Shader "Frozen/SpaceMapping"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		yFlip ("display name", Int) = 0
	}
	SubShader
	{
		Tags { "RenderType"="Opeque" }
		LOD 100
		//Blend One Zero
		Blend One OneMinusSrcAlpha
		
		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			
			#include "UnityCG.cginc"

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

			struct v2f
			{
				float4 vertex : SV_POSITION;
				float2 uv : TEXCOORD0;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;
			int yFlip;

			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				return o;
			}
			
			float4x4 homography[3];
			float3 homo_space;
			float2 texture_size;

			fixed4 frag (v2f i) : SV_Target
			{
				float2 uv = i.uv;
				//if (yFlip == 1) uv = i.uv * float2(1.0, -1.0) + float2(0.0, 1.0);
				fixed4 col = tex2D(_MainTex, uv);
				col.rgb *= col.a;
			
				const float3 space = homo_space;
				//const float2 size = float2(space.x + space.z * 2.0, space.y + space.z * 2.0);
				//const float dim = space.x + space.z * 2.0;
				const float2 clipped_size = texture_size;

				float2 pos = uv * clipped_size;
				
				if (pos.y <= space.z)
				{
					if (pos.x < space.z || pos.x > space.z + space.x)
					{
						pos = float2(0, 0);
					}
					else
					{
						float4 homo_pos = mul(homography[0], float4(pos, 0, 1));
						pos = homo_pos.xy / homo_pos.w;
					}
				}
				else if (pos.x <= space.z)
				{
					float4 homo_pos = mul(homography[1], float4(pos, 0, 1));
					pos = homo_pos.xy / homo_pos.w;
				}
				else if (pos.x >= space.z + space.x)
				{
					float4 homo_pos = mul(homography[2], float4(pos, 0, 1));
					pos = homo_pos.xy / homo_pos.w;
				}

				
				uv = pos / clipped_size;
				if (yFlip == 1) uv = uv * float2(1.0, -1.0) + float2(0.0, 1.0);
				col = any(length(pos)) ? tex2D(_MainTex, uv) : float4(0, 0, 0, 1);

				//col = tex2D(_MainTex, i.uv * float2(1.0, -1.0) + float2(0.0, 1.0));

				//col = float4(i.uv, 0.0, 1.0);

				return col;
			}
			ENDCG
		}
	}
}