OpenGL OpenGL Lighting and Materials 3

Question 1

Which OpenGL light type simulates illumination from a very distant source like the sun, with parallel rays and no positional falloff?

Accepted Answer

Directional light

Answer

A directional light has no defined position and casts parallel rays in a single direction, approximating a light source at infinite distance such as the sun.

Question 2

When specifying a light position with glLightfv(), what does setting the homogeneous w component to 0.0 indicate?

Accepted Answer

The light is a directional (infinite distance) source

Answer

A w=0.0 in the position vector tells OpenGL the light is at infinity in the given direction, making it directional rather than positional.

Question 3

Which spotlight parameter in OpenGL's fixed-function lighting defines the half-angle of the light cone in degrees?

Accepted Answer

GL_SPOT_CUTOFF

Answer

GL_SPOT_CUTOFF sets the maximum half-angle (0–90 degrees, or 180 for omnidirectional) of the spotlight cone; fragments outside this cone receive no spotlight contribution.

Question 4

What real-world phenomenon does light attenuation model in OpenGL?

Accepted Answer

Decrease in light intensity as distance from the source increases

Answer

Attenuation models the inverse-square (and linear) falloff of light intensity with distance, using GL_CONSTANT_ATTENUATION, GL_LINEAR_ATTENUATION, and GL_QUADRATIC_ATTENUATION.

Question 5

How does the Blinn-Phong shading model differ from the classic Phong model in GLSL implementation?

Accepted Answer

Blinn-Phong uses the halfway vector instead of the reflection vector for the specular term

Answer

Blinn-Phong replaces the expensive reflection vector computation with the halfway vector (H = normalize(L + V)), which is cheaper and often produces more physically plausible highlights.

OpenGL Practice Test

OpenGL Practice Test

OpenGL OpenGL Lighting and Materials 3