This Week's Dumb Question About Multiple Simultaneous INKEY$ Handling

[Qwerkey]

I feel rather ashamed to ask this question (but that hasn't stopped me asking it!).  I am constructing a program where I'd like to allow 2 keys to be pressed at the same time, and for the program to recognise that with two different responses.

I don't suppose that that would be possible (either by INKEY$ or _KEYHIT).  How would the hardware be behaving?  How would the software recognise such?  If, by some remote possibility, this could be done in some way I shan't feel quite so dumb!  But pardon me for cluttering up the site with ridiculous questions (I'm trying to get the keyboard to have the property of a game controller left&right hand).  If I were Odin, I'd create a Special Section for Qwerkey's Stupid Questions with an automatic flushing facility.

[bplus]

Checkout _KEYDOWN, it reports when a key is down (or not) and is good for discerning key combinations.

[Petr]

Hi Qwerkey,
None of us is perfect and none of us knows everything. Which particular combinations would you like to try?

[Pete]

I handle stuff like that with PEEK and POKE. That way, I can highlight text if the shift key is held down and an arrow key is pressed, etc. If the _KEYDOWN doesn't work out, take a look at something I wrote many years ago. It still works in '64...

https://www.tapatalk.com/groups/qbasic/viewtopic.php?f=13959&t=30059&p=177576&hilit=def+seg#p177576

Pete

[FellippeHeitor]

I feel rather ashamed to ask this question (but that hasn't stopped me asking it!).  I am constructing a program where I'd like to allow 2 keys to be pressed at the same time, and for the program to recognise that with two different responses.

I don't suppose that that would be possible (either by INKEY$ or _KEYHIT).  How would the hardware be behaving?  How would the software recognise such?  If, by some remote possibility, this could be done in some way I shan't feel quite so dumb!  But pardon me for cluttering up the site with ridiculous questions (I'm trying to get the keyboard to have the property of a game controller left&right hand).  If I were Odin, I'd create a Special Section for Qwerkey's Stupid Questions with an automatic flushing facility.

Code: QB64: [Select]

1. This:
2.    _KEYDOWN

[Qwerkey]

Thanks guys, it seems that I was so stupid that I hadn't realised that the Question wasn't actually that dumb!  Naturally, before posing the question here I had looked at the _KEYHIT, _KEYDOWN & _KEYCLEAR wiki pages, and assumed that the key combinations only worked for the Sys, ScL, Pause, CapL, Shift, Ctrl, Win, Alt & Menu keys in combination with other keys (they're the one in the wiki which have a "+" next to them, indicating their special combinatory abilities).

But I've now had a go with the example given on the _KEYDOWN wiki page, and indeed you DO seem to be able to have two keys down at once, and both the hardware and software can sort it out.  Quite amazing!

Petr, no need to worry about the mocking self-deprecation.  That's more-or-less the default British trait.  It's all done in the greatest of humour!

Pete, whenever I've seen other members' efforts with PEEK/POKE, I've never understood a thing.

[SMcNeill]

You can also use _KEYHIT to track multiple key presses.  Remember, _KEYHIT gives us TWO values for each keypress — one when the key is pressed down, and a negative value for when the key is released.

Instead of storing the KEYHIT in a single variable (such as just K = _KEYHIT), instead you save it into an array of keys down, and then remove it from the array when keys are let up.

I can give an example, if you’re curious, once I get back home and at my PC later.  (Currently, I’m in town, on my iPad, which is impossible for me to code much from.)

[Qwerkey]

Steve, thanks.  I'll work with _KEYDOWN for the present, using the wiki page example as my guide.  You'll hear from me, no doubt, if I'm struggling.

None of us is perfect and none of us knows everything.

Petr, there you are quite wrong.  Steve McNeill not only knows everything, but he understands everything!

