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HTML

              
                <div class="perspectiveCont">

  <div class="grid js-landscape">

  </div>

</div>

<p class="label--dragInstruct js-label--dragInstruct">Drag to rotate freely</p>

<p class="label--generating js-label--generating active">Generating...</p>

<div class="mouseZone js-mouseZone">

</div>

<p class="credit">
  <a href="https://www.twitter.com/sebastianlenton" target="_blank">
    @sebastianlenton
  </a>
</p>
              
            
!

CSS

              
                /********************************************************
Div rotatable with mouse when button held down
********************************************************/

//so using a CSS custom property on a linear gradient background on a transformed element seems to absolutely tank the frame rate! So I removed all background colour custom properties...
//doesn't seem to make a difference to rotation of the base grid though (the units are being rotated via injection of an inline style anyway).
$backgroundBlue:    25;       //blue component of background/div gradient/base
$backgroundRGB:     rgb(0,0,$backgroundBlue);
$backgroundRGBA-zero:     rgba(0,0,$backgroundBlue, 0);

* {
  box-sizing: border-box;
}

html, body {
  height: 100%;
  overflow: hidden;
}

body {
  margin: 0;
  background: linear-gradient(darken( blue, 10% ), darken( $backgroundRGB, 0% ), darken( $backgroundRGB, 3% ));
  overflow: hidden;
}

p {
  background: rgba(0,0,0,0.3);
  padding: 1rem;
  color: white;
  font-family: sans-serif;
  position: absolute;
  transform: translate(-50%, -50%);
  z-index: 2;
  line-height: 0;
  user-select: none;
  opacity: 1;
  transition: opacity 1.5s;

  &.fadeOut {
    opacity: 0;
  }
}

  .label--dragInstruct {
    top: 75%;
    left: 50%;
  }

  .label--generating {
    display: none;
    top: 50%;
    left: 50%;

    &.active {
      display: block;
    }
  }

.perspectiveCont {
  perspective: 2500px;
  top: 0;
  left: 0;
  height: 100%;
}

.grid {

  $maxWidth: 50rem;
  $maxHeight: 50rem;

  --rotX: 50deg;
  --rotY: 0deg;
  --rotZ: 45deg;


  /** background */

  background-color: $backgroundRGB;


  /** dimensions */

  width: 70vh;
  height: 70vh;
  max-width: $maxWidth;
  max-height: $maxHeight;


  /** position */

  position: absolute;
  z-index: 1;

  top: 50vh;
  left: 50%;
  transform: translate(-50%, -50%) rotateX(var(--rotX)) rotateY(var(--rotY)) rotateZ(var(--rotZ));
  transform-style: preserve-3d;
  transform-origin: center center;

}

  .landscape__unit {
    position: absolute;
    transform-origin: top;

    //using a custom property in a linear gradient on transformed elements seems to absolutely tank the frame rate!
    background-image: linear-gradient(
      180deg, $backgroundRGB, $backgroundRGBA-zero
    );
  }


.mouseZone {
  width: 100%;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  z-index: 3;
}


/* GUI */
.dg.ac {
  z-index: 5 !important;
}


/** credit **/

.credit {
  padding: 0;
  position: absolute;
  bottom: 1.5rem;
  right: 1rem;
  margin-bottom: 0;
  font-weight: bold;
  text-shadow: .1rem .1rem 0 darken(#84AFC8,25%);
  font-size: 1.2rem;
  z-index: 999;
  transform: none;
  
  a {
    color: white;
    text-decoration: none;
    display: block;
    transition: transform .25s;
    transform: scale(1);
    
    &:hover {
      transform: scale(1.2)  translate(-.75rem, -.15rem);
    }
  }
}
              
            
!

JS

              
                /********************************************************
Perlin Noise Landscape Generator
By Sebastian Lenton

Depends on https://github.com/josephg/noisejs (see settings)
22/08/19

This assumes all maps will be square
Think the library outputs between -.6 and .6 I think (if you see any weird results then this is incorrect!)

