uniform float4    _GS_SnowData1;	// x = relief, y = occlusion, z = glitter, w = brightness
	uniform float4    _GS_SnowData2;	// x = minimum altitude for vegetation
	uniform float4    _GS_SnowData4;    // w = billboard coverage
    uniform float4    _GS_SnowCamPos;
    unfiorm half4     _GS_SnowTint;
    uniform sampler2D_float _GS_DepthTexture;

	struct v2f {
		float4 pos : SV_POSITION;
		float3 worldPos : TEXCOORD0;
		float2 uv: TEXCOORD1;
	};


	// get snow coverage on tree billboards
	void SetTreeBillboardCoverage(v2f input, inout fixed4 col) { 
		
		float minAltitude = saturate((input.worldPos.y - _GS_SnowData2.x) * 0.1);
		float solid       = col.g * 2.0 - _GS_SnowData4.w;
		float snowCover   = minAltitude * saturate(solid) * 0.95;

        // mask support
        #if defined(GLOBALSNOW_MASK)
            float4 st = float4(input.worldPos.xz - _GS_SnowCamPos.xz, 0, 0);
            st *= _GS_SnowData2.z;
            st += 0.5;
            float zmask = tex2Dlod(_GS_DepthTexture, st).g;
            snowCover   = max(snowCover - zmask, 0);
        #endif

		// pass color data to output shader
		col.rgb = (1.0 + col.g) * (0.25 + _GS_SnowData1.w) * solid;
        col.rgb *= _GS_SnowTint.rgb;
		col.a   = snowCover;
	}