Q5Computer Graphics and Multimedia
Question
4 marks
Explain the concept of Hidden Surface Removal.
Answer
Hidden Surface Removal (HSR) determines which surfaces of a 3D scene are occluded from the viewpoint and should not be rendered.
Hidden Surface Removal (HSR) or Visible Surface Detection is the problem of determining which parts of a 3D scene are visible from a given viewpoint. When multiple surfaces overlap in screen space, only the frontmost surface should be rendered. Efficient HSR is critical for correct 3D rendering.
- Back-Face Culling: Remove polygon faces whose normals point away from viewer. Eliminates ~50% of polygons for closed objects.
- Z-Buffer Algorithm: Maintain depth values per pixel; update only if new surface is closer. Simple and universally implemented in hardware.
- Painter's Algorithm: Sort polygons by depth (back to front) and render in that order. Fails with cyclic overlaps.
- BSP Tree: Pre-process scene into binary space partition tree for correct back-to-front order from any viewpoint.
- Scan-Line Algorithm: Process scene scan line by scan line, tracking active polygon spans.
- Warnock's Algorithm: Subdivide screen recursively until each area contains only one visible surface.