Comparing the rotation of an object to it's previous rotation value (and controlling a movieclip from it)

[KeelyM]

Hi (it's me again),

I'm continuing work on a project which I posted previously about here - Rotating a movieclip with javascript - pressmove method  which helped me to get a movieclip to rotate. Now, however, I'm trying to control a movieclip based off of the rotation of rotating movieclip. So the name of the MC I'm rotating is 'yoke' and the name of the MC I'd like to control through it's timeline is called 'firstplane' This is what my code looks like so far -

this.stop();
var i = this.firstplane.currentFrame;
var shape = this.yoke;
var mouseMove = function () {
var rads = Math.atan2(stage.mouseY - shape.y, stage.mouseX - shape.x);
var angle = rads * (180 / Math.PI) - offset;
shape.rotation = angle;
console.log("angle:" + angle);
};
alert (shape.rotation);
this.yoke.addEventListener("pressmove", planespin.bind(this));
function planespin(){
if (shape.rotation>=0) {
this.firstplane.gotoAndStop(++i/2);
} else {
this.firstplane.gotoAndStop(--i/2);
}
} 
var offset = 0;
stage.addEventListener("stagemousedown", function(){
stage.addEventListener("stagemousemove",mouseMove);
// Determine initial offset, and take off shape rotation
var rads = Math.atan2(stage.mouseY - shape.y, stage.mouseX - shape.x);
offset = rads * (180 / Math.PI) - shape.rotation;
mouseMove();
});
stage.addEventListener("stagemouseup", function (){
stage.removeEventListener("stagemousemove",mouseMove);
alert (shape.rotation);
});

The chunk I'm trying to write myself (and failing at) is the 'planespin' function added to the yoke movieclip. I'd like it, so that as the yoke MC rotates clockwise (increasing the rotations number) my other movieclip, firstplane, will travel forwards in it's timeline - and vice verse - when the yoke MC rotates counterclockwise I'd like my firstplane MC to move backwards in it's timeline.

How I have it set up works a little - but after rotating the yoke around a little bit the firstplane MC stops going through it's timeline completely. I imagine I have to somehow detect the yoke's current rotation value and compare it to it's previous value to see if it is increasing or decreasing? I'm not entirely sure how to do that. (I promise I try to figure these things out on my own before taking to the forums).

Any help would be much appreciated!

[RandomlyFish]

You need a variable to store the previous rotation and then an if statement before that variable is updated.

// Variable for storing the previous rotation
var rotationPrevious = mc.rotation;
// Replace this with the function that you use
function Update () {
    // Optional variable to store the difference between the previous and current rotation
    var rotationDifference = mc.rotation - rotationPrevious;
    // Example if statements
    if (rotationDifference > 0) { // Greater than 0
          // Rotate clockwise
    } else if (rotationDifference < 0) { // Less than 0
          // Rotate counter clockwise
    }
    // Updated last
    rotationPrevious = mc.rotation;
}

[Colin Holgate · Accepted solution]

I would use another external variable to make it easy to talk to:

var thefirstplane = this.firstplane;

Don't use the pressmove/planespin approach, instead add some code to the mouseMove function. Don't just advance the current frame of firstplane, work out where it should be based on the rotation of shape.

It might be something like:

var f = Math.floor((shape.rotation + 360) % 360);

thefirstplane.gotoAndStop(f);

The + 360 % 360 will make the rotation value be 0-359, instead of perhaps -180 - +179. Inside the firstplane movieclip you would have 360 frames, that would be exactly what it needs to look like in order to match the rotation value of the yoke.

[KeelyM]

Thank you for the response. Adding that code as is seems to be working! My firstplane MC only has 31 frames though, could I simply change it to something like -

thefirstplane.gotoAndStop(f/2);

(or some number to divide by) to make it go slower/match better?

[Colin Holgate]

The rotation value will be 0-359, but you could scale that to any amount. You want 359 to be the same as 30 (your movieclip really goes from frame 0 to 30, even if it looks like 1 to 31), and you want 0 to be 0. So this should work:

var f = (shape.rotation + 360) % 360;

f = Math.floor(f / (360/thefirstplane.totalFrames));

thefirstplane.gotoAndStop(f);

[KeelyM]

I don't know if I inputted this code wrong, but when I tried using that it seemed to break my project. (I checked it a couple of times for typos).

The code you provided earlier works well enough to suite my needs though I believe. Thank you!!

[Colin Holgate]

Your movieclip isn't going to change the number of frames it has, so you could hard code the right value. This line:

var f = Math.floor((shape.rotation + 360) % 360);

would become:

var f = Math.floor(((shape.rotation + 360) % 360) * 0.086);

The 0.086 is 31/360.

[KeelyM]

That works wonderfully, thank you!