移动端大规模草渲染的实现

//用位置信息作为随机种子
#ifdef GRASS_OBJECT_MODE
	float3 randCalcPos = p[0].objectSpacePos;
#else
	float3 randCalcPos = oPos;
#endif
进一步获得xz的随机
fixed randX = rand(randCalcPos.xz + 1000) * _Disorder * 2 - _Disorder;
fixed randZ = rand(randCalcPos.xz - 1000) * _Disorder * 2 - _Disorder;
//Random value from 2D value between 0 and 1
inline float rand(float2 co)｛
	return frac(sin(dot(co.xy, float2(12.9898,78.233))) * 43758.5453);
｝
//If grass is looked at from the top, it should still look like grass
#ifdef GRASS_TOP_VIEW_COMPENSATION
	fixed topViewCompensation = 1 + pow(max(0, dot(viewDir, up)), 20) * 0.8;
	width *= topViewCompensation;
	fixed2 windDir = wind(randCalcPos, fixed2(randX, randZ) * (topViewCompensation));
#else
	fixed2 windDir = wind(randCalcPos, fixed2(randX, randZ));
#endif
inline fixed2 wind(float3 pos, fixed2 offset)
｛
	float3 realPos = float3(pos.x * cos(_WindRotation) - pos.z * sin(_WindRotation), pos.y, pos.x * sin(_WindRotation) + pos.z * cos(_WindRotation));
//这个是绕原点旋转之后的新坐标，具体推倒可以参考https://blog.csdn.net/u012138730/article/details/80320162
	fixed2 windWaveStrength = _WindParams.x * sin(0.7f*windStrength(realPos)) * cos(0.15f*windStrength(realPos));
	windWaveStrength += windRipple(realPos);
	fixed2 wind = fixed2(windWaveStrength.x + offset.x, windWaveStrength.y + offset.y);
	return fixed2(wind.x * cos(_WindRotation) - wind.y * sin(_WindRotation), wind.x * sin(_WindRotation) + wind.y * cos(_WindRotation));
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//这个风力函数比较复杂，用四个正余弦函数弄出的一个波动效果
inline fixed windStrength(float3 pos)
｛
	return pos.x + _Time.w*_WindParams.y + 5*cos(0.01f*pos.z + _Time.y*_WindParams.y * 0.2f) + 4*sin(0.05f*pos.z - _Time.y*_WindParams.y*0.15f) + 4*sin(0.2f*pos.z + _Time.y*_WindParams.y * 0.2f) + 2*cos(0.6f*pos.z - _Time.y*_WindParams.y*0.4f);
｝
inline fixed windRippleStrength(float3 pos)
｛
	return sin(100*pos.x + _Time.y*_WindParams.w*3 + pos.z)*cos(10*pos.x + _Time.y*_WindParams.w*2 + pos.z*0.5f);
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inline fixed2 windRipple(float3 pos)
｛
	return _WindParams.z * fixed2(windRippleStrength(pos), windRippleStrength(pos + float3(452, 0, 987)));
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//lod是这个草要分成几段，是曲面细分那边的内容
for(fixed i = 1; i <= lod; i++)
｛
	fixed segment = i*invLod;
	fixed sqrSegment = segment*segment;
        //segment是草的长度的百分比，pos就是最终的实际高度
	float3 pos = float3(up*segment*realHeight);
        //xz要加上风所带来的影响,
	pos.xz += windDir.xy * sqrSegment * stiffnessFactor;
        //高度也要矫正
	pos.y  -= length(windDir) * sqrSegment * 0.5f * stiffnessFactor;
	fixed uvHeight = segment;
	viewDir = normalize(rendererPos - pos);
	fixed3 localUp = pos - lastPos;
	//Simple grass has no texture, so the mesh has to look like a blade of grass
	pIn.vertex =  float4((pos - width * groundRight * (1 - sqrSegment)).xyz, 1);
	getNormals(localUp, lightDir, groundRight, /*out*/ pIn.normal, /*out*/ pIn.reflectionNormal);
	triStream.Append(geomToFrag(pIn));
	//Simple grass has no texture, so the mesh has to look like a blade of grass
	pIn.vertex =  float4((pos + width * groundRight * (1 - sqrSegment)).xyz, 1);	
	getNormals(localUp, lightDir, groundRight, /*out*/ pIn.normal, /*out*/ pIn.reflectionNormal);
	triStream.Append(geomToFrag(pIn));
	lastPos = pos;
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v2f o;
float4 vertex = v.vertex;
o.vertex = UnityObjectToClipPos(v.vertex);
o.pos = mul(unity_ObjectToWorld, v.vertex);
float r = v.vertex.x + 0.5;
float b = v.vertex.z + 0.5;
float len = length(v.vertex.xz * 2);
o.color.r = r;
o.color.g = pow(1 - len, 1);
o.color.b = b;
o.color.a = 1;
return o;

 v2f vert(appdata v, uint vid : SV_VertexID)
	            ｛
			v2f o;
			float index = floor(vid / ((_GrassSeg + 1) * 2));
			float grid = _GrassRange / _GrassNum;
			float row = floor(index / _GrassNum);
			float col = index % _GrassNum;
			float4 objectPos = float4(-_GrassRange / 2 + row * grid, 0, -_GrassRange / 2 + col * grid, 1);
			float4 worldPos1 = mul(unity_ObjectToWorld, objectPos);
			float4 vertex = v.vertex;
			float3 worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
			float3 randCalcPos = worldPos;
			float2 windDir = wind(randCalcPos);
			float4 grassuv1 = mul(GrassMatrix, worldPos1);
			float2 grassuv2 = grassuv1.xy / grassuv1.w * 0.5 + 0.5;
#if UNITY_UV_STARTS_AT_TOP
			grassuv2.y = 1 - grassuv2.y;
#endif
		        float4 n = tex2Dlod(_GrassTex, float4(grassuv2, 0, 0));
			n.xz = (n.xz - 0.5) * 2;
			float2 off = (windDir.xy) * pow(v.vertex.y * 2, 2);// +n.xyz;
			worldPos.y -= 10 * dot(off, off);
			float2 newOff = off * (1 - n.g) + normalize(n.xz) * v.vertex.y * n.g * 0.6;
			worldPos.y *= (1 - n.g);
			//off = float2(-0.3, 0) * v.vertex.y;
			worldPos.xz += newOff;
			o.pos = mul(UNITY_MATRIX_VP, float4(worldPos, 1));
			//o.pos = UnityObjectToClipPos(vertex);
			o.uv = v.uv;
			half3 worldNormal = UnityObjectToWorldNormal(v.normal);
			half nl = max(0, dot(worldNormal, _WorldSpaceLightPos0.xyz));
			o.diff = nl * _LightColor0;
			o.diff *= v.color;
			o.diff.rgb += +ShadeSH9(half4(worldNormal, 1));
			TRANSFER_SHADOW(o)
			return o;
		｝