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RASP-PYGAME-GUI-Analogique (voir la source)
Version du 11 juillet 2016 à 10:34
, 11 juillet 2016 à 10:34→Le thread du potentiomètre
== Le thread du potentiomètre ==
== Le thread du potentiomètre ==
A thread is used to constantly read the potentiometer. If you take the reading in-line in the scene update method then you'll slow down the screen refresh rate. This separate thread allows the screen to be redrawn in parallel with us reading a value from the ADC.
The class is defined as a callable - hence the {{đname|__call__}} method. It takes a reference to the pitft class so we can update values on it. There's a simple termination scheme used by checking a flag on every loop. Later on you'll see how we cleanly close the program by setting this flag.
So we simply read the voltage value from the ADC and set the label and progress bar position on the pitft.
<syntaxhighlight lang="python">
class PotReader():
def __init__(self, pitft):
self.pitft = pitft
self.terminated = False
def terminate(self):
self.terminated = True
def __call__(self):
while not self.terminated:
# Read channel 0 in single-ended mode using the settings above
volts = adc.readADCSingleEnded(0, gain, sps) / 1000
self.pitft.set_volts_label(volts)
self.pitft.set_progress(volts / 3.3)
</syntaxhighlight>
== Définition de l'interface utilisateur ==
We've added a couple more widgets to the scene now and resized the buttons to accommodate them. We're showing the voltage on a label and a progress widget. The {{fname|set_progress}} and {{fname|set_volts_label}} methods are called from the PotReader thread to update the values in these widgets.
<syntaxhighlight lang="python">
class PiTft(ui.Scene):
def __init__(self):
ui.Scene.__init__(self)
self.on17_button = ui.Button(ui.Rect(MARGIN, MARGIN, 130, 60), '17 on')
self.on17_button.on_clicked.connect(self.gpi_button)
self.add_child(self.on17_button)
self.on4_button = ui.Button(ui.Rect(170, MARGIN, 130, 60), '4 on')
self.on4_button.on_clicked.connect(self.gpi_button)
self.add_child(self.on4_button)
self.off17_button = ui.Button(ui.Rect(MARGIN, 100, 130, 60), '17 off')
self.off17_button.on_clicked.connect(self.gpi_button)
self.add_child(self.off17_button)
self.off4_button = ui.Button(ui.Rect(170, 100, 130, 60), '4 off')
self.off4_button.on_clicked.connect(self.gpi_button)
self.add_child(self.off4_button)
self.progress_view = ui.ProgressView(ui.Rect(MARGIN, 200, 280, 40))
self.add_child(self.progress_view)
self.volts_value = ui.Label(ui.Rect(135, 170, 50, 30), '')
self.add_child(self.volts_value)
def gpi_button(self, btn, mbtn):
logger.info(btn.text)
if btn.text == '17 on':
GPIO.output(17, False)
elif btn.text == '4 on':
GPIO.output(4, False)
elif btn.text == '17 off':
GPIO.output(17, True)
elif btn.text == '4 off':
GPIO.output(4, True)
def set_progress(self, percent):
self.progress_view.progress = percent
def set_volts_label(self, volts):
self.volts_value.text = '%.2f' % volts
def update(self, dt):
ui.Scene.update(self, dt)
</syntaxhighlight>
== Et pour finir... ==
To start everything going we initialise pygameui, construct the pitft class and then start the potreader thread with a reference to pitft.
Since we're running this extra thread we need a clean way to stop the program. A signal handler is used to trap ctrl+c and terminate the PotReader thread before calling sys.exit - otherwise the program will not close.
<syntaxhighlight lang="python">
ui.init('Raspberry Pi UI', (320, 240))
pygame.mouse.set_visible(False)
pitft = PiTft()
# Start the thread running the callable
potreader = PotReader(pitft)
threading.Thread(target=potreader).start()
def signal_handler(signal, frame):
print 'You pressed Ctrl+C!'
potreader.terminate()
sys.exit(0)
signal.signal(signal.SIGINT, signal_handler)
ui.scene.push(pitft)
ui.run()
</syntaxhighlight>
You can run this final example from the pygamelcd project:
<syntaxhighlight lang="bash">
sudo python test5.py
</syntaxhighlight>
{{RASP-PYGAME-GUI-TRAILER}}
{{RASP-PYGAME-GUI-TRAILER}}