on postcompose in ol6 - how to draw on canvas on every render

Question

In ol6 the rendering context was removed from the postcompose event (according to the release notes).

How would I achieve to draw on a context on every render of one of the map layers? Currently (ol < 6) I simply was drawing on the context in postcompose. I already tried to add a separate vector layer and to draw in the postrender - but did not find an easy way to ensure a render on this layer if one of the lower layers is rendered (e.g. due to pan/zoom/...). Currently I guess I have to move outside of Openlayers and create an own canvas context on top of the map - so I can still draw in the postcompose (into my own context) . Not very elegant however...

Answer 1

A radius 0 circle will not be seen but with infinite render buffer there should always be a postrender event

new ol.layer.Vector({
    source: new ol.source.Vector({
        features: [new ol.Feature(new ol.geom.Point([0,0]))]
    }),
    style: new ol.style.Style({
        image: new ol.style.Circle({
            radius: 0
        })
    }),
    renderBuffer: Infinity,
    zIndex: Infinity
});