Draw order of PointPlacemarks

问题:

Is there a way to fix the drawing order of PointPlacemarks in World Wind?

Even in the Placemarks example the ordering of Placemark B and the Audio Placemark can change just by moving the mouse at certain zoom levels:

So far I have tried:

• Adding PointPlacemarks to separate layers
• Using RenderableLayer.setRenderables rather than RenderableLayer.addRenderable
• Related question on World Wind forums

回答1:

Hacky solution (requires modifying World Wind source code)

In gov.nasa.worldwind.render.DrawContextImpl change orderedRenderables from

protected PriorityQueue<OrderedRenderableEntry> orderedRenderables =
    new PriorityQueue<OrderedRenderableEntry>(100, new Comparator<OrderedRenderableEntry>()
    {
        public int compare(OrderedRenderableEntry orA, OrderedRenderableEntry orB)
        {
            double eA = orA.distanceFromEye;
            double eB = orB.distanceFromEye;

            return eA > eB ? -1 : eA == eB ? (orA.time < orB.time ? -1 : orA.time == orB.time ? 0 : 1) : 1;
        }
    });

to

protected Queue<OrderedRenderableEntry> orderedRenderables = new ArrayDeque<>();

(or modify the comparator to do what you want). This will fix the drawing order.

Alternate solution (does not require modifying World Wind source code)

Extend PointPlacemark and override makeOrderedRenderable():

public class OrderedPointPlacemark extends PointPlacemark {
    public OrderedPointPlacemark(Position position) {
        super(position);
    }
    @Override
    protected void makeOrderedRenderable(DrawContext dc) {
        super.makeOrderedRenderable(dc);

        if (this.intersectsFrustum(dc) || this.isDrawLine(dc)) {
            dc.pollOrderedRenderables();
            dc.addOrderedSurfaceRenderable(this);
        }
    }
}