Make switch/case expression choose any option except the current one?

[andrewmarston]

After doing the Workbench L-System tutorial, I've been trying to modify the script so that the path doesn't double back on itself. My goal is create a script generated paths that sort of looks like growing circuitry. Below is the code from the tutorial. I believe this involves making the switch(r) function remember it's current case and choose any case that isn't that. However, after researching expressions and javascript switch/case functions, this is clearly above my current coding ability. Anyone know how to solve this, or point me in the right direction? I'm a bit stumped. I've also attached a screenshot with the bits where the path backtracks on itself I'm trying to get rid of.

s = thisComp.layer("Controller").effect("Random Seed")("Slider");
n = thisComp.layer("Controller").effect("Steps")("Slider");
l = thisComp.layer("Controller").effect("Max Length")("Slider");
seedRandom(s, true);
var pts = [];
var x = y = 0;
pts.push([x,y]);
for(i = 0; i < n; i++) {
    var d = Math.floor(random(l));
    var r = Math.floor(random(4));
    switch(r) {
        case 0:
            x += d;
            break;
        case 1:
            y += d;
            break;
        case 2:
            x -= d;
            break;
        case 3:
            y -= d;
            break;
    }
    pts.push([x,y]);
}
createPath(pts, [], [], false);

[Mylenium]

Long and short: You wouldn't use switch() in such a scenario and simply refactor it with calssic if()else() statements. switch() may have better performance, but it doesn't have persistent branching, which is what your use case would need - only go to the next lower level if the parent levels are not identical. Another option might of course be to optimize the generated array after the fact and remove redundancies, but that would be equalyl complex and not offer much advantage over the other method.

Mylenium

[Dan Ebberts]

Try it this way:

s = thisComp.layer("Controller").effect("Random Seed")("Slider");
n = thisComp.layer("Controller").effect("Steps")("Slider");
l = thisComp.layer("Controller").effect("Max Length")("Slider");
var pts = [];
var x = y = 0;
pts.push([x,y]);
rPrev = 0;
for(i = 0; i < n; i++) {
    var d = Math.floor(random(l));
    var r = (rPrev + 3 + Math.floor(random(3)))%4;
    switch(r) {
        case 0:
            x += d;
            break;
        case 1:
            y += d;
            break;
        case 2:
            x -= d;
            break;
        case 3:
            y -= d;
            break;
    }
    pts.push([x,y]);
    rPrev = r;
}
createPath(pts, [], [], false);

[Dan Ebberts]

I left out the seedRandom(), and this is better anyway:

s = thisComp.layer("Controller").effect("Random Seed")("Slider");
n = thisComp.layer("Controller").effect("Steps")("Slider");
l = thisComp.layer("Controller").effect("Max Length")("Slider");
seedRandom(s,true);
var pts = [];
var x = y = 0;
pts.push([x,y]);
rPrev = Math.floor(random(4));
for(i = 0; i < n; i++) {
    var d = Math.floor(random(l));
    var r = (rPrev + 3 + Math.floor(random(3)))%4;
    switch(r) {
        case 0:
            x += d;
            break;
        case 1:
            y += d;
            break;
        case 2:
            x -= d;
            break;
        case 3:
            y -= d;
            break;
    }
    pts.push([x,y]);
    rPrev = r;
}
createPath(pts, [], [], false);

Dan

[andrewmarston]

Thanks Dan! I must admit that the math here is a bit beyond me at the moment. How would I adapt this for 8 cases? I've tried the following but without luck:

rPrev = Math.floor(random(8));
for(i = 0; i < n; i++) {
    var d = Math.floor(random(l));
    var r = (rPrev + 7 + Math.floor(random(7)))%8;

[Dan Ebberts]

I'm making a guess as to what the other directions would be, but it could be something like this:

s = thisComp.layer("Controller").effect("Random Seed")("Slider");
n = thisComp.layer("Controller").effect("Steps")("Slider");
l = thisComp.layer("Controller").effect("Max Length")("Slider");
seedRandom(s,true);
var pts = [];
var x = y = 0;
pts.push([x,y]);
rPrev = Math.floor(random(8));
for(i = 0; i < n; i++) {
    var d = Math.floor(random(l));
    var r = (rPrev + 5 + Math.floor(random(7)))%8;
    switch(r) {
        case 0:
            x += d;
            break;
        case 1:
            x += d;
            y += d;
            break;
        case 2:
            y += d;
            break;
        case 3:
            x -= d;
            y += d;
            break;
        case 4:
            x -= d;
            break;
        case 5:
            x -= d;
            y -= d;
            break;
        case 6:
            y -= d;
            break;
        case 7:
            y -= d;
            x += d;
            break;
    }
    pts.push([x,y]);
    rPrev = r;
}
createPath(pts, [], [], false);

Dan