[Gambas-user] Joystick interface class (optimising and ioctl)

[Jean-Francois Perreault]

Hi,

ok , I tought about this some more and I understand why it needed a 
string I see now how that
can be very useful to name the observer that way , I guess this is also 
how groups are made

now that I can catch and properly interpret de joystick events
I want to optimise the procedure a bit
it's extremely minimalistic already so the only thing I can see I could 
do to make it faster
is to fill the b array in only one read operation

a quick benchmark reveal that in normal operation the joystick will 
easily generate 200
events with peaks up to 400 events per seconds

while doing all 8 reads only take between 0.00001 and 0.000024 seconds 
to complete reducing
that by 8 could be useful to someone making a game (where input control 
lag is intolerable)

is there a way I could fill the b array in one operation ?

right now the code is

 dim b[7] as byte

 FOR i = 0 TO 7
    READ #hJoystick , b[i]
 NEXT

I tried READ #jJoystick , b
but I get an error that READ wants a standard type , not an array
it doesn't sounds like it is possible , at least not with READ , but if 
there's a way I'd like to hear it

also while doing this , I got the feeling I'm missing some events
so I tried to change the code to

 dim b[7] as byte
 WHILE NOT Eof(hJoystick)
    FOR i = 0 TO 7
       READ #hJoystick , b[i]
    NEXT
 WEND

but that doesn't work because I'm reading for a character device and it 
cannot reach eof

I'm not sure I'm missing events because I'm not clear on how File_Read 
gets called
if there is at least one readable byte in the file File_Read gets called 
, but what if I don't read it all ?
does File_Read gets called as soon as the previous File_Read returns ? 
(creating an endless loop if I don't read at least one byte)

next , to complete my joystick interface class I need to implement 
something called ioctls
please wait I need to read up on that ... ;)

oh ok , trusty man ioctl tells me that ioctl is a function to control 
character devices and probably other special files

it works like this you call it with 3 arguments the first is a valid 
file descriptor
the second is a signed interger and the value is driver dependant
that second argument at the same time tells the command you want to 
perform (the driver then knows wether this is a in or a out command) 
also the size the data to input or output , the third argument is a 
pointer to memory

since there's no pointers in gambas I guess this means I need a ioctl 
interpreted gambas function which I suppose doesn't exist according to 
the built-in doc ?

am I stuck ?

/me goes on to search how you guys managed to use the serial port if you 
can't ioctl it
......

ok searching the mailing list the only match on ioctl I found is a very 
old ( [Gambas-devel] Parallel port on 02/06/2003) thread I replied to ( 
off course I completely missed the point back then ;) )

so I guess only a component can do this ...

this is a bit off topic I was just wondering if it was possible to get 
the pointer of a variable like in vb6 ?
I know this is totally bad hackery that shouldn't ever be used but it 
could be a work around for things like this

this is stuff I learned reading visual basic hardcore a long while ago 
http://vb.mvps.org/hardcore/
in vb you can use pointers , when you do an api call since variables are 
passed byref the pointer gets passed by default
you also have CopyMemory, VarPtr, StrPtr, and ObjPtr (oh and AddressOf 
for the pointer to SUBs , a must for using Callbacks) (I think 
CopyMemory at least is another api call and that the real name is 
RtlCopyMemory)

http://vb.mvps.org/hardcore/html/bringyourhatchet.htm

copymemory is fun to do stuff like
    READ #hJoystick , mysignedinteger
    CopyMemory(VarPtr(mysignedinteger) + 2,thethirdbyte,1)

    I guess these might not work because there is no garantee how 
variable are actually stored in memory and how is the interpreter going 
to react if the variables change without it's knowledge , like would 
happen if you used CopyMemory

but still while there are no garantee this could work , it just might 
(for the current version anyway) that's why , at least for vb6 those 
functions are undocumented and I think it could be fun to have those 
function in gambas , just don't document them , don't support then and 
warn anyone who use them that they could break anytime

... well now I am really off-topic , I'm just throwing this in the wind 
tell me what you think and I'm going to resume working on my current 
problem (ioctls)

...


oh btw , about the event I mostly got confused because the AS keyword 
has multiple uses apparently and the documentation isn't very clear on 
making the distinction

I'm not sure it's necessary to force a string constant for event 
observer name ? maybe this could be useful in some unseen way ? I mean , 
if it doesn't get in the way other than getting noobs like me confused 
..  maybe just spelling out how this all works better in the doc will be 
enough .. in fact maybe is it explained properly somewhere in the docs 
and I just haven't found where ?

anyway .. I'm going to publish this class to gambasforge when it's done 
so it will server also as a good example on how to use custom class' events

-Jean-Francois Perreault