Glass Shader

I’ve seen a lot of posts recently from folks trying to create shaders that recreate the appearance of glass. I guess the reason is that glass is a pretty common material, but modelling its appearance is surprisingly complex – requiring transparency, reflection, specular highlights, texture maps, and more.

For what it’s worth, here’s my attempt at a transparent specular shader suitable for use in a glass material. It’s pretty self-explanatory I think:

Shader "Custom/Transparent Specular" {
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
		
		// Colour property is used only to set influence of alpha, i.e. transparency
		_Colour ("Transparency (A only)", Color) = (0.5, 0.5, 0.5, 1)
		// Reflection map
		_Cube ("Reflection Cubemap", Cube) = "_Skybox" { TexGen CubeReflect }
		// Reflection Tint - leave as white to display reflection texture exactly as in cubemap
		_ReflectColour ("Reflection Colour", Color) = (1,1,1,0.5)
		// Reflection brightness
		_ReflectBrightness ("Reflection Brightness", Float) = 1.0
		// Specular
		_SpecularMap ("Specular / Reflection Map", 2D) = "white" {}
		// Rim
		_RimColour ("Rim Colour", Color) = (0.26,0.19,0.16,0.0)
	}
	SubShader {
		// This will be a transparent material
		Tags {
			"Queue"="Transparent"
			"IgnoreProjector"="True"
			"RenderType"="Transparent"
		}
		CGPROGRAM
		// Use surface shader with function called "surf"
		// Use the inbuilt BlinnPhong lighting model
		// Use alpha blending
		#pragma surface surf BlinnPhong alpha

		// Access the Shaderlab properties
		sampler2D _MainTex;
		sampler2D _SpecularMap;
		samplerCUBE _Cube;
		fixed4 _ReflectColour;
		fixed _ReflectBrightness;
		fixed4 _Colour;
		float4 _RimColour;

		struct Input {
			float2 uv_MainTex;
			float3 worldRefl; // Used for reflection map
			float3 viewDir; // Used for rim lighting
		};

		// Surface shader
		void surf (Input IN, inout SurfaceOutput o) {
		
			// Diffuse texture
			half4 c = tex2D (_MainTex, IN.uv_MainTex);
			o.Albedo = c.rgb;
			
			// How transparent is the surface?
			o.Alpha = _Colour.a * c.a;
			
			// Specular map
			half specular = tex2D(_SpecularMap, IN.uv_MainTex).r;
			o.Specular = specular;
			
			// Reflection map
			fixed4 reflcol = texCUBE (_Cube, IN.worldRefl);
			reflcol *= c.a;
			o.Emission = reflcol.rgb * _ReflectColour.rgb * _ReflectBrightness;
			o.Alpha = o.Alpha * _ReflectColour.a;
			
			//Rim
			// Rim lighting is emissive lighting based on angle between surface normal and view direction.
			// You get more reflection at glancing angles
			half intensity = 1.0 - saturate(dot (normalize(IN.viewDir), o.Normal));
			o.Emission += intensity * _RimColour.rgb;
		}
		ENDCG
	} 
	FallBack "Diffuse"
}

The Colour property is used only to set the overall transparency of the surface. The MainTex can be used to show grime, fingerprints, smudges, and smears on the surface. The SpecularMap should be set to match this by adjusting the degree to which specular highlights are shown. The Cube map contains the reflected environment image (which can be created using the script in my previous post). Here’s example textures for the maintex and spec map:

 

When rendered in a scene, this gives a result as follows: