NeHe OpenGL Lesson37 – Cel-Shading(卡通渲染)

This sample shows us how to do Cel-Shading with OpenGL. The cel-shading contain two part: one is the color grading on the object surface; the other one is the outline effect.
To get the color grading effect, we usually use the brightness of vertex as the vertex texture coordinates to sample a 1D texture that already color graded. The method that used in this sample is calculating the dot product between the triangle surface normal and light direction, take the result as the texture coordinates value.  A 1d texture that already color graded may like following:

As you see, some range will fall into one fix color. This will make the object surface appears to be color grading. The texture coordinates calculating process is on fly, we will do the computation on every frame.  Of course, you could provide paint it with color by command glColor3f, just as the screen shot, I gave it a blue color.

To get the outline effect. At first, we define the outline are the edges between front surfaces and back surfaces. So we just draw the back surfaces with wireframe mode, and less or equal for the depth comparing function. Of source, some options like set the line color, or width also be provided here with OpenGL commands.

 

The full source code could be checked from here.