Function sampleCurve

docs/app/js/sanddance-app.js:119930–119972

(f, extent, minSteps, maxSteps)

// subdivide up to accuracy of 0.5 degrees
const MIN_RADIANS = 0.5 * Math.PI / 180; // Adaptively sample an interpolated function over a domain extent
function sampleCurve(f, extent, minSteps, maxSteps) {
    minSteps = minSteps || 25;
    maxSteps = Math.max(minSteps, maxSteps || 200);
    const point = (x)=>[
            x,
            f(x)
        ], minX = extent[0], maxX = extent[1], span = maxX - minX, stop = span / maxSteps, prev = [
        point(minX)
    ], next = [];
    if (minSteps === maxSteps) {
        // no adaptation, sample uniform grid directly and return
        for(let i = 1; i < maxSteps; ++i)prev.push(point(minX + i / minSteps * span));
        prev.push(point(maxX));
        return prev;
    } else {
        // sample minimum points on uniform grid
        // then move on to perform adaptive refinement
        next.push(point(maxX));
        for(let i = minSteps; --i > 0;)next.push(point(minX + i / minSteps * span));
    }
    let p0 = prev[0];
    let p1 = next[next.length - 1];
    const sx = 1 / span;
    const sy = scaleY(p0[1], next);
    while(p1){
        // midpoint for potential curve subdivision
        const pm = point((p0[0] + p1[0]) / 2);
        const dx = pm[0] - p0[0] >= stop;
        if (dx && angleDelta(p0, pm, p1, sx, sy) > MIN_RADIANS) // maximum resolution has not yet been met, and
        // subdivision midpoint is sufficiently different from endpoint
        // save subdivision, push midpoint onto the visitation stack
        next.push(pm);
        else {
            // subdivision midpoint sufficiently similar to endpoint
            // skip subdivision, store endpoint, move to next point on the stack
            p0 = p1;
            prev.push(p1);
            next.pop();
        }
        p1 = next[next.length - 1];
    }
    return prev;
}
function scaleY(init, points1) {
    let ymin = init;
    let ymax = init;