Easter eggs (4)

I found a pattern. The keys that are grouped ("neighbors") behaves similarly, especially those in the median part and the right part of the alphanumeric region. I mean it's difficult to catch three of them pressed simultaneously. Any combination of two, or two + other key shows no problem.

Using an US keyboard, the alphanumeric region
4 5 6 7
E R T Y U
D F G H J K
C V B N M ,

0 - = (zero, minus, equal)
P [ ]
L ; '

The numeric keypad
/ * -
0 . 2
0 . 3
1 2 4
1 2 5
2 4 5
a.s.o

The test code used by me (click or press the command button to experiment different combinations):

CLEAR

PUBLIC ofrm

ofrm = CREATEOBJECT("myform")

ofrm.show()

DEFINE CLASS myform as form

      Autocenter = .T.

      l1 = .F. && .T. while key #1 is pressed

      l2 = .F. && .T. while key #2 is pressed

      l3 = .F. && .T. while key #3 is pressed

      ln1 = -1 && Store scan code 1

      ln2 = -1 && Store scan code 2

      ln3 = -1 && Store scan code 3

      ADD OBJECT txt1 as textbox

      ADD OBJECT cmd as commandbutton WITH top = 50, caption = "Reset" && reset the combination

      PROCEDURE init

            UNBINDEVENTS(This.hwnd)

            BINDEVENT(This.hwnd,0x0100,This,"detectkeydown")

            BINDEVENT(This.hwnd,0x0101,This,"detectkeyup")

      ENDPROC

      PROCEDURE detectkeydown

            LPARAMETERS p1,p2,p3,p4

            * p3 = Virtual-key code

            IF This.ln3 = -1 AND !INLIST(This.ln1, -1, m.p3) AND !INLIST(This.ln2, -1, m.p3)

                  This.ln3 = m.p3

            ENDIF

            IF m.p3 = This.ln3

                  This.l3 = .T.

            ENDIF

            IF This.ln2 = -1 AND !INLIST(This.ln1, -1, m.p3)

                  This.ln2 = m.p3

            ENDIF

            IF m.p3 = This.ln2

                  This.l2 = .T.

            ENDIF

            IF This.ln1 = -1

                  This.ln1 = m.p3

            ENDIF

            IF m.p3 = This.ln1

                  This.l1 = .T.

            ENDIF

            ACTIVATE SCREEN

            ? m.p3

            IF This.l1 AND This.l2 AND This.l3

                  ? 'Bingo!'

                  ? 'An ' + LTRIM(STR(This.ln1)) + '+' + LTRIM(STR(This.ln2)) + '+' + LTRIM(STR(This.ln3)) + ' occures'

            ENDIF

                  ACTIVATE SCREEN

            ?This.l1 ,This.l2 ,This.l3

      ENDPROC

      PROCEDURE detectkeyup

            LPARAMETERS p1,p2,p3,p4

            * p3 = Virtual-key code

            IF p3 = This.ln1

                  This.l1 = .F.

            ENDIF

            IF p3 = This.ln2

                  This.l2 = .F.

            ENDIF

            IF p3 = This.ln3

                  This.l3 = .F.

            ENDIF

      ENDPROC

      PROCEDURE cmd.click

            STORE -1 TO ThisForm.ln1, ThisForm.ln2, ThisForm.ln3

            STORE .F. TO ThisForm.l1, ThisForm.l2, ThisForm.l3

      ENDPROC

ENDDEFINE

Update
The previous test was on a Dell keyboard with a US layout (Windows 7 32 bit).
I repeated the same test, but this time using a Fujitsu keyboard with a German layout (Windows 10 prof 64 bit). And what do you know? I managed to catch a 3+4+5. Not easy, but Bingo!
The patterns are almost the same.
Ha! So most probably it's a hardware issue.

Later
A new test using a Genius keyboard (Windows 10 home 32 bit), with an US layout, behaves poorly.
Another test. A HP notebook (Windows 10 home 64 bit) with a Germanic layout, behaves even better than Fujitsu.
A final test using a Lenovo laptop (Windows 10 home 64 bit) with an US layout, behaves poorly.

Again
This article https://en.wikipedia.org/wiki/Rollover_(key) explains everything.

Related posts
http://praisachion.blogspot.com/2017/08/easter-eggs-4.html
http://praisachion.blogspot.com/2017/08/easter-eggs-3.html
http://praisachion.blogspot.com/2017/08/easter-eggs-2.html
http://praisachion.blogspot.com/2017/08/easter-eggs-1.html

http://praisachion.blogspot.com/2016/02/interceptin-ctrlshiftenter.html
http://praisachion.blogspot.com/2015/06/detect-keyup-like-mouseup.html
http://praisachion.blogspot.com/2015/01/how-can-i-prevent-undocking-docked-form.html