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The algorithm can fail in certain cases. In this example, Polygons A, B and C overlap each other. It's not possible to decide which polygon is above the others or when two polygons intersect one another in three dimensions.
In basic implementations, painter's algorithm can be inefficient. It forces the system to [[Computer rendering|render]] each point on every polygon in the visible set, even if that polygon is occluded in the finished scene. This means that, for detailed scenes, the painter's
These and other flaws with the algorithm led to the development of [[Z-buffer]] techniques, which can be viewed as a development of the painter's algorithm by resolving depth conflicts on a pixel-by-pixel basis, reducing the need for a depth-based rendering order. Even in such systems, a variant of painter's algorithm is sometimes employed. As Z-buffer implementations generally rely on fixed-precision depth-buffer registers implemented in hardware, there is scope for visibility problems due to rounding error. These are overlaps or gaps at joins between polygons. To avoid this, some graphics engine implementations "overrender" - drawing the affected edges of both polygons in the order given by painter's algorithm. This means that some pixels are actually drawn twice (as in the full painters algorithm) but this happens on only small parts of the image and has a negligible performance effect.
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