CM30075: PC Representation bath.ac.uk/~maspmh/.


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CM30075: PC Illustrations www.bath.ac.uk/~maspmh/Subside Corridor pmh@cs.bath.ac.uk !! Cautioning !! These slides don't supplant course book perusing L01: about this course Point: to instruct the components of PC Representation Traditional 3D photorealism Modern utilization of pictures, and non-photorealism
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CM30075: Computer Graphics www.bath.ac.uk/~maspmh/Peter Hall pmh@cs.bath.ac.uk

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!! Cautioning !! These slides don\'t supplant reading material perusing

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L01: about this course Aim: to instruct the components of Computer Graphics Traditional 3D photorealism Modern utilization of pictures, and non-photorealism Method: conventional structures lectures personal perusing personal down to earth work Assumptions: information of systematic science vectors and lattices integration and separation

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Reading Lecture Slides are NOT expected to supplant course book perusing. Standard writings Watt, 3D Computer Graphics , Addison Wesley. Foley et al, 3D Computer Graphics , Addison Wesley. Watt and Watt, Advanced Computer Graphics , Addison Wesley. For the intrigued. SIGGRAPH procedures (distributed as diary exceptional issue; Transactions on Graphics) Eurographics procedures IEEE Transactions on Visualization and Computer Graphics Computer Graphics Forum

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Practical Aim: You are to compose a basic beam throwing/beam following project. The down to earth work is broken into three stages beam caster with self-shading cast-shadows full beam tracer. You ought to spend close to 15 hours on this part; including time to set up the reports required for your appraisal.

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Assessment will cover all material given in addresses, in relegated perusing and in commonsense work. 75% Sat Examination Questions more often than not contain 4 sections: a) Basic information (3 rd class) b) Moderate learning, fundamental comprehension (2.2 nd class) c) Good learning/moderate comprehension (2.2 nd class) d) Good comprehension – can take care of new issues (1 st class) 25% practical work Already clarified

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camera item point (pixel) center window Computer Graphics Basics Traditional: What shading is this pixel?

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Make 3D models change models into spot light up models undertaking models cut imperceptible parts raterization showcase Rendering Pipeline The rendering pipeline demonstrates the stream of data uses and the procedures expected to orchestrate a picture. Truth be told, there are numerous rendering pipelines. The request of procedures can change depending, for instance, on whether rendering time or rendering quality is more critical. These diverse pipelines contrast just in points of interest – the general stream of data from 3D model to 2D picture is dependably the same.

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target picture source picture point (pixel) Modern methodologies What shading is this pixel?

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L02: B-rep nuts and bolts The B-rep displaying plan is acquainted as only restricted with fabricate objects. focuses and lines focuses, lines, and polygons

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B-rep fundamentals Brep = Boundary Representation Start with an arrangement of M points p = { (x, y, z) i : i = 1…M } Make an arrangement of N lines from points L = { (i, j) k : k = 1…N } Make an arrangement of m polygons from lines B = { (k 1 , k 2 , …, k n } l : l = 1…m } A model is three-dimensional (3D), if the focuses are 3D (as above).

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focuses and lines focuses, lines, and polygons Different data bolsters distinctive rendering focuses just dots (utilized as a part of Chemistry, additionally in advanced Point based Rendering ) lines Wire-casing rendering, useful for fast tests in activity, say polygons shaded surfaces

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Practical Issues !! Continuously INDEX POINTS !! polygon table point table line table maintains a strategic distance from rehashed focuses so more productive evades numerical mistake when vitalizing

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Different tables can be utilized point table triangle table Triangles are the most widely recognized polygon, on the grounds that triangles are constantly level. In any case, triangles are lavish – a large portion of them; so different polygons utilized for demonstrating are frequently decayed into triangles for rendering.

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hostile to clockwise A Minor Complication !! POINT ORDER MATTERS !! The requesting gives the polygon a “front” and “back”. eh! which side is which?

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The typical of a triangular polygon The ordinary of a polygon is utilized as a part of lighting figurings (and in different estimations as well). Assume a triangle has focuses, p, q, r, every point in 3D. The typical bearing is n = (p-q) x (q-r) where x is the vector cross item. Exercise : Show that turning around the request of focuses likewise switches the typical\'s bearing .

