A multi post break down of a recent post here it's gonna be pretty technical, a little dry, but lightweight. It just goes over my process with some tips. (there might be grammar error's I usually don't type this much)


If you're not familiar with Blender or Upbge here's a stockpile of youtubers I learned from about Upbge and Blender in general.

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Blender Guru (the quintessential blender teacher, but check his oldest video's for context)
John Hamilton (good material shader tutorials)
ThaTimster (good tutorials and a resource for GLSL shaders)

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<<FA Post Transcript>>
The shader setup is mainly just color mixing.
The Color Ramp takes the Base Material's "Color" output and clamps the
shading to black and white while allowing it to be edited.
It's then mixed with the geometry's Vertex Color via a Mix RGB node
set to Soft Light. The result is plugged into the shader output and makes a
decent toon shader. The Initial Material Node does need to set be to "Toon"
to get the cel shading. The color of the Materials Diffuse does affect the
shading due to the Color Ramp Node though. I could have baked the
vertex colors into a image texture format and painted details in,
but I love just using them directly in a node tree for mesh colors or
masking multiple textures in a single Material Shader.