canvas-sketch-util

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👋 Hey @mattdesl. I've been doing some sketches with triangles recently and I might have some building blocks that would allow for a new random.onTriangle() feature that will randomly choose n number of random points that fall on the side(s) of the triangle.

given: a triangle with vertices A, B, and C similar to below.

           A
           /\
          /  \
         /    \
        /      \
       /        \
      /          \
     /            \
    /              \
B  /________________\  C

which is made of an array of three coordinate pairs

const triangle = [[xa,ya],[xb,yb],[xc,yc]]

or maybe an object?

const triangle = {
  pointA: {
    xa: 1,
    ya: 0
  },
  pointB: {
    xb: 0,
    yb: 1
  },
  pointC: {
    xc: 1,
    yc: 1
  }
};

choose n number of random points that fall on the side(s) of the triangle.

command:

[x, y] = random.onTriangle(triangle as object or array, n as number, s as int for side number)

valid arguments: required
triangle object (as above)

optional
number of points to return
default = 1

optional
which "side" of the triangle
default = 0 side options:

• 0 = any segment
• 1 = segment between point A and B
• 2 = segment between point B and C
• 3 = segment between point A and C

future enhancement? 12 as valid argument (side 1 and side 2)

Does this sound like something you'd like to see in the library? If so, I'd love to help. (but I might need a little help helping 😕)

Hey! Thanks for the issue request. I do agree this would be useful, I would say something like:

random.insideTriangle(a, b, c, out = [], u = random.value(), v = random.value());

I already have an implementation I am using in my local code:

https://gist.github.com/mattdesl/4337f1ad890d3fc713e1b42dbb1603ff

I think adding insideTriangle should also probably have onTriangle (i.e. on the perimeter of the triangle) for parity with circle/sphere, but finding a random point around a triangle edge may be a little trickier (i.e. weighted random based on line segment lengths?).

Oops, I misread your comment! It seems like you want points on the edge not inside the triangle. But yes maybe both variations would be good to have!

Matt,

Yes, I was thinking that in and on triangle would be complementary code 😄

I looked at your current implementation. It's very concise! That would have taken me probably 50 lines at least 😐

Do I understand it correctly?

• Pass in 3 coordinate pairs a, b, c
• Generate 2 random numbers < 1.0 u, v
• Check that they aren't too big
• Create a 3rd random factor Q by subtracting u, v from 1.0
• Apply the random factors to each member of each coordinate pair
• Return a single [x,y] pair

That's a clever way of doing it!

I have some working code that calculates the slope-intercept y=mx+b formula for the side of the triangle, generates a random X coordinate, and then calculates which Y coordinate intersects at that X. I think I could translate that into a generic module if you want.