Digital Differential Analyzer (graphics algorithm)

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This article is about a graphics algorithm. For other uses of DDA, see DDA. For the digital implementation of a Differential Analyzer, see Digital Differential Analyzer.

In Computer graphics, Digital Differential Analyzer (DDA) is an algorithm used to determine which points need to be plotted in order to draw a straight line between two given points. It employs the equation for line representation (example: y=mx+c), then scan through an axis. Each scan it would determine the value on the other axis using the equation, this way the proper pixel can be located.

1 Overview
2 The algorithm in code
3 See also
4 External links

[edit] Overview

The DDA method is not very efficient due to the need for division and rounding. Bresenham's line algorithm is a more efficient method to draw lines because it uses only addition, subtraction and bit shifting.

[edit] The algorithm in code

This is a sample implementation of the DDA algorithm in the C programming language:

/* Draw a straight line between the points (xa, ya) and (xb, yb) */
void line DDA(int xa, int ya, int xb, int yb) {
           
            int dx=xb-xa; // horizontal difference
            int dy=yb-ya; // vertical difference
            int steps, k;
            float xIncrement, yIncrement;
            float x=xa, y=ya; // the drawing points x and y are initiated to one endpoint of the line

            // calculate the number of steps used to draw the line (number of pixels)
            if(abs(dx)>abs(dy)) 
                steps=abs(dx);
            else 
                steps=abs(dy);        

            // calculate the increment for x and y in each step
            xIncrement=dx/(float)steps;
            yIncrement=dy/(float)steps;

            // point out the starting pixel
            setPixel(ROUND(x), ROUND(y));

            // loop through the line from one end to the other and point out the pixels
            for(k=0; k<steps; k++) {
                    
                    // the points are incremented an equal amount for every step
                    x += xIncrement;
                    y += yIncrement;
                        
                    // since the values for x and y are float they are rounded before they are plotted
                    setPixel(ROUND(x), ROUND(y));
            }
}