automated light sweep

[Dan Ebberts]

OK – you’ll need to add 3 sliders to the text layer: Left Margin (set to 100), Right Margin (set to 100) and Duration (set to your desired sweep time). Add this expression, and set a layer marker wherever you want to trigger a sweep:


M = marker;
n = 0;
if (M.numKeys > 0){
n = M.nearestKey(time).index;
if (M.key(n).time > time) n--;
}
t = n > 0 ? time - M.key(n).time : 0;
leftMargin = effect("Left Margin")("Slider");
rightMargin = effect("Right Margin")("Slider");
duration = effect("Duration")("Slider");
for (i = 0; i <= width; i++){
temp = sampleImage([i,height/2],[0.5,height/2],true,time);
if (temp[3] > 0) break;
}
leftMargin = i - leftMargin;
for (i = width; i >= 0; i--){
temp = sampleImage([i,height/2],[0.5,height/2],true,time);
if (temp[3] > 0) break;
}
rightMargin += i;
x = linear(t,0,duration,leftMargin,rightMargin);
[x,value[1]]


Dan

[Jack Parks]

Thanks, this looks great, I will give this a try.
Thanks again.

[Jack Parks]

Hi Dan

I have been trying your expression and it seems to work but it’s making after effects go a little erratic, sometimes the expression stops working, the interface graphic glitches and there’s error messages. Is it just my setup? (Mac Snow Leopard CS4)

It’s a bit odd.
Any ideas?

Thanks

[Dan Ebberts]

What are the error messages?

The expression includes a hack to find the edges of the text layer and there may be scenarios where it doesn’t work well. Hard to say without seeing how you have things set up though.

Dan

[Jack Parks]

Thanks for your reply, after effects doesn’t seem to be happy with it, please could I bother you again?
To avoid the problem could the expression work by finding the center and then the left/right margin sliders determine the start and end? or a value is entered say 1000 pixels to travel across.
Thanks again for your help.

[Dan Ebberts]

This version will work with the margins based on where the anchor point is (so if your text is left justified, the right margin will need to be a lot bigger than the left):


M = marker;
n = 0;
if (M.numKeys > 0){
n = M.nearestKey(time).index;
if (M.key(n).time > time) n--;
}
t = n > 0 ? time - M.key(n).time : 0;
leftMargin = anchorPoint[0] - effect("Left Margin")("Slider");
rightMargin = anchorPoint[0] + effect("Right Margin")("Slider");
duration = effect("Duration")("Slider");

x = linear(t,0,duration,leftMargin,rightMargin);
[x,value[1]]


Dan

[Jack Parks]

Hello

I have been testing out the expression and simplified it a little.
Does it look ok? Would there be any obvious glitches?
How would you specify a frame amount in the duration? (1 at the moment = 1 second).

Thanks for your help with this.

M = marker;
n = 0;
if (M.numKeys > 0){
n = M.nearestKey(time).index;
if (M.key(n).time > time) n--;
}
t = n > 0 ? time - M.key(n).time : 0;
leftMargin = transform.position[0] - effect("Width")("Slider");
rightMargin = transform.position[0] + effect("Width")("Slider");
duration = effect("Duration")("Slider");

x = linear(t,0,duration,leftMargin,rightMargin);
[x,value[1]]

[Dan Ebberts]

If you want to enter the duration in frames, just change the appropriate line to this:

duration = effect(“Duration”)(“Slider”)*thisComp.frameDuration;

Dan

[Jack Parks]

That works.
Thanks for your patience.