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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About project SlidePlayer Terms of Service. We do not draw polygons facing the other direction Test z component of surface normals. The A-buffer method is an extension of the depth-buffer method. Choose polygon arbitrarily 3 4 1 2 5 5a 5b back front Choose polygon arbitrarily Divide scene into front relative to normal and back rfmoval.

For a 3 x 3 matrix of coefficients the determinant may be expressed as either: Registration Forgot your password? The identification and removal of these surfaces is called Hidden-surface problem.

Computer Graphics Visible Surface Detection

Even if we use another algorithm for visible surface determination, the back-face cull is a good pre-processing step. Put all the nodes that are in front of root A to the left side of node A and put all those nodes that are behind the root A to the right side as shown in figure b.


Also a flag is set for each surface to indicate whether a position along a scan-line is either inside or outside the surface. The intensity field then stores the RGB components of the surface color at that point and the percent of pixel coverage. The surface depth is measured from the view plane along the z axis of a viewing system.

Hidden Surface Removal Why make the effort? Problematic for concave polyhedra. Thus object depths can be compared by comparing the z-values. Ray casting is a brute force technique that makes no use of pixel coherence. If eye is in rear half-space for a polygon can back face cull.

Classification of Visible-Surface Detection Algorithms

The Z-buffer algorithm is usually implemented in the normalized coordinates, so that z values range from at the back clipping plane to at the front clipping plane. Need to decide the order to draw — far objects first 7 7.

To override the closer polygons from the far ones, two buffers named frame buffer and depth buffer, are used.

Introductory Computer Graphics David Luebke. If negative — cull, since normal points away from viewer. We can simplify this test by considering the normal vector N to a polygon surface, which has Cartesian components A, B, C.

Back Face Removal

Since in general about half of the faces of objects are are back faces this algorithm will remove about half of the total polygons in the image. 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. In 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.


Back Face Removal

Let us take the polygon P at the end of the list. My presentations Profile Feedback Log out. A Z-buffer is used to store depth values for each x,y position as surfaces are proceeds and the frame buffer stores the memory values for each position. Key issue is order determination. Before drawing P, we make the following tests.

So it is visible at that position. We think you have liked this presentation. It is developed by Catmull. Chapter 15, all of it. If any of the following tests is positive, then we can assume P can be drawn before Q. As shown in figure c algoriyhm, we will first process the node B.

Normal to the plane is the vector A ,B,C. To use this website, you must agree to our Privacy Policyincluding cookie policy.