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Materials & Shading
CPSC 453 – Fall 2018 Sonny Chan
Materials
Rendered by Unreal Engine
Materials & Shading CPSC 453 Fall 2018 Sonny Chan Materials - - PowerPoint PPT Presentation
Materials & Shading CPSC 453 Fall 2018 Sonny Chan Materials - - PowerPoint PPT Presentation
Materials & Shading CPSC 453 Fall 2018 Sonny Chan Materials Rendered by Unreal Engine The appearance of a material is determined by the manner in which light is reflected from it, or transmitted through it. What is the most basic
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The appearance of a material is determined by the manner in which light is reflected from it, or transmitted through it.
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What is the most basic
material property?
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Colour: Spectral Reflectance Curves
[from scratchapixel.com]
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But not the only factor!
RenderMan PxrLM
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Let’s take a look at some
real world materials
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Hand with Reflecting Sphere (Self-Portrait)
M.C. Escher, 1935
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Ideal Specular Reflections
r = d − 2(d · ˆ n)ˆ n Trace another ray, as if you were looking from underneath.
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Real surfaces are not perfectly specular!
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Real surfaces are not perfectly specular!
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Mixed Specular Reflections
r = d − 2(d · ˆ n)ˆ n Add fraction of ray’s light with to surface material colour.
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But wait a minute…
What’s the difference? dielectric (non-conductor) metallic (conductor)
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Metallic Specular Reflections
r = d − 2(d · ˆ n)ˆ n Multiply reflected ray’s light with the surface material colour.
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A Glass Marble
What do we do with this material?
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Snell’s Law
- Ratio of sines of angles is
equal to ratio of velocities:
sin θ sin φ = v vt = nt n
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n Material 1.0001 air 1.333 water 1.47
- live oil
1.52 crown glass 1.62 flint glass 2.15 cubic zirconia 2.42 diamond
Index of Refraction
- f some common materials
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Ray Tracing Refraction
n sin θ = nt sin φ cos2 φ = 1 − n2(1 − cos2 θ) n2
t
t = n(d + ˆ n cos θ) nt − ˆ n cos φ
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A Diffuse Reflector
M.C. Escher, 1946
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Three Spheres II
M.C. Escher, 1946
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Properties of Diffuse Reflectors
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Diffuse Reflection
- Brightness dependent
- nly on the direction of
incident light
- View direction has no
effect on appearance
- Lambert’s cosine law:
c ∝ ˆ n ·ˆ l c = crcl max(0, ˆ n ·ˆ l)
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Specular Highlights
A Heuristic Approximation
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Moonlight Reflection
What do you see in this picture?
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Plastic, Magnified
[image from gelsight.com]
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Microfacet Geometry Model
[images from Real-Time Rendering, A K Peters, 2008]
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Phong Lighting Model
r = −l + 2(l · ˆ n)ˆ n c = cl max(0, ˆ e · ˆ r)p
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Blinn-Phong Lighting Model
ˆ h = e + l ||e + l|| c = cl max(0, ˆ h · ˆ n)p
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The Phong Exponent
y = cosp θ
p = 1 p = 64
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Phong Highlights
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Summary: Types of Surface Reflectance
- Ideal specular (mirror)
- reflection law
- Ideal diffuse (matte)
- Lambert’s law
- Specular (glossy)
- directional diffuse
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What about
ambient light?
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Indirect Lighting
Material reflection works both ways!
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Global Illumination
direct indirect combined Global illumination is really hard and expensive to compute!
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Ambient Light
Approximated by a constant light source that represents the average indirect light energy in the scene.
c = crca
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Our final heuristic shading equation…
- with ambient, diffuse, and specular terms:
- cr is reflectance (diffuse) colour of material
- cp is specular colour of material
- p is Phong exponent, or shininess of material
- cl is light source intensity (colour)
- ca is ambient light intensity (colour)
c = cr ⇣ ca + cl max(0, ˆ n ·ˆ l) ⌘ + cl cp ⇣ ˆ h · ˆ n ⌘p
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Things to Remember
- The appearance of a material is determined by the
manner in which light is reflected from it
- The Phong lighting equation approximates material
colour, diffuse and specular reflection, and ambient light
- Ideal specular reflection and refraction are relatively easy
to achieve with ray tracing