/[svn]/doc/docbase/instrument_scripts/nksp/01_nksp.html
ViewVC logotype

Contents of /doc/docbase/instrument_scripts/nksp/01_nksp.html

Parent Directory Parent Directory | Revision Log Revision Log


Revision 2763 - (show annotations) (download) (as text)
Wed May 6 21:14:19 2015 UTC (5 years, 1 month ago) by schoenebeck
File MIME type: text/html
File size: 51757 byte(s)
* Article "NKSP Language": updated "Polyphonic Variables" section with
  details about the polyphonic variable scope.

1 <html>
2 <head>
3 <meta name="author" content="Christian Schoenebeck">
4 <title>NKSP Language</title>
5 <meta name="description" content="Introduction to the NKSP real-time instrument script language.">
6 </head>
7 <body>
8 <p>
9 This document intends to give you a compact introduction and overview to
10 the NKSP real-time instrument script language, so you can start writing
11 your own instrument scripts in short time. It concentrates on describing
12 the script language. If you rather want to learn how to modify and
13 attach scripts to your sounds, then please refer to the gigedit manual for
14 <a href="gigedit_scripts.html">how to manage instrument scripts with gigedit</a>.
15 </p>
16
17 <h3>At a Glance</h3>
18 <p>
19 <img src="nksp_file.png" style="height:111px; margin-right:12px;">
20 NKSP stands for "is <b>N</b>ot <b>KSP</b>", which denotes its distinction
21 to an existing proprieatary language called <i>KSP</i>.
22 NSKP is a script language specifically designed to write real-time capable
23 software extensions to LinuxSampler's sampler engines that can be bundled
24 individually with sounds by sound designers themselves.
25
26 Instead of defining a completely new script language, NKSP is leaned on
27 that mentioned properiatary script language. The biggest advantage is that
28 sound designers and musicians can leverage the huge amount of existing KSP
29 scripts which are already available for various purposes on the Internet,
30 instead of being forced to write all scripts from scratch in a completely
31 different language.
32 </p>
33 <p>
34 That also means however that there are some differences between those two
35 languages. Some extensions have been added to the NKSP core language to
36 make it a bit more convenient and less error prone to write scripts, and
37 various new functions had to be added due to the large difference of the
38 sampler engines and their underlying sampler format. Efforts have been
39 made though to make NKSP as much compatible to KSP as possible.
40 The NKSP documentation will emphasize individual differences in
41 the two languages and function implementations wherever they may occur, to
42 give you immediate hints where you need to take care of regarding
43 compatibility issues when writing scripts that should be spawned on both
44 platforms.
45 </p>
46 <p>
47 Please note that the current focus of NKSP is the sound controlling aspect
48 of sounds. At this point there is no support for the graphical user
49 interface function set of KSP in NKSP.
50 </p>
51
52 <h2>Event Handlers</h2>
53 <p>
54 NKSP is an event-driven language. That means you are writing so called
55 <i>event handlers</i> which define what the sampler shall do on individual
56 events that occur, while using the sound the script was bundled with.
57 An event handler in general looks like this:
58 </p>
59 <code lang="nksp">
60 on ??event-name??
61
62 ??statements??
63
64 end on
65 </code>
66 <p>
67 There are currently four events available:
68 </p>
69 <table>
70 <tr>
71 <th>Event Type</th> <th>Description</th>
72 </tr>
73 <tr>
74 <td><code>on note</code></td> <td>This event handler is executed when a new note was triggered, i.e. when hitting a key on a MIDI keyboard.</td>
75 </tr>
76 <tr>
77 <td><code>on release</code></td> <td>This event handler is executed when a new note was released, i.e. when releasing a key on a MIDI keyboard.</td>
78 </tr>
79 <tr>
80 <td><code>on controller</code></td> <td>This event handler is executed when a MIDI control change event occurred. For instance when turning the modulation wheel at a MIDI keyboard.</td>
81 </tr>
82 <tr>
83 <td><code>on init</code></td> <td>Executed only once, as very first event handler, right after the script had been loaded. This code block is usually used to initialize variables in your script with some initial, useful data.</td>
84 </tr>
85 </table>
86 <p>
87 You are free to decide for which ones of those event types you are going to
88 write an event handler for. You can write an event handler for only one
89 event type or write event handlers for all of those event types. Also
90 dependent on the respective event type, there are certain things you can
91 do and things which you can't do. But more on that later.
92 </p>
93
94 <h3>Note Events</h3>
95 <p>
96 As a first example, the following tiny script will print a message to your
97 terminal whenever you trigger a new note with your MIDI keyboard.
98 </p>
99 <code>
100 on note
101 message("A new note was triggered!")
102 end on
103 </code>
104 <p>
105 Probably you are also interested to see which note you triggered exactly.
106 The sampler provides you a so called
107 <i title="A script variable which is provided by the sampler and which has a very specific purpose which you cannot override for other purposes.">
108 built-in variable
109 </i>
110 called <code>$EVENT_NOTE</code> which reflects the note number
111 (as value between 0 and 127) of the note that has just been triggered. Additionally
112 the built-in variable <code>$EVENT_VELOCITY</code> provides you the
113 velocity value (also between 0 and 127) of the note event.
114 </p>
115 <code>
116 on note
117 message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
118 end on
119 </code>
120 <p>
121 The <code>&</code> character concatenates text strings with each other.
122 In this case it is also automatically converting the note number into a
123 text string.
124 </p>
125 <note class="important">
126 The message() function is not appropriate for being used with your final
127 production sounds, since it can lead to audio dropouts.
128 You should only use the message() function to try out things, and to spot
129 and debug problems with your scripts.
130 </note>
131
132 <h3>Release Events</h3>
133 <p>
134 As counter part to the <code>note</code> event handler, there is also the
135 <code>release</code> event handler, which is executed when a note was
136 released. This event handler can be used similarly:
137 </p>
138 <code>
139 on release
140 message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
141 end on
142 </code>
143 <p>
144 Please note that you can hardly find MIDI keyboards which support release
145 velocity. So with most keyboards this value will be 127.
