A texturing
artifact of
3d games where a
perspective
correct textured1 polygonal sky is used.
This is produced by the fact that the
corners of the sky model will invariably be more
distanced than the centres of those
polygons, provided that the viewer is at the centre of
the
sky model, and the sky model is a
regularly shaped one. Thus,
at the corners, the
texels2 will be more widely spaced when
rasterized, causing lower
detail of the sky in these areas.
This effect can be dampened slightly by
bilinear filtering3 of the texture and other such
texture
interpolation techniques, as many other texturing artifacts can be. The effect is amplified
by a low
field of vision.
The most
effective solution to this artifact, when using
hardware rendering, is using a higher
detail sky model. For example, a
sphere approximation4 with twenty polygons would make this artifact
greatly less noticable, than using a cube with six. Whether this extra
overhead is worthwhile,
however, is an entirely
different matter. If
software rendering is used,
ray tracing5 may produce the best results, graphically. This also allows for use of
procedural
textures and the like, which are seldom implemented when hardware rendering is used.
It appears to be most
prominent in games utilising the
Quake 2 engine.
1 - This produces more realistic results on large polygons - otherwise, the texture is
linearly interpolated over the polygon, with the distance of each point not taken into account.
2 - A texel is an individual element of the texture map, when it is scaled onto a polygon.
3 - When the colour of the pixel to be drawn is computed by a linear interpolation of all
four neighbouring texels. See also, bicubic interpolation.
4 - A sphere approximation is a perfect sphere, simplified into basic polygons.
5 - This is, in general, much slower than polygon rasterization, but is able to produce
smoother, and more realistic results.
(nodeshell rescue)