Possibility for meta node manipulation

[chaosprint]

It would also be great to support dynamic node.

o: sin 440 >> dnode "for i in range(128): output[0][i] = input[0][i] * 0.5"

grame-cncm/faust#685 (comment)

Edit:

I have been looking for options for this embedding language and finally landed on rhai.

the syntax of rhai is really intuitive and I think it has merged the syntax sugar of js and rust.

embedding Rhai in Glicol is a very straightforward experience thanks to its well-designed api and docs (rhai.rs)

now, users can write:

a: script `
    output.pad(128, 0.0);
    for i in 0..128 {
        output[i] = sin(2*PI()*phase) ;
        phase += 440.0 / sr;
    };
    while phase > 1.0 { phase -= 1.0 };
    output
` >> script `
    output = input.map(|i|i*0.2);
    output
`

see the interactive example on https://glicol.org/guide#rhai2

from my current testing, for this real-time audio scripting, creating new variables, especially arrays should be avoided.

for now the script node provides outout, input (if there is one), sr and phase to the Scope of rhai, as well as variables from a to z. x0, x1, x2, y0, y1, y2.

I am still exploring the possibility to share a ringbuf in rhai Scope; some functions such as random can also be useful.

---

Add an example:

// a sawtooth osc chained with a onepole filter
a: meta `
	f = 220.;
	output.pad(128, 0.0);
	if phase == 0 {
		p = 0.0;
	}
	for i in 0..128 {
		output[i] = p * 2. - 1.;
		p += f / sr;
	};
	if p > 1.0 { p -= 1.0 };
	output
` >> meta `
	r = 1./2000.;
	if phase == 0.0 {
		z = 0.0
	}
	output.pad(128, 0.0);
	b = (-2.0 * PI() * r).exp();
	a = 1.0 - b;
	for i in 0..128 {
		y = input[i] * a + b * z;
		output[i] = y;
		z = y;
	};
	output
`

---

TODOs:

• Solve the popping during update
• Improve the performance

[chaosprint]

done with expr and eval; will finalise them right away.