146 </p>
147
148 <h3>Controller Events</h3>
149 <p>
150 Now let's extend the first script to not only show note-on and note-off
151 events, but also to show a message whenever
152 you use a MIDI controller (i.e. modulation wheel, sustain pedal, etc.).
153 </p>
154 <code>
155 on note
156 message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
157 end on
158
159 on release
160 message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
161 end on
162
163 on controller
164 message("MIDI Controller " & $CC_NUM " changed its value to " & %CC[$CC_NUM])
165 end on
166 </code>
167 <p>
168 It looks very similar to the note event handlers. <code>$CC_NUM</code>
169 reflects the MIDI controller number of the MIDI controller that had been
170 changed and <code>%CC</code> is a so called <i>array variable</i>, which not only
171 contains a single number value, but instead it contains several values at
172 the same time. The built-in <code>%CC</code> array variable contains the current
173 controller values of all 127 MIDI controllers. So <code>%CC[1]</code> for
174 example would give you the current controller value of the modulation
175 wheel, and therefore <code>%CC[$CC_NUM]</code> reflects the new controller
176 value of the controller that just had been changed.
177 </p>
178 <p>
179 There is some special aspect you need to be aware about: in contrast to the MIDI standard,
180 monophonic aftertouch (a.k.a. channel pressure) and pitch beend wheel are
181 handled by NKSP as if they were regular MIDI controllers. So a value change
182 of one of those two triggers a regular <code>controller</code> event handler
183 to be executed. To obtain the current aftertouch value you can use
184 <code>%CC[$VCC_MONO_AT]</code>, and to get the current pitch bend wheel
185 value use <code>%CC[$VCC_PITCH_BEND]</code>.
186 </p>
187
188 <h3>Script Load Event</h3>
189 <p>
190 As the last one of the four event types available with NKSP, the following
191 is an example of an <code>init</code> event handler.
192 </p>
193 <code>
194 on init
195 message("This script has been loaded and is ready now!")
196 end on
197 </code>
198 <p>
199 You might think, that this is probably a very exotic event. Because in
200 fact, this "event" is only executed once for your script: exactly when
201 the script was loaded by the sampler. This is not an unimportant event
202 handler though. Because it is used to prepare your script for various
203 purposes. We will get more about that later.
204 </p>
205
206 <h2>Comments</h2>
207 <p>
208 Let's face it: software code is sometimes hard to read, especially when you
209 are not a professional software developer who deals with such kinds of
210 things every day. To make it more easy for you to understand, what you
211 had in mind when you wrote a certain script three years ago, and also if
212 some other developer might need to continue working on your scripts one
213 day, you should place as many comments into your scripts as possible. A
214 comment in NKSP is everything that is nested into a an opening and closing
215 pair of curly braces.
216 </p>
217 <code>{ This is a comment. }</code>
218 <p>
219 You cannot only use this to leave some human readable explanations here
220 and there, you might also use such curly braces to quickly disable parts
221 of your scripts for a moment, i.e. when debugging certain things.
222 </p>
223 <code>
224 on init
225 { The following will be prompted to the terminal when the sampler loaded this script. }
226 message("My script loaded.")
227
228 { This code block is commented out, so these two messages will not be displayed }
229 {
230 message("Another text")
231 message("And another one")
232 }
233 end on
234 </code>
235
236 <h2>Variables</h2>
237 <p>
238 In order to be able to write more complex and more useful scripts, you
239 also need to remember some data somewhere for being able to use that
240 data at a later point. This can be done by using
241 <i title="A variable is a storage location paired with an associated symbolic name.">
242 variables
243 </i>.
244 We already came across some <i>built-in variables</i>, which are already
245 defined by the sampler for you. To store your own data you need to declare
246 your own <i>user variables</i>, which has the following form:
247 </p>
248 <p>
249 <code>declare $??variable-name?? := ??initial-value??
250 </p>
251 <p>
252 The left hand side's <code>??variable-name??</code> is an arbitrary name
253 you can chose for your variable. That name might consist of English
254 letters A to Z (lower and upper case) and the underscore character "<code>_</code>".
255 Variable names must be unique. So you can neither declare several variables
256 with the same name, nor can you use a name for your variable that is
257 already been reserved by <i>built-in variables</i>.
258 The right hand side's <code>??initial-value??</code> is simply the first
259 value the variable should store right after it was created. You can also
260 omit that.
261 </p>
262 <p>
263 <code>declare $??variable-name??
264 </p>
265 <p>
266 In that case the sampler will automatically assign <code>0</code> for you
267 as the variable's initial value. This way we could for example count the
268 total amount of notes triggered.
269 </p>
270 <code>
271 on init
272 declare $numberOfNotes := 0
273 end on
274
275 on note
276 $numberOfNotes := $numberOfNotes + 1
277
278 message("This is the " & $numberOfNotes & "th note triggered so far.")
279 end on
280 </code>
281 <p>
282 In the <code>init</code> event handler we create our own variable
283 <code>$numberOfNotes</code> and assign <code>0</code> to it as its
284 initial value. Like mentioned before, that initial assignment is optional.
285 In the <code>note</code> event handler we then increase the
286 <code>$numberOfNotes</code> variable by one, each time a new note was
287 triggered and then print a message to the terminal with the current total
288 amount of notes that have been triggered so far.
289 </p>
290 <note>
291 NKSP allows you to declare variables in all event handlers, however if
292 you want to keep compatibility with KSP, then you should only
293 declare variables in <code>init</code> event handlers.
294 </note>
295
296 <h3>Variable Types</h3>
297 <p>
298 There are currently three different variable types, which you can easily
299 recognize upon their first character.
