I want to make a beer foam, not just for an image. I want the beer fluid to pour in the glass and automatically make foam on the top of the glass and drop down due to over flow.
It should be in animated not a static render.
I have seen video that shows how to render the foam, but not as animated video. Is there a brief explanation how it works?
I would animate a simple UVWarp with a texture with transparency.
I would model the foam as a single object, not detailed at all. Look for a texture with transparent parts, apply it to the foam object. Apply a UVWarp modifier to the object (this modifier moves the texture), and animate the modifier using an armature and two bones.
The texture should have a big transparent part, so when it is animated it looks like if its going down from nothing. Pretty sure it could do the trick for a couple of seconds.
Your simplest solution is probably to use shapekeys and animate them. For this, you'll need to work backwards. First, animate your beer liquid (the nonfoamy part) from start to end; if you want your foam to keep foaming after the liquid stops pouring, make sure to add some frames for padding at the end. On the final frame, model your end result foam and add it as a shapekey. Then without adding or subtracting any vertices, model it to a new shape a little further up the glass and a little less foamy, and make a shapekey for that. Continue on in this manner until you reach the beginning of your foam. To finish up, either scale everything to zero and add a final shapekey for it, or add a transparent shader to to your material setup and keyframe a mix node at the appropriate points.
Now the fun part! Go along your animation and tweak your shape keys at whatever points you feel necessary, playing with the sliders. When you have something you want, keyframe all the strength sliders.
I hope this helps! Happy Blending!
So what I would actually do, (and this should work with any version of blender) create the foam in its final stage and then add bubbles. Use a boolean modifier to delete these "bubbles" and then make them invisible. Add some transparency to the foam and maybe if you want bring back the bubbles and make them reflective. You can animate the foam going down by just shrinking it while keeping the base in a shape key.