********************************************************/


/********************************************************
2d noise map output
********************************************************/

var PerlinNoiseGenerator = function() {

  this.seed = 49
  this.zoom = 3.8;              //zoom subtracted from map start (0) and map end (mapSizeMax), so can't be more than mapSizeMax / 2
  this.resolution = 24;

  this.lastSeed = this.seed;  //this is to do with DAT.gui- to prevent a reseed if the same value gets entered (the change event fires if you even click into the field...)
  this.lastZoom = this.zoom;
  this.lastResolution = this.resolution;

  this.mapSizeMax = 10;       //map runs from 0 to 10

  this.mapData = [];

  //"check has changed" functions- prob better/less repetitive ways to do these
  //again, this is to stop DAT.gui triggering an update if the value hasn't actually changed
  this.checkSeedHasChanged = function() {
    if(this.seed != this.lastSeed) {
      this.lastSeed = this.seed;
      return true;
    }
    return false;
  }

  this.checkZoomHasChanged = function() {
    if(this.zoom != this.lastZoom) {
      this.lastZoom = this.zoom;
      return true;
    }
    return false;
  }

  this.checkResolutionHasChanged = function() {
    if(this.resolution != this.lastResolution) {
      this.lastResolution = this.resolution;
      return true;
    }
    return false;
  }

  //return an array containing a noise map
  this.outputMap = function() {

    this.mapData = [];

    //clamp zoom if bigger than workable
    if(this.zoom >= this.mapSizeMax / 2) {
      this.zoom = this.mapSizeMax / 2;
    }

    noise.seed(this.seed);

    var mapSize = (this.mapSizeMax - this.zoom) - (0 + this.zoom);
    var units = mapSize / this.resolution;

    for(var q=0;q<this.resolution;q++) {
      var mapRow = [];

      for(var r=0;r<this.resolution;r++) {
        var currentValue = noise.perlin2(
          (q * units) - (mapSize / 2),
          (r * units) - (mapSize / 2),
        );
        mapRow.push(currentValue);
      }

      this.mapData.push(mapRow);
    }

  }
}



/********************************************************
Landscape Div Output
********************************************************/

var LandscapeDOM = function() {
  this.elm = document.querySelector('.js-landscape');
  this.rotX = 0;
  this.rotY = 0;
  this.rotZ = 0;
  this.map = [];

  this.minMaxRot = 60;        //the min or max rotation allowed on the X axis

  //stuff to do with autorotate
  this.autoRotate = true;
  this.timer;
  this.autoRotSpeed = 18/1000;    //degrees per second
  this.lastFrame = 0;

  this.elmLabelGenerating = document.querySelector('.js-label--generating');


  //copy in a perlin noise map array
  //hmm, does it actually need to make its own copy, given (in the current implementation) the map is just being read from, not changed?
  this.loadMap = function(arrMap) {

    this.map = [];

    for (var m = 0; m < arrMap.length; m++) {
      var mapRow = [];

      for (var n = 0; n < arrMap[0].length; n++) {
        var valToCopy = arrMap[m][n];
        mapRow.push(valToCopy);
      }

      this.map.push(mapRow);
    }

  }


  //clear map child divs
  this.deleteDivs = function() {

    while (this.elm.firstChild) {
      this.elm.removeChild(this.elm.firstChild);
    }

  }


  //create the divs within the map
  this.createDivs = function() {

    for (var m = 0; m < this.map.length; m++) {
      for (var n = 0; n < this.map[0].length; n++) {
        var newLandscapeUnit = document.createElement('div');
        newLandscapeUnit.classList.add('landscape__unit', 'js-landscape__unit');
        this.elm.appendChild(newLandscapeUnit);
      }
    }
  }


  //set styles for each div (dimensions, colour, position- not setting transform here)
  this.setStyles = function() {
    var divs = document.querySelectorAll('.js-landscape__unit');

    var widthMod = 1;               //tweak the width of each elem to cover up the gaps (or show them). Not bothering as I like the gaps, plus it affects the mid placement of the elemns atm (should fix but CBA right now)

    var counter = 0;

    var perlinMinMax = .55;          //roughly the min/max value of the library- I think!

    for (var m = 0; m < this.map.length; m++) {
      for (var n = 0; n < this.map[0].length; n++) {
        divs[counter].style.width = ( 100 / this.map.length ) * widthMod + '%';
        divs[counter].style.top = ((100 / this.map.length) * m) + ((100 / this.map.length / 2)) + '%';
        divs[counter].style.left = ((100 / this.map.length) * n) + '%';

        //set height- need to ensure it's not negative, or value from prev seed would be re-used (when seed gets changed)
        var height = (this.map[n][m] + perlinMinMax) * 50;

        if(height <= 0) {
          height = 0;
        }

        divs[counter].style.height = height + '%';

