I have canvas drawing tab and want lineWidth to be based on distance between two last mousemove coordinate updates. I will make translation of distance to width myself, I just need to know how to get distance between those points (I already have coordinates of those pointes).
You can do it with pythagoras theorem
If you have two points (x1, y1) and (x2, y2) then you can calculate the difference in x and difference in y, lets call them a and b.
var a = x1 - x2 var b = y1 - y2 var c = Math.sqrt( a*a + b*b ); // c is the distance
a shorter way to write the above would be
var d = Math.sqrt( (x1-x2)*(x1-x2) + (y1-y2)*(y1-y2) );
...thanks to Jonas for this slightly minimized way: (caution - this will change the values of your original variables)
var d = Math.sqrt( (x2-=x1)*x2 + (y2-=y1)*y2 );