Unity Shader billboard effect

Billboard effect means that a normal direction of the two-dimensional plane is always the same line of sight (viewing direction of the camera). Widely used in rendering smoke, clouds, flash and so on.

Its essence is to construct a rotation matrix, then we can choose to build three basis vectors of this matrix.

Direction (X-axis) is directed →

Direction (Y-axis) is directed ↑

Plane normal direction (Z-axis)

It is generally calculated:

1. Determine the normal direction (the nature of the billboard effect) according to the current direction of the camera, and normalized

normal=normalize(viewDir);

2. Calculate the rightward direction and the normal direction according to the initial upward direction (in the local space is the float3 (0,1,0)) obtained and normalized

right = normalize (cross (up, normal)); (calculated using the vector cross product)

3. After calculating the right direction and the normal direction recalibrate the upward direction, the exact value of

up'=normalize(cross(right,normal));

 

Offset in the direction of the respective original vertices After calculating the rotation matrix

 

Script is as follows:

 1 // Upgrade NOTE: replaced '_World2Object' with 'unity_WorldToObject'
 2 
 3 Shader "MyUnlit/Billboarding"
 4 {
 5     Properties
 6     {
 7         _MainTex ("Texture", 2D) = "white" {}
 8         _Color("Color Tint",color)=(1,1,1,1)
 9     }
10     SubShader
11     {
12          // vertices must be disabled engagement transform P 
13 is          Tags { " Queue " = " Transparent "  " RenderType " = " Transparent "  " IgnoreProjector " = " to true "  " DisableBatching " = " True " }
 14  
15          Pass
 16          {
 . 17              / / alpha blending 
18 is              Tags { " LightMode " = "forwardbase" }
19             ZWrite off
20             Blend SrcAlpha OneMinusSrcAlpha
21             Cull off
22 
23             CGPROGRAM
24             #pragma vertex vert
25             #pragma fragment frag
26             #pragma multi_compile_fog
27 
28             #include "UnityCG.cginc"
29 
30             struct appdata
31             {
32                 float4 vertex : POSITION;
33                 float2 uv : TEXCOORD0;
34 is              };
 35  
36              struct V2f
 37 [              {
 38 is                  float2 UV: TEXCOORD0;
 39                  UNITY_FOG_COORDS ( . 1 )
 40                  float4 Vertex: SV_POSITION;
 41 is              };
 42 is  
43 is              sampler2D _MainTex;
 44 is              float4 _MainTex_ST;
 45              fixed4 _Color;
 46 is  
47              V2f Vert (AppData V)
 48              {
 49                  V2f O;
 50                  // gaze direction calculating model space 
51                 MUL = objViewDir float3 (unity_WorldToObject, float4 (_WorldSpaceCameraPos, . 1 ));
 52 is  
53 is                  // respective base vector calculating rotation matrix 
54 is                  float3 normalDir = the normalize (objViewDir);
 55                  float3 upDir float3 = ( 0 , . 1 , 0 );
 56 is                  float3 = rightDir the normalize (Cross (normalDir, upDir));
 57 is                  upDir = the normalize (Cross (normalDir, rightDir));
 58  
59                  // rotation matrix of offset vertices 
60                 * = rightDir v.vertex.x localPos float3 + + normalDir v.vertex.y upDir * * v.vertex.z;
 61 is  
62 is                  // value as a new offset after transfer calculations vertex 
63 is                  o.vertex UnityObjectToClipPos = ( float4 (localPos, . 1 ));
 64                  o.uv = TRANSFORM_TEX (v.uv, _MainTex);
 65                  UNITY_TRANSFER_FOG (O, o.vertex);
 66                  return O;
 67              }
 68  
69              fixed4 the frag (V2f I): SV_Target
 70              {
 71 is                  fixed4 COL = tex2D (_MainTex, i.uv);
 72                 col.rgb *= _Color.rgb;
73                 UNITY_APPLY_FOG(i.fogCoord, col);
74                 return col;
75             }
76             ENDCG
77         }
78     }
79     fallback "Transparent/VertexLit"
80 }