        //set background colour
        var bgColor = Math.round(((this.map[n][m] + perlinMinMax) * 255));

        if(bgColor > 255) {
          bgColor = 255;
        }

        divs[counter].style.backgroundColor = 'rgb(' + bgColor + ',0,70)';

        counter++;
      }
    }
  }


  //set initial rot values
  this.initRot = function() {
    var elmStyles = getComputedStyle(this.elm);
    this.rotX = parseInt(elmStyles.getPropertyValue('--rotX').trim());
    this.rotY = parseInt(elmStyles.getPropertyValue('--rotY').trim());
    this.rotZ = parseInt(elmStyles.getPropertyValue('--rotZ').trim());
  }


  //update rotation values of rect by incrememting
  this.updateInc = function(rotX, rotY, rotZ) {
    this.rotX += rotX;
    this.rotY += rotY;
    this.rotZ += rotZ;

    //clamp values (90 being the centre value)
    var degCentre = 90;

    //Upper:
    if(this.rotX > degCentre + this.minMaxRot ) {
      this.rotX = degCentre + this.minMaxRot;
    }

    //Lower:
    if(this.rotX < degCentre - this.minMaxRot) {
      this.rotX = degCentre - this.minMaxRot;
    }

  }


  //update the rotation CSS values themselves
  this.updateCSS = function() {
    this.elm.style.setProperty('--rotX', this.rotX + 'deg');
    this.elm.style.setProperty('--rotY', this.rotY + 'deg');
    this.elm.style.setProperty('--rotZ', this.rotZ + 'deg');
  }


  //counter rotate the child elements
  //this also has to be called when a new map gets generated
  this.updateChildren = function() {
    var children = document.querySelectorAll('.js-landscape__unit');
    var thisRotZ = this.rotZ;

    children.forEach(function(item) {
      item.style.transform = 'rotatex(90deg) rotatey(' + ( thisRotZ * -1) + 'deg)';
    });
  }

  //autorotate animation
  this.autorotate = function() {
    if(this.autoRotate) {

      var thisFrameTime = performance.now();

      this.updateInc(0,0,this.autoRotSpeed * (thisFrameTime - this.lastFrame));
      this.lastFrame = thisFrameTime;
      this.updateCSS();
      this.updateChildren();

      window.requestAnimationFrame(this.autorotate.bind(this));       //https://stackoverflow.com/questions/6065169/requestanimationframe-with-this-keyword
    }
  }

  this.autorotateOn = function() {
    this.autoRotate = true;
  }

  this.autorotateOff = function() {
    this.autoRotate = false;
  }

  //show or hide "regenerating" label
  //true to show, false to hide
  this.showLabelGenerating = function(showHide) {
    var classShowerHider = 'active';
    if(showHide) {
      this.elmLabelGenerating.classList.add(classShowerHider);
    } else {
      this.elmLabelGenerating.classList.remove(classShowerHider);
    }
  }

}



/********************************************************
Mouse Listener for dragging of LandscapeDiv
********************************************************/


var MouseListener = function(rotRect, instruction) {
  this.elm = document.querySelector('.js-mouseZone');
  this.mouseX;
  this.mouseY;
  this.mouseXLast;
  this.mouseYLast;
  this.deltaX;
  this.deltaY;

  this.rotRect = rotRect;         //the div to rotate

  this.rotDampen = 4;             //how much to dampen rotation by (X only I think?)

  this.instruction = instruction; //the p saying "drag to rotate"

  //set values to initial ones
  this.initValues = function() {
    this.mouseX = false;
    this.mouseY = false;
    this.mouseXLast = false;
    this.mouseYLast = false;
    this.deltaX = 0;
    this.deltaY = 0;
  }

  //update values
  this.update = function(newMouseX, newMouseY) {
    this.mouseXLast = this.mouseX;
    this.mouseYLast = this.mouseY;
    this.mouseX = newMouseX;
    this.mouseY = newMouseY;

    //if no values are false, there are at least two frames of movement (current and previous) so we can calculate a delta
    //otherwise set deltas to 0 (or else it will jerk around on drag start)
    if(this.mouseX && this.mouseXLast && this.mouseY && this.mouseYLast ) {
      this.deltaX = this.mouseX - this.mouseXLast;
      this.deltaY = this.mouseY - this.mouseYLast;
    } else {
      this.deltaX = 0;
      this.deltaY = 0;
    }
  }

  //do some normalisation on the deltas to reverse the drag direction, make it a bit slower etc
  this.normaliseDeltas = function() {
      this.deltaX = ( this.deltaX * -1 );
      this.deltaY = ( this.deltaY * -1 );
      this.deltaX = this.deltaX / this.rotDampen;
      this.deltaY = this.deltaY / this.rotDampen;
  }

  //add the event listeners to enable control
  this.addMouseListener = function() {

