1. Cel shading
By jared brock

2. Overview Project Description What I must implement
What I would like to implement
Technique: Cel-Shading
What is cel-shading?
Requirements for Cel-shading
Generate Lighting Map
Calculate Light intensity
Draw the outline
Demo
Questions
References

3. Project Description Render a model in 3D
Implement multiple material shaders
Use the shaders on the different pieces of the model
Include cel-shading

4. Project description What I must do
Implement multiple material shaders (steel, wood, leather, and plastic)
Implement cel-shading
Be able to use shaders on specific pieces of the model
Be able to switch between multiple shaders
What I would like to do
Include multiple models
Add a GUI for switching between shaders

5. Cel Shading
What is cel-shading? - A type of shading that is used to mimic the style of a comic book or a cartoon

6. Requirements for cel shading
Generate a Lighting Map
Calculate Light Intensity
Draw Outlines

7. Generating a Lighting Map
A lighting map is a 1d grayscale texture
Basically a strip of 16 colors
Can modify the values to create different effects
Texture is used as a lookup table

8. Calculating Light intensity
N dot L
Value is used as an index into the lookup table
This works because N dot L returns the cosine of the angle between them
Negative values are mapped to 0

9. Drawing the outline
A cel shaded model is not truly cel shaded if the outline is not drawn

10. Drawing the outline
Here are two possible methods for drawing the outline
Use 2D Image Processing
Render scene to screen sized color texture
Render depth and world space surface normal to textures
Apply an edge-detection filter to depth and normal textures to generate edge texture
Combine edge texture with color texture
Use Built-in OpenGL functions
Render in wireframe mode
Only draw back facing polygons
Change the line width
Render again normally

11. Demo

12. Questions?

13. references
[1] S. Hamlaoui, “Cel-Shading,” and-theory/cel-shading-r1438 (current Jul )
[2] K.  Khanyants, “Cel-Shading Explained Visually,” (current 2002)
[3] J. Mahsman, “Fragment Shaders: Toon Shading,”
Pictures came from