300 </p>
301 <table>
302 <tr>
303 <th>Variable Form</th> <th>Data Type</th> <th>Description</th>
304 </tr>
305 <tr>
306 <td><code>$??variable-name??</code></td> <td>Integer Scalar</td> <td>Stores one single integer number value.</td>
307 </tr>
308 <tr>
309 <td><code>%??variable-name??</code></td> <td>Integer Array</td> <td>Stores a certain amount of integer number values.</td>
310 </tr>
311 <tr>
312 <td><code>@??variable-name??</code></td> <td>String</td> <td>Stores one text string.</td>
313 </tr>
314 </table>
315 <p>
316 So the first character just before the actual variable name, always
317 denotes the data type of the variable. Also note that all variable types
318 share the same variable name space. That means you cannot declare a
319 variable with a name that has already been used to declare a variable of
320 another variable type.
321 </p>
322
323 <h3>Array Variables</h3>
324 <p>
325 We already used the first two variable types. However we have not seen yet
326 how to declare such array variables. This is the common declaration form
327 for creating your own array variables.
328 </p>
329 <code>
330 on init
331 declare %??variable-name??[??array-size??] := ( ??list-of-values?? )
332 end on
333 </code>
334 <p>
335 So let's say you wanted to create an array variable with the first 12
336 prime numbers, then it might look like this.
337 </p>
338 <code>
339 on init
340 declare %primes[12] := ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 )
341 end on
342 </code>
343 <p>
344 Like with integer variables, assigning some initial values with
345 <code>??list-of-values??</code> is optional. The array
346 declaration form without initial value assignment looks like this.
347 </p>
348 <code>
349 on init
350 declare %??variable-name??[??array-size??]
351 end on
352 </code>
353 <p>
354 When you omit that initial assignment, then all numbers of that array will
355 automatically be initialized with <code>0</code> each. With array
356 variables however, it is always mandatory to provide
357 <code>??array-size??</code> with an array
358 variable declaration, so the sampler can create that array with the
359 requested amount of values when the script is loaded. In contrast to many
360 other programming languages, changing that amount of values of an array
361 variable is not possible after the variable had been declared. That's due
362 to the fact that this language is dedicated to real-time applications, and
363 changing the size of an array variable at runtime would harm real-time
364 stability of the sampler and thus could lead to audio dropouts. So NKSP
365 does not allow you to do that.
366 </p>
367
368
369 <h3>String Variables</h3>
370 <p>
371 You might also store text with variables. These are called <i>text string
372 variables</i>, or short: <i>string variables</i>. Let's skip the common declaration
373 form of string variables and let us modify a prior example to just use
374 such kind of variable.
375 </p>
376 <code>
377 on init
378 declare $numberOfNotes
379 declare @firstText := "This is the "
380 declare @secondText
381 end on
382
383 on note
384 $numberOfNotes := $numberOfNotes + 1
385 @secondText := "th note triggered so far."
386 message(@firstText & $numberOfNotes & @secondText)
387 end on
388 </code>
389 <p>
390 It behaves exactly like the prior example and shall just give you a
391 first idea how to declare and use string variables.
392 </p>
393 <note class="important">
394 Like with the message() function, you should not use string variables
395 with your final production sounds, since it can lead to audio dropouts.
396 You should only use string variables to try out things, and to spot
397 and debug problems with your scripts.
398 </note>
399
400 <h3>Variable Scope</h3>
401 <p>
402 By default, all variables you declare with NKSP are
403 <i title="A variable that is accessible throughout an entire script.">
404 global variables
405 </i>. That means every event handler can access the data of such a global
406 variable. Furthermore, each instance of an event handler accesses the same
407 data when it is referencing that variable. And the latter fact can be a
408 problem sometimes, which we will outline next.
409 </p>
410 <p>
411 Let's assume you wanted to write an instrument script that shall resemble
412 a simple delay effect. You could do that by writing an note event handler
413 that automatically triggers several new notes for each note being
414 triggered on a MIDI keyboard. The following example demonstrates how that
415 could be achieved.
416 </p>
417 <note class="important">
418 The following example does not fully work with LinuxSampler yet. That's
419 because the used <code>wait()</code> function is not fully implemented
420 yet. Currently a <code>wait()</code> function call suspends execution,
421 but since the respective scheduler code is yet missing, the script
422 will automatically be resumed with the next audio fragment cycle. So
423 effectively a <code>wait()</code> call will pause your script for a few
424 miliseconds with LinuxSampler right now, no matter which function argument
425 you provided. Hopefully this will be implemented soon though.
426 </note>
427 <code>
428 on init
429 { The amount of notes to play }
430 declare const $delayNotes := 4
431 { Tempo with which the new notes will follow the orignal note }
432 declare const $bpm := 90
433 { Convert BPM to microseconds (duration between the notes) }
434 declare const $delayMicroSeconds := 60 * 1000000 / $bpm
435 { Just a working variable for being used with the while loop below }
436 declare $i
437 { For each successive note we trigger, we will reduce the velocity a bit}
438 declare $velocity
439 end on
440
441 on note
442 { First initialize the variable $i with 4 each time we enter this event
443 handler, because each time we executed this handler, the variable will be 0 }
444 $i := $delayNotes
445
446 { Loop which will be executed 4 times in a row }
447 while ($i)
448 { Calculate the velocity for the next note being triggered }
449 $velocity := 127 * $i / ($delayNotes + 1)
450 { Suspend this script for a short moment ... }
451 wait($delayMicroSeconds)
452 { ... and after that short break, trigger a new note. }
453 play_note($EVENT_NOTE, $velocity)
454 { Decrement loop counter $i by one }
455 $i := $i - 1
456 end while
457 end on
458 </code>
459 <p>
460 In this example we used a new keyword <code>const</code>. This additional
461 variable qualifier defines that we don't intend to change this variable
462 after declaration. So if you know beforehand, that a certain variable should
463 remain with a certain value, then you might use the <code>const</code>
464 qualifier to avoid that you i.e. change the value accidently when you
465 modify the script somewhere in future.
