Creating "volumetric" 2D Clouds

by David Goodman

Here is a simple way to create "volumetric" clouds using a flat plane and a 2d noise map. If you've ever had the need for an object such as an airplane to break through the clouds, then you've probably succombed to the use of a combustion effect. IMHO, this is a vast waste of time and resources for many reasons. The first obstacle is gizmos. Not only do you need the gizmo for the main cloud, but you'll need several more to populate the scene. You can waste a lot of time figuring out where to place each gizmo for a "random" appearance and then you have the further job of setting up a combustion routine for each gizmo if you want them truly random in appearance. The next challenge is to line up the gizmos with your scene objects so they interact exactly as you want during each and every frame of the animation. And here's the final thought before we proceed. Once any scene is rendered to a frame, everything in that scene is 2D anyway. "3d" is an illusion and is truly only 3d at a given point of reference. Follow along and download the sample avi to see the results. Render time for the above example was 7 minutes on a Pentium III, 800 mhz, piece of crap, old laptop that's been bumping around Iraq with me for the last year.

Okay, let's get down to work:

First, open a new scene in Max or save your current work and reset. It doesn't matter what object you use to fly through the scene; if you have an airplane model, then use that. But, you can use a box or a teapot for this tutorial. In the top view, draw a curved line using a nurbs point curve. Click on Shapes, then NURBS Curves from the drop-down box, then click on Point Curve. Draw the curve downward in the Top viewport so that you can see the whole line without zooming the viewport. Create a box, a teapot or import your object that is going to fly through the scene. Right Click in the Animation Time section (lower-right-hand corner) of Max and change the number of frames to 149. Since Max starts at frame 0, this will give you an even 150 frames of animation.

Select the object and click on the Motion tab. Under Assign Controller, select Position, then click on the assign controller button. When the window pops up, select the Path controller. Under Path Parameters, click on Pick Path and select the curve. Set up the path parameters however you like.

For the sky, we're going to use 2 flat planes. One plane will have a bitmap of the sky on it, the other plane will have the clouds. In the front view, create a plane and apply a bitmap image to it of a sky. Position this plane far behind the object in flight and make sure the size of the plane is large enough to fit in the frame no matter how you animate the camera. Alternately, you can simply assign a photo or procedural noise map sky to the background in the environment dialogue. Since my example file had a moving camera, I chose to use a second plane in the far background for the bitmap image. Either way you do it, it does not matter. The goal of this tutorial is more aid you in setting up the actual noise map and apply it to the situation. Experiment until you get what YOU want. Create another plane for the clouds. You need to position this plane in the foreground. In my example animation, I put the cloud plane about halfway down the flight path toward the camera so that the airplane would break through the clouds about half-way through the animation.

It's now time to set up the cloud material. Open the material editor and select an unused slot. Name this material Clouds. Select 2-Sided in the Shader Basic Parameters rollout. Click on the Maps rollout and select the Diffuse map slot. Choose NEW and select a noise map. In the Noise Parameters rollout, Change the Noise Type to Turbulence and set the Levels to 10. Under Noise Threshold, change the High to .8 and the low to .25. Leave the Size at 25. Do not change the colors of the map unless you want clouds that are colored other than white. The swatch in Color #1 must remain black as it will be invisible in a few moments.

Click on the Go to Parent icon to go back to the maps rollout. Click an drag on the Noise map and drag it to the Opacity Channel. When prompted for the method of copying, select Instance. The original noise map is being used to mask itself basically, so if you change the parameters to the original map, then you want the opacity map to change in exactly the same way. Look up at the Material Editor sample area. Your cloud material should be opaque everywhere except for where the clouds are. Apply this material to the second plane you created.

Render now and see the results. If you're not sure what just happened, delete or hide the FIRST plane you created and render again. Change the Environment background to an off-the-wall color for results that stand out during testing if that helps. Because we masked the original noise map with a copy of itself, everything that was black is now invisible. Everything in the white area is not. To make the clouds thicker, whiter, darker, bigger, smaller, whatever, is beyond the scope of this tutorial so now you can take what you've learned and experiment on your own. The possiblilities are limitless. As always, experiment to see what you can come up with. Please let me know if this tutorial was helpful to you! Thanks!