Adds 14 types of airlocks (#887)

Does what the title says!

Co-authored-by: CosmicCoincidence <cosmiccoincidence1991@gmail.com>

Author: EikoBiko

Assets/Art/Models/Structures/Doors/SS13Airlocks.fbx

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+// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'
+
+Shader "Custom/GlassBackfaceCull"
+{
+	
+	Properties
+	{
+		_MainTex("Texture", 2D) = "white" {}
+		_Color("Color", Color) = (1, 1, 1, 1)
+		_EdgeColor("Edge Color", Color) = (1, 1, 1, 1)
+		_EdgeThickness("Silouette Dropoff Rate", float) = 1.0
+	}
+
+		SubShader
+		{
+			Tags
+			{
+				"Queue" = "Transparent"
+			}
+
+			Pass
+			{
+				ZWrite Off
+				Blend SrcAlpha OneMinusSrcAlpha // standard alpha blending
+
+				CGPROGRAM
+
+				#pragma vertex vert
+				#pragma fragment frag
+
+			// Properties
+			sampler2D		_MainTex;
+			uniform float4	_Color;
+			uniform float4	_EdgeColor;
+			uniform float   _EdgeThickness;
+
+			struct vertexInput
+			{
+				float4 vertex : POSITION;
+				float3 normal : NORMAL;
+				float3 texCoord : TEXCOORD0;
+			};
+
+			struct vertexOutput
+			{
+				float4 pos : SV_POSITION;
+				float3 normal : NORMAL;
+				float3 texCoord : TEXCOORD0;
+				float3 viewDir : TEXCOORD1;
+			};
+
+			vertexOutput vert(vertexInput input)
+			{
+				vertexOutput output;
+
+				// convert input to world space
+				output.pos = UnityObjectToClipPos(input.vertex);
+				float4 normal4 = float4(input.normal, 0.0);
+				output.normal = normalize(mul(normal4, unity_WorldToObject).xyz);
+				output.viewDir = normalize(_WorldSpaceCameraPos - mul(unity_ObjectToWorld, input.vertex).xyz);
+
+				output.texCoord = input.texCoord;
+
+				return output;
+			}
+
+			float4 frag(vertexOutput input) : COLOR
+			{
+				// sample texture for color
+				float4 texColor = tex2D(_MainTex, input.texCoord.xy);
+
+				// apply silouette equation
+				// based on how close normal is to being orthogonal to view vector
+				// dot product is smaller the smaller the angle bw the vectors is
+				// close to edge = closer to 0
+				// far from edge = closer to 1
+				float edgeFactor = abs(dot(input.viewDir, input.normal));
+
+				// apply edgeFactor to Albedo color & EdgeColor
+				float oneMinusEdge = 1.0 - edgeFactor;
+				float3 rgb = (_Color.rgb * edgeFactor) + (_EdgeColor * oneMinusEdge);
+				rgb = min(float3(1, 1, 1), rgb); // clamp to real color vals
+				rgb = rgb * texColor.rgb;
+
+				// apply edgeFactor to Albedo transparency & EdgeColor transparency
+				// close to edge = more opaque EdgeColor & more transparent Albedo 
+				float opacity = min(1.0, _Color.a / edgeFactor);
+
+				// opacity^thickness means the edge color will be near 0 away from the edges
+				// and escalate quickly in opacity towards the edges
+				opacity = pow(opacity, _EdgeThickness);
+				opacity = opacity * texColor.a;
+
+				float4 output = float4(rgb, opacity);
+				return output;
+			}
+
+			ENDCG
+		}
+		}
+
+}