqtProperty(float, angle, setAngle)

#>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

if __name__ == "__main__":

    app = QApplication(sys.argv)

    window = QWidget()
    compass = CompassWidget()
    spinBox = QSpinBox()
    spinBox.setRange(0, 359)

    #compass.angleChanged.connect(compass.setAngle)
    spinBox.valueChanged.connect(compass.setAngle)

    layout = QVBoxLayout()
    layout.addWidget(compass)
    layout.addWidget(spinBox)
    window.setLayout(layout)

    window.show()

    sys.exit(app.exec_())

Answer 1

The QPropertyAnimation class is designed for exactly this purpose, and is very easy to use. There are a whole range of built-in easing-curves which can help make the animation appear more natural.

Here is a demo based on your example script. (Note that you need to press enter in the spinbox to change the value):

class CompassWidget(QWidget):

    angleChanged = pyqtSignal(float)

    def __init__(self, parent = None):

        QWidget.__init__(self, parent)

        self._angle = 0.0
        self._margins = 10
        self._pointText = {0: "N", 45: "NE", 90: "E", 135: "SE", 180: "S",
                           225: "SW", 270: "W", 315: "NW"}

        self.animation = QPropertyAnimation(self, 'angle')
        self.animation.setEasingCurve(QEasingCurve.InOutExpo)
        self.animation.setDuration(1500)

    def paintEvent(self, event):

        painter = QPainter()
        painter.begin(self)
        painter.setRenderHint(QPainter.Antialiasing)

        painter.fillRect(event.rect(), self.palette().brush(QPalette.Window))
        self.drawMarkings(painter)
        self.drawNeedle(painter)

        painter.end()

    def drawMarkings(self, painter):

        painter.save()
        painter.translate(self.width()/2, self.height()/2)
        scale = min((self.width() - self._margins)/120.0,
                    (self.height() - self._margins)/120.0)
        painter.scale(scale, scale)

        font = QFont(self.font())
        font.setPixelSize(10)
        metrics = QFontMetricsF(font)

        painter.setFont(font)
        painter.setPen(self.palette().color(QPalette.Shadow))

        i = 0
        while i < 360:
            if i % 45 == 0:
                painter.drawLine(0, -40, 0, -50)
                painter.drawText(-metrics.width(self._pointText[i])/2.0, -52,self._pointText[i])
            else:
                painter.drawLine(0, -45, 0, -50)
            painter.rotate(1)
            i += 1

        painter.restore()

    def drawNeedle(self, painter):

        painter.save()
        painter.translate(self.width()/2, self.height()/2)
        painter.rotate(self._angle)
        scale = min((self.width() - self._margins)/120.0,
                    (self.height() - self._margins)/120.0)
        painter.scale(scale, scale)

        painter.setPen(QPen(Qt.NoPen))
        painter.setBrush(self.palette().brush(QPalette.Shadow))

        painter.drawPolygon(
            QPolygon([QPoint(-10, 0), QPoint(0, -45), QPoint(10, 0),
                      QPoint(0, 45), QPoint(-10, 0)])
            )

        painter.setBrush(self.palette().brush(QPalette.Highlight))

        painter.drawPolygon(
            QPolygon([QPoint(-5, -25), QPoint(0, -45), QPoint(5, -25),
                      QPoint(0, -30), QPoint(-5, -25)])
            )

        painter.restore()

    def sizeHint(self):

        return QSize(600, 600)

    def angle(self):
        return self._angle

    def setAngle(self, angle):
        if angle != self._angle:
            self._angle = angle
            self.update()

    angle = pyqtProperty(float, angle, setAngle)

    def animate(self, angle):
        self.animation.setStartValue(self._angle)
        self.animation.setEndValue(angle)
        self.animation.start()

if __name__ == "__main__":

    app = QApplication(sys.argv)

    window = QWidget()
    compass = CompassWidget()
    spinBox = QSpinBox()
    spinBox.setRange(0, 359)

    spinBox.editingFinished.connect(
        lambda: compass.animate(spinBox.value()))

    layout = QVBoxLayout()
    layout.addWidget(compass)
    layout.addWidget(spinBox)
    window.setLayout(layout)

    window.show()

    sys.exit(app.exec_())

Answer 2

Using example from Python PySide and Progress Bar Threading I got

import sys
import time

from PyQt4.QtCore import *
from PyQt4.QtGui import *


class Worker(QThread):

    updateAngle = pyqtSignal(float)

    def __init__(self):
        QThread.__init__(self)

    def run(self):
        for i in range(360):
            self.updateAngle.emit(i)
            time.sleep(0.2)


class CompassWidget(QWidget):

    angleChanged = pyqtSignal(float)

    def __init__(self, parent = None):

        QWidget.__init__(self, parent)

        self._angle = 0.0
        self._margins = 10
        self._pointText = {0: "N", 45: "NE", 90: "E", 135: "SE", 180: "S",
                           225: "SW", 270: "W", 315: "NW"}               
        self._worker = Worker()
        self._worker.updateAngle.connect(self.setAngle)
        self._worker.start()

    def paintEvent(self, event):

        painter = QPainter()
        painter.begin(self)
        painter.setRenderHint(QPainter.Antialiasing)

        painter.fillRect(event.rect(), self.palette().brush(QPalette.Window))
        self.drawMarkings(painter)
        self.drawNeedle(painter)

        painter.end()

    def drawMarkings(self, painter):

        painter.save()
        painter.translate(self.width()/2, self.height()/2)
        scale = min((self.width() - self._margins)/120.0,
                    (self.height() - self._margins)/120.0)
        painter.scale(scale, scale)

        font = QFont(self.font())
        font.setPixelSize(10)
        metrics = QFontMetricsF(font)

        painter.setFont(font)
        painter.setPen(self.palette().color(QPalette.Shadow))

        i = 0
        while i < 360:
            if i % 45 == 0:
                painter.drawLine(0, -40, 0, -50)
                painter.drawText(-metrics.width(self._pointText[i])/2.0, -52,self._pointText[i])
            else:
                painter.drawLine(0, -45, 0, -50)
            painter.rotate(1)
            i += 1

        painter.restore()

    def drawNeedle(self, painter):

        painter.save()
        painter.translate(self.width()/2, self.height()/2)
        painter.rotate(self._angle)
        scale = min((self.width() - self._margins)/120.0,
                    (self.height() - self._margins)/120.0)
        painter.scale(scale, scale)

        painter.setPen(QPen(Qt.NoPen))
        painter.setBrush(self.palette().brush(QPalette.Shadow))

        painter.drawPolygon(
            QPolygon([QPoint(-10, 0), QPoint(0, -45), QPoint(10, 0),
                      QPoint(0, 45), QPoint(-10, 0)])
            )

        painter.setBrush(self.palette().brush(QPalette.Highlight))

        painter.drawPolygon(
            QPolygon([QPoint(-5, -25), QPoint(0, -45), QPoint(5, -25),
                      QPoint(0, -30), QPoint(-5, -25)])
            )

        painter.restore()

    def sizeHint(self):

        return QSize(600, 600)

    def angle(self):
        return self._angle

    @pyqtSlot(float)
    def setAngle(self, angle):

        if angle != self._angle:
            self._angle = angle
            self.angleChanged.emit(angle)
            self.update()

    angle = pyqtProperty(float, angle, setAngle)


if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = QWidget()
    compass = CompassWidget()
    spinBox = QSpinBox()
    spinBox.setRange(0, 359)

    spinBox.valueChanged.connect(compass.setAngle)

    layout = QVBoxLayout()
    layout.addWidget(compass)
    layout.addWidget(spinBox)
    window.setLayout(layout)

    window.show()

    sys.exit(app.exec_())

In few words, if you use Qt, you should use QThread instead of native python threading.

Answer 3

How about using QTimer? Connect it's timeout signal to some method that increases a counter and tells the compass widget to update.