One 、 Overview of basic lighting

1. Contains objects

• The light source —— The measure ： Radiation （ The cosine value perpendicular to the surface normal multiplied by the radiance on the slash ）
• Absorption and scattering —— The light is scattered , One will scatter into the interior of the object , One is reflected to the outside of the object

• To color —— The calculation process of object surface illumination model is carried out by using material attributes and light source information , Called coloring .
• BRDF Illumination model —— The rendering equation for calculating the interaction between light and object surface .

2. Standard illumination model

• The ambient light —— Describe the indirect illumination of the object surface ： Before the light enters the camera , After more than one reflection of the object .
• Spontaneous light —— Light is emitted directly from the light source into the camera
• Diffuse reflection —— The radiance of light scattered randomly from the object surface to all directions is modeled . At this time, the incident direction is not important , Because it will scatter in all directions . The intensity of the scattered light is directly proportional to the cosine of the angle between the direction of the light source
• highlights —— The calculation of highlights consists of two models , One is Blinn Model , The other is Phong Model

3. Pixel by pixel or vertex by vertex

• For calculating the position of the lighting model ： The calculation in the slice shader is called per pixel illumination , The calculation in the vertex shader is called per vertex illumination .
• Phong To color ： On a per pixel basis , Calculating normals , Then interpolate the vertex normals between patches
• Gorod coloring ： Then calculate the illumination on each vertex , Then linear interpolation is performed inside the rendering entity , Finally, output the imager color

4.Blinn-Phong Model

• Definition ： Diffuse and specular reflections are used to model the reflected light , An empirical method for calculating specular reflection is proposed .
• advantage ： Simplify the calculation , faster
• limitations ： Because it is an empirical model , For some complex phenomena , For example, the Fresnel reflex does not show , In addition, the characteristics of isotropy lead to rotating objects , The reflective surface will not be changed by any . Not applicable for hair, etc .

5. Ambient light and self illumination

• The ambient light ： Light already available in the space before adding Rehe lighting
  
• Spontaneous light ： Before the slice shader outputs the last color , Add the self luminous color of the material to the output color

Two 、 stay Unity Shader The diffuse illumination model is realized on