[SMcNeill]

A quick demo of how one could use _KEYHIT to track multiple key presses at the same time, for those who might be curious about the process:

Code: QB64: [Select]

1. DIM KeysDown(10)
2. DO
3.     k = _KEYHIT
4.     SELECT CASE k
5.         CASE IS > 0 'key is pressed down
6.             AlreadyDown = 0 'Assume it's not recorded as down, by default
7.             FOR i = 1 TO KeysDown(0) 'check to see if the key is already recorded as "down"
8.                 IF k = KeysDown(i) THEN
9.                     AlreadyDown = -1 'It's already down
10.                     EXIT FOR
11.                 END IF
12.             NEXT
13.             IF NOT AlreadyDown THEN
14.                 KeysDown(0) = KeysDown(0) + 1 '0th element is to track how many keys are down
15.                 KeysDown(KeysDown(0)) = k 'elements 1 to 10 represent the keys which are actually down
16.             END IF
17.         CASE IS < 0 'key is released
18.             FOR i = 1 TO 10
19.                 IF KeysDown(i) = -k THEN 'remove the key from the array as it's lifted up
20.                     FOR j = i TO 9
21.                         KeysDown(j) = KeysDown(j + 1)
22.                     NEXT
23.                     KeysDown(0) = KeysDown(0) - 1 'subtract the total numbers of keys held down from our counter
24.                     EXIT FOR
25.                 END IF
26.             NEXT
27.         CASE 0 ' we don't do anything if there's no keys being held/released
28.     END SELECT
29.  
30.     'Display some results
31.     CLS
32.     PRINT "There are currently"; KeysDown(0); " keys being held down."
33.     FOR i = 1 TO KeysDown(0)
34.         PRINT KeysDown(i)
35.     NEXT
36.  
37.     _DISPLAY 'reduce flicker
38.     _LIMIT 30 'reduce CPU usage
39. LOOP UNTIL ESCAPE

[Pete]

So getting this into something useful like my highlighting example, this is what came to my mind, first...

Find out if either shift key is held down while a right or left arrow key is pressed

Code: QB64: [Select]

1. DIM KeysDown(10)
2. GOSUB dsp
3. DO
4.     k = _KEYHIT
5.     SELECT CASE k
6.         CASE IS > 0 'key is pressed down
7.             AlreadyDown = 0 'Assume it's not recorded as down, by default
8.             FOR i = 1 TO KeysDown(0) 'check to see if the key is already recorded as "down"
9.                 IF k = KeysDown(i) THEN
10.                     AlreadyDown = -1 'It's already down
11.                     EXIT FOR
12.                 END IF
13.             NEXT
14.             IF NOT AlreadyDown THEN
15.                 KeysDown(0) = KeysDown(0) + 1 '0th element is to track how many keys are down
16.                 KeysDown(KeysDown(0)) = k 'elements 1 to 10 represent the keys which are actually down
17.             END IF
18.             GOSUB dsp
19.         CASE IS < 0 'key is released
20.             FOR i = 1 TO 10
21.                 IF KeysDown(i) = -k THEN 'remove the key from the array as it's lifted up
22.                     FOR j = i TO 9
23.                         KeysDown(j) = KeysDown(j + 1)
24.                     NEXT
25.                     KeysDown(0) = KeysDown(0) - 1 'subtract the total numbers of keys held down from our counter
26.                     EXIT FOR
27.                 END IF
28.             NEXT
29.             GOSUB dsp
30.         CASE 0 ' we don't do anything if there's no keys being held/released
31.     END SELECT
32.     _LIMIT 30 'reduce CPU usage
33. LOOP UNTIL ESCAPE
34.  
35. dsp:
36. 'Display results
37. CLS
38. PRINT "There are currently"; KeysDown(0); "keys being held down."
39. FOR i = 1 TO KeysDown(0)
40.     PRINT KeysDown(i)
41. NEXT
42.  
43. _DISPLAY 'reduce flicker
44.  
45. ' See if shift and left arrow are down
46. IF KeysDown(0) = 2 THEN
47.     IF KeysDown(1) + KeysDown(2) >= 100303 + 19200 AND KeysDown(1) + KeysDown(2) <= 100304 + 19200 THEN
48.         PRINT "Highlighting left initiated!"
49.         _DISPLAY
50.         _DELAY 1
51.     ELSEIF KeysDown(1) + KeysDown(2) >= 100303 + 19712 AND KeysDown(1) + KeysDown(2) <= 100304 + 19712 THEN
52.         PRINT "Highlighting right initiated!"
53.         _DISPLAY
54.         _DELAY 1
55.     END IF
56. END IF
57. RETURN
58.  

