As with normal mapping, POM is expected to improve the visualization of the already acceptable geometry. It cannot be used to create the appearance of an acceptable geometry from a poor-quality geometry.
Each texel in a POM material has a single channel of heightmap data, normalized between 0.0 (countersunk in the geometry to the maximum amount) and 1.0 (increased from the geometry to the normal amount). What this exactly means depends on the material used. Typical mesh materials have 1.0 flush with the geometry, with the result that it is only possible to penetrate the geometry, never to pull it out. Base materials, on the other hand, have 0.5 at the reference base height, where 0.0 is moved below the reference and 1.0 above the reference – this is effectively achieved by extruding the soil nodes before applying the POM effect.
Heightmap data can be manually edited in a program such as Adobe Photoshop if a linear color space is used. Using a nonlinear color space results in a wrong center point and distorted height ranges. If you edit heightmap data manually, make sure you use a tool to restore the normal map data so that the two data sets remain in sync – with the two effects simulating conflicting surface details producing poor results.
Parallax Occlusion Mapping can be very GPU intensive. We expect that users with GPUs in the lower to medium performance range will have this effect disabled. Disabling the effect is a switching of settings and simply causes the elevation data to be ignored.
There are a number of possible artifacts that result from using the POM technique. POM is not a “Set and Forget” technique – content creators must design a suitable geometry, use a suitable UV mapping method, and carefully test the results. In particular, it is the responsibility of the creator to address the following issues:
- POM can make textiles visible that are outside the UV-imaged area of the texture.
- The more extreme the viewing angle and the deeper the parallax, the further outside the intended assignment the user can see.
- The simplest use of POM, which completely avoids this problem, is to use the entire area of a texture that uses texturing along both axes.
- In some cases, this requires the use of a number of additional materials, as textures that could previously be part of a texture atlas now require their own unique tile texture.
- If you increase the number of materials in this way, make sure you use a different strategy in your lower LODs to avoid inflating the number of draw calls. Disabling POM at lower LODs is a valid strategy.
- Alternatively, the content creator can use different strategies to prevent this artefact from becoming visible to the user.
- If the POM geometry is completely enclosed by another geometry so that it cannot be viewed at a sharp angle, this artifact may not be problematic.