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assemble a table of triangles from these focuses 1 Exercise : The focuses are haphazardly numbered. From the perspective given, point 4 is at the 3D square\'s back, point 5 is the closest corner. Fabricate a table of triangles in which vertices are reliably requested clockwise, when every face of the solid shape is seen from the outside . 2 6 4 5 7 3 8

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B-rep nuts and bolts: outline B-rep = limit representation Models objects with focuses, lines, polygons Points are bosses around a polygon Best to list into tables The type of tables manages rendering calculations Exercise : Build a 3D shape from all around requested triangles, render it as a wire-outline. See L03 for projection routines.

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L03: Cameras and Projection Camera models presented. Focuses are anticipated , with the goal that questions models can be rendered as wire-casings .

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object window picture center beam optical hub The Linear Camera In a direct camera beams of light go in straight lines from a question the camera catches all beams going through a solitary center cross a planar window to make the picture the ordinary from the plane to the center is the optical pivot

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article picture window center The Linear Camera Two variations exist: the “physical” model – appeared in the past slide has the center between the item and the window, in which the picture is rearranged the “mathematical model” – which we utilize , is appeared beneath has the window between the item and center leaving the picture the right far up

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Basic Perspective Projection Uses comparable triangles to figure the picture\'s tallness item picture center

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3D is just about as simple as 2D In the standard camera, central length (f) is taken as 1.

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Homogeneous Points Make projection simple and helpful 3D point (x, y, z) composed as (x,y,z,1) homogeneous point (x, y, z, a ) maps to genuine point 1/a (x, y, z) The homogeneous focuses p = (x,y,z,1) and q = (sx, sy, sz, s) vary just by a scale component s; this makes them proportionate in homogenous space. Notice (x,y,z) and (sx,sy,sz) are two focuses on the same straight line going through the root. This makes them identical – they speak to the same line! In homogeneous space, lines and focuses are double ideas!

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somewhat homogeneous geometry the arrangement of all beams extend regularly onto the window to make an example of “spokes” item point a scaled form of the picture straight line (a beam of light) picture point a scaled rendition of the article window center: at the root a specific line – the optical pivot – goes ordinarily through the window and through the core interest. This line has the center\'s picture – a vanishing point.

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Projection with a lattice Using homogeneous directions, projection can be composed as a network we do need to partition by homogeneous profundity, a , after this Compare this to with f = 1.

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The camera as a framework Using a network for projection is exceptionally advantageous from various perspectives. It implies we can display the camera as a lattice, C , say. Presently projection of a homogenous point p is just q = pC and we realize that the homogeneous picture point q is only a scale calculate far from being right – and everything we need do is scale it by its profundity (last component). It implies we can move the camera about in space just by pre-increasing by a grid change q = pMC It implies we can change the internals of the camera (central length, viewpoint proportion, and so forth) by post-duplicating by a network q = pMCK We can do the greater part of this without a moment\'s delay! simply set A = MCK , now A will be a straight camera q = pA

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Setting utilizing pivots then deciphers the camera before projection. Notice this is equal to applying M - 1 to the point. A few Examples

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Another sample To change central length, set now post-reproduce

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Define another direct projective camera in another spot and with another central length It is anything but difficult to utilize this camera… obviously, you can set M and K however you see fit not simply turn and interpret and new central length! Exercise : See notes for an activity All without a moment\'s delay

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Rendering with a Projection Matrix If we had a model manufactured recently of focuses (no lines, planes and so forth) then we could make a straightforward pictures utilizing this basic system: Project all focuses utilizing the projection framework Keep all focuses that exist in the window limits Connect focuses in the photo that are associated in 3D This delivers a “wire frame” picture – simple, and quick! On the off chance that all pixels inside an anticipated triangle can be distinguished, then they also can be shaded. This is the premise of output change .

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L04: Ray-Casting Lines are crossed with planar polygons. The outcome utilized as a premise for beam throwing . Presently questions can be rendered to look strong.

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Ray-throwing calculation For every pixel Cast a beam from the center through the pixel Compute all crossing points with all polygons Find the closest polygon Colour pixel with polygon shading Actually, the polygon shading is altered to make the impact of shading, as on a circle.

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Ray Casting Basics One beam for every pixel, cast into the scene Look for closest crossing point Color pixel in like manner scene of items camera pixel center window Expensive part: figuring the convergence of a beam with a polygon

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Line/Polygon c

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