View source for Hedgehog Engine 2 - Physically Based Rendering (PBR)

Physically based rendering is used in HE2 games and mostly associated with "PRM" textures. By combining several textures of various properties, you can create a wide range of materials to render physically accurate looking surfaces.

== Components ==

=== Albedo ===

Albedo is the base color of a surface and is used with “diffuse” lighting.
[[File:SXSG PBR Albedo.png|Materials with various albedo colors in Shadow Generations|center]]

=== Smoothness ===
Smoothness determines how reflective a surface is. The lower the smoothness, the blurrier the reflection. This is represented by a value between 0 and 1.
[[File:SXSG PBR Smoothness.png|Materials with full specularity and a gradually increasing smoothness in Shadow Generations|center]]

=== Specular ===
Seperately from diffuse lighting, specular lighting controls the visibility of specular lighting and reflections. You can imagine it as a “layer” on top of the diffuse lighting, with the specularity acting as the “layer transparency”. Hedgehog Engine 2 specifically makes use of “F0 reflectance”.

It’s represented by a value between 0 and 1; Usually a specular value of 0.125 is considered the “default”.
[[File:SXSG PBR Specular.png|center|Gold-ish (#FFAA00) materials with a gradually increasing specularity in Shadow Generations]]

{{Notice|type=info|content=When used in a <code>PBRFactor</code> shader parameter, the specular value is used as is.

In PRM textures however, it is divided by 4. Thus, the highest specular value achievable with a standard image format is 0.25.

This can be circumvented by using using an HDR image format such as <code>R16G16B16A16_FLOAT.</code>}}

=== Metallic ===
Metallic is similar to specular, with the 2 differences:

* The albedo color affects the color of reflection
* A more linear value progression

Similarly to specular, it also can be seen as a seperate “layer” that is placed above the specular lighting.

It too is represented by a value between 0 and 1. Usually a metallic value of 0 is considered the “default”.
[[File:SXSG PBR Metallic.png|center|Gold-ish (#FFAA00) materials with a gradually increasing metallicness in Shadow Generations]]
{{Notice|type=note|content=Usually, metallic is done either 0 or 1, and rarely anything in between.}}

=== Combining Specular and Metallic ===
While rarely done, it is possible to use specular and metallic lighting together.
[[File:SXSG PBR Specular Metallic.png|center|Gold-ish (#FFAA00) materials with a smoothness of 0.85 and gradually increasing specularity and metallicness in Shadow Generations]]

=== Emission ===
Emission is essentially the colored “glow” of the surface, like the light coming from a lamp. This is unaffected by any lighting that may hit the surface.
[[File:SXSG PBR Emission.png|center|Black materials with various emission colors in Shadow Generations]]
Unlike the other surface values, emission supports high-dynamic-range images, and can use values beyond the 0-1 range, which the rendering engine may process in various ways.

Additionally, emission is often accompanied by a “Luminance” parameter that changes how bright the emission texture appears.
[[File:SXSG PBR Luminance.png|center|Black materials with white emission and gradually increasing luminance in Shadow Generations]]

=== Ambient Occlusion / Cavity ===
Ambient occlusion (often abbrivated with “AO” or “A/O”) is, as the name implies, responsible for occluding/removing ambient lighting. There are several types of ambient lighting, but this part solely focusses on the material surface AO, sometimes also referred to as "Cavity".

In Hedgehog Engine 2 games, ambient lighting consists of

* Global illumination (GI)
* Environment reflections (“Image based lighting”; IBL)
* Screen space reflections (SSR)

Ambient occlusion too is represented by a value between 0 and 1. However, unlike the other values, where a higher greater value “increases” the effect, here a lower value increases the occlusion of ambient lighting.

Thus the default value, at which no ambient light is occluded, is 1.
[[File:SXSG PBR Ambient occlusion.png|center|Gold-ish (#FFAA00) materials with different lighting values and gradually decreasing ambient occlusion in Shadow Generations]]
{{Notice|type=info|content=Note how, in the chart above, the “sun” in the reflection is still visible. That is because it is a sun light and not actually part of the environmental reflections, which are handled as seperate part of the lighting in HE2.}}

== Examples ==
Now, with all the info above, even moreso when combined with Normal maps, we can create a wide range of materials to use!

Let’s look at some examples:

=== Example 1: ARK Techno Panels ===
[[File:SXSG PBR Example 1.png|center|<code>m01_techno_panel_emsa_sy1</code> from the ARK in Shadow Generations]]

=== Example 2: Rail Canyon Asphalt ===
[[File:SXSG PBR Example 2.png|center|<code>m06_ds_asphalt_base_sy1</code> from Rail Canyon in Shadow Generations]]

=== Example 3: Kingdom Valley Wood bark ===
[[File:SXSG PBR Example 3.png|center|<code>m03_kdv_wood02_dfsp_n_ih1</code> from Kingdom Valley in Shadow Generations]]

=== Example 4: Sunset Heights Building wall ===
[[File:SXSG PBR Example 4.png|center|<code>m06_ds_wall_window18_fh1</code> from Sunet Heights in Shadow Generations]]

=== Example 5: Chaos Island Rock Cliff ===
[[File:SXSG PBR Example 5.png|center|<code>m05_rockcliff01_sy1</code> (top layer) from Chaos Island in Shadow Generations]]

=== Example 6: Radical Highway Tunnel Wall ===
[[File:SXSG PBR Example 6.png|center|<code>m06_ds_tunnel_d_kk1</code> from Radical Highway in Shadow Generations]]