I have a mesh object passing in front of a camera; the camera is locked in a fixed upward view.
The background to the scene is a sky full of moving procedural clouds. I believe the node setup is Andrew Price's. As the scene progresses, the clouds constantly change shape and position, as suggested below:
I am creating a video which must loop... which is a pain against a background of moving clouds.
I would like to use the object passing in front of the camera as a wiper to transition from the current frame's clouds to an earlier frame, creating the loop. Here's a suggestion of the transition need:
The mesh is traveling from bottom to top. The portion below the mesh object reflects the earlier cloud position. Above the mesh is the current frame's clouds position.
I am open to compositor solutions or render-pass solutions, but have been unable to figure one out that uses the mesh as a key to a transition. Also, the use of Z-depth and mist makes artifacting a problem with foreground images rendered transparent and then composited onto the sky.
All that said, I would welcome recommendations. Although the wiper mesh object does go edge-to-edge, I cannot have it scaled so large as to be large enough to completely fill the frame, which would hide all of the clouds for a frame or two.
Imagine the mesh as an airplane: The wings -- which are irregularly shaped -- move across the scene, but at most points you can see quite a bit of cloud cover above and below the wing.
Compositor, render pass, Object ID.... I've fiddled with all and would welcome so best practices.
All ideas welcome!
EDIT: And, more generally, I went with this 'wiper' approach because it seemed to offer the most potential. There are seconds of the video during which nothing but clouds are visible -- but doing a fade between one series of clouds and another did not seem very elegant... As the opacity levels changed in the VSE between the 'new' clouds and 'old' clouds, it left a muddle of clouds that did not make for a pretty loop... but I am open to different approaches altogether.