I learned a technique from the Ben Fry books for doing trails. Its very simple and effective but I have come across an issue that I don’t understand and wonder if someone can explain.
The technique is to, at the top of draw, draw a black filled rectangle with a low opacity (12 is what fry uses in examples).
Super simple code
/void draw() {
fill(0,0,0,12); // black low opacity fill, for trails.
rect(0,0,width,height); // screen size rect over all the last draw pass work/
note: I am using HSB so thats why my fill has 3 values, 4 val is opacity. I had the same issues I describe below when using RGB.
In my code I have replaced the alpha value with a variable. I would like to be able to set it to zero so that it will just draw a twisty mess on the screen and then pull it to higher numbers and get a nice variation on the trails. They could be dynamically changing.
This works but I have found a curious thing. When my Alpha goes below 12. The screen never totally blacks out the screen.
Why? Even at 2 for alpha I would think it would eventually go completely black???. My patterns are a bit random so its not that the path gets retraced before it can build up.
I am making my variable an int, to make sure its not a rounding, error, though I don’t know why that would matter either…
Does the adding up of values stop short of full black for some reason? I would think it would just “go over” and give the effect I want. I have attached some screens below.
This is for a project that will be projected, so while it IS a very subtle thing, I am concerned that on a projector, its going to really show.
Besides… it makes no sense.!! :). I am sure its doing exactly what I am telling it too, and I just need to talk to it better, but how might I do that?
Screens attached, hope it makes sense title tells what the variable value is at time of capture.
Thank you!!
First here is the effect when alpha = 12. The original standard application of Frys approach.
And here it is, alpha = 0. For graffiti like goodness.
But as I try to dial in the inbetween good ness and the REAaaaalllly longgggggg traaaaiiiiilzzzzz
I get left over cruft…
Alpha = 10:
alpha = 8:
alpha = 6
alpha = 4
alpha = 2
Toof