466 </p>
467 <p>
468 Now when you trigger one single note on your keyboard with that script,
469 you will hear the additional notes being triggered. And also when you
470 hit another note after a while, everything seems to be fine. However if
471 you start playing quick successive notes, you will notice something goes
472 wrong. The amount of notes being triggered by the script is now incorrect
473 and also the volume of the individual notes triggered by the script is wrong.
474 What's going on?
475 </p>
476 <p>
477 To understand the problem in the last example, let's consider what is
478 happening when executing that script exactly: Each time you play a note
479 on your keyboard, a new instance of the <code>note</code> event handler
480 will be spawned and executed by the sampler. In all our examples so far
481 our scripts were so simple, that in practice only one handler instance
482 was executed at a time. This is different in this case though. Because
483 by calling the <code>wait()</code> function, the respective handler
484 execution instance is paused for a while and in total each handler
485 instance will be executed for more than 2 seconds in this particular
486 example. As a consequence, when
487 you play multiple, successive notes on your keyboard in short time, you
488 will have several instances of the <code>note</code> event handler running
489 simultaniously. And that's where the problem starts. Because by default,
490 as said, all variables are global variables. So the handler instances
491 which are now running in parallel, are all reading and modifying the same
492 data. Thus the individual handler instances will modify the
493 <code>$i</code> and <code>$velocity</code> variables of each other, causing
494 an undesired misbehavior.
495 </p>
496 <note>
497 NKSP's built-in function <code>play_note()</code> allows you to pass
498 between one and four function arguments. For the function arguments you
499 don't provide to a <code>play_note()</code> call, NKSP will automatically
500 use default values. If you want your script to be compatible with KSP,
501 then you should always pass four arguments to that function though.
502 </note>
503
504 <h3>Polyphonic Variables</h3>
505 <p>
506 As a logical consequence of the previously described data concurrency
507 problem, it would be desirable to have each event handler instance use
508 its own variable instance, so that the individual handler instances stop
509 interfering with each other. For this purpose the so called
510 <i title="A variable which is effectively a separate variable for each event handler instance.">
511 polyphonic variable
512 </i>
513 qualifier exists with NKSP. Declaring such a variable is identical to
514 declaring a regular variable, just that you add the keyword <code>polyphonic</code>.
515 </p>
516 <code>
517 declare polyphonic $??variable-name??
518 </code>
519 <p>
520 So to fix the bug in our previous example, we simply make the variables
521 <code>$i</code> and <code>$velocity</code> polyphonic variables.
522 </p>
523 <code>
524 on init
525 { The amount of notes to play }
526 declare const $delayNotes := 4
527 { Tempo with which the new notes will follow the orignal note }
528 declare const $bpm := 90
529 { Convert BPM to microseconds (duration between the notes) }
530 declare const $delayMicroSeconds := 60 * 1000000 / $bpm
531 { Just a working variable for being used with the while loop below }
532 declare polyphonic $i { < --- NOW POLYPHONIC !!! }
533 { For each successive note we trigger, we will reduce the velocity a bit}
534 declare polyphonic $velocity { < --- NOW POLYPHONIC !!! }
535 end on
536
537 on note
538 { First initialize the variable $i with 4 each time we enter this event
539 handler, because each time we executed this handler, the variable will be 0 }
540 $i := $delayNotes
541
542 { Loop which will be executed 4 times in a row }
543 while ($i)
544 { Calculate the velocity for the next note being triggered }
545 $velocity := 127 * $i / ($delayNotes + 1)
546 { Suspend this script for a short moment ... }
547 wait($delayMicroSeconds)
548 { ... and after that short break, trigger a new note. }
549 play_note($EVENT_NOTE, $velocity)
550 { Decrement loop counter $i by one }
551 $i := $i - 1
552 end while
553 end on
554 </code>
555 <p>
556 And that's it! The script works now as intended. Now you might wonder, why
557 are variables not <i>polyphonic</i> by default? Isn't that more common and
558 wouldn't that be more safer than using global variables by default? The reason is that
559 a polyphonic variable consumes a lot more memory than a regular (global) variable.
560 That's because for each polyphonic variable, the sampler has to allocate
561 in advance (when the script is loaded) as many instances of that
562 polyphonic variable as there are maximum events
563 allowed with the sampler. So that's a lot! Considering that today's
564 computers have plenty of RAM this might be a theoretical aspect, but in the
565 end: this default scope of variables was already like this with <i>KSP</i>
566 so we are also doing it like this with NKSP for compatibility reasons.
567 </p>
568 <p>
569 Please note that the <i>polyphonic</i> qualifier only exists for integer
570 variables. So you cannot declare polyphonic string variables, nor can you
571 declare polyphonic array variables. Like in the previous explanation,
572 this is due to the fact that it would consume a huge amount of memory
573 for such variables. And with string variables and array variables, the
574 required amount of memory would be much higher than with simple integer
575 variables.
576 </p>
577 <p>
578 As summary, the following are guideline rules describing when you should
579 use the polyphonic qualifier for a certain variable. You should declare
580 a particular variable polyphonic if one (or even both) of the following two
581 conditions apply to that variable.
582 </p>
583 <ol>
584 <li>
585 If you call the <code>wait()</code> function within your event
586 handlers and the respective variable is modified and read before
587 and after at least one of the individual <code>wait()</code> calls.
588 </li>
589 <li>
590 If you have loops that might run for a very long time, while accessing
591 the respective variable in between. That's because if your script is
592 running consecutively for too long, the sampler will automatically suspend your
593 script for a while to avoid your script becoming a real-time stability
594 hazard for the sampler. Your script will then automatically be resumed
595 after a short moment by the sampler, so effectively this is similar to
596 something like an "automated" <code>wait()</code> function call by
597 the sampler.
598 </li>
599 </ol>
600 <p>
601 In all other cases you should rather use regular (global) variables instead.
602 But keep in mind that you might need to re-assign a certain value for
603 some global variables when you enter the respective event handler, just
604 like we did with <code>$i := $delayNotes</code> right from the start
605 during discussion of the previous example script.
