A texturing artifact
of 3d games
where a perspective
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
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
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
however, is an entirely different matter
. If software rendering
may produce the best results, graphically. This also allows for use of procedural
and the like, which are seldom implemented when hardware rendering is used.
It appears to be most prominent
in games utilising the Quake 2
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.