UBI 516 Advanced Computer Graphics. Visible Surface De tection. Aydın Öztürk ozturk @ ube.ege.edu.tr http://www. ube.ege.edu.tr/~ozturk. Review : Rendering Pipeline. Almost finished with the rendering pipeline: Modeling transformations Viewing transformations Projection transformations
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Visible Surface Detection
There are many algorithms developed for the visible surface detection
● Some methods involve more processing time.
● Some methods require more memory.
● Some others apply only to special types of objects.
They are classified according to whether they deal with object definitions or with their projected images.
● Object space methods.
● Image-space methods.
Most visible-surface algorithms use image space method.
depth(x, y) = 0,
refresh(x, y) = Ibackground
● Calculate the depth z for each (x,y) position
on the polygon.
● If z >depth(x,y), then
depth(x, y) = z,
refresh(x, y) = Isurf(x,y).
Ibackground is the value for the bacground intensity and
Isurf(x,y), is the projected intensity value for the surface at (x,y).
Depth values for a surface position (x,y) are calculated from the plane equation
z-value for the horizontal next position
z-value down the edge(starting at top vertex)
top scan line
bottom scan line
Scan Line 1
Scan Line 2
Scan Line 3
This method performs the following basic functions:
BSPtree *near, *far;
if (eye on left side of T->plane)
near = T->left; far = T->right;
near = T->right; far = T->left;
if (T is a leaf node)
OpenGL Visibility Detection Functions