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A fractal landscape being rendered using the painter's algorithm on an Amiga. The painter's algorithm (also depth-sort algorithm and priority fill) is an algorithm for visible surface determination in 3D computer graphics that works on a polygon-by-polygon basis rather than a pixel-by-pixel, row by row, or area by area basis of other Hidden-Surface Removal algorithms.
The rule can be seen in effect in many vector graphic programs (such as Freehand or Illustrator), where a crossing of an outline with itself causes shapes to fill in strange ways. On a simple curve, the even–odd rule reduces to a decision algorithm for the point in polygon problem.
Flood fill, also called seed fill, is a flooding algorithm that determines and alters the area connected to a given node in a multi-dimensional array with some matching attribute. It is used in the "bucket" fill tool of paint programs to fill connected, similarly colored areas with a different color, and in games such as Go and Minesweeper for ...
If the point is on the inside of the polygon then it will intersect the edge an odd number of times. The status of a point on the edge of the polygon depends on the details of the ray intersection algorithm. This algorithm is sometimes also known as the crossing number algorithm or the even–odd rule algorithm, and was known as early as 1962. [3]
The Greiner-Hormann algorithm is used in computer graphics for polygon clipping. [1] It performs better than the Vatti clipping algorithm, but cannot handle degeneracies. [2] It can process both self-intersecting and non-convex polygons. It can be trivially generalized to compute other Boolean operations on polygons, such as union and difference.
A curve (top) is filled according to two rules: the even-odd rule (left), and the non-zero winding rule (right). In each case an arrow shows a ray from a point P heading out of the curve.
Candidate polygons should not be self-intersecting (i.e., re-entrant). The algorithm can support holes (as counter-clockwise polygons wholly inside their parent polygon), but requires additional algorithms to decide which polygons are holes, after which merging of the polygons can be performed using a variant of the algorithm.
All steps for clipping concave polygon 'W' with a 5-sided convex polygon. The Weiler–Atherton algorithm overcomes this by returning a set of divided polygons, but is more complex and computationally more expensive, so Sutherland–Hodgman is used for many rendering applications. Sutherland–Hodgman can also be extended into 3D space by ...