CG

1. VISIBLE SURFACE DETECTION
METHODS

2. Classification of Visible Surface
Detection Algorithms
1) Object-space Methods:
Compare objects and parts of objects in a scene
and to determine which surfaces are visible in
a scene.

3. Classification of Visible Surface
Detection Algorithms
2) Image-space Methods:
Visibility is determined point by point at each
pixel position on the scene.

4. 1) Painter's Algorithm
Painters paints the distant parts of a scene
before parts which are nearer thereby
covering some areas of distant parts.

5. Painter's Algorithm

6. ALGORITHM FOR PAINTERS
ALGORITHM
1) Sort al the Polygons in the decreasing depth.
2) If overlap is detected in the polygon it must
be sorted net.

7. 2) Binary space partitioning Alg
It is defined as “polygon is drawn if all the
polygons which is away from the viewpoint is
drawn first, then the polygon which is closer
to the viewer is drawn next”.

8. Binary space partitioning Alg
1) Find the distance of position Camera
2) If the distance is greater than 0 then
a. Go to Back node
b. Note down the polygon vertices
3) If step 2 is false then
a. Go to Front node
b. Note down the polygon vertices

9. 3) Back Face Detection
In an object, there are 2 surfaces namely Front face
and Back faces.
Each surface has a vector. If this vector is pointing in
the direction of the center of projection, it is a
front face and can be seen by the viewer.
If it is pointing away from the center of projection,
it is a back face and cannot be seen by the viewer.

10. Back Face Detection

11. A BUFFER METHOD
Each position in the A-buffer has 2 fields
Depth field − It stores a positive or negative
number
Intensity field − It stores surface-intensity
information

12. A BUFFER METHOD

13. A BUFFER METHOD
If depth >= 0, It is a single surface. The intensity
field stores the RGB components of the surface
color at that point and the percent of pixel
coverage.
If depth < 0, it indicates multiple surface. It also
includes
1)RGB intensity components
2) Depth
3) Percent of area coverage