**Shading:**- Shading, shadows
- How do we use ray to determine shade of pixel?
- At closest intersection point, perform Phong shading.
Gives essentially the same images as standard polygon renderer, but with more primitives.

- Idea: Before adding contribution from a light, cast
ray to light.
- If ray hits another object before hitting light, then don't perform shading calculation.
- This gives shadows.

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**Shading:**- Reflections
- Idea: Cast a ray in the mirror direction.
- Add the colour coming from this ray to the shade of the initial ray.
- This gives mirror reflections
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- We perform a full lighting calculation at the first intersection of this reflected ray.
- If we send another reflected ray from here, when do we stop?
- Answer 1: Stop at a fixed depth.
- Answer 2: Accumulate product of reflection coefficients and stop when this product is too small.

- Refraction similar

CS488/688: Introduction to Interactive Computer Graphics

University of Waterloo

Computer Graphics Lab