Positioning images

Our images are evenly dispersed within the #rotator-node, but we want start them off below the screen. To do this, we will create a helper function in our galleryData.js file to add random initial positions for the vertical animations.

Understanding the coordinates

Since we rotated our main #rotator-node, the coordinates used for positioning the #gallery-items are also flipped by 90 degrees. This means that modifying the Z coordinates (not the Y coordinates) will move our image nodes up and down and the Y coordinates now control the depth.


If understanding this is a bit confusing, think of it as if we're now looking at the red box above ( #rotator-node ) from a bird eye's view and we need to position the children (#gallery-items) from this angle.

Animating the nodes up

We want to start our images off the screen and slowly move them up. To do this, we will start at a positive Z value off the screen (window height + random starting point) and then slowly decrement that Z value to move them up.

Currently X and Y are randomly dispersed using: Math.random()*500. However, we can't use this same function for Z since we want to slowly increment the value without the Math.random() being called on every frame. Instead, we will initialize random Z values in our state using a helper function.

Helper function to the rescue

Open up galleryData.js and add the following lines below the imageData array:

  //store window size before the scene is loaded
  var contextSize = window.innerHeight

  function randomCoordinates(imageData){
      var result = [];
      for(var i=0; i < imageData.length; i++){
      //start outside of the viewing window and random disperse below
      return result;

We will use this function to create an array of random Z positions outside of the frame. Next, update the state value for positionZ so it calls on this function passing in our imageData. This will give us an array of random Z positions for each item in our image data.

states: {
      rotationValue: 0,
      srcs: imageData,
      contextSize: contextSize, //update this value as well

We also update our context size to the contextSize reference so the items will fill the stage.

Great! We have everything set up to animate our images. In the next section, we will add events to do just that.

Up next: Creating animations »