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**Basic Raster Graphics Algorithms for Drawing 2D Primitives**

Prof. Lizhuang Ma Shanghai Jiao Tong University

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**Contents Architecture of a Raster Display Scan Converting Lines**

Filling Rectangles Filling Polygons Clipping Lines Clipping Polygons Antialiasing

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**Architecture of a Raster Display Video**

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**Definitions Pixel: a screen consists of N x M pixels**

Bilevel = monochrome, 1 bit / pixel Color: RGB/CYK/LUV… Bitmap / pixmap Frame buffer: an array of data in memory mapped to screen

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Scan Converting Line A scan-converted line showing intensified pixels as black circles

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**The Basic Incremental Algorithm**

A scan-converted line showing intensified pixels as black circles

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**The Basic Incremental Algorithm**

void Line (intx0, inty0, intx1, inty1, value) { intx; floatdy, dx, y, m; dy=y1-y0; dx=x1-x0; m=dy/dx; y=y0; for(x=x0; x<=x1; x++) { WritePixel(x, (int)floor(y+0.5), value); y+=m; }

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**Midpoint Line Algorithm**

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**Midpoint Line Algorithm**

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**Midpoint Line Algorithm**

void MidpointLine(intx0, inty0, intx1, inty1, value) { int dx, dy, incrE, incrNE, d, x, y; dy=y1-y0;dx=x1-x0;d=dy*2-dx; incrE=dy*2;incrNE=(dy-dx)*2; x=x0;y=y0; WritePixel(x, y, value); while(x<x1) { if(d<=0) {d+=incrE;x++; } else {d+=incrNE;x++;y++;

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**Filling Rectangles for(y from ymin to ymax of the rectangle) {**

for(x from xmin to xmax) { WritePixel(x, y, value); }

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Filling Polygons

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Filling Polygons

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Filling Polygons Find the intersections of the scan line with all edges of the polygon Sort the intersections by increasing x coordinate Fill in all pixels between pairs of intersections that lie interior to the polygon

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Special Cases Slivers Horizontal Edges

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Clipping Lines

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**The Cohen-Sutherland Algorithm**

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**The Cohen-Sutherland Algorithm**

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Clipping Polygons

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**The Sutherland-Hodgman Polygon-Clipping Algorithm**

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Antialiasing

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