Material properties, one at a time

Material component stack

The large sphere on the left carries the material you are editing. The small grey sphere beside it is a witness — it never changes. Turn the four material colours on and off to build the final image one term at a time, and note what happens to the witness when you add emission. Hover the scene to probe any surface point.

Scene hover to probe

Hover a surface to read its terms

left sphere — your material right sphere — fixed grey witness emission — off

Ambient —

m_a ⊙ l_a

Diffuse —

m_d ⊙ l_d max(0, N·L)

Specular —

m_s ⊙ l_s max(0, R·V)^m_h

Emission —

m_e — added, never cast

Probe point

—

N · L there

—

Sum before clamp

—

Final RGBA

—

Building the image one term at a time each panel adds the next component

Ambient only

flat, shapeless

+ Diffuse

form appears

+ Specular

surface finish

+ Emission

glow, no spill

Ambient alone gives a silhouette with no shape, because it does not depend on the normal at all. Diffuse is what makes the sphere read as round. Specular says what the surface is made of. Emission only brightens the object itself — compare the floor underneath it in the last two panels.

Material colours

Ambient m_a
—

Diffuse m_d
—

Specular m_s
—

Emission m_e
—

Surface

Shininess 32

Alpha 1.00

Alpha is the fourth number in the diffuse colour array, and it is the only alpha OpenGL 1.1 uses. Drop it and the witness sphere and floor start showing through.

Light

Ambient l_a
—

Diffuse l_d = l_s
—

Azimuth -34°

Elevation 46°

Emission is not a light source

Emission adds colour to the surface it belongs to and stops there. The sphere looks like it is glowing, but it contributes nothing to any other surface — no bounce onto the floor, no highlight on the witness sphere, no shadow softening. That is why a glowing object in a fixed-function scene almost always needs a real GL_LIGHT placed inside it as well, doing the actual illuminating.