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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Hidden Surface Removal – ppt download

Cells or compute Edges: Surface color and pixel coverage. This method for solving the hidden-surface problem is often referred to as the painter’s algorithm. Standard equation of a plane in 3 space: If polygon is on edge — either can be used.

The sides will be invisible for an orthographic projection, algorihm not for a perspective projection. You only need to perform depth calculations when multiple surfaces have their flags turned on at a certain scan-line position. When we view a picture containing non-transparent objects and surfaces, then we cannot see those objects from view which are behind from objects closer to eye.


If viewer is in front half-space, draw polygons behind root first, then the root polygon, then polygons in front.

Explain Back – Face Removal Algorithm.

Begin at top vertex of polygon 2. The z-coordinates are usually normalized to the range [0, 1]. Let us take the polygon P at the end of the list.

Display the left subtree behind. If the 3 points are collinear then the normal A ,B,C will be 0,0,0.

Hidden Surface Removal

Surfaces can be processed in any order. Same as with normal vector. Lecture 9 Choose polygon arbitrarily 3 4 1 2 5 5a 5b back front Choose polygon arbitrarily Divide scene into front relative to normal and back half-spaces. Memory for z-buffer is now not expensive Diversity of primitives — not just polygons. The tests for determining surface visibility within an area can be stated in terms of these four classifications. Also, for color shading we must compute the normal for all of the polygons anyway.

Key issue is order determination. Dealing with only one edge at a time, extend each edge so that it splits the plane in two. If all the tests fail, then we split either P or Q using the plane of the other. Display the left subtree back. It is developed by Catmull. The basic idea is to test the Z-depth of each surface to determine the closest visible surface. We think you have liked this presentation. For a perspective projection, we must determine if the Center of Projection COP is inside or outside of the planes of the polygons of the object.


The new cut polygons are inserting into the depth order and the process continues.

A fast and simple object-space method for identifying the back faces of a polyhedron is based on the “inside-outside” tests. Choose a polygon from each side — split scene again. It is an image-space grphics. The main advantage of the ray casting algorithm for hidden surfaces is that ray casting can be used even with non-polygonal surfaces. A simple object space algorithm is Back-Face removal or back face backcace where no faces on the back of the object are displayed.

Their determinants are det A x and det A y respectively. Registration Forgot your password? Binary space partitioning is used to calculate visibility. Reject intersections that lie outside the polygon.

backfxce The surface depth is measured from the view plane along the z axis of a viewing system. Even if we use another algorithm for visible surface determination, the back-face cull is a good pre-processing step.