scan - Graphics Primitives Chapter 3 & 4 Intro. to...

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raphics Primitives Graphics Primitives Chapter 3 & 4 Intro. to Computer Graphics pp Spring 2008, Y.G. Shin
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Graphic Output and Input Pipeline ± Scan conversion nverts rimitives ch s es rcles tc ± converts primitives such as lines, circles, etc. into pixel values eometric escription nite ene rea ± geometric description a finite scene area ± Clipping ± the process of determining the portion of a primitive lying within a region called clip region
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Graphic Output Pipeline ± Output pipeline (rendering process) application model : descriptions of objects application program : generates a sequence of functions to display a model graphics package : clipping, scan conversion, shading, etc. display H/W
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Graphic Input Pipeline ± Input pipeline ser interaction (e g mouse click) ± user interaction (e.g., mouse click) raphic package (by sampling or ± graphic package (by sampling or event-driven input functions) ± application program ± modify the model or the image on the screen
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Graphic Output Pipeline ± displays with frame buffers and display ntrollers controllers ± common in pug-in graphics card ± scan conversion by a graphic package and display processor ± displays with frame buffers only ± scan conversion by a graphic package
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Output Pipeline in Software When scan conversion and clipping? ± Clipping before scan conversion ± for lines, rectangles, and polygons clipping after scan converting each primitive (scissoring) ± Clipping after scan converting the entire collection of primitives into a temporary canvas ± for text
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Scan Converting Lines A line from (x0,y0) to (x1,y1) a series of pixels [Criteria] traight es ould ppear raight ± Straight lines should appear straight ± Line end-points should be constrained - grids, snaps ± Uniform density and intensity ± Line algorithms should be fast
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Why Study Scan Conversion Algorithms? ± Every high-end graphics card support this. ou will never have to write these routines yourself ± You will never have to write these routines yourself, unless you become a graphics hardware designer. o why learn this stuff? ± So why learn this stuff? ± Maybe you will become a graphics hardware designer. ut seriously the same basic tricks underlie lots of ± But seriously, the same basic tricks underlie lots of algorithms: ± 3-D shaded polygons ± Texture mapping ± etc.
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Simple Scan Converting Lines Based on slope-intercept algorithm from algebra: y = mx + b Simple approach: increment x, solve for y Floating point arithmetic required
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Digital Differential Analyzer(DDA) ± Idea o to starting end ) , ( y x )) ( , 1 ( m y Round x + + 1. Go to starting end point crement x and y i i i i 2. Increment x and y values by constants proportional to x and y such that one of them is 1. 3. Round to the closest raster osition )) ( , ( i i y Round x ) , 1 ( m y x i i + + position
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Digital Differential Analyzer(DDA) ± Drawbacks ± rounding toan integer takes time ± floating-point operations ± Is there a simpler way ?
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This note was uploaded on 04/29/2010 for the course CSE 4190.411 taught by Professor Shinyeonggil during the Fall '08 term at Seoul National.

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scan - Graphics Primitives Chapter 3 & 4 Intro. to...

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