GAMES101 Lecture 07 - Shading 1 (Illumination, Shading and Graphics Pipeline)

GAMES101_Lecture_07.pdf

I. Illumination and Shading

• Shading: In this course, the process of applying a material to an object.

Bling-Phong Reflectance Model

A simplified reflectance model.

Definitions:

• $\mathbf{\text{v}}$$\textbf{v}$ - viewer direction (unit vector)

• $\mathbf{\text{n}}$$\textbf{n}$ - surface normal (unit vector)

• $\mathbf{\text{l}}$$\textbf{l}$ - light direction (unit vector)

• $I$$I$ - intensity of light

• Surface parameters: color, shininess, ...

   

Characteristics:

• Local: No shadows will be generated.

Components:

• Diffuse Reflection: Light is scattered uniformly in all directions.

  $$L_d=\frac{k_{d}I}{r^2}max(0,\mathbf{\text{n}}\cdot \mathbf{\text{l}})$$

  where

  • $L_d$$L_d$ is the diffusely reflected light, and

  • $k_d$$k_d$ is the diffuse coefficient (color).

• Specular Reflection: Light intensity depends on view direction. Bright near mirror reflection direction.

  $$L_s=\frac{k_{s}I}{r^2}max(0,\mathbf{\text{n}}\cdot \mathbf{\text{h}}{)}^p$$

  where

  • $L_s$$L_s$ is the specularly reflected light,

  • $k_s$$k_s$ is the specular coefficient,

  • $\mathbf{\text{h}}=\frac{\mathbf{\text{v}}+\mathbf{\text{l}}}{\Vert \mathbf{\text{v}}+\mathbf{\text{l}}\Vert }$$\textbf{h} = \frac{\textbf{v} + \textbf{l}}{\lVert \textbf{v} + \textbf{l} \rVert}$ is the bisector of $\mathbf{\text{v}}$$\textbf{v}$ and $\mathbf{\text{l}}$$\textbf{l}$, and

  • $p$$p$ is used control the width of the reflection lobe.

    

• Ambient Reflection: Constant color to account for disregarded illumination and fill in black shadows. This is only an approximation.

  $$L_a=k_a{I}_a$$

  where

  • $L_a$$L_a$ is the reflected ambient light, and

  • $k_a$$k_a$ is the ambient coefficient.