Remove need to check ready before calling getGeometryInstanceAttributes

[pjcozzi]

This leads to workarounds like:

var frameNumber = 0;
var scratch = new Cesium.Cartesian3();
var ready = false;

viewer.clock.onTick.addEventListener(function() {
    var length = updates.length;
    var k;
    var u;

    if (!ready && primitive.ready) {
        ready = true;
        for (k = 0; k < length; ++k) {
            u = updates[k];
            u.attributes = primitive.getGeometryInstanceAttributes(k);
        }

        return;
    }

    if (ready) {
        for (k = 0; k < length; ++k) {
            u = updates[k];
            scratch = Cesium.Cartesian3.multiplyByScalar(u.direction, (Math.sin(frameNumber * u.speed) * u.maxHeight), scratch);
            u.attributes.offset = Cartesian3InstanceAttribute.toValue(scratch, u.offsetArray);
        }
    }

    ++frameNumber;
});

Full example: https://gist.github.com/pjcozzi/4bc8fbf5a2907de6c3a9

We can just buffer the attributes, which will also eliminate the need for a scratch variable each time an attribute is set (u.offsetArray above), which caught me recently. I suspect this can be done without creating GC pressure so the performance drop should be insignificant compared to the usability gain.

CC #766

[pjcozzi]

@bagnell any chance this was part of the batch table changes?

[bagnell]

The batch table fixes this mostly. The only thing that needs to wait for the primitive to be ready is the bounding sphere. If it's OK to return undefined for the bounding sphere until it's ready, this would be a simple change.

[pjcozzi]

Yeah, I think it will be fine for the bounding sphere property to require the primitive being ready. Labeled this as beginner.

[bampakoa]

@pjcozzi will the bounding sphere wait synchronously or asynchronously for the primitive to be ready?

[pjcozzi]

The bounding sphere get property function could just throw a DeveloperError if the primitive is not ready.