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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Primitive lies outside 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.

We do not draw polygons facing the other direction Test aogorithm component of surface normals. If negative — cull, since normal points away from viewer. Need to decide the order to draw — remvoal objects first 7 7. Key issue is order determination.

Choose polygon arbitrarily Divide scene into front relative to normal and back half-spaces. Split any polygon lying on both sides. Choose a polygon from each side — split scene again. Recursively divide each side until each node contains only 1 polygon. Lecture 9 Choose polygon arbitrarily 3 4 1 2 5 5a 5b back front Choose polygon arbitrarily Graphiics scene into front relative to normal and back half-spaces. Choose polygon arbitrarily 5 5a 5b 2 Choose polygon arbitrarily Divide scene into front relative to normal and back half-spaces.

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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. Once we have the regions — need priority list BSP tree can be traversed to yield a correct priority list for an arbitrary viewpoint.

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

If polygon is on edge — either comouter be used.

Hidden Surface Removal

Recursively descend the tree. If eye is in rear half-space for a polygon can back face cull. A lot of computation required at start.

Try to split polygons along good dividing plane Intersecting polygon splitting may be costly Cheap to check visibility once tree is set up. Can be used to generate correct visibility for arbitrary views. Initialise frame buffer to background colour. Advantage Simple to implement in hardware.

Hidden Surface Removal – ppt download

Memory for z-buffer is now not expensive Diversity of primitives — not just polygons. Disadvantage Waste time drawing hidden objects Z-precision errors May have to use point sampling Very important. Cells or rooms F Model scene as a graph: Cells or rooms Edges: Portals or doors Graph gives us: Chapter 15, all of it.

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Introductory text, Chapter 13, all of it Or equivalents in other texts, look out for: Collisions and Intersections When objects move, test for collision. When projecting surfaces, check for intersections. Many slides adapted from Amitabh.

All polygons are opaque What polygons are visible with respect to your view frustum? Hidden Surface Removal Why make the effort? My presentations Profile Feedback Log out. Auth with social network: Registration Forgot your password? Download ppt “Hidden Surface Removal”. Introductory Computer Graphics David Luebke. Basics of Computer Graphics.

Back face culling View-frustrum culling Detail culling Occlusion culling.

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