function getBBox(c, r, theta) {
const [u, v] = getUV(r, theta);
const [exsqr, eysqr] = vec2.add(
vec2.create(),
vec2.mul(vec2.create(), u, u),
vec2.mul(vec2.create(), v, v)
);
const e = vec2.fromValues(Math.sqrt(exsqr), Math.sqrt(eysqr));
const cMinusE = vec2.sub(vec2.create(), c, e);
const cPlusE = vec2.add(vec2.create(), c, e);
return bounds(cMinusE, cPlusE);
}