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# load a program from command line, wait for button/key press event on raspi and
# react by closing the previously launched program and re-opening it with a
# different parameter
import RPi.GPIO as GPIO # Import Raspberry Pi GPIO library (for external button)
import subprocess # Import subprocess to start camera view in background
import sys, termios, tty, time # for character input from command line
# magnification when calling raspivid without parameters
# adapt this value to your screen, by measuring the default scale factor with 2 rulers
# pre-defined scale factors (press button/enter for next), should be in ascending order
factor = SCALE_FACTORS[0] # use first entry as initial factor on boot up
PIN_NUMBER = 10 # physical pin number of GPIO used for button
BOUNCE_TIME = 300 # ms to wait till a new button event is generated (avoid double click artefacts)
DELAY = 0.01 # s to sleep between polling the keyboard
# default view of raspivid without specific scaling
# raspivid -f -t 0 -rot 180
# -f is full screen
# -t gets a timeout value in ms (0 for no timeout)
# -rot is rotation, depends on the way the camera is mounted
# -ifx controls image effects, allows e.g. colour inversion
RASPIVID = ['raspivid', '-f', '-t', '0', '-rot', '180', '-ifx', 'none']
# read a single character, taken from
def getch():
fd = sys.stdin.fileno()
old_settings = termios.tcgetattr(fd)
ch =
termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
return ch
# convert a scale factor to the values needed by raspivid's roi parameter
def scale2roi(scale_factor):
diameter = DEFAULT_FACTOR / scale_factor
radius = diameter / 2
start = 0.5 - radius
# assure that values are in allowed range (e.g. factor 1 is not supported on bigger screens)
start = max(start, 0)
diameter = min(diameter, 1)
# y value is always 0, to have the same upper position regardless of scale factor ()
roi = "%.2f,%.2f,%.2f,%.2f" % (start, 0, diameter, diameter)
return roi
# react on button pressed
def nextFactor(channel):
global factor
# find the highest entry in SCALE_FACTORS that is <= current factor
# if the current factor is less (due to direct factor input), switch to default value
same_or_less = [v for v in SCALE_FACTORS if v <= factor]
if len(same_or_less) == 0:
# step to next scale factor, after last entry go back to first
closest_factor = max(same_or_less)
i = SCALE_FACTORS.index(closest_factor)
i_next = (i + 1) % len(SCALE_FACTORS)
factor = SCALE_FACTORS[i_next]
# change to given scale factor
def scale(new_factor):
global proc
global factor
factor = max(new_factor, DEFAULT_FACTOR)
#print("Scale factor", factor)
# terminate current camera view, to restart with a different scale factor
# @TODO: wait till it's really terminated
# convert factor to raspivid's -roi parameters
roi = scale2roi(factor)
# start with new scale factor
#print(RASPIVID + ['-roi', roi])
proc = subprocess.Popen(RASPIVID + ['-roi', roi])
#print("Started new process", proc)
# push button through GPIO
def initPushbutton():
GPIO.setwarnings(False) # Ignore warning for now
GPIO.setmode(GPIO.BOARD) # Use physical pin numbering
GPIO.setup(PIN_NUMBER, GPIO.IN, pull_up_down=GPIO.PUD_DOWN) # Set pin 10 to be an input pin and set initial value to be pulled low (off)
GPIO.add_event_detect(PIN_NUMBER, GPIO.RISING, callback=nextFactor, bouncetime=BOUNCE_TIME) # Setup event on pin 10 rising edge, ignore additional signals in under BOUNCE_TIME ms
# start displaying the default camera view
#proc = subprocess.Popen(['raspivid', '-f', '-t', '9000', '-rot', '180', '-roi', '0.3,0,0.4,0.4'])
proc = subprocess.Popen(RASPIVID)
# loop forever, or till escape is pressed
char = ' '
while ord(char) != ESCAPE_KEY:
# try to read character from stdin
char = getch()
# pressing a digit key will use its value as the scale factor
if '0' <= char and char <= '9':
if char == '0':
# 0 is interpreted as 10
# other digits are interpreted as their number
factor = ord(char) - ord('0')
# pressing enter switches to next higher zoom factor, same as pressing the push button
elif ord(char) == ENTER_KEY:
# pressing '/' toggles colour inversion
elif char == '/' and '-ifx' in RASPIVID:
i = RASPIVID.index('-ifx')
if RASPIVID[i + 1] == 'none':
RASPIVID[i + 1] = 'negative'
RASPIVID[i + 1] = 'none'
# reload with toggled image effect
# wait a bit to not block the processor
GPIO.cleanup() # Clean up