【Shader】實驗07——低消耗的水體渲染

水體渲染往往性能消耗較大，在性能較差的機器上就很難做複雜的水體渲染。所以需要在性能消耗與視覺效果之間找一個好的平衡點。

所以在寫完之前的水體渲染後，又嘗試寫了這個僅通過採樣法線貼圖後固定顏色的反射光，加上對texture的偏移模擬的折射光，低性能消耗渲染水。

實際只能模擬一片淺水窪，不過加上之前琢磨的環形漣漪，整體效果還行吧，在一些視覺效果要求不高但性能消耗要低的情況還是比較適用的。

反射reflection

區別於之前的水體渲染使用的，用反射光線採樣cubemap得到反射顏色。

這裏直接使用法線貼圖採樣的法線，再配合恰當的顏色來模擬波光粼粼的感覺。

fixed3 worldViewDir = normalize(UnityWorldSpaceViewDir(worldPos));
float2 speed = half2(_BumpSpeed, _BumpSpeed) * _Time.y;
fixed3 bump = UnpackNormal(tex2D(_Bump, i.uv.zw + speed)).rgb;
bump.xy *= _BumpScale;
bump.z = sqrt(1 - saturate(dot(bump.xy, bump.xy)));
bump = normalize(half3(dot(bump, i.Ttw0.xyz), dot(bump, i.Ttw1.xyz), dot(bump, i.Ttw2.xyz)));
half3 reflColor = dot(worldViewDir, bump) * _ReflectionColor;

折射refraction

區別於之前的水體渲染使用的GrabPass，這裏直接對貼圖進行折射偏移，所以水看起來很淺，加大折射力度可以改良些許。

float2 mainTex_uv_offset = bump.xy * _MainTex_TexelSize.xy * _RefractionScale;
fixed3 refrColor = tex2D(_MainTex, i.uv.xy + mainTex_uv_offset).rgb * _MainColor;

水面的環形漣漪wave

主要思路是給panel掛上碰撞檢測的c#腳本，一旦碰撞，就給shader傳遞碰撞點，並以碰撞點爲圓心模擬環形漣漪。
具體的環形漣漪模擬shader部分下篇再寫吧。

Shader

Shader "MyShaderTest/7_SimpleWater"
{
	Properties
	{
		_MainTex("Main Tex",2D) = "white"{}
		_MainColor("Main Color",Color) = (1,1,1,1)

		_Bump("Bump",2D) = "bump" {}
		_BumpScale("Bump Scale",float) = 1
		_BumpSpeed("Bump Speed",Range(0,2)) = 1

		_ReflectionColor("Reflection Color",Color) = (1,1,1,1)

		_RefractionScale("Refraction Scale",float) = 1

		_Frequency("Frequency",float) = 0
		_Amplitude("Amplitude",float) = 1
	}

	SubShader
	{
		Tags{ "RenderType" = "Opaque" }

		Pass
		{
			Tags{ "LightMode" = "ForwardBase" }

				CGPROGRAM
				#pragma vertex vert
				#pragma fragment frag
				#pragma multi_compile_fwdbase

				#include "UnityCG.cginc"
				#include "Lighting.cginc"

				struct a2v
				{
					float4 vertex : POSITION;
					float3 normal : NORMAL;
					float4 tangent : TANGENT;
					float2 texcoord : TEXCOORD0;
				};

				struct v2f
				{
					float4 pos : SV_POSITION;
					float4 uv : TEXCOORD0;
					float4 Ttw0 : TEXCOORD2;
					float4 Ttw1 : TEXCOORD3;
					float4 Ttw2 : TEXCOORD4;
				};

				sampler2D _MainTex;
				half4 _MainTex_ST;
				half4 _MainTex_TexelSize;
				half4 _MainColor;

				sampler2D _Bump;
				half4 _Bump_ST;
				half _BumpScale;
				half _BumpSpeed;

				fixed4 _ReflectionColor;
				half _RefractionScale;

				float _Frequency;
				float _Amplitude;

				float4 _wavePos;
				float _StartWaveWidth;
				float _EndWaveWidth;


				v2f vert(a2v v)
				{
					v2f o;
					float3 worldPos = mul(unity_ObjectToWorld, v.vertex);

					float3 worldNormal = UnityObjectToWorldNormal(v.normal);
					float3 worldTangent = UnityObjectToWorldDir(v.tangent.xyz);
					float3 worldBitangent = cross(worldNormal, worldTangent) * v.tangent.w;

					o.pos = mul(UNITY_MATRIX_VP, float4(worldPos, 1));
					o.uv.xy = TRANSFORM_TEX(v.texcoord, _MainTex);
					o.uv.zw = TRANSFORM_TEX(v.texcoord, _Bump);

					#if UNITY_UV_STARTS_AT_TOP
						if (_MainTex_TexelSize.y < 0.0)
						{
							o.uv.y = 1.0 - o.uv.y;
							o.uv.w = 1.0 - o.uv.w;
						}
					#endif

					o.Ttw0 = float4(worldTangent.x, worldBitangent.x, worldNormal.x, worldPos.x);
					o.Ttw1 = float4(worldTangent.y, worldBitangent.y, worldNormal.y, worldPos.y);
					o.Ttw2 = float4(worldTangent.z, worldBitangent.z, worldNormal.z, worldPos.z);

					return o;
				}

				fixed4 frag(v2f i) : SV_Target
				{
					float3 worldPos = float3(i.Ttw0.w,i.Ttw1.w,i.Ttw2.w);
					fixed3 worldViewDir = normalize(UnityWorldSpaceViewDir(worldPos));
					float2 speed = half2(_BumpSpeed, _BumpSpeed) * _Time.y;
					float2 dv = i.uv.xy - float2(_wavePos.x, _wavePos.y);
					dv = dv * float2(_wavePos.z / _wavePos.w, 1);//消除scale縮放影響

					float distance = sqrt(dv.x * dv.x + dv.y * dv.y);
					float sinFactor = sin(_Frequency * distance);
					float amplitude = _Amplitude * smoothstep(0, _StartWaveWidth, _StartWaveWidth - distance.x) * smoothstep(0, _EndWaveWidth, distance.x - _EndWaveWidth);
					float2 direction = normalize(dv);
					float2 wave_offset = normalize(dv) * sinFactor * amplitude;
					fixed3 bump = UnpackNormal(tex2D(_Bump, i.uv.zw + speed + wave_offset)).rgb;

					bump.xy *= _BumpScale;
					bump.z = sqrt(1 - saturate(dot(bump.xy, bump.xy)));
					bump = normalize(half3(dot(bump, i.Ttw0.xyz), dot(bump, i.Ttw1.xyz), dot(bump, i.Ttw2.xyz)));

					float2 mainTex_uv_offset = bump.xy * _MainTex_TexelSize.xy * _RefractionScale;
					fixed3 refrColor = tex2D(_MainTex, i.uv.xy + mainTex_uv_offset).rgb * _MainColor;
					half3 reflColor = dot(worldViewDir, bump) * _ReflectionColor;

					return fixed4(reflColor + refrColor, 1);
				}
				ENDCG
		}
	}
	FallBack "Diffuse"
}