Game Development Reference
Figure 9.52 Animating the Brush
Position of the Write-on effect
can create animated drawings.
As mentioned before, the real value of this effect is its ability to
reveal the layer it's applied to. We can use this to create the ani-
mated vines look that is so ubiquitous these days. If you go to the
Growing Vines FINISH comp, you'll see the complete animation
with growing vines. Note that the trick here is to have on separate
layers the vines (or whatever else you want revealed gradually).
This gives you greater control over what parts to reveal and when
( Fig. 9.53 ).
In the Growing Vines START comp, you'll fi nd fi ve layers of
vines to animate as they are revealed. Select the Main Vine layer.
You may want to turn off the visibility of the other vines if they
distract. Apply the Write-on effect to the Main Vine layer. Take
the Brush Position control point down to the bottom of the vine,
as we'll be revealing it from the bottom up. Increase the Brush
Size value until it completely covers the vine. Currently, it's only
painting white on the vine. But, when we take the Paint Style
value to Reveal Original Image, the paint only reveals the vine.
So, animate the Brush Position covering the vine, and your vine
will appear to grow. It's just that simple. I fi nd it easier to leave
the Paint Style on its default setting while I'm painting so that I
can see what value to animate the Brush Position. Also, note that
if you animate a property such as Brush Size, it will apply to all