OpenGL OpenGL Transformations and Matrices 2

Question 1

When transforming surface normals from object space to world space, why can you not simply use the model matrix?

Accepted Answer

Non-uniform scaling would distort normal directions

Answer

Non-uniform scale changes the angle of normals, so the correct transform is the transpose of the inverse of the model matrix.

Question 2

Which matrix converts a flat frustum-shaped view volume to a cube for perspective rendering?

Accepted Answer

Perspective projection matrix

Answer

A perspective projection matrix applies the 1/z depth foreshortening that makes distant objects appear smaller.

Question 3

What does the glViewport function define in OpenGL?

Accepted Answer

The rectangular window area on screen that NDC maps to

Answer

glViewport(x, y, width, height) sets the pixel region on the window where NDC space (-1 to 1) is mapped.

Question 4

Which OpenGL function sets the depth range mapping from NDC z to window z?

Accepted Answer

glDepthRange

Answer

glDepthRange(near, far) remaps the NDC z range [-1, 1] to a custom window-space depth range, defaulting to [0, 1].

Question 5

What rotation representation avoids gimbal lock and is commonly used in 3D graphics for smooth interpolation?

Accepted Answer

Quaternions

Answer

Quaternions represent rotations in a compact 4D form that supports smooth SLERP interpolation without gimbal lock.

OpenGL Practice Test