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by Dinesh Thakur

Digital Differential Analyzer is a scan conversion line algorithm based on calculating either dy or dx. We sample the line at unit intervals in one coordinate & determine corresponding integer values nearest to the line path for the other coordinate.

The algorithm accepts as input the two endpoint pixel positions. Horizontal & vertical differences between the endpoint positions are assigned to parameters dx & dy. The difference with the greater magnitude determines the increment of the parameter steps. Starting with the pixel position (xa , ya), we determine the offset needed at each step to generate the next pixel position along the line path. We loop through this process ‚Äěsteps? times. If the magnitude of dx is greater that the magnitude of dy & xa is less that xb, the values of the increments in the x & y directions are i & m. It is a faster method of calculating pixel positions. However, the accumulation of round off error in successive additions can cause the calculated pixel positions to draft away from the true line path for long line segments.