Now maybe there is some "bitwise" way of calculating combined values, which is better than what I presented here. Like I stated, I still use PEEK/POKE routines for these activities. In an actual WP, you have to add highlighting up and down methods, too. Anyway, it's what I love about BASIC, there's more than one way to peel a banana.

800lb gorilla out,

Pete

[bplus]

Steve's code looks like handy way to get key code numbers.

[Qwerkey]

Just to confirm, I have included a sequence of _KEYDOWN statements in my code and indeed more than 1 key pressed at the same time has multiple consequences which QB64 handles perfectly.  Wow!

[Raven_Singularity]

Just to add to this:

The number of simultaneous key-downs that a system can handle is determined by the actual keyboard hardware.  The most advanced USB keyboards allow detection of key up/down states for EVERY key simultaneously.  With cheap keyboards, sometimes even 3 simultaneous keypresses can fail!  All keyboards can handle Ctrl, Alt, Shift combinations because OSes so commonly use them as modifiers, but once you get into uncommon combinations like A+B+C, it's much less likely to register the keypresses.

Also to note, PS/2 and the original keyboard connectors physically limit how many keypresses can be sent simultaneously.  USB keyboards, in theory, have no such limits, but in practise most cheap USB keyboards emulate PS/2 under-the-hood, along with their crappy limitations.  Gaming keyboards often advertise how many keys can be held down simultaneously, though some lie about this!  My current piece-of-shit Amazon Basics keyboard is terrible for this, it often fails with three-key combos, despite saying it can handle 128 simultaneous keys or some rubbish.

Back in the day I can remember trying tons of key combos to figure out which could be handled for multiplayer gaming on the same keyboard.  It was tricky to find keys that wouldn't block each other.

[Jack002]

Years ago I was looking at this topic for the commodore 64. Even two keypresses were not always detectable. There were row and column wires and when you pressed one key the pressing of others was hidden. Not a think on a c64, I am surprised you can do it on any keyboard.

[SMcNeill]

Just to add to this:

The number of simultaneous key-downs that a system can handle is determined by the actual keyboard hardware.  The most advanced USB keyboards allow detection of key up/down states for EVERY key simultaneously.  With cheap keyboards, sometimes even 3 simultaneous keypresses can fail!  All keyboards can handle Ctrl, Alt, Shift combinations because OSes so commonly use them as modifiers, but once you get into uncommon combinations like A+B+C, it's much less likely to register the keypresses.

Also to note, PS/2 and the original keyboard connectors physically limit how many keypresses can be sent simultaneously.  USB keyboards, in theory, have no such limits, but in practise most cheap USB keyboards emulate PS/2 under-the-hood, along with their crappy limitations.  Gaming keyboards often advertise how many keys can be held down simultaneously, though some lie about this!  My current piece-of-shit Amazon Basics keyboard is terrible for this, it often fails with three-key combos, despite saying it can handle 128 simultaneous keys or some rubbish.

Back in the day I can remember trying tons of key combos to figure out which could be handled for multiplayer gaming on the same keyboard.  It was tricky to find keys that wouldn't block each other.

The term of importance here is, “key rollover”.  https://en.m.wikipedia.org/wiki/Rollover_(key)

Most keyboards are listed with a “#-key rollover” rating.  (Or #KRO.)  A very cheep keyboard is called a 2KRO and allows simultaneous pressing of 2 keys.  A standard keyboard is often a 4KRO (4 key presses allowed), and many gaming keyboards are 6KRO.  The truly expensive keyboards which allow EVERY key to be pressed and handled at once are called NKRO.  (n-key rollover)

From my personal experience, most USB keyboards top out at 6KRO, while you need a PS/2 keyboard for NKRO usage.