Light Rays

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Light Rays

Ray types can be divided into four categories:

1. Camera: the ray comes straight from the camera.
2. Reflection: the ray is generated by a reflection off a surface.
3. Transmission: the ray is generated by a transmission through a surface.
4. Shadow: the ray is used for (transparent) shadows.

Reflection and transmission rays can further have these properties:

• Diffuse: the ray is generated by a diffuse reflection or transmission (translucency).
• Glossy: the ray is generated by a glossy specular reflection or transmission.
• Singular: the ray is generated by a perfectly sharp reflection or transmission.

The Light Path node can be used to find out the type of ray the shading is being computed for.
../../_images/render_cycles_introduction_rays.svg

 > See also

The object ray visibility settings.
ray visibility
※メモ：Object Settings » Object 追加の必要性あり

Transparency Rays

The transparent BSDF shader is given special treatment. When a ray passes through it, light passes straight on, as if there was no geometry there. The ray type does not change when passing through a transparent BSDF.

BSDF

Alpha pass output is also different for the transparent BSDF. Other transmission BSDFs are considered opaque, because they change the light direction. As such they cannot be used for alpha-over compositing, while this is possible with the transparent BSDF.

Note that, while semantically the ray passes through as if no geometry was hit, rendering performance is affected as each transparency step requires executing the shader and tracing a ray.