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

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Graphics Primitives Chapter 3 & 4 Intro. to Computer Graphics Spring 2008, Y.G. Shin
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Graphic Output and Input Pipeline Scan conversion converts primitives such as lines circles etc converts primitives such as lines, circles, etc. into pixel values 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 hi k li i graphics package : clipping, scan conversion, shading, etc. display H/W
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Graphic Input Pipeline Input pipeline user interaction (e g mouse click) user interaction (e.g., mouse click) graphic 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 controllers common in pug-in graphics card i b hi k d di l scan conversion by a graphic package and display processor di l ith f b ff l 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] 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. You will never have to write these routines yourself You will never have to write these routines yourself, unless you become a graphics hardware designer. So why learn this stuff? Maybe you will become a graphics hardware designer. But 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 l ith f l b algorithm from algebra : y = mx + b Simple approach: increment x, solve for y Floating point h d arithmetic required
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