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HTML
!

CSS 

              
                body {
  margin: 0;
  padding: 0;
}

canvas {
  display: block;
  float: left;
}
!

JS 

              
                var previewCanvas = document.createElement('canvas');
var width = previewCanvas.width = 100;
var height = previewCanvas.height = 100;
var pctx = previewCanvas.getContext('2d');

var PI = Math.PI;
var TAU = PI*2;


renderTallGrass();
renderTallGrass();
renderBushes();
renderForest();
renderBushes();
renderMountainRange();
renderForest();
renderMountainRange();
renderRiver();


var imgData = pctx.getImageData( 0, 0, width, height ).data;
var scale = Math.floor( Math.max( window.innerWidth, window.innerHeight ) / 20 );

document.body.style.width = width * scale + 'px';

var colorRenderers = {
  // empty
  // '#000000': function( ctx ) {
  //   ctx.fillStyle = '#FD9';
  //   circle( ctx, 0.5, 0.5, 0.25 );
  // },
  '#000000': function( ctx ) {
    ctx.fillStyle = '#FD9';
    // circle( ctx, 0.5, 0.5, 0.475 );
    emptyDot( ctx, 0.25, 0.25 );
    emptyDot( ctx, 0.25, 0.75 );
    emptyDot( ctx, 0.75, 0.25 );
    emptyDot( ctx, 0.75, 0.75 );
  },
  // water
  '#1199FF': function( ctx ) {
    ctx.fillStyle = '#19F';
    circle( ctx, 0.5, 0.5, 0.475 );
  },
  // mountain
  '#CC5500': function( ctx ) {
    ctx.fillStyle = '#C50';
    ctx.beginPath();
    ctx.moveTo( 0, 1 );
    ctx.lineTo( 0.5, 0 );
    ctx.lineTo( 1, 1 );
    ctx.lineTo( 0, 1 );
    ctx.fill();
    ctx.closePath();
  },
  // forest
  '#88CC88': function( ctx ) {
    ctx.fillStyle = '#2C5';
    ctx.beginPath();
    ctx.moveTo( 0, 1 );
    ctx.lineTo( 0.5, 0.5 );
    ctx.lineTo( 1, 1 );
    ctx.lineTo( 0, 1 );
    ctx.moveTo( 0, 0.5 );
    ctx.lineTo( 0.5, 0 );
    ctx.lineTo( 1, 0.5 );
    ctx.lineTo( 0, 0.5 );
    ctx.fill();
    ctx.closePath();
  },

  // tall grass
  '#CCEEBB': function( ctx ) {
    ctx.fillStyle = '#CDB';
    ctx.beginPath();
    ctx.moveTo( 0, 0.75 );
    ctx.lineTo( 0.25, 0 );
    ctx.lineTo( 0.25, 0.75 );
    ctx.lineTo( 0, 0.75 );
    ctx.moveTo( 0.5, 1 );
    ctx.lineTo( 0.5, 0.25 );
    ctx.lineTo( 0.75, 1 );
    ctx.lineTo( 0.5, 1 );
    ctx.fill();
    ctx.closePath();
  },
  