A line drawing algorithm is a graphical algorithm for approximating a line segment on discrete graphical media. On discrete media, such as pixel-based displays and printers, line drawing requires such an approximation (in nontrivial cases).

On continuous media, by contrast, no algorithm is necessary to draw a line. For example, oscilloscopes use natural phenomena to draw lines and curves.

A naïve line-drawing algorithm

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dx = x2 - x1 dy = y2 - y1 for x from x1 to x2 { y = y1 + (dy) * (x - x1)/(dx) plot(x, y) } It is assumed here that the points have already been ordered so that $x\_2\; >\; x\_1$. This algorithm works just fine when $dx\; >=\; dy$, but it is quite slow on a digital computer, as it requires floating-point calculations. If , the line becomes quite sparse, and in the limiting case of $dx\; =\; 0$, only a single point is plotted!

List of line drawing algorithms

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The following is a partial list of line drawing algorithms:

• Bresenham's line algorithm — optimized to use only additions (i.e. no divisions or multiplications); it also avoids floating-point computations.
• Xiaolin Wu's line algorithm — can perform anti-aliasing

Geometric algorithms

Algorithme de tracé de segment | Algoritmo di rasterizzazione di linea | Алгоритам за исцртавање линија