Function setFirstScatter

src/traces/scatter/calc.js:266–270

* mark the first scatter trace for each subplot * note that scatter and scattergl each get their own first trace * note also that I'm doing this during calc rather than supplyDefaults * so I don't need to worry about transforms, but if we ever do * per-trace calc this will get confused.

(fullLayout, trace)

 * per-trace calc this will get confused.
 */
function setFirstScatter(fullLayout, trace) {
    var group = firstScatterGroup(trace);
    var firstScatter = fullLayout._firstScatter;
    if(!firstScatter[group]) firstScatter[group] = trace.uid;
}

function firstScatterGroup(trace) {
    var stackGroup = trace.stackgroup;