Hi all,

I would like to know how can i calculate a point on a line.

For example, I have a "line (0,0,10,10);" what i must to do so i can know any point of that line? Logically i know that the points are 1,1 | 2,2 | 3,3 and so on... But there is any expression that let me do this automatically?


If there is another answered question about this on the forum i'm sorry, but i didn't find it...

Hope you can help me guys! Thnx

you can easily use lerp() to do that...

http://processing.org/reference/lerp_.html

PhiLho  wrote on Dec 11^th, 2009, 8:10am:


can you show me an example with line coordenates
And the meaning of the expression

Example: line(5, 10, 30, 50)
We have:
10 = a * 5 + b
50 = a * 30 + b
Subtraction: 40 = a * 25 so a = 40/25 = 1.6
So b = 10 - 5 * 1.6 = 2

Implementation:
Code:

int x1 = 5, y1 = 10;
int x2 = 30, y2 = 50;
float a, b;
float x, y, px, py;
float step = 0.1;

void setup()
{
  size(100, 100);
  a = y2 - y1;
  if (x1 == x2)
  {
    a = 0;
  }
  else
  {
     a /= x2 - x1;
  }
  b = y1 - x1 * a;
  px = x1; py = y1;
}

void draw()
{
  x = px + step;
  if (x > x2) noLoop();
  y = fun(x);
  line(px, py, x, y);
  px = x; py = y;
}

float fun(float x)
{
  return a * x + b;
}
 

Just to make 5 posts... (sorry guys)

PhiLho  wrote on Dec 11^th, 2009, 2:25pm:


Ok i tryed to implement it without success, i will post a picture of what i'm doing...



So i draw random lines, and when i call a function it will draw objects along the line in a random point of that line.
Imagine drawing ellipses where the x, y position are the image p1, p2.

Can someone help me coding the function with those expression

Cheers

I'm not sure if this is what you need but I needed something similar the other day. After several hours of searching I found this and it was exactly what I was looking for.

Quote:


If Ratio is at 0, it will give you x1 any y1. If Ratio is 1 it will give you x2 and y2. Anything between 0 and 1 will give you an x and y co-ordinate on that line that's appropriate to the ratio along it. You might be able to adapt this if it isn't what you wanted.

PhiLho  wrote on Dec 12^th, 2009, 2:11am:


O didn't understand how to get the x and y of the new point, i suck at math... :S Sorry...