606 </p>
607 <p>
608 There is another special aspect regarding the variable scope of polyphonic
609 variables: <code>note</code> handlers and <code>release</code> handlers of
610 the same script share the same polyphonic variable scope, that means you
611 may pass data from a particular note's <code>note</code> handler to its
612 <code>release</code> handler by using the same polyphonic variable name.
613 </p>
614
615 <h2>Control Structures</h2>
616 <p>
617 A computer is more than a calculator that adds numbers and stores them
618 somewhere. One of the biggest strength of a computer, which makes it
619 such powerful, is the ability to do different things depending on various
620 conditions. For example your computer might clean up your hard drive
621 while you are not sitting in front of it, and it might immediately stop
622 doing so when you need all its resources to cut your latest video which
623 you just shot.
624 </p>
625 <p>
626 In order to do that for you, a computer program allows you to define
627 conditions and a list of instructions the computer shall
628 perform for you under those individual conditions. These kinds of
629 software mechanisms are called <i>Control Structures</i>.
630 </p>
631
632 <h3>if Branches</h3>
633 <p>
634 The most fundamental control structure are <i>if branches</i>, which has
635 the following general form.
636 </p>
637 <code>
638 if (??condition??)
639
640 ??statements??
641
642 end if
643 </code>
644 <p>
645 The specified <code>??condition??</code> is evaluated each time script
646 execution reaches this control block. The condition can for example be
647 the value of a variable, some arithmetic expression, a function call or
648 a combination of them. In all cases the sampler expects the
649 <code>??condition??</code> expression to evaluate to some numeric
650 (or boolean) value. If the evaluated number is exactly <code>0</code> then
651 the condition is interpreted to be <i>false</i> and thus the list of
652 <code>??statements??</code> is not executed. If the evaluated value is any
653 other value than <code>0</code> then the condition is interpreted to be
654 <i>true</i> and accordingly the list of <code>??statements??</code> will be
655 executed.
656 </p>
657 <p>
658 Alternatively you might also specify a list of instructions which shall be
659 executed when the condition is <i>false</i>.
660 </p>
661 <code>
662 if (??condition??)
663
664 ??statements-when-true??
665
666 else
667
668 ??statements-when-false??
669
670 end if
671 </code>
672 <p>
673 In this case the first list of statements is executed when the
674 <code>??condition??</code> evaluated to <i>true</i>, otherwise the second
675 list of statements is executed instead.
676 </p>
677 <p>
678 Once again, let's get back to the example of counting triggered notes.
679 You might have noticed that it did not output correct English for the
680 first three notes. Let's correct this now.
681 </p>
682 <code>
683 on init
684 declare $numberOfNotes
685 declare @postfix
686 end on
687
688 on note
689 $numberOfNotes := $numberOfNotes + 1
690
691 if ($numberOfNotes == 1)
692 @postfix := "st"
693 else
694 if ($numberOfNotes == 2)
695 @postfix := "nd"
696 else
697 if ($numberOfNotes == 3)
698 @postfix := "rd"
699 else
700 @postfix := "th"
701 end if
702 end if
703 end if
704
705 message("This is the " & $numberOfNotes & @postfix & " note triggered so far.")
706 end on
707 </code>
708 <p>
709 We are now checking the value of <code>$numberOfNotes</code> before we
710 print out a message. If <code>$numberOfNotes</code> equals one, then we
711 assign the string <code>"st"</code> to the variable <code>@postfix</code>,
712 if <code>$numberOfNotes</code> equals 2 instead we assign the string
713 <code>"nd"</code> instead, if it equals 3 instead we assign
714 <code>"rd"</code>, in all other cases we assign the string
715 <code>"th"</code>. And finally we assemble the text message to be
716 printed out to the terminal on line 23.
717 </p>
718
719 <h3>Select Case Branches</h3>
720 <p>
721 The previous example now outputs the numbers in correct English. But the
722 script code looks a bit bloated, right? That's why there is a short hand
723 form.
724 </p>
725 <code>
726 select ??expression??
727
728 case ??integer-1??
729
730 ??statements-1??
731
732
733 case ??integer-2??
734
735 ??statements-2??
736
737 .
738 .
739 .
740 end select
741 </code>
742 <p>
743 The provided <code>??expression??</code> is first evaluated to an integer
744 value. Then this value is compared to the integer values of the nested
745 <code>case</code> lines. So it first compares the evaluated value of
746 <code>??expression??</code> with <code>??integer-1??</code>, then it
747 compares it with <code>??integer-2??</code>, and so on. The first integer
748 number that matches with the evaluated value of <code>??expression??</code>,
749 will be interpreted as being the current valid condition. So if
750 <code>??expression??</code> equals <code>??integer-1??</code>,
751 then <code>??statements-1??</code> will be executed, otherwise if
752 <code>??expression??</code> equals <code>??integer-2??</code>,
753 then <code>??statements-2??</code> will be executed, and so on.
754 </p>
755 <p>
756 Using a select-case construct, our previous example would look like follows.
757 </p>
758 <code>
759 on init
760 declare $numberOfNotes
761 declare @postfix
762 end on
763
764 on note
765 $numberOfNotes := $numberOfNotes + 1
766 @postfix := "th"
767
768 select $numberOfNotes
769 case 1
770 @postfix := "st"
771 case 2
772 @postfix := "nd"
773 case 3
774 @postfix := "rd"
775 end if
776
777 message("This is the " & $numberOfNotes & @postfix & " note triggered so far.")
778 end on
779 </code>
780 <note>
781 If you like, you can also put parentheses around the select expression,
782 like <code>select (??expression??)</code>. Some developers familiar with
783 other programming languages might prefer this style. However if you want
784 to keep compatibility with KSP, you should not use parentheses for
785 select expressions.
786 </note>
787 <p>
788 The amount
789 of case conditions you add to such select-case blocks is completely up
790 to you. Just remember that the case conditions will be compared one by one,
791 from top to down. The latter can be important when you define a case line
792 that defines a value range. So for instance the following example will
793 not do what was probably intended.
