Unity Shader's basic lighting

How the camera looks at the world

The world that the camera sees in the game is almost the same as what we see in reality.

• First, the light is emitted from the light source.
• Then, the light intersects with some objects in the scene (scattering, absorbing).
• Finally, the camera absorbs some light and produces an image.

There are two results of the intersection of light and objects: scattering (scattering) and absorption (absorption)

• Scattering: Changes the direction of light only, but does not change the light's density and color, there are two directions: internal and external, corresponding to refraction and reflection.
  • Refraction (refraction): Scattered inside the object, calculated using a diffuse (diffuse) model.
  • Reflection (Reflection): Outside of the scattering object, calculated using a specular reflection (specular) model.
• Absorption: Only changes the density and color of the light, but does not change the direction of the light.

Different illumination models are used to calculate two different scattering directions: diffuse model and specular reflection model.

• Diffuse reflection: Indicates how much light is refracted, absorbed, and scattered out of the surface.
• Specular reflection: Indicates how the surface of an object reflects light.

Standard illumination Model

The light entering into the camera is divided into 4 parts, and each part uses a method to calculate its contribution.

• Self-Illumination (emissive): How much radiation a surface itself emits when given a direction. (does not illuminate the surrounding object, just appears to be bright)
• Specular reflection (Specular): The amount of radiation that the surface scatters in the full specular direction when the light shines from the light source to the model surface.
• Diffuse reflection (diffuse): The amount of radiation that the surface scatters in each direction when light shines from the light source to the model surface.
• Ambient light (Ambient): Describes all other indirect lighting.

Self-luminous

The spontaneous light color of the material is used directly.

High Light Reflection

Phong Model Formula

Specular = (Light • shininess) max (0, v R) ^gloss

• • Light: Source Color
  • Shininess: Inverse luminosity
  • v: Vector of object to camera direction
  • R: The reflection direction vector of the light, which can be calculated using the normal direction and the incident direction of the light, the equation is:r = 2 (n l)n - l)
  • Gloss: Gloss (The larger the number, the smaller the highlight)

Blinn Model Formula

Specular = (Light • shininess) max (0, v H) ^gloss

• • Light: Source Color
  • Shininess: Inverse luminosity
  • v: Vector of object to camera direction
  • h: After averaging the v and l , then normalization, formula:h = v + l /| v + L |
  • Gloss: Gloss (The larger the number, the smaller the highlight)

Diffuse reflection

Lambert's Law

Diffuse = (Light • diffusecolor) max (0, n l)

• • Light: Source Color
  • Diffusecolor: Material Diffuse color
  • n: Surface normal direction
  • l: unit vector for light source

code example (ambient light + diffuse + specular)

Shader"Unity My shader/diffuse Light"{Properties {_color ("Color", Color) = (1,1,1,1) _specular ("Specular", Color) = (1,1,1,1) _gloss ("Gloss", Range (8.0, the)) = -} subshader {Pass {tags{"Lightmode"="Forwardbase"} cgprogram#pragmaVertex vert#pragmaFragment Frag#include"Unitycg.cginc"#include"Lighting.cginc"fixed4 _color;            Fixed4 _specular; float_gloss; structa2v {float4 vertex:position;            FLOAT3 Normal:normal;            }; structv2f {float4 pos:sv_position;                FLOAT3 worldpos:texcoord0;            FLOAT3 Worldnormal:texcoord1;                        };                v2f Vert (a2v v) {v2f o; O.pos=Unityobjecttoclippos (V.vertex); O.worldpos= Mul (Unity_objecttoworld, V.vertex);//model coordinate vertex transform world coordinate vertexO.worldnormal = Unityobjecttoworldnormal (v.normal);//model coordinate normals transform world coordinate normals                returno; } fixed4 Frag (v2f i): sv_target {fixed3 worldnormal= Normalize (i.worldnormal);//Normal DirectionFixed3 Worldlightdir = Normalize (Unityworldspacelightdir (I.worldpos));//Illumination DirectionFixed3 Worldviewdir = Normalize (Unityworldspaceviewdir (I.worldpos));//Viewing Directionfixed3 Ambient= UNITY_LIGHTMODEL_AMBIENT.XYZ;//Ambient LightFixed3 Diffuse= _lightcolor0.rgb * _color.rgb * MAX (0, Dot (Worldnormal, worldlightdir));//Diffuse Reflectionfixed3 Halfdir= Normalize (Worldviewdir + worldlightdir);//Blinn Model Calculation HFIXED3 specular = _lightcolor0.rgb * _specular.rgb * POW (max (0, Dot (Worldviewdir, Halfdir)), _gloss);//High Light Reflection                returnFIXED4 (ambient + diffuse + specular,1);//Output Color after addition} ENDCG} }}

Unity Shader's basic lighting