The Write-on method in After Effects

Here is a simple method using the Write-on filter, which sometimes looks a little chunky to me (sprite chunk, sprite chunk, etc). You can borrow the alpha channel of a text layer for the top copy of duplicate base sources. This will keep the integrity of your source and keep the shape of your text intact. You can use the text layer to trace the Write-on brush positions in the layer Layer Window (enable the view in the Controls pop-up). Copy those keyframes to the top source layer and delete Write-on from the text layer. Here is the method by layer:

• layer 1 -- make solid layer adding Basic Text, apply Write-on to text, use Hold keyframes or multiple filters to jump spaces (see note below), and copy keyframes to layer 2 (then delete Write-on).
• layer 2 -- source1 copy w/Track Matte set to layer1 and Write-on keyframes from layer 1 (see note below).
• layer 3 -- source1 original.

Use Roving Keyframes to smooth the motion (click the little box under the keyframe in the speed graph of the Brush Position). Animate the Brush Size on the start of the stroke.

Note on strokes: If you use Hold keyframes, use Layer>Toggle Hold Keyframe at the end of the particular stroke (e.g., to cross a T or jump to the next letter). If you use multiple instances of Write-on, remember that AE copies keyframe data to the first instance of the effect. To paste data into a new instance, drag that instance to the top of the Effect Controls window then paste.

Other Methods that you can try at Home

Frame by Frame rotoscoping from end to beginning

Fractal Painter supports animations stacks that make this easy. Make your type in a new stack and copy the frame into the next stack. Erase from the end of the last letter, and copy that frame into the next frame. Repeat as necessary and save as a QuickTime movie. Reverse the frames in AE using a negative Time Stretch, or in Premiere using the Backwards Video filter.

Use an animated mask in AE to reveal text

Split the letters into pieces in Photoshop. Animate the masks in AE to reveal each piece. This method was used by Lynda Weinman her "L-Train" animation in the After Effects Classroom-in-a-Book. You could also leave the text whole and pre-compose as needed to use multiple masks.

Use the Gradient Wipe filter in AE to draw the strokes

Split the letters into pieces in Photoshop. Use the Gradient Editor to design progressively lighter strokes for each letter. It might be easier create this for each word separately. Then you can use these gradients to reveal layers in AE with the Gradient Wipe transition filter. Brian Maffitt is the champion of gradient wipes, which are used in a wide variety of systems. This method was also used by Tom Wolsky in his article, "Using Gradients to Paint Onto the Screen," at the "Media Worldwide" Web site at http://www.wwug.com/site/articles/graphics/adobe/after_effects/wolsky_tom1/wolsky1.html.