794 </p>
795 <code>
796 on init
797 declare $numberOfNotes
798 end on
799
800 on note
801 $numberOfNotes := $numberOfNotes + 1
802
803 select $numberOfNotes
804 case 1 to 99
805 message("Less than 100 notes triggered so far")
806 exit
807 case 1
808 message("First note was triggered!") { Will never be printed ! }
809 exit
810 case 2
811 message("Second note was triggered!") { Will never be printed ! }
812 exit
813 case 3
814 message("Third note was triggered!") { Will never be printed ! }
815 exit
816 end if
817
818 message("Wow, already the " & $numberOfNotes & "th note triggered.")
819 end on
820 </code>
821 <p>
822 You probably get the idea what this script "should" do. For the 1st note
823 it should print <code>"First note was triggered!"</code>, for the 2nd
824 note it should print <code>"Second note was triggered!"</code>, for the 3rd
825 note it should print <code>"Third note was triggered!"</code>, for the 4th
826 up to 99th note it should print <code>"Less than 100 notes triggered so far"</code>,
827 and starting from the 100th note and all following ones, it should print
828 the precise note number according to line 23. However, it doesn't!
829 </p>
830 <p>
831 To correct this problem, you need to move the first case block to the end,
832 like follows.
833 </p>
834 <code>
835 on init
836 declare $numberOfNotes
837 end on
838
839 on note
840 $numberOfNotes := $numberOfNotes + 1
841
842 select $numberOfNotes
843 case 1
844 message("First note was triggered!")
845 exit
846 case 2
847 message("Second note was triggered!")
848 exit
849 case 3
850 message("Third note was triggered!")
851 exit
852 case 1 to 99
853 message("Less than 100 notes triggered so far")
854 exit
855 end if
856
857 message("Wow, already the " & $numberOfNotes & "th note triggered.")
858 end on
859 </code>
860 <p>
861 Or you could of course fix the questioned case range from <code>case 1 to 99</code>
862 to <code>case 4 to 99</code>. Both solutions will do.
863 </p>
864 <p>
865 We also used the <i>built-in function</i> <code>exit()</code> in the
866 previous example. You can use it to stop execution at that point of your
867 script. In the previous example it prevents multiple messages to be
868 printed to the terminal.
869 </p>
870 <note class="important">
871 The <code>exit()</code> function only stops execution of the <b>current</b>
872 event handler instance! It does <b>not</b> stop execution of other
873 instances of the same event handler, nor does it stop execution of other
874 handlers of other event types, and especially it does <b>not</b> stop or
875 prevent further or future execution of your entire script! In other words,
876 you should rather see this function as a return statement, in case you are
877 familiar with other programming languages already.
878 </note>
879
880 <h3>while Loops</h3>
881 <p>
882 Another fundamental control construct of program flow are loops.
883 You can use so called
884 <i title="Repeats a given list of instructions until the defined condition turns false.">
885 while loops
886 </i>
887 with NKSP.
888 </p>
889 <code>
890 while (??condition??)
891
892 ??statements??
893
894 end while
895 </code>
896 <p>
897 A while loop is entered if the provided <code>??condition??</code>
898 expression evaluates to <i>true</i> and will then continue to execute
899 the given list of <code>??statements??</code> down to the end of the statements
900 list. The <code>??condition??</code> is re-evaluated each time execution
901 reached the end of the <code>??statements??</code> list and according to
902 that latest evaluated <code>??condition??</code> value at that point, it
903 will or will not repeat executing the statements again. If the condition
904 turned <i>false</i> instead, it will leave the loop and continue executing
905 statements that follow after the while loop block.
906 </p>
907 <p>
908 The next example will print the same message three times in a row to the
909 terminal, right after the script had been loaded by the sampler.
910 </p>
911 <code>
912 on init
913 declare $i := 3
914
915 while ($i)
916 message("Print this three times.")
917 $i := $i - 1
918 end while
919 end on
920 </code>
921 <p>
922 When the while loop is reached for the first time in this example, the
923 condition value is <code>3</code>. And as we learned before, all integer
924 values that are not <code>0</code> are interpreted as being a <i>true</i> condition.
925 Accordingly the while loop is entered, the message is printed to the
926 terminal and the variable <code>$i</code> is reduced by one. We reached
927 the end of the loop's statements list, so it is now re-evaluating the
928 condition, which is now the value <code>2</code> and thus the loop
929 instructions are executed again. That is repeated until the loop was
930 executed for the third time. The variable <code>$i</code> is now
931 <code>0</code>, so the loop condition turned finally to <i>false</i> and the
932 loop is thus left at that point and the text message was printed
933 three times in total.
934 </p>
935
936 <h2>Operators</h2>
937 <p>
938 A programming language provides so called <i>operators</i> to perform
939 certain kinds of transformations of data placed next to the operators.
940 These are the operators available with NKSP.
941 </p>
942
943 <h3>Arithmetic Operators</h3>
944 <p>
945 These are the most basic mathematical operators, which allow to add,
946 subtract, multiply and divide integer values with each other.
947 </p>
948 <code>
949 on init
950 message("4 + 3 is " & 4 + 3) { Add }
951 message("4 - 3 is " & 4 - 3) { Subtract }
952 message("4 * 3 is " & 4 * 3) { Multiply }
953 message("35 / 5 is " & 35 / 5) { Divide }
954 message("35 mod 5 is " & 35 mod 5) { Remainder of Division ("modulo") }
955 end on
956 </code>
957 <p>
958 You may either use direct integer literal numbers like used in the upper
959 example, or you can use integer number variables or integer array variables.
