Shader "PaintTextureAdvance"{

    Properties{ _MainTex("Texture", any) = "" {} }

    SubShader{

        ZTest Always Cull Off ZWrite Off

        CGINCLUDE
            #include "UnityCG.cginc"
            #include "Packages/com.unity.terrain-tools/Shaders/TerrainTools.hlsl"


            sampler2D _MainTex;
            float4 _MainTex_TexelSize;      // 1/width, 1/height, width, height

            sampler2D _BrushTex;
            sampler2D _FilterTex;

            float4 _BrushParams;
            #define BRUSH_STRENGTH      (_BrushParams[0])
            #define BRUSH_TARGETHEIGHT  (_BrushParams[1])

            struct appdata_t {
                float4 vertex : POSITION;
                float2 pcUV : TEXCOORD0;
            };

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

            v2f vert(appdata_t v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.pcUV = v.pcUV;
                return o;
            }
        ENDCG

        Pass    // 0 paint splat alphamap
        {
            Name "Paint splat texture"

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment PaintSplatAlphamap

            float ApplyBrush(float height, float brushStrength)
            {
                float targetHeight = 1.0f;
                if (targetHeight > height)
                {
                    height += brushStrength;
                    height = height < targetHeight ? height : targetHeight;
                }
                else
                {
                    height -= brushStrength;
                    height = height > targetHeight ? height : targetHeight;
                }
                return height;
            }

            float4 PaintSplatAlphamap(v2f i) : SV_Target
            {
                float2 brushUV = PaintContextUVToBrushUV(i.pcUV);
                float2 normalUV = PaintContextUVToBrushUV(i.pcUV);

                // out of bounds multiplier
                float oob = all(saturate(brushUV) == brushUV) ? 1.0f : 0.0f;

                float brushStrength = BRUSH_STRENGTH * oob * UnpackHeightmap(tex2D(_FilterTex, i.pcUV)) * UnpackHeightmap(tex2D(_BrushTex, brushUV.xy));
                float splatMap = tex2D(_MainTex, i.pcUV).r;
                float targetAlpha = BRUSH_TARGETHEIGHT;

                return lerp(splatMap, targetAlpha, brushStrength);
            }

            ENDCG
        }
    }
    Fallback Off
}