Computer Graphics ECS 175
Popular in Course
Popular in Engineering Computer Science
This 13 page Class Notes was uploaded by Ashleigh Dare on Tuesday September 8, 2015. The Class Notes belongs to ECS 175 at University of California - Davis taught by Staff in Fall. Since its upload, it has received 55 views. For similar materials see /class/191699/ecs-175-university-of-california-davis in Engineering Computer Science at University of California - Davis.
Reviews for Computer Graphics
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 09/08/15
ViiIrf D in Identifying those parts of a scene that are visible from a chosen viewing position and only process scanconvert those parts Q Q Two approaches 1 Objectspace methods 2 Imagespace methods Two main strategies 1 Sorting 2 Coherence Visible Surface Detection Algorithms Backface detection Zbu er Abuffer Scanline method Painter s algorithm BSPtree method Areasubdivision method Octree methods Raycasting method Wireframe methods ommVQmeNA A Backface detection N VN1 gt O V N2 lt0 Zbu er most widely used simple to implement use a depth buffer with the same resolution as the image buffer scanconvert each polygon and compare the 2 value of each resulting pixel with the value stored in the zbuffer Undate the image buffer only when the new 2 value is smaller than the saved 2 value ll l I lll ll Zbuffer cont d 2 values can be calculated incrementally Hr y1 ll XX1 AXByCzDO Z D A C top y scan line bottom z 39AX 1m By1 D Z Am B C Zbuffer cont d Large amount of memory space is needed What to do if short of memory space Aliasing problem Handle only opaque surfaces Other use of zbuffer Abuffer antialiased areaaverage accumulation buffer deal with nonopaque surfaces more than one surface intensity can be taken into consideration at each pixel position Idepthl r s1lls2 lssl Each surface data field includes RGB intensity components opacity parameter percent of transparency depth surface identifier percent of area coverage other surfacerendering parameters ScanLine Algorithm combine polygon scan conversion with hIdden surface removal scanline by scanline rather than polygon by polygon perform depth calculation only when more than one polygon intersects with the current scaane require sophisticated data structures to quickly locate the polygonedges intersecting with current scanline Painter s algorithm depth sort the polygons an object space algorithm analogous to the way an oil painter might render a scene scanconvert polygons in backtofront order How to depth sort 1 sort all polygons according to the minimum 2 coordinate of each 2 resolve any ambiguities this may cause when polygons z extents overlap splitting polygons if necessary zmin E quotquotquotquotquotquotquotquotquotquotquotquotquotquotquot quot zmax p xmax g 2 min 92 p1 p1 p2 Five tests do the polygons x extents not overlap do the polygons y extents not overlap ls P1 entirely on the opposite side of P2 plane from the view point ls p2 entirely on the same side of P1 s plane as the viewpoint Do the projections of the polygons onto the xy plane not overlap 01 L JON Troublesome situations Cyclic overlap Piercing polygon BSPtree Method binary space partitioning tree storing relative positioning information applicable to data of arbitrary dimensions at each stage the space is partitioned into two parts of arbitrary size each subdivision plane or line can have an arbitrary orientation viewdependent operations can be applied apropriately to the resulting two halfspaces Area Subdivision Warnock s algorithm try to make an easy decision about which polygon is visible in a section of the image If a decision cannot be made subdivide the area recursively until one can be made work at image precision for subdivision and at object precision for depth comparison For each area do the following tests 1 surrounding are all polygons disjoint from area if yes display background color only one intersecting or contained polygon if yes fill with background color and then draw contained polygon or intersecting portion one single surrounding polygon no intersecting or contained polygons if yes draw area with that polygon s color more than one polygon is intersecting contained in or surrounding but only one polygon is surrounding the area and is in front of others if yes draw area with that front polygon s color othenNise subdivide the area into 4 equal areas and recurse V 4 intersecting contained disjoint