Help with getting proper rotation value

[Boombanguk]

Hi,

I'm using this code to give me a rotation of a line.

var dy:Number = bounds.yMax-bounds.yMin;

var dx:Number = bounds.xMax-bounds.xMin;

var angle:Number = Math.atan2(dy, dx);

rot = angle*180/Math.PI;

Problem is it gives me the same rotation result regardless of how the line is orientated, i.e if the line is sloping from top right to bottom left gives the same result if its sloping from top left to bottom right. It always seems to give me positive results. How do I change it so it knows which way the line is facing and gives me the correct result in rot?

[phreax]

Well, from what you are showing, all I can tell is that angle and rot works. My guess is you derive your bounds from a static bounding rectangle...not really sure why you use the bounding rectangle at all!?

[Boombanguk]

Thats exactly right, I'm drawing a line into that rect, but I need to get the rotation of the line for my line/ball code to work correctly. What I've found is that the code gives me the same result whether the line is sloping down to the left or down to the right. This is different though if I just draw a line into a MC, and then rotate the mc, that gives the correct result (i.e it gives a positive result for one orientation, but a neg result for the other way), but drawing the line dynamically and then trying to work out the rot of the line doesn't seem to work.

[Boombanguk]

to give a quick example, if I draw a line such as x1=100,y1=300 to x2=200,320....and then use the above code to get the rotation, that result is the same as if the line I draw is x1=100m,y1=300 to x2=200, y2=280........even though the orientation of the lines is different.

[rachil0]

Sounds like you need to conceptually decouple the bounding box of a line from its orientation.

Either create state variables for both...

class Line {
var x0, y0 : Number; // Start
var x1, y1 : Number; // End
var xmin, ymin : Number; // Upper left
var xmax, ymax : Number; // Lower right.
}

... or store only the orientation and compute bounding box information on demand:

class Line {
var x0, y0 : Number
var x1, y1 : Number
function xmin() : Number { return Math.min(x0,x1) }
function ymin() : Number { return Math.min(y0,y1) }
function xmax ...
function ymax ...
}

[Boombanguk]

um..thanks, but I'm allowing the user to draw the line, from x1,y1 to x2, y2...and they draw that line from left to right, or right to left.....what I don't understand is I'm sure it's possible to compute the correct angle from the start and end points, but im not sure how!

I'm storing the points with a Line class as you suggested.

[BlinkOk]

a) you are drawing a line inside an mc right?
b) if so then place the mc at the beginning of the line
c) then just use the x,y position of the ending of the line in your calculations

the problem is you're trying to get the orientation from the bounding box which doesn't take into consideration the direction of the slope

[rachil0]

Use the start/end oriented points inside your angle computation instead of the bounding box points.

var dy:Number = line.y1-line.y0;
var dx:Number = line.x1-line.x0;
var angle:Number = Math.atan2(dy, dx);

[Boombanguk]

Use the start/end oriented points inside your angle computation instead of the bounding box points.

var dy:Number = line.y1-line.y0;
var dx:Number = line.x1-line.x0;
var angle:Number = Math.atan2(dy, dx);

Thanks everyone for the help so far.

Thats exactly what I'm trying but because the start and end points can be set by the user, i'm finding that the above code works when the start point is set a certain way, so lets say when you draw a line from 142x258 to 365x75 it works, but when you draw basically the same line but from the other direction so, from 371x115 to 175x268 it doesn't. I'm thinking I'm going to have to check for 4 possibilities and then swap the x and y's around to make it work?

[slight]

You shouldn't need to check for the 4 possible orientations at all, just forget about the bounds object completely and get the angle from the start point to the end point, instead of getting the angle from the top left to the bottom right as you're doing.

If you're still having trouble maybe post the line drawing code you're using so that people can see how you've positioned the line MC and how you've named the start and end points.

[BlinkOk]

DON'T USE GETBOUNDS

when i calculate the angle of 142x258 to 365x75 i get -39
when i calculate the angle of 371x115 to 175x268 i get 142

what's the problem??

[Boombanguk]

DON'T USE GETBOUNDS

when i calculate the angle of 142x258 to 365x75 i get -39
when i calculate the angle of 371x115 to 175x268 i get 142

what's the problem??

haha, I'm not using getbounds anymore! btw, I've got it working now. Thanks!