Monday, June 21, 2010

'champix' plasma

Whist at Cutting Edge, I worked on developing some Plasma effects.
The plasma was to 'arc' between the packet of cigarettes and the inner bell jar
walls. The arcs were also to travel around a little and change positions after a certain amount of time.

This could be achieved several ways - but time was short so I belted out this solution.

The plasma needed to have two contact points, so i used scatter to generate points over each object - the bell jar and the box inside it - to use as a base for the contact points. I then used a sort to randomise the point numbers so that  when the seed is changed - the point numbers change. When the arc of plasma uses just one of these points as a template or contact  point, this can be animated randomly simply by changing the seed.

The important part - was to change the seed every few seconds only - not every frame. I used the expression:
int($F/25) in the seed parameter of the sort SOPS. As the animation plays - every 25 frames, the expression grows by a value of one.

I used a line copied to one point only of the scatter SOP as the foundation of the arc of plasma.  At this stage in the network - the line only has 2 points - a start point and an end point. The other point is then 'rayed' onto the box that sits inside of the bell jar.

So now I have straight lines that seem to randomly change both at the start and end point positions - yet are always touching the surface of both the box and the inside of the belljar. So now i need some noise, but in order for the noise to get results - I also need more points. After resampling - the noise is achieved in a VOPSOP with Turbulence added to the original point position.

The noise creates pseudo random movement - and moves some points away from each other more than others - creating different lengths of line segments with in the line. I decided to resample again after this just to get a nice consistency of length in the line segments.

One interesting aspect I have in this SOP network that I didn't use in the original TVC was the third sort SOP that causes the point numbers to shift and wrap around down the line. this allowed me create an effect or energy actually traveling along the line from the belljar toward the box inside it. To achieve this I had to give random colours based on the points and then create groups from this. This forced the newly assigned point colours to follow the motion of the changing point numbers and thus travel along the length of the line.

To accentuate this I swept a grid along the lines to create tubes and then 'peaked' out only certain points from my group that cause a little bulge to travel down the line. In this network I have disabled the sweep, as I realised this could probably be done with mantra and the width attribute.

So now I had one plasma arc buzzing and popping around - so a copy SOP allowed me to duplicate this around and stamping allowed me to randomise the noise seed so each arc was unique.
Stamping was also used to to offset the animation timing and point colour assignment.

Finally - a trail SOP gave me my velocity for motion blur and a point sop with a min expression allowed me to clamp my velocity and thus motion blur to a threshold The attribute create SOP gave me width so my lines could be rendered as curves.

The final result which also used some real footage of electrical arcs.


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