960 </p>
961
962 <h3>Boolean Operators</h3>
963 <p>
964 To perform logical transformations of <i>boolean</i> data, you may use the
965 following boolean operators:
966 </p>
967 <code>
968 on init
969 message("1 and 1 is " & 1 and 1) { logical "and" }
970 message("1 and 0 is " & 1 and 0) { logical "and" }
971 message("1 or 1 is " & 1 or 1) { logical "or" }
972 message("1 or 0 is " & 1 or 0) { logical "or" }
973 message("not 1 is " & not 1) { logical "not" }
974 message("not 0 is " & not 0) { logical "not" }
975 end on
976 </code>
977 <p>
978 Remember that with boolean operations, all integer values other than <code>0</code>
979 are interpreted as boolean <i>true</i> while an integer value of
980 precisely <code>0</code> is interpreted of being boolean <i>false</i>.
981 </p>
982
983 <h3>Comparison Operators</h3>
984 <p>
985 For branches in your program flow, it is often required to compare data
986 with each other. This is done by using comparison operators, enumerated
987 below.
988 </p>
989 <code>
990 on init
991 message("Relation 3 < 4 -> " & 3 < 4) { "smaller than" comparison }
992 message("Relation 3 > 4 -> " & 3 > 4) { "greater than" comparison }
993 message("Relation 3 <= 4 -> " & 3 <= 4) { "smaller or equal than" comparison}
994 message("Relation 3 >= 4 -> " & 3 >= 4) { "greater or equal than" comparison}
995 message("Relation 3 # 4 -> " & 3 # 4) { "not equal to" comparison}
996 message("Relation 3 = 4 -> " & 3 = 4) { "is equal to" comparison}
997 end on
998 </code>
999 <p>
1000 All these operations yield in a <i>boolean</i> result which could then
1001 by used i.e. with <code>if</code> or <code>while</code> loop statements.
1002 </p>
1003
1004 <h3>String Operators</h3>
1005 <p>
1006 Last but not least, there is exactly one operator for text string data;
1007 the string concatenation operator <code>&</code>, which
1008 combines two text strings with each other.
1009 </p>
1010 <code>
1011 on init
1012 declare @s := "foo" & " bar"
1013 message(@s)
1014 end on
1015 </code>
1016 <p>
1017 We have used it now frequently in various examples before.
1018 </p>
1019
1020 <h2>Preprocessor Statements</h2>
1021 <p>
1022 Similar to low-level programming languages like C, C++, Objective C
1023 and the like, NKSP supports a set of so called preprocessor statements.
1024 These are essentially "instructions" which are "executed" or rather
1025 processed, before (and only before) the script is executed by the sampler,
1026 and even before the script is parsed by the actual NKSP language parser.
1027 You can think of a preprocessor as a very primitive parser, which is the
1028 first one getting in touch with your script, it modifies the script code
1029 if requested by your preprocessor statements in the script, and then
1030 passes the (probably) modified script to the actual NKSP language parser.
1031 </p>
1032 <p>
1033 When we discussed <a href="#comments">comments</a> in NKSP scripts before,
1034 it was suggested that you might comment out certain code parts to disable
1035 them for a while during development of scripts. It was also suggested
1036 during this language tour that you should not use string variables or use
1037 the <code>message()</code> function with your final production sounds.
1038 However those are very handy things during development of your instrument
1039 scripts. You might even have a bunch of additional code in your scripts
1040 which only satisfies the purpose to make debugging of your scripts more easy,
1041 which however wastes on the other hand precious CPU time. So what do you
1042 do? Like suggested, you could comment out the respective code sections as
1043 soon as development of your script is completed. But then one day you
1044 might continue to improve your scripts, and the debugging code would be
1045 handy, so you would uncomment all the relevant code sections to get them
1046 back. When you think about this, that might be quite some work each time.
1047 Fortunately there is an alternative by using preprocessor statements.
1048 </p>
1049
1050 <h3>Set a Condition</h3>
1051 <p>
1052 First you need to set a preprocessor condition in your script. You can do
1053 that like this:
1054 </p>
1055 <code>
1056 SET_CONDITION(??condition-name??)
1057 </code>
1058 <p>
1059 This preprocessor "condition" is just like some kind of
1060 <i title="A variable which can only have two states: i.e. true or false.">
1061 boolean variable
1062 </i>
1063 which is only available to the preprocessor and by using
1064 <code>SET_CONDITION(??condition-name??)</code>, this is like setting this
1065 preprocessor condition to <i>true</i>. Like with regular script
1066 variables, a preprocessor condition name can be chosen quite arbitrarily
1067 by you. But again, there are some pre-defined preprocessor conditions
1068 defined by the sampler for you. So you can only set a condition name here
1069 which is not already reserved by a built-in preprocessor condition. Also
1070 you shall not set a condition in your script again if you have already set it
1071 before somewhere in your script. The NKSP preprocessor will ignore setting
1072 a condition a 2nd time and will just print a warning when the script is
1073 loaded, but you should take care of it, because it might be a cause for
1074 some bug.
1075 </p>
1076
1077 <h3>Reset a Condition</h3>
1078 <p>
1079 To clear a condition in your script, you might reset the condition like so:
1080 </p>
1081 <code>
1082 RESET_CONDITION(??condition-name??)
1083 </code>
1084 <p>
1085 This is like setting that preprocessor condition back to <i>false</i> again.
1086 You should only reset a preprocessor condition that way if you did set it
1087 with <code>SET_CONDITION(??condition-name??)</code> before. Trying to
1088 reset a condition that has not been set before, or trying to reset a
1089 condition that has already been reset, will both be ignored by the samlper,
1090 but again you will get a warning, and you should take care about it.
1091 </p>
1092
1093 <h3>Conditionally Using Code</h3>
1094 <p>
1095 Now what do you actually do with such preprocessor conditions? You can use
1096 them for the NKSP language parser to either
1097 </p>
1098 <ul>
1099 <li>use certain parts of your code</i>
1100 <li><b>and</b> / <b>or</b> to ignore certain parts of your code</i>
1101 </ul>
1102 <p>
1103 You can achieve that by wrapping NKSP code parts into a pair of either
1104 </p>
1105 <code>
1106 USE_CODE_IF(??condition-name??)
1107
1108 ??some-NKSP-code-goes-here??
