added gradient mapping shader (#763)

put in a grayscale texture and a gradient, get out a cool picture

Assets/Shaders/GradientMap.shader

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+Shader "Sprites/GradientMap"
+{
+	Properties
+	{
+		[PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
+		_GradientMap ("Color Map", 2D) = "white" {}
+		_Color ("Tint", Color) = (1,1,1,1)
+		[MaterialToggle] PixelSnap ("Pixel snap", Float) = 0
+	}
+
+	SubShader
+	{
+		Tags
+		{ 
+			"Queue"="Transparent" 
+			"IgnoreProjector"="True" 
+			"RenderType"="Transparent" 
+			"PreviewType"="Plane"
+			"CanUseSpriteAtlas"="True"
+		}
+
+		Cull Off
+		Lighting Off
+		ZWrite Off
+		Blend SrcAlpha OneMinusSrcAlpha
+
+		Pass
+		{
+		CGPROGRAM
+			#pragma vertex vert
+			#pragma fragment frag
+			#pragma multi_compile _ PIXELSNAP_ON
+			#include "UnityCG.cginc"
+			
+			struct appdata_t
+			{
+				float4 vertex   : POSITION;
+				float4 color    : COLOR;
+				float2 texcoord : TEXCOORD0;
+			};
+
+			struct v2f
+			{
+				float4 vertex   : SV_POSITION;
+				fixed4 color    : COLOR;
+				float2 texcoord  : TEXCOORD0;
+			};
+			
+			fixed4 _Color;
+
+			v2f vert(appdata_t IN)
+			{
+				v2f OUT;
+				OUT.vertex = UnityObjectToClipPos(IN.vertex);
+				OUT.texcoord = IN.texcoord;
+				OUT.color = IN.color * _Color;
+				#ifdef PIXELSNAP_ON
+				OUT.vertex = UnityPixelSnap (OUT.vertex);
+				#endif
+
+				return OUT;
+			}
+
+			sampler2D _MainTex;
+			sampler2D _AlphaTex;
+			sampler2D _GradientMap;
+			float _AlphaSplitEnabled;
+
+			fixed4 SampleSpriteTexture (float2 uv)
+			{
+				fixed4 color = tex2D (_MainTex, uv);
+
+				#if UNITY_TEXTURE_ALPHASPLIT_ALLOWED
+				if (_AlphaSplitEnabled)
+					color.a = tex2D (_AlphaTex, uv).r;
+				#endif //UNITY_TEXTURE_ALPHASPLIT_ALLOWED
+
+				return color;
+			}
+
+			fixed4 frag(v2f IN) : SV_Target
+			{
+				fixed4 input = SampleSpriteTexture (IN.texcoord);
+				float grayscale = (input.r + input.g + input.b) / 3;
+				fixed4 c = tex2D (_GradientMap, grayscale);
+				c *= _Color;
+				c.a *= input.a;
+
+				return c;
+			}
+		ENDCG
+		}
+	}
+}

Assets/Shaders/GradientMap.shader.meta

@@ -0,0 +1,10 @@
+fileFormatVersion: 2
+guid: 8024c6ce5677cd84e8efbea718c0cb71
+ShaderImporter:
+  externalObjects: {}
+  defaultTextures: []
+  nonModifiableTextures: []
+  preprocessorOverride: 0
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: