6.20.2 Boiling Water

Another good example of procedural creation is boiling water. When the temperature reaches a certain level, bubbles begin to appear randomly inside the water and start to go up until they reach the surface of the water and disappear.

Right, let's do this.

1. Create a CREATION method.

2. Create a bubble under the method and add the following tags to it:

                   SCRE l=1
                   SDEL l=y>0.0

Because the value of the "I" variable in the SCRE tag is always 1, a new bubble is created in each frame. The SDEL tag defines that the bubble will be deleted as soon as its y coordinate reaches the value 0.

3. Use the function Modify/Properties/Velocity to define a velocity for the bubble. The idea is that as soon as the bubble is created, it will start to go upwards.

4. Create a PATH method to the same level with the bubble. Set the Frequency of the method to 5, and draw a strongly oscillating curve under the PATH method. The way we define the original position for the bubbles is quite "deterministic", but if the path is very curved and complicated, it will look as if the bubbles were created randomly all over the water (We will demonstrate you later how to use a real random function to define the position for the bubbles using RPL).

5. Create the PROCESSOR method to the same level with the CREATION method. As mentioned earlier, an attribute itself (such as mass, velocity etc.) does not move the object anywhere. The PROCESSOR method is needed for converting the attributes to real motions. Because we did not create a PROCESSOR method at the same level with the sample bubble, the sample won't go up (the velocity is there, but it is not converted to a motion).

6. Create a pot and a circle inside it representing the surface of the water in the pot. Note that we used the conditional expression "y>0" to define when bubbles should disappear, so the circle representing the level of the water should be placed to that height.

7. Make the CREATION method object invisible, to make the bubbles appear out of nothing.

Now our boiling water example is ready. I strongly suggest that you save this project now and spend some time to render it photo-realistically. Use an animated bumpmap on the water surface and with these bubbles, the boiling water should look pretty good.