Displacement

Displacement physically raises and lowers a model’s surface according to the values in a height map. That is the key difference from bump and normal maps: they only fool the lighting, while displacement creates real geometry. Look along a displaced stone wall and the stones break the silhouette; real shadows fall into the joints.

How it works

At render time the engine subdivides the surface into very small triangles (tessellation) and pushes each vertex along the surface normal by the height-map value. The quality of the detail depends on how fine that subdivision is. Some engines adapt it to camera distance so that far-away surfaces do not generate geometry nobody will see.

Practical points

• Memory use and render time can rise sharply, so use it only where it counts.
• A height map with higher bit depth, such as 16-bit, reduces stepping.
• Set the height to a real-world amount; exaggerated displacement looks fake.
• Check that model and map agree so cracks do not open along UV seams.

In architectural visualization, displacement makes a clear difference in close-up shots of stone cladding, slate paving, grass, carpet and rough plaster.