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The Nicholl–Lee–Nicholl algorithm is a fast line-clipping algorithm that reduces the chances of clipping a single line segment multiple times, as may happen in the Cohen–Sutherland algorithm. The clipping window is divided into a number of different areas, depending on the position of the initial point of the line to be clipped.
The simplest method of drawing a line involves directly calculating pixel positions from a line equation. Given a starting point (,) and an end point (,), points on the line fulfill the equation = +, with = = being the slope of the line. The line can then be drawn by evaluating this equation via a simple loop, as shown in the following pseudocode:
The Liang–Barsky algorithm uses the parametric equation of a line and inequalities describing the range of the clipping window to determine the intersections between the line and the clip window. With these intersections, it knows which portion of the line should be drawn. So this algorithm is significantly more efficient than Cohen ...
The intersection of the outpoint and extended viewport border is then calculated (i.e. with the parametric equation for the line), and this new point replaces the outpoint. The algorithm repeats until a trivial accept or reject occurs. The numbers in the figure below are called outcodes. An outcode is computed for each of the two points in the ...
A naive approach to anti-aliasing the line would take an extremely long time. Wu's algorithm is comparatively fast, but is still slower than Bresenham's algorithm. The algorithm consists of drawing pairs of pixels straddling the line, each coloured according to its distance from the line. Pixels at the line ends are handled separately.
ComputeIntersection is a function, omitted here for clarity, which returns the intersection of a line segment and an infinite edge. Note that the intersecting point is only added to the output list when the intersection is known to exist, therefore both lines can always be treated as being infinitely long.
Here the parametric equation of a line in the view plane is = + where . Now to find the intersection point with the clipping window, we calculate the value of the dot product . Let p E {\displaystyle \mathbf {p} _{E}} be a point on the clipping plane E {\displaystyle E} .
Initially it is given all the points between the first and last point. It automatically marks the first and last point to be kept. It then finds the point that is farthest from the line segment with the first and last points as end points; this point is always farthest on the curve from the approximating line segment between the end points.