© Joel Hagen
Nearly everyone who has experimented with animation software has discovered
how easy it is to spin, move and zoom a brush using automated motion features.
DeluxePaint has it's Move requester, Brilliance it's Tweening, Animator
Pro it's Optics and so on. With these features you can enter values for
brush movement and rotation on the X, Y and Z axes of computer image space.
The software creates the frames of that motion for you. Not so obvious
are techniques for creating complex brush movements by compounding multiple
motion paths. This column will help you set up some revealing experiments
that can add new dimensions to your animations and paintings.
A brain teaser I sometimes pose to animation students is to paint a small
moon and cause it to trace a convincing orbital path around a planet as
viewed from near the equatorial plane. If you are in a puzzle solving mood,
give that a try before reading much further. At the end of the column I
will outline one solution using DPaint's Move requester. I will refer to
DPaint's tools in this article, but the techniques apply to any program
with similar features. If you are completely unfamiliar with the Move requester
and animbrushes, study the tutorials in your manual to learn the basics.
From Anim/Frames/Set# create a 40 frame blank animation, stamp a round
brush on the screen and Undo. The values I suggest assume a 640 x 400 screen,
but work in any resolution you like. Just to orient yourself, Use the Move
requester (Shift M from the keyboard) to animate the brush across the screen
from left to right by entering 200 in the "X Dist" window. Be
sure your "Count" equals the number of frames in your animation.
Hit "Draw" and DPaint creates a 40 frame animation of the brush
moving in a straight line in the positive "X" direction. Clear
all frames of the animation, stamp the brush down again, Undo, then return
to Move and hit it's "Clear" button. Now try the same idea for
a simple movement in the "Y" direction. Notice which direction
the brush moves for positive and negative "Y" values. Clear everything
and try "Z" movement.
The next experiment involves compound motion. Use a quarter inch brush
and 20 frames. Enter a "Y Dist" of 20 and hit Draw. Use Anim/Animbrush/Pick
Up to grab that 20 frame vertical movement as an animbrush. Clear all frames
and hit "Shift 7" to reset the animbrush to the first cel. Stamp
it on the screen and Undo. Return to Move and Clear all Distance values.
Enter 200 for "X Dist" and set "Count" to 200. In Move
requester's "Direction" panel, hit the center "Pause"
button under "Record". This allows you to render the movement
to a single frame which makes the path of the brush easy to see. When you
hit Draw, you should see ten diagonal lines similar to those at the top
left of the illustration (a Count of 200 with a 20 cel animbrush equals
ten lines). Next, select the ping-pong button in Animbrush/Settings. Locate
the animbrush on the page again ("Shift 7," stamp, Undo) then
Move. Use the same settings and Draw. You should see an up and down zig-zag
as in the upper left.
To add another layer to the exploration, repeat the procedure in the previous
paragraph with the following variation. When you first enter the "Y"
Distance, enter a value of 10 in both "Ease Out" and "Ease
In". This causes the brush to accelerate away from its starting position
and decelerate into its end position. When that animation is used as an
animbrush in the Move requester, the result should be similar to the center
left pair of illustrations. This could be used to draw screw threads by
varying the "X Dist" and "Count". Ping-pong the animbrush
and it describes a sine wave as it moves in the X direction. The "Ease"
settings have a powerful effect on brush paths and can be used to simulate
the motion of bodies affected by gravity and acceleration. The bottom pair
of motion paths shows the result of only using "Ease Out" values.
This can be used in animating bouncing or ballistic movements.
The next experiment is the "entwining" trick shown at the top
right of the illustration. You might use it to paint interesting borders
or designs. Place two or three dots side by side and pick them up as a
brush as shown. Stamp and Undo to locate the brush on the page. In Move,
enter -100 in "Y Dist" and 1200 in the "Z Angle". Hit
Draw to render the rope-like form to a single screen. The dots make several
full revolutions around each other as they move down the screen. Experiment
with other values and brush configurations. See what happens if you create
an animbrush using this technique and use it on a new path in Move. Combinations
of these techniques can produce spirals, cycloids and other complex paths
and shapes.
The planetary orbit is a fun challenge and can produce impressive animations.
The realistic motion relys on compound sequences of "Ease" in
and out values. Set up a 40 frame animation and use a half inch round brush
for your experiments. For a smoother animation, you can use more frames
once you are sure of the technique. To simplify things, I will present
the steps as succinctly as possible. In Move, keep the Count always at
10 for this 40 frame animation. The orbit is rendered in four steps, one
quadrant at a time (eg. for a 200 frame animation, use a 50 frame count).
You will use either "Ease Out" or "Ease In" for each
step, not both. All X Y and Z values given are Distance settings.
The first step shrinks the brush into Z space and back in 4 steps.
1) Z=+250 ease out 10
2) Z=+250 ease in 10
3) Z=-250 ease out 10
4) Z=-250 ease in 10
Pick up this motion as an animbrush and use it in Move for the next path after clearing everything.
The second step creates a vertical path.
1) Y=-30 ease out
2) Y=-30 ease in
3) Y=+30 ease out
4) y=+30 ease in
Pick up this motion as an animbrush and use it in Move for the next path after clearing everything.
The third step uses a horizontal path to trace the final orbit.
1) X=+200 ease in
2) X=-200 ease out
3) X=-200 ease in
4) X=+200 ease out
As a variation, combine steps one and two and compare the final result. Try your own solutions. You can render the orbital path around a central planet by using "Stencil" to protect the planet as the distant brush passes behind it in two quadrants. The orbit animation is especially effective if you begin with an animbrush of a spinning planet. In that case, use a total number of frames in your orbit that is a multiple of the number of frames in the spinning planet animbrush. For more on creating a spinning planet, see my article in Amigaworld, October 1991 or the tutorial in the DPaint IV manual. Alternatively, try using the tumbling asteroid and starfield from Accent #39.
For an interesting effect try adding a brush rotation on the Y axis as you create step one of the orbit. Use a value of 90 in the "Y Angle" for all four phases of step 1. This is especially effective as a titling trick. The brush always faces away from the center of the orbit. As the reverse side of the brush rotates into view, darken it to enhance the spatial illusion
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