[Tutor] Event loop logic question

[Dennis Lee Bieber]

On Sat, 18 Jun 2022 15:04:50 +1000, Phil <phillor9 at gmail.com> declaimed the
following:


>Any hints or alternative methods will be, as always, greatly appreciated.
>
>By the way, this project sends commands to a controller which is easily 
>overwhelmed if too many commands are received per second.
>

	For the last matter, one solution would be to use an elapsed time
counter.

	rate = 1.0 / commands_per_second
	last_command_time = 0.0	#or get the time (fractional seconds) 
								#at start of program

	Then, when you issue a command, some logic like

	if last_command_time + rate < time_now:
		issue_command
		last_command_time = time_now

... optional if you return a status that "command skipped -- rate limited"


	For the former/general... I see too many flags that should (as I
understand it) be mutually exclusive (only one should be set/cleared
[depending on overall logic] at any moment in the program). Instead I'd
suggest using a "state" variable (maybe check on what Python has for
"enums" -- I've not used them in my dribblings, so the following is just
using "constants"

	STATE_QUIT, STATE_FORWARD, STATE_STOPPED = range(3)

	current_state = STATE_STOPPED
	requested_state = STATE_STOPPED

...	key-press
	if key == keys.UP:
		requested_state = STATE_FORWARD
	elif key == keys.SPACE:
		requested_state = STATE_QUIT
	else:
		pass	#log an unused key press		

...	key-release
	requested_state = STATE_STOPPED

...	update section

	if requested_state != current_state:
		#if the requested state is the same as current_state, 
		#it may signal a repeating key (but only if the OS doesn't
		#issue a key release and key press at the start of each repeat --
		#if it does -- you'll need to incorporate some nasty rate timer
		#to determine what is a repeat vs a real release/press)

		if requested_state == STATE_QUIT:
			#initiate shutdown?
			#log change?
		elif requested_state == STATE_FORWARD:
			#issue forward command to device
			#log change
		elif requested_state == STATE_STOPPED:
			#issue stop command to device
			#log change
		else:
			#unexpected STATE!
		current_state = requested_state	#update state



-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
	wlfraed at ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/