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bounce ball from floor expression help
bouncesPerSecond = 1.5 bounceStrength = 200 decayRate = .5 floor = thisComp.layer("floor").transform.position[1] bounceOffset = Math.abs(Math.cos(bouncesPerSecond * time * 2 * Math.PI)) y = bounceStrength * bounceOffset/Math.exp(decayRate * time) floor = floor - (height/2) [position[0],floor] - [0,y]Above is an expression that bounces a ball from a floor. This is from the book After Effects Expressions by Marcus Geduld
My problem here is with the variable called height. Is there such a variable in AE java script?
TONY T
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5 Replies
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That would be the height attribute of the layer to which the expression is applied.
Dan
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Hey thanks but I have one more thing.
When I copy and paste this expression into AE I get an AE warning:
invalid numeric result(divide by zero?)
Expression disabled.
Error occurred at line 7.
Comp: “ball and floor”
Layer: 1(“ball”)
Property: ‘Position’line 7 is the height/2 statement. Can you see the error? Is it trickling down or is it height/2.
TONY T
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Try putting a semi-colon at the end of line 7. Actually, it’s a good idea to put them at the end of each line.
Dan
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Hmmm. This javascript is not as forgiving as the other. Seems my habits doing javascript inside web applications are doing me in with AE3. Thanks again, I will use semi-colons. And thanks for responding so quickly.
TONY T
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Aha. It seems that you are better off without the seventh line. If the anchor point for the floor layer is set at the top of the floor and the anchor point for the ball is set at the bottom of the ball, the ball will always bounce from the floor, independent of where the floor is in the comp. The seventh line enforces the floor being placed halfway up the comp. Perhaps this was for presentation.
TONY T
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