ITPEC FE Morning April 2019 Question 25

Rendering only the part of the object visible from the viewpoint — hidden-line and hidden-surface removal drop whatever is blocked from view.

In a 3D scene, some edges and faces lie behind other faces, of the same object or of objects in front of it. Hidden-line removal (for wireframe drawings) and hidden-surface removal (for solid models) work out, for the given viewpoint, which lines and surfaces are occluded and draw only the rest. A common method is the Z-buffer, which keeps for each pixel the depth of the nearest surface drawn so far.

Answer (c)

Why not others:

• •(a) — working out colour and brightness from the position of the light source is shading
• •(b) — drawing only the part that fits the display area is clipping; it cuts along the edges of the view window, not by what is in front of what
• •(d) — showing the inside of an object through translucent surfaces is the opposite of hiding what lies behind

Key rule: Each rendering step answers its own question: clipping asks what is inside the window, hidden-surface removal asks what is in front, and shading asks how bright it is.

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