# BACKFACE REMOVAL ALGORITHM IN COMPUTER GRAPHICS PDF

Object space algorithm: Back-Face removal. · No faces on the back of the object are displayed. · In general – about half of objects faces are back faces. Computer Graphics Lecture 8 Hidden Surface Removal Taku Komura 1 1 Or if N.V > 0 we are viewing the back face so polygon is obscured. . Tree construction and traversal (object-space ordering algorithm – good for relatively few static. Occluded surfaces: hidden surface removal (visibility). ▫ Back faces: back face culling. ▫ Faces OpenGL): Z-buffer (or depth buffer) algorithm. ▫ Requires lots .

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This method has a depth information for only single scan-line.

## Hidden Surface Removal

It is applied very efficiently on surfaces of polygon. Share buttons are a little bit lower. The algorithm proceeds just like the depth buffer algorithm.

The new cut polygons are inserting into the depth order and the process continues. You get question papers, syllabus, subject analysis, answers – all in one app. Partition all the other polygons in the scene to the back left subtree or the front right subtree. This algorithm compares surface depths at each pixel position on the on the projection plane. The main disadvantage of ray casting is that the method is slow. Build the left and right subtrees recursively. Recursively divide each side until each node contains only 1 polygon.

Surfaces can be processed in any order. Surface color and pixel coverage. Display the right subtree front. Spatial Sorting Chung Ji Hye Simplest to use maximum z value. Choose polygon arbitrarily 5 5a 5b 2 Choose polygon ermoval Divide scene into front relative to normal and back half-spaces. Need to decide the order to draw — far objects first 7 7. Grahpics order to require one scan-line of depth values, we must group and process all polygons intersecting a given scan-line at the same time before processing the next scan-line.

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### Back Face Removal

Intersect the ray with each polygonal plane. Algorithn scan conversion of the polygon surfaces is performed in image space. The key data structure in the A-buffer is the accumulation buffer. By examining parameter C for the different planes defining an object, we can immediately identify all the back faces. Primitive lies compuher field of view last lecture Primitive is back-facing Primitive is occluded by one or more objects nearer the viewer hidden surface removal 3 3.

Same as with normal vector. Many slides adapted from Amitabh. Similar methods can be used in packages that employ a left-handed viewing system.

To build the BSP trees, one should start with polygons and label all the edges. Registration Forgot your password? Ray casting is a brute force technique that ni no use of pixel coherence. You only need to perform depth calculations when multiple surfaces have their flags turned on at a certain scan-line position.

If eye is in rear half-space for a polygon can back face cull. Split any polygons lying on both sides of the root see below.

Two important tables, edge table and polygon table, are maintained for this. In this method each surface is processed separately one pixel position at a time across the surface. For a perspective projection, it is a little more complicated.

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vomputer Can be used to generate correct visibility for arbitrary views. The basic idea is to test the Z-depth of each surface to determine the closest visible surface. The intensity field then stores the RGB components of the surface color at that point and the percent of pixel coverage.

The z-coordinates are usually normalized to the range [0, 1]. Standard equation of a plane in 3 space: In general, if V is a vector in the viewing direction from the eye or “camera” position, then this polygon is a back face if.

### Computer Graphics

The main advantage of the ray casting algorithm for hidden surfaces is that ray casting can be used even with non-polygonal surfaces. Ray Casting Algorithm Through each pixel, fire a ray to the eye: Portals or doors Graph gives us: To facilitate the search for surfaces crossing a given scan-line, an active list of edges is formed.

Place the first edge in the tree as root. For a 3 x 3 matrix of coefficients the determinant may be expressed as either: If viewer is in back half-space, draw polygons in front of root first, then the root polygon, then polygons behind. As there is nothing in front of the node Bwe have put NIL.