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16.69.6 - Expression Evaluator in Transitions




The above example was created with the aid of the expression evaluator. The default color palette was used. Accumulate Changes was selected, the animation was generated once to create the underlying spiral, then generated a second time and saved as a GIF animation directly from the filmstrip using the parameters below to give the impression of an infinite loop.

The time range was also set from 0.0 to 0.97 to avoid a skip where the circle goes from 2*pi radians back to 0 which are, functionally, exactly alike.

Note that "scale to transition" was also selected, this scaled the source image so that instead of a "moving window" effect, the the whole picture is rotating


To build the transition, consider a parametric circle.

Y = sin(t) X = cos(t)

Where t goes from 0 to 2*pi

From this we build into a simple Transition Control File:

; Square transition ; initxy !0.25*(cos(ttime(0)*2*3.1415926))+0.25 !0.25*(sin(ttime(0)*2*3.1415926))+0.25 repeats 1 1 offsets 0.0 0.0 xscales 1.0 1.0 yscales 1.0 1.0 rotate 0 0 line 0.00 0.00 0.25 0.00 line 0.25 0.00 0.25 0.25 line 0.25 0.25 0.00 0.25 line 0.00 0.25 0.00 0.00 ; This code was used, as shown here, to create the animation above

Explanation:

initxy !0.25*(cos(ttime(0)*2*3.1415926))+0.25 !0.25*(sin(ttime(0)*2*3.1415926))+0.25
  • Because ttime(0) is a fraction that ranges from 0 to 1, it has to be multiplied by 2*pi in order to produce a useful result.

    This result is the fractional part of 2*pi radians completed, therefore, it will trace 1 whole circle over the course of time (from 0 to 1)

  • The multiplication by 0.25 reduces the radius of the circle so it stays on-screen.
  • The addition of 0.25 moves the center of the circle inside of the action image.
  • Note that ! (exclamation) was used before each expression.
  • Note that there were only 2 spaces, each to separate arguments.
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