Shader "Unlit/IsoShader"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		_CenterPoint ("Object Center", Vector) = (0,0,0,0)
		_TextureOffset("Texture Offset", Vector) = (0,0,0,0)
		_PixelsPerUnit("Pixels Per World Unit", Float) = 1
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			// make fog work
			#pragma multi_compile_fog
			
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				UNITY_FOG_COORDS(1)
				float4 vertex : SV_POSITION;
				float4 screenPos : TEXCOORD1;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;
			float4 _MainTex_TexelSize;

			float4 _CenterPoint;
			float4 _TextureOffset;
			float _PixelsPerUnit;
			
			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				o.screenPos = ComputeScreenPos(o.vertex)
				UNITY_TRANSFER_FOG(o,o.vertex);
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				// unity_OrthoParams.xy / 0.70710678   = Wu/Vp
				// PixelsPerUnit         = Px/Wu
				// _MainTex_TexelSize.xy = Uv/Px

				// we want Uv from:
				// (i.screenPos.xy - CenterPoint.xy) = Vp
				// (i.screenPos.xy - CenterPoint.xy) * unity_OrthoParams.x * _PixelsPerUnit * _MainTex_TexelSize.xy = Uv				

				float2 worldUnitScale = unity_OrthoParams.xy / 0.70710678;
				float2 offset = float2(i.screenPos.x - _CenterPoint.x, _CenterPoint.y - i.screenPos.y);
				float2 uvs = float2((offset.x * worldUnitScale.x * _PixelsPerUnit - _TextureOffset.x) * _MainTex_TexelSize.x,
									1 - (offset.y * worldUnitScale.y * _PixelsPerUnit - _TextureOffset.y) * _MainTex_TexelSize.y);
				
				// sample the texture
				fixed4 col = tex2D(_MainTex, uvs);

				clip(col.a - 0.5);
				//fixed4 col = fixed4(uvs.x, 0, 0, 1);
				//fixed4 col = fixed4(uvs.xy, 0, 1);

				// apply fog
				//UNITY_APPLY_FOG(i.fogCoord, col);

				return col;
			}
			ENDCG
		}
	}
}