RFE: XY interface for controlling 2 hsliders

[DBraun]

It would be great to have a 2D XY user interface like pictslider in Max/MSP or this interface in Ableton:

possible use basic use case below, but what would be the best syntax for it? Maybe we shouldn't change the language for it since it's out of scope.

import("stdfaust.lib");
gain = hslider("gain", 0, 0, 1, .01) : si.smoo;
freq = hslider("note", 60, 1, 127, .01) : si.smoo : ba.midikey2hz;
process = os.osc(freq)*gain;