95 lines
5.2 KiB
Markdown
95 lines
5.2 KiB
Markdown
# Unity Terrain Shader with Height Blending and more features
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## About
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This shader is meant to be used on terrains, providing features additional to the standard Unity Terrain shader.
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Those features were developed especially with a use case of large and sparse landscapes in mind but can also be useful in other cases.
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## Features
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### Height Blend
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In order to achieve a more realistic appearance the blending between different terrain textures is done based on height information.
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For example sand can go in the cracks between stones this way:
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The Property "Height Blend Overlap Depth" defines an overlapping distance where the default linear blending behavior will be used.
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This is useful to smooth out the boarders between the different textures.
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### Avoid Texture Tile Repetition
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On larger terrains, especially if they are sparse, it is difficult to avoid a distracting appearance of texture tile repetition.
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To solve this problem, this shader uses an algorithm developed by Inigo Quilez to randomize orientation and offset of the texture tiles.
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### Distant Map
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On large terrains there is still the problem that from a distant view point the individual textures can become visible as blots of colors, leaving an otherwise featureless landscape.
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Therefore this shader offers to use a separate larger scale map that will be blended in based on distance to the viewer.
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The property "Distant Map Blend Distance" controls the distance at which the large scale map will start to blend in.
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"Distant Map Influence Min" can be set to always have a minimum amount of the large scale map visible to provide a bit more variety even from up close.
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With "Distant Map Influence Max" the maximum visibility of the large scale map can be reduced to always leave some of the detailed textures visible.
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### Parallax
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The available height information will also be used to create a parallax 3D effect.
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This can be controlled using the "Parallax Height" property.
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## Installation
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To use this shader in your project, simply drop the .shader and .cginc files into your project in any place you like.
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The variants of this shader will then be available to be selected in a material inspector:
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## Variants
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### "UnityTerrain" variants
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The "UnityTerrain" variants are meant to work as a drop-in replacement for the standard Unity Terrain shader.
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While all other variants only support 4 texture layers, the "UnityTerrain" variants can use more than that, just like the standard Unity Terrain shader.
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Though, only the first 4 layers will provide the additional the features of this shader.
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All standard texture maps are set in the Terrain Layers of the Terrain object as usual.
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The additional height maps and settings are available in the inspector panel of the material.
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To apply this shader to a Terrain Object, a Material using this shader must be created.
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In the Terrain Object that material can then be set as a "Custom Material" in the "Terrain Settings".
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### "Independent" variants
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In contrast to the "UnityTerrain" variants, the "Independent" variants can be used on simple meshes.
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Here all texture maps and settings are available in the inspector panel of the material.
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This also allows to use any texture as a "Splat Map" to control where the individual layers appear.
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Thus the Splat map can be prepared externally and imported into Unity instead of needing to draw it manually inside of Unity.
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The alpha channel of the Albedo Maps will act as Smoothness Maps.
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### "NormalMap Gamma Correction"
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Since the shader will flip texture tiles in X or Y directions randomly it is possible that the normal maps will create a kind of checker board pattern if the normals are not level on average and light hits them from and angle.
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As a solution to this, the "NormalMap Gamma Correction" variant offers additional properties to apply a gamma correction to the individual red and green channels of the normal maps to level them out.
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To do this, use a directional light and adjust it once to light the scene from a direction along the X-Axis (West/East) and adjust the Red channel,
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then adjust the light again to light the scene from a direction along the Z-Axis (North/South) and adjust the Green channel.
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It is recommended to use this variant **only to find the correcting gamma values** and then apply those to the normal maps themselves using an external program.
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### "Simple Tiling"
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The feature to avoid texture tile repetition is the one that is the most heavy on performance.
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Because of that the "Simple Tiling" variants are created, not implementing that feature, to offer a choice where it is not needed.
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## Useful links
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* <a href="https://www.iquilezles.org/www/articles/texturerepetition/texturerepetition.htm">Algorithm to avoid texture tile repetition by Inigo Quilez</a>
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* <a href="https://unity3d.com/get-unity/download/archive">Unity download archive (including Built in shader sources)</a>
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