Games101 Lesson 8 shading 2 Notes

One 、 highlights （Specular Term）

（1） The highlight vector and the light source vector are symmetrical with the normal line as the symmetry axis .

（2）Blinn-Phong The model calculates the energy of the highlight

①Blinn-Phong The light source vector is introduced into the model l And observation vector v The half range vector of h To facilitate the calculation of .
②Blinn-Phong The model is a simplified model , There is no consideration that objects will absorb energy .
③ Because the highlight can only be seen in a small range , Therefore, the penalty index is introduced p. The following function image shows the value of cosine function with exponent .

（3） The following figure shows the highlight coefficient ks and p The observation of the sphere when the value changes .

① This image gives the observation results that both highlights and diffuse reflections exist .

Two 、 The ambient light （Ambient Term）

（1） Definition of ambient light

① Ambient light is independent of light source and observation vector .
② Ambient light is a constant （ It's a certain color ）.
③ The ambient light calculation in this section is a simplified calculation .

3、 ... and 、Blinn-Phong Reflection model

（1）Blinn-Phong Single point coloring of reflection model = Ambient shading + Diffuse shading + Highlight shading

Four 、 Coloring frequency （Shading Frequencies）

（1） Coloring frequency refers to coloring a certain area of size , It's about face . Here are the observations corresponding to three different coloring frequencies .

（2） Three coloring models with different coloring frequencies
①Flat Shading It is coloring triangle by triangle , Each triangle has the same color .

②Gouraud Shading Is shading per vertex , Each triangle is colored according to three vertices , It looks smooth .

③Phong Shading It is shading per pixel .

（3） Comparison of three coloring models
① If the vertices of the model / More faces , The gap between the three coloring models will become smaller until they are the same .
② The more complex the model , The effect of the first two shading models will be enhanced , But at the same time, the cost will be greater .

（4） How to calculate the normals of vertices ？

① Usually, a vertex belongs to multiple planes , The normals of vertices can be obtained by averaging the sum of normals of these planes .
② If the weighted average is carried out according to the area of each face , It works better .
（5） How to calculate the normal of pixels ？

① The vertex normals on both sides are known , Using the barycentric coordinates, you can calculate the normals of each point inside .
② Find various vectors, and finally remember the normalization operation .

5、 ... and 、 pipeline （Pipeline）

（1） Pipeline refers to the whole rendering process from model to pixel , It can be seen as a pipeline from model to drawing . The pipeline is divided into the following steps ：

① Vertex Processing
② Triangle processing
③ Rasterize
④ Pixel processing
⑤ Mix all pixels into one image
（2） Be careful
① If the shading model is Phong Shading, Then the coloring step is carried out in the pixel processing link ; If the shading model is Gouraud Shading, Then the shading operation can be carried out in vertex processing .

6、 ... and 、 Texture mapping （Texture Mapping）

（1） Texture mapping defines different attributes in different positions of objects .

（2） Some definitions

① The surface of any three-dimensional object is two-dimensional .
② We can think of texture as a picture .
③ Applying texture to the surface of an object can be understood as mapping it .

（3） Texture coordinate system

① Defines a texture coordinate system （u, v）. Each triangle corresponds to a position in the texture coordinate system .
② Different positions can also be mapped to the same texture , That is, textures can be reused .

reference

Course video link : GAMES101 Lecture08 Shading 2