HI RJ,
When you say that the XML is good for usabiity, do you mean because you do
not consider editing a XML file as "writing code", or because it is
automatically edited by Mixxx preferences GUI?
In the later case, it could still be used internally, but get rid of it
for scripting purposes, where it adds a lot of noise and makes the scripts
hard to maintain.
Also, for the performance argument, that convinces me that we really need
an API like this:
engine.connectMidiToControl(status, midino, group, control, options);
engine.connectControlToMidi(group, control, status, midino,options);
If I want some control X just to be enabled when button Y is pressed, I
should do this with scripting, but there is no reason why X messages
should not be processed in the same way as XML-configured values.
Anyway, your email convinces me that my approach is conservative and good.
The XML file is still there, it is just generated. And the XML contains
direct-bindings whenever possible, so there is no general performance
loss. Also the use of literate programming and a very declarative API
might lower the barrier to scripting for non-advanced users.
Cheers!
JP
> 1) It's valuable to have a structured representation of the mappings.
Code is a black box and Mixxx has no visibility into it. This means that
mappings expressed purely in code are not manipulatable by Mixxx. It
doesn't matter what the declarative format is (JSON, YAML, XML, etc.)
but a practical consideration is that breaking compatibility with the
extensive set of controller scripts in the wild would be an extremely
sub-optimal outcome.
>
> 2) QtScript is nice because it supports natural interoperation with Qt core
> features (Qt properties, signals and slots, etc.).
>
> 3) Distribution-wise, QtScript is a no-brainer since it comes with Qt.
>
> 4) Controller scripts do not run in the engine thread so it doesn't
affect audio processing whether the script VM is realtime or not.
However, currently the standard way of implementing scratching via
controller scripts routes all the ticks from the controller through the
QtScript VM. This adds unpredictable latency to scratch processing.
>
> If you care about performance, you should instead be coming up with a
standard, non-script way to implement scratching. Compared to executing
code in a VM, the current XML bindings are orders of magnitude more
efficient (It's a hash-map lookup to figure out which control to
dispatch a message to).
>
> 5) Controller scripts are a mechanism for advanced script authors to get
full control and customization. Throwing out the mappings eliminates all
possibility for non-advanced users to customize their controller without
writing code.
>
> For all these reasons, it would be a very bad outcome for our users to
remove the XML mappings.
>
> Best regards,
> RJ
>
> On Sun, May 26, 2013 at 10:52 AM, Juan Pedro Bolívar Puente <
> raskolni...@gnu.org> wrote:
>
>> I disagree.
>>
>> First, there is nothing intrinsically "more performant" in Lua than in
JavaScript -- they are both dynamically typed languages with objects
and first-class functions. Also, there is a wide choice of VMs in in
Javascript. While QtScript uses the webkit JS engine, which is fairly
good and nothing prevents us to moving to V8 or something like that.
>>
>> Lua does not meet the realtime constraints neither anyway. In my
experience, the scripting language should not be the fastest, but the
most expressive, because its goal is to allow very fast development and
hackability. If you look around, other music software are also using a
wide variety of similar approaches, like Ableton Live, which uses
Python (which is slower but more expressive than JS), or Max/MSP, which
uses JavaScript.
>>
>> What its missing in Mixxx is, however, an API in the scripting engine
to bind a MIDI signal to a control. This way, the script can handle
mode selection, but for every mode, the important MIDI messages (cue
button, knobs and faders) still go through the engine directly.
Something like:
>>
>>
>> Which would be equivalent to defining an entry in the <controls> or
<outputs> section of the XML file.
>>
>> If I were to critisize JavaScript, on the other hand, it would be
because it is not always as concise and expressive as it could be.
Fortunatelly, a wide range of languages nowadays compile to JavaScript,
and that is one of the reasons my CoffeeScript project can exist at
all.
>>
>> JP
>>
>>
>>
>> On 25/05/13 15:38, petah wrote:
>> > Hi there,
>> >
>> > first post but I am NOT a student looking to rubberstamp GSoC all over
>> my resume :)
>> >
>> > RJ, you may remember me from www.hackerdjs.com/software/cdj2midi.html,
>> introduced by Mark Hills, through Adam D, I think. Since we last spoke
I've
>> become a linux-head, been stalking Mixxx-devel for a month. Seeing you're
>> into 3D/games I'm surprised Mixxx uses Javascript, Python and qtScript but
>> not Lua.
>> >
>> > I'm guessing the initial choice of XML/Javascript was to attract more
>> people to write controller glue code but Mixxx has gotten a lot of
traction/attention since then. With a new focus on reliability,
Mixxx/hardware-interface drivers should really be written by somewhat
experienced programmers (at least not invite bad code). QA's a bitch
now cause you often don't have the hardware but if Mixxx's user base
keeps growing as it does you'll soon be able to threaten manufacturers
*not* to
>> support their device:)
>> >
>> > Assuming Mixxx maintains its growth (vs withers & dies), driver and
>> hardware availability is a given, what matters is runtime
>> quality/efficiency. Porting the current ./res/controllers/ is a
one-time effort. Also, the majority of users will be non-techie DJs; at
the top DJs
>> with a coding assistant :)
>> >
>> > Wrt speed, Javascript engines can afford many luxuries when running in
>> web browsers (or servers) because they're not dealing with 10ms latencies.
>> A web-surfing user won't notice a garbage collector hiccup but in a
"critical realtime" app like Mixxx it's the end of the world for a very
pissed DJ. Hardcore videogames are somewhat similar and there's
virtually
>> no Javascript; #1 engine is Lua because it's tiny and predictable;
where the VM falls short you bind native C code in a handful of lines.
>> >
>> > Either way I think it'd make sense to use the same VM for both drivers
>> and macros since they're really on the same path between the hardware
interface and Mixxx.
>> >
>> > (bowing out)
>> >
>> > -- p
>> >
>> >
>> ------------------------------------------------------------------------------
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>>
>>
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