1. Explain Back face detection method and Depth buffer method
Backface Detection method
• Fast and simple object space method
• For identifying the back faces of a polyhedron
• Based ion inside outside test
• Plane parameters A, B, C, D Ax +By+ Cz +D < 0
• Inside point is along the line of sight to the surface V.N = Vz C
• Polygon is back face if C < 0
• Polygon cannot see on any face if C = 0
• Z component value is C <= 0
Depth Buffer Method
• To compare the surface depths at each pixel position on the plane projection
• Also referred as z- buffer method
• Two buffer areas
• Depth buffer to store depth values
• Refresh buffer to store intensity values
• Depth value for a surface position (x, y) Z( -Ax – By– D)/C
• Depth z’ of next position (x + 1, y) Z’( -A(x + 1)-By – D)/C
2. Explain area subdivision and A- Buffer method
A Buffer Method
• Extension idea of the depth buffer method
• It represents an antialiased, area averaged, accumulation-buffer method
• Only one visible surface
• Two fields
• Depth field
- Stores a positive or negative real number
• Intensity field
- Stores a surface intensity information or a pointer value
• Data for each surface in the linked list includes
• RGB intensity components
• Opacity parameters
• Depth
• Percent of area coverage
• Surface identifier
• Pointer to next surface
Area Sub Division Method
• Image space method
• The relative characteristic of surface are
• Surrounding surface
• Inside surface
• Outside surface
• Conditions for subdivision
• All surfaces are outside surfaces with respect to the area
• Only one inside
• A surrounding surface with in the area boundaries
