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

[Benoit Minisini]

On Monday 07 March 2005 17:14, Jean-Francois Perreault wrote:
> 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

You can use a dynamic array: DIM b AS NEW Byte[](8)
and use the b.Read() method.

>
> 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)

File_Read is called if there is something to read on the opened file.

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

You can't do ioctl() with Gambas at the moment.

> 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
>
>

Components are written in C/C++ at the moment, so they can do what they want. 
A component to get joystick event should be written in C, not in Gambas, 
because of the ioctl() stuff, and because of the number of events generated. 
Note that the sdl component will have joystick management too in it, thanks 
to the sdl library.

Regards,

-- 
Benoit Minisini
mailto:gambas at ...1...