I have a line with a start point (x1, y1) and an end point (x2, y2), and I want to draw a number of shapes evenly spaced along that line.  The number of shapes will vary, however.  For example, here's a very rough approximation of what I want.  The line with three dots drawn:

Code:

  .   .   .
____________ 

But that same line could be drawn with 7 dots:

Code:

. . . . . . .
____________ 

Of course, if the line were horizontal at all times, this would be easy (a matter of dividing the line length by the # of shapes), but its end points will be moving, so the line's length and angle will be changing.  So I need a way to calculate, with each frame, where to place the shapes, given the line's start and end points, and the # of shapes.

I think this involves trigonometry, but maybe there's a simpler way.  How can I loop through each shape and get the x/y value for where to plot it, each one further out along the line?

Thanks in advance for your ideas!

Nice!  Thanks, PhiLho.

I just figured out another way, thanks to some guidance from this Java example:

http://www.java-forums.org/java-2d/10984-calculate-x-y-given-starting-angle-distance.html

The key is to use cosine to calculate the x point, and sine to calculate the y point.

Code:

//we know start and end points of line from.x, from.y and to.x, to.y
//get the angle of the line
float angle = atan2((to.y - from.y), (to.x - from.x));

//get the dist() of the line
float lineLength = dist(from.x, from.y, to.x, to.y);

//segmentLength = divide that amount by the # of shapes to be drawn
float segmentLength = lineLength / count;

//loop through, once for each shape:
for(int i = 1; i < count+1; i++) {                
      float distFromStart = segmentLength * i;
      float px = from.x + distFromStart * cos(angle);
      float py = from.y + distFromStart * sin(angle);
      point(px, py);
    }
 

It looks like you could accomplish the same thing without trig using lerp().  Thanks!