a static cloud skydome::..
several ways to animate a static cloud bitmap. Some are easy, some
are not-so-easy. One harder way would be to overlay the bitmaps
using the blue channel (hence the sky) of the bitmap as a transparent
colour and creating an opacity map or alpha channel in a bitmap
editing package such as Photoshop, overlay it on another cloud bitmap
and offset the two over time, so there appears to be two layers
of cloud travelling at different velocities.
way would be to use an amended cloud map as an opacity map for another
animated shader effect such as smoke or noise. A more simpler and
quicker way is to map the bitmap (preferably a panoramic cloud view)
onto a sky-dome (a hemisphere with the normals flipped)
mapping, select the top most vertex and using a selection method
with intensity falloff, or similar, animate the vertex rotating
a few degrees so the top of the sky-dome rotates and the translation
fades off down the sides, ending in virtually no rotation at the
a camera the centre of the sky-dome viewing from ground level (or
just slightly above), it will apprear that the clouds are all moving
horizontally at the same speed, relative to their distance from
the camera. However, this method will only be effective if the camera
does not pan around too far to the sides or to the rear or the rotating
effect will be visible and the illusion will be lost.
sky dome with a panoramic cloud texture applied|
selection falloff, animate the top vertex of the skydome rotating to give the
illusion of moving clouds|
published: 3D World website,
Draper, June 2000. Reproduction without permission prohibited.