View Full Version : animating a rainbow across the sky

pdp editor
09-07-2009, 09:50 AM
:help:I'm trying to make a rainbow animated across the sky. I search here and found some topics about using a null and transparency or the alpha channel without much luck. The null just creates a black spot allowing every thing else to show the other methods rehide the object after the null has passed. I think I need some pointers on the process to make something like this work. all tips greatly appreciated. :help:

09-07-2009, 11:18 AM
Create a texture thats a circle thats half black/half white. Use that as a clip or transparency map. Use a reference null to rotate the texture to reveal the rainbow.

09-07-2009, 12:26 PM
Create a texture thats a circle thats half black/half white. Use that as a clip or transparency map. Use a reference null to rotate the texture to reveal the rainbow.

damn! good answer .

pdp editor
09-07-2009, 02:04 PM
OK that sounds good let me try that, thanks!

pdp editor
09-07-2009, 06:58 PM
I played with this for a few hours without getting anywhere. (See attached.)

I created a null called reveal and used it as a reference for the clipmap Image. The animation I get is a constant rainbow image with flashing black. I want the rainbow to appear along the X as the null passes under it. In the graph editor I set the the rotation channel "P" to go from 0 to 180 to reveal the rainbow. Is my thought process wrong with any of the above?

09-07-2009, 07:37 PM
You need to probably cange the scale. For example say that the arch of the rainbowis centered at the origin and is 2 meters tall. If you autosize the texture it will place the centerline between the black and white part of the texture 1 meter up.
So youll need to move the y position of the texture 1 meter down AND double the scale in the y direction.
Also after thinking about it a bit you probably want the white portion to be a white striipe rather then a circle. The stripe should correspond to the arch of the rainbow.
Get this going in the color channel first so you can see whats going on. Once you know its working copy and paste the texture to the clip map or transparency channel and turn it off in the color channel.

pdp editor
09-07-2009, 08:10 PM
you read my mind I was just thinking if I could only see what was going with the clip map. your response is just what I needed.

pdp editor
09-07-2009, 09:33 PM
I got it. Scaling the image and increasing the x position by 8 was the key. I also change the projection to spherical and used automatic sizing.

one problem remaining: the wipe does not start until frame 20.

09-07-2009, 09:47 PM
Rotate the reference null then start it going on frame 20

09-08-2009, 03:21 AM
can't you just create the arc and rotate it in the horizon (sorry if this sounds too simple)

09-14-2009, 01:23 PM
Hey there, pdp editor.

Are you looking for something like this? All I did was make a flat box, texture it with the rainbow colors, & copy & paste to another layer. Using a couple of oval discs for guides, I took the 2nd layer and made it an arch. Then, I did a Back ground to morph. I took layer 1 into layout and setup motion mixer to morph the flat box into the arch. When you do it this way the texture will bend with it. You keep the shape to planar. Finally, I just used transparency, over time, to go from 100% transparency to about 35%

It's actually really easy, once you get the hang of it.

Sorry I didn't composite it to the background image. If I had the time, I would do it.

pdp editor
11-02-2009, 07:17 PM
just to tie up this loose end. I did complete the rainbow as desired.
here's what I learned: the null does not need to pass through the object being revealed. some how my mind convinced me that it needed to move in the shape of the object. I had it move along the x under the object instead. I rotated the image used in the clipmap along the rotate-P to 180
and that was that.