# Polygon Occluder Culling¶

## Introduction¶

One method of occlusion culling is to explicitly define a shape which will block out objects behind it. This is called a Polygon Occluder and is represented in Panda by the OccluderNode.

## Creating an OccluderNode¶

An occluder is defined by four vertices. The order of the vertices is important as this defines which way the normal of the polygon is facing.

occluder = OccluderNode('my occluder', Point3(0, 0, 0), Point3(1, 0, 0),
Point3(1, 1, 0), Point3(0, 1, 0))
occluder_nodepath = render.attachNewNode(occluder)
render.setOccluder(occluder_nodepath)


It is hidden by default, but can be shown for debug purposes using the show method on its NodePath. The occluder only needs to be parented into the scene if you want to show it, or if it needs to move with an object in the scene. Use the setOccluder method on any NodePath to make the occluder active on that NodePath and its children. It is much more efficient to call setOccluder on a parent node with children as opposed to calling setOccluder on many different nodes.

## Occluder Configuration¶

Besides the shape of the occluder, there are other settings which affect how the occluder behaves. Use the setDoubleSided method on the OccluderNode to enable the occluder to work on both sides. This is desirable for example if the occluder is placed inside of a wall. A double-sided occluder is more efficient than creating two occluders with opposite normals. Use the setMinCoverage method to ignore an occluder that doesn’t take up at least a certain amount of screen space.