    //copy over the ref to this and this's element (as I'm a dumbass who can't program properly)
    var that = this;
    var thatElm = this.rotRect;

    //mouse control
    if(this.elm !== null) {
      this.elm.addEventListener('mousemove', function(e) {
        if(e.buttons === 1) {
          that.update(e.clientX, e.clientY);
          that.normaliseDeltas();
          thatElm.updateInc(that.deltaY, 0, that.deltaX);
          thatElm.updateCSS();
          thatElm.updateChildren();
        }
      });

      this.elm.addEventListener('mousedown', function(e) {
        e.preventDefault();  //prevent selection etc
        that.initValues();
        thatElm.autorotateOff();
        that.instruction.classList.add('fadeOut');
      });

      //touch control
      this.elm.addEventListener('touchmove', function(e) {
        e.preventDefault();   //prevent iOS scrolling
        that.update(e.changedTouches[0].clientX, e.changedTouches[0].clientY);
        that.normaliseDeltas();
        thatElm.updateInc(that.deltaY, 0, that.deltaX);
        thatElm.updateCSS();
        thatElm.updateChildren();
      });

      this.elm.addEventListener('touchstart', function(e) {
        e.preventDefault();   //prevent selection etc
        thatElm.autoRotate = false;
        that.initValues();
        that.instruction.classList.add('fadeOut');
      });

    }

  }

  //switch mouse zone on and off
  //this is to disable mouse rotation when starting a click in DAT.gui and moving off (otherwise it starts rotating the element, and it all looks a bit crap)
  this.mouseZoneOff = function() {
    this.elm.style.display = 'none';
  }

  this.mouseZoneOn = function() {
    this.elm.style.display = 'block';
  }
}



/********************************************************
Main
********************************************************/

var noiseGenerator = new PerlinNoiseGenerator();

noiseGenerator.outputMap();

var landscapeDOM = new LandscapeDOM();
landscapeDOM.initRot();
landscapeDOM.loadMap(noiseGenerator.mapData);
landscapeDOM.createDivs();
landscapeDOM.setStyles();
landscapeDOM.showLabelGenerating(false);
landscapeDOM.updateChildren();
landscapeDOM.autorotate();

var mouseListener = new MouseListener(landscapeDOM, document.querySelector('.js-label--dragInstruct'));
mouseListener.addMouseListener();



/********************************************************
Controls for GUI in top right (uses DAT.gui)
********************************************************/

var gui = new dat.GUI();
var seedChange = gui.add(noiseGenerator, 'seed', 0, 65535).step(1);
var zoomChange = gui.add(noiseGenerator, 'zoom', .1, 5);
var resolutionChange = gui.add(noiseGenerator, 'resolution', 1, 70).step(1);

//hmm, seems like we have to duplicate code for these- is there a better way?
seedChange.onChange(function(value) {
  landscapeDOM.showLabelGenerating(true);
  mouseListener.mouseZoneOff();
});

zoomChange.onChange(function(value) {
  landscapeDOM.showLabelGenerating(true);
  mouseListener.mouseZoneOff();
});

resolutionChange.onChange(function(value) {
  landscapeDOM.showLabelGenerating(true);
  mouseListener.mouseZoneOff();
});

seedChange.onFinishChange(function(value) {
  if( noiseGenerator.checkSeedHasChanged() ) {
    noiseGenerator.outputMap();
    landscapeDOM.loadMap(noiseGenerator.mapData);
    landscapeDOM.setStyles();
    landscapeDOM.updateChildren();
    landscapeDOM.autorotateOn();
    landscapeDOM.autorotate();
  }

  mouseListener.mouseZoneOn();
  landscapeDOM.showLabelGenerating(false);
});

zoomChange.onFinishChange(function(value) {
  if( noiseGenerator.checkZoomHasChanged() ) {
    noiseGenerator.outputMap();
    landscapeDOM.loadMap(noiseGenerator.mapData);
    landscapeDOM.setStyles();
    landscapeDOM.updateChildren();
  }

  mouseListener.mouseZoneOn();
  landscapeDOM.showLabelGenerating(false);
});

resolutionChange.onFinishChange(function(value) {
  if( noiseGenerator.checkResolutionHasChanged() ) {
    noiseGenerator.outputMap();
    landscapeDOM.loadMap(noiseGenerator.mapData);
    landscapeDOM.deleteDivs();
    landscapeDOM.createDivs();
    landscapeDOM.setStyles();
    landscapeDOM.updateChildren();
  }

  mouseListener.mouseZoneOn();
  landscapeDOM.showLabelGenerating(false);
});
              
            
!
999px

Console