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Basic Raster Graphics Algorithms for Drawing 2D Primitives Prof. Lizhuang Ma Shanghai Jiao Tong University.

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Presentation on theme: "Basic Raster Graphics Algorithms for Drawing 2D Primitives Prof. Lizhuang Ma Shanghai Jiao Tong University."— Presentation transcript:

1 Basic Raster Graphics Algorithms for Drawing 2D Primitives Prof. Lizhuang Ma Shanghai Jiao Tong University

2 Contents Architecture of a Raster Display Scan Converting Lines Filling Rectangles Filling Polygons Clipping Lines Clipping Polygons Antialiasing

3 Architecture of a Raster Display Video

4 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

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

6 The Basic Incremental Algorithm A scan-converted line showing intensified pixels as black circles

7 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; }

8 Midpoint Line Algorithm

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10 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

11 Filling Rectangles for(y from y min to y max of the rectangle) { for(x from x min to x max ) { WritePixel(x, y, value); }

12 Filling Polygons

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14 1.Find the intersections of the scan line with all edges of the polygon 2.Sort the intersections by increasing x coordinate 3.Fill in all pixels between pairs of intersections that lie interior to the polygon

15 Special Cases Horizontal Edges Slivers

16 Clipping Lines

17 The Cohen-Sutherland Algorithm

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19 Clipping Polygons

20 The Sutherland-Hodgman Polygon-Clipping Algorithm

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22 Antialiasing

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