Part 12: REFLECTIONS

When light hits a surface, it can scatter in two ways:

1. Diffuse — Light scatters in all directions, creating the "base color" we see
2. Specular — Light bounces in a mirror-like direction, creating reflections

Reflections are specular light — the portion of incoming light that bounces off a surface at a predictable angle, showing the environment around it.

Every surface has some amount of reflection. Even matte paper reflects a tiny bit. The difference between a mirror and a matte wall is how much light reflects specularly vs diffusely, and how sharp that reflection is.

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Two material properties control how surfaces reflect:

Metallic

Metallic determines what reflects:

Non-metals (plastic, wood, skin) reflect white/neutral light. Metals (gold, copper, chrome) reflect colored light matching their Base Color.

Roughness

Roughness determines how sharp the reflection is:

Think of roughness as surface texture at a microscopic level. A polished surface has aligned micro-facets (sharp reflection). A rough surface has random micro-facets (scattered, blurry reflection).

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To properly evaluate reflections, we need reference materials that show the full range of reflective behavior.

Creating the Material Instances

We'll create 4 material instances from M_LHT_01 (our master material from Part 8):

Why these values?

• Base Color 0.9 (not 1.0): Pure white (1.0) doesn't exist in the real world. Even the whitest materials reflect ~90% of light. Using 1.0 can cause energy conservation issues in PBR.
• Base Color 0.18 (mid grey): This is the actual photographic mid-grey value — 18% reflectance. It's the standard reference for neutral surfaces.
• Metallic 1.0 or 0.0: In PBR, Metallic is almost always binary. Real materials are either metal or not — there's no "50% metal."

Creating the instances:

1. Right-click M_LHT_01 → Create Material Instance
2. Name it MI_LHT_RF_Chrome
3. Set Metallic = 1.0, Roughness = 0.0, BaseColor = (0.9, 0.9, 0.9)
4. Repeat for the other 3 instances

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Create a portable reflection test rig:

1. Create Blueprint: Content Browser → Right-click → Blueprint Class → Actor
2. Name it: BP_LHT_RF_Reference
3. Open the Blueprint and add 4 Sphere components (or Static Mesh components with sphere mesh)
4. Arrange them in a row, spaced apart so they don't reflect each other
5. Assign materials:
   • Sphere 1: MI_LHT_RF_Chrome
   • Sphere 2: MI_LHT_RF_BrushedMetal
   • Sphere 3: MI_LHT_RF_GlossyPlastic
   • Sphere 4: MI_LHT_RF_MattePlastic
6. Compile and Save

Now you can drop BP_LHT_RF_Reference into any scene to evaluate reflections.

TODO: Screenshot - BP_LHT_RF_Reference with 4 spheres showing different reflection behaviors

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Key Points:

• Reflections are specular light — light bouncing in a mirror-like direction
• Metallic controls what reflects (environment vs tinted by Base Color)
• Roughness controls sharpness (0 = mirror, 1 = diffuse)
• Use realistic values: 0.9 for white (not 1.0), 0.18 for mid-grey
• Metallic is binary in PBR — materials are either metal (1.0) or not (0.0)
• Create reference materials (MI_LHT_RF_*) and a test Blueprint (BP_LHT_RF_Reference)

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You now understand what reflections are and have reference materials to evaluate them. But where does the reflection data come from? In Part 13: Reflection Systems, we'll explore the different methods Unreal uses to generate reflections — from simple Sky Light cubemaps to hardware ray traced reflections — and when to use each.

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