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Class3 - Hidden Surfaces and Introduction to Transforms and...

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Hidden Surfaces and Introduction to Transforms and Projections HW3 Ulrich Neumann CS580 (Computer Graphics Rendering)
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Hidden Surface Removal (HSR) Image-order (pixel) or object-order (poly) methods Edge (line) or surface visibility methods wireframe lines are hard to deal with simple z-buffer does not work edge-crossing and object sorting methods
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Raycasting For every ray through a pixel, perform a ray-intersection with every object. Keep the closest intersection. Image plane View point or focal point
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Painter's algorithm Just render in order front to back or back to front. View dependent and doesn’t work for overlapping tris.
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Painter’s Algorithm (2) Failure cases: - Farthest z extent is insufficient - Cannot resolve dependency cycles top front View direction
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Warnock algorithm Overcomes problem of view dependent ordering and intersecting geometry by approach based on divide and conquer. Subdivide screen until single region has simple front/back relationship Sub areas are completely visible / hidden, or area is too small to subdivide again Usually use quad tree subdivision Useful for curved surfaces and antialiasing where the subdivision is done to sub-pixel levels. Efficient and concentrates work where needed --adaptively -- common theme in graphics
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Area Subdivision (Warnock) 1. Initialize the area to be the image plane 2. Four cases: 1. No polygons in area: done 2. One polygon in area: draw it 3. Pixel sized area: draw closest polygon 4. Front polygon covers area: draw it Otherwise, subdivide and recurse
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BSP tree view-independent binary tree structure that allows view dependent front to back or back to front traversal. More detail in later class.
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BSP Trees Advantages view-independent tree anti-aliasing transparency Disadvantages many, small polygons over-rendering hard to balance tree
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BSP Trees Advantages view-independent tree anti-aliasing transparency Disadvantages many, small polygons over-rendering hard to balance tree
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Portals Separate environment into cells Preprocess to find potentially visible polygons from any cell
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Portals Treat environment as a graph Nodes = cells, Edges = portals Cell to cell visibility must go along edges
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Z buffer
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This note was uploaded on 04/22/2010 for the course CS 580 at USC.

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Class3 - Hidden Surfaces and Introduction to Transforms and...

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