Z-Buffer
记录每个像素的当前最近距离，初始距离为∞
在判断绘制时，如果当前的距离 < 深度缓存中该像素的最近距离，就绘制该像素，并更新深度缓存中的最近距离。
This is the algorithm that eventually won.
Idea:
• Store current min. z-value for each sample (pixel)
• Needs an additional buffer for depth values
- frame buffer stores color values
- depth buffer (z-buffer) stores depth
IMPORTANT: For simplicity we suppose
z is always positive (smaller z -> closer, larger z -> further)
Complexity 复杂度
• O(n) for n triangles (assuming constant coverage)
• How is it possible to sort n triangles in linear time?
Drawing triangles in different orders?
和三角形绘制顺序没有关系
Most important visibility algorithm
• Implemented in hardware for all GPUs
Q&A：
对于MSAA来说，每一个采样点都会利用Z-Buffer进行判断
对于透明的物体而言，需要特殊处理
Shading 着色
Shading：The process of applying a material to an object
Blinn-Phong Reflectance Model
Compute light reflected toward cameraat a specific shading point
Inputs:
• Viewer direction, v
• Surface normal, n
• Light direction, l (for each of many lights)
• Surface parameters (color, shininess, …)
此处没有生成阴影（shadow）shading ≠ shadow
Diffuse Reflection
• Light is scattered uniformly in all directions
–Surface color is the same for all viewing directions
• But how much light (energy) is received?
–Lambert’s cosine law
Lambertian (Diffuse) Shading
为什么要使用max?
当向量点乘为负数的时，没有物理意义，对亮度没有贡献。
漫反射系数：
kd = 0 完全吸收
kd = 1 完全不吸收