Metal and glass — Parallax Sketchbook

SKETCHBOOK / 04 The Lantern Room · 2-week chapter

Page 1 of 3: Start with a smooth mirror

Specular / delta events

Start with a smooth mirror

A smooth mirror sends a chosen incident direction to a specific reflected direction. That is a delta event, not a broad directional density that can be evaluated like the diffuse PDF. Give scattering results an explicit event kind so the integrator can make the distinction.

Begin with a bounded RGB-tinted ideal mirror and label it as a teaching model. A conductor model uses angle- and wavelength-dependent optical properties; a colored perfect mirror is not a measured rough-metal material. Add rough microfacet scattering only after you can account for the distribution and its PDF.

Test a perpendicular incident direction and one oblique reflection against an independently drawn normal. Preserve a fixed path limit and a ray-origin policy. The companion supplies geometry queries and the bounded diffuse/emission model. Extend that working baseline with an explicit mirror event; the specular material and its tests are your implementation.

TRY IT IN YOUR STUDIO

Create one original mirror object in the room, then record the event kinds and termination reasons for a ray that reflects twice.

From the page to your own work

Your studio assignment.

Make one mirror and one bounded smooth-glass experiment in your own renderer.

A finish line you can see

A material triptych, reflection/refraction tests, and a statement of supported media.

Label the mirror and glass approximations.
Test entering, exiting, and total internal reflection.
Keep an explicit maximum path depth.
Do not claim roughness, absorption, or nested-media support you did not implement.

Keep the evidence in your weekly notebook ↗

Explain it like an engineer

Try answering aloud before opening the review notes. Use your own implementation as evidence.

Why is a mirror event not interchangeable with the diffuse PDF?

A delta event is concentrated on a prescribed direction.
Ordinary density evaluation and discrete branch probability are different.
The integrator needs event information for later light sampling.

These prompts support practice; they are not an automatic assessment of your work.

A tip for this exercise

Make the triptych from one camera and one lighting setup. First keep separate tiny tests for mirror direction and a single glass interface, so an attractive reflection cannot hide an orientation mistake.

Hints, when you need them.

Try a first step, then reveal as much help as you need. Each hint gets a little more specific.

1Hint 1 · Find a starting point

Draw the geometric normal and label the medium on each side. Determine the incident and transmitted indices before choosing a facing normal or a reflection/transmission branch.

2Hint 2 · Choose an approach

Tag mirror and transmission events explicitly. For the full glass exercise, pair exact Fresnel and total-internal-reflection handling with your stated radiance convention; the entry-only Schlick helper covers a smaller domain.

3Hint 3 · Check your reasoning

Check normal entry from index 1 to 1.5 against reflectance 0.04. An exiting ray from 1.5 to 1 at 60 degrees from the normal should produce reflection only; test it outside the restricted helper.

A small creative variation ↗

Restrict the scene to one refractive interface and explain its normal and eta choices.

Optional. Save it for later if this chapter already feels full.

Coming back after a break? ↩

Run only the reflection-direction test, then add one normal-incidence dielectric case.

Books & principles behind this study +

Original Parallax explanations and assignments, with these works for further reading.

YOUR MARGIN NOTES

Leave yourself a good question.

What changed your mind? What would you try next?

Notes for Metal and glass

Notes are private to this browser and saved as you write.

A CHECKPOINT, NOT A SCORE

Can you explain the idea and try the exercise yourself?

Completion records your own assessment. It does not compile or test your C++.

Companion source 10 files