Parallax mapping shaders (relief and POM) for the bevy game engine

Bevy parallax mapping

parallax mapping is a graphical effect adding the impression of depth to simple 2d textures by moving the texture's pixel around according to the viewport's perspective.

This is NOT a "parallax" à la Super Mario World. This is intended for 3D rendering. This technic has been used with success in the Demon's Souls Bluepoint remake.

This crate adds a custom material that extends the default bevy PBR material with parallax mapping. The ParallaxMaterial asset is a straight copy of bevy's PBR material with the addition of the height_map: Handle<Image> filed (it's not Option since you might as well use the default shader if there is no height maps).

height_map is a greyscale image representing the height of the object at the specific pixel.

ParallaxMaterial allows selecting the algorithm used for parallaxing. By setting the algorithm field to the ParallaxAlgo of your choosing, you may opt into using Relief Mapping. By default, ParallaxMaterial uses the Parallax Occlusion Mapping (POM) method. (see the shader source code for explanation on what the algorithms do)

Examples

This repo contains two examples. to modify ParallaxMaterial values dynamically at run time, add the inspector-def feature flag.

cargo run --example <example_name> --features "inspector-def"

• earth3d: a spinning view of the earth. Takes advantage of height map, but also of all the bevy PBR fields. This a good demonstration of bevy's capabilities.
  You can orbit the earth by holding down the right mouse button, and zoom in/out with the mouse wheel.

• cube: A spinning cube with a parallaxed material in a basic 3d scene, mouse left click to switch point of view.

Bugs and limitations

• This doesn't implement silhouetting, so the meshes's silhouette will not change with the height map
  • As a result, height maps that are top-heavy should be favored (tree bark, bricks)
• This doesn't implement self-shadowing, resulting in potentially surprising sharp cutoffs
  • self-shadowing is described in the sunblackcat article, but bevy's lighting system requires handling several light types and multiple light sources at once, which is more complex than I can handle right now.
• The height map is inverted from the more common usage

Literature

The code is basically copied from the sunblackcat implementation linked on Wikipedia.

Optimization leads include:

1. https://www.diva-portal.org/smash/get/diva2:831762/FULLTEXT01.pdf
2. https://www.gamedevs.org/uploads/quadtree-displacement-mapping-with-height-blending.pdf
3. https://developer.nvidia.com/gpugems/gpugems3/part-i-geometry/chapter-4-next-generation-speedtree-rendering
4. https://old.reddit.com/r/GraphicsProgramming/comments/pgkogk/whatever_happened_to_quadtree_displacement_mapping/

Note that (1) says that (2) is slower than POM, while (3) is beyond out-of-scope for a small opensource crate (unless you want to pay me).

TODO

• Useability
  • bevy-inspector-egui definition (behind compile flag)
  • Generic over shader (should be possible to use with a traditional phong shader)
  • Conversion methods from_standard(StandardMaterial, height_map)
  • Automatic height_map computation based on a normal_map if possible
    • https://old.reddit.com/r/gamedev/comments/fffskm/convert_normal_map_to_displacement_map/
    • https://forums.unrealengine.com/t/invert-normal-to-height/145496
    • https://houdinigubbins.wordpress.com/2019/08/09/from-normal-to-height/
    • https://stannum.io/blog/0IwyJ-
    • Search keywords are a bit silly, I found that "invert displacement map from normal map" gave satisfactory results on ddg.

License

Earth images in assets/earth are public domain and taken from Wikimedia. I edited them myself, you are free to re-use the edited version however you want without restrictions.

• height map: elevation_water.png and elevation_surface.png adjust the values to highlight different topological features of earth, the normal_map.jpg is also derived from it.
• albedo (aka base color) is a scalled-down version of the 2002 Nasa blue marble earth satellite view using a equirectangular projection. metallic_roughness.png and base_color.jpg are derived from that image.
• emissive texture is from the 2012 Nasa blue marble project. It's a night time satellite view of earth.
• An alternative higher-quality height map is available at: https://commons.wikimedia.org/wiki/File:Srtm_ramp2.world.21600x10800.jpg

Copyright of code and assets go to their respective authors.

Original code is copyright © 2022 Nicola Papale

This software is licensed under Apache 2.0.