1109
1110 END_USE_CODE
1111 </code>
1112 <p>
1113 preprocessor statements, or between
1114 </p>
1115 <code>
1116 USE_CODE_IF_NOT(??condition-name??)
1117
1118 ??some-NKSP-code-goes-here??
1119
1120 END_USE_CODE
1121 </code>
1122 <p>
1123 statements. In the first case, the NKSP code portion is used by the NKSP
1124 language parser if the given preprocessor <code>??condition-name??</code> is set
1125 (that is if condition is <i>true</i>).
1126 If the condition is not set, the NKSP code portion in between is
1127 completely ignored by the NKSP language parser.
1128 </p>
1129 <p>
1130 In the second case, the NKSP code portion is used by the NKSP
1131 language parser if the given preprocessor <code>??condition-name??</code> is <b>not</b> set
1132 (or was reset)
1133 (that is if condition is <i>false</i>).
1134 If the condition is set, the NKSP code portion in between is
1135 completely ignored by the NKSP language parser.
1136 </p>
1137 <p>
1138 Let's look at an example how to use that to define conditional debugging
1139 code.
1140 </p>
1141 <code>
1142 SET_CONDITION(DEBUG_MODE)
1143
1144 on init
1145 declare const %primes[12] := ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 )
1146 declare $i
1147
1148 USE_CODE_IF(DEBUG_MODE)
1149 message("This script has just been loaded.")
1150
1151 $i := 0
1152 while ($i < num_elements(%primes))
1153 message("Prime " & $i & " is " & %primes[$i])
1154 $i := $i + 1
1155 end while
1156 END_USE_CODE
1157 end on
1158
1159 on note
1160 USE_CODE_IF(DEBUG_MODE)
1161 message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
1162 END_USE_CODE
1163 end on
1164
1165 on release
1166 USE_CODE_IF(DEBUG_MODE)
1167 message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
1168 END_USE_CODE
1169 end on
1170
1171 on controller
1172 USE_CODE_IF(DEBUG_MODE)
1173 message("MIDI Controller " & $CC_NUM " changed its value to " & %CC[$CC_NUM])
1174 END_USE_CODE
1175 end on
1176 </code>
1177 <p>
1178 The <i>built-in function</i> <code>num_elements()</code> used above, can
1179 be called to obtain the size of an array variable at runtime.
1180 As this script looks now, the debug messages will be printed out. However
1181 it requires you to just remove the first line, or to comment out the first
1182 line, in order to disable all debug code portions in just a second:
1183 </p>
1184 <code>
1185 { Setting the condition is commented out, so our DEBUG_MODE is disabled now. }
1186 { SET_CONDITION(DEBUG_MODE) }
1187
1188 on init
1189 declare const %primes[12] := ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 )
1190 declare $i
1191
1192 USE_CODE_IF(DEBUG_MODE) { Condition is not set, so this entire block will be ignored now. }
1193 message("This script has just been loaded.")
1194
1195 $i := 0
1196 while ($i < num_elements(%primes))
1197 message("Prime " & $i & " is " & %primes[$i])
1198 $i := $i + 1
1199 end while
1200 END_USE_CODE
1201 end on
1202
1203 on note
1204 USE_CODE_IF(DEBUG_MODE) { Condition is not set, no message will be printed. }
1205 message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
1206 END_USE_CODE
1207 end on
1208
1209 on release
1210 USE_CODE_IF(DEBUG_MODE) { Condition is not set, no message will be printed. }
1211 message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
1212 END_USE_CODE
1213 end on
1214
1215 on controller
1216 USE_CODE_IF(DEBUG_MODE) { Condition is not set, no message will be printed. }
1217 message("MIDI Controller " & $CC_NUM " changed its value to " & %CC[$CC_NUM])
1218 END_USE_CODE
1219 end on
1220 </code>
1221 <p>
1222 Now you might say, you could also achieve that by declaring and using
1223 a regular NKSP variable. That's correct, but there are two major
1224 advantages by using preprocessor statements.
1225 </p>
1226 <ol>
1227 <li>
1228 <b>Saving Resources</b> -
1229 The preprocessor conditions are only processed before the script is
1230 loaded into the NKSP parser. So in contrast to using NKSP variables,
1231 the preprocessor solution does not waste any CPU time or memory
1232 resources while executing the script. That also means that variable
1233 declarations can be disabled with the preprocessor this way
1234 and thus will also safe resources.
1235 </li>
1236 <li>
1237 <b>Cross Platform Support</b> -
1238 Since the code portions filtered out by the preprocessor never make it
1239 into the NKSP language parser, those filtered code portions might also
1240 contain code which would have lead to parser errors. For example you
1241 could use a built-in preprocessor condition to check whether your script
1242 was loaded into LinuxSampler or rather into another sampler. That way
1243 you could maintain one script for both platforms: NKSP and KSP.
1244 Accordingly you could
1245 also check a built-in variable to obtain the version of the sampler in
1246 order to enable or disable code portions of your script that might
1247 use some newer script features of the sampler which don't exist in older
1248 version of the sampler.
1249 </li>
1250 </ol>
1251 <p>
1252 As a rule of thumb: if there are things that you could move from your
1253 NKSP executed programming code out to the preprocessor, then you should
1254 use the preprocessor instead for such things. And like stated above,
1255 there are certain things which you can only achieve with the preprocessor.
1256 </p>
1257
1258 <h2>What Next?</h2>
1259 <p>
1260 You have completed the introduction of the NKSP real-time instrument
1261 script language at this point. You can now dive into the details of the
1262 NKSP language by moving on to the
1263 <a href="nksp_reference.html">NKSP reference documentation</a>.
1264 Which provides you an overview and quick access to the details of all
1265 built-in functions, built-in variables and more.
1266 </p>
1267
1268 </body>
1269 </html>

  ViewVC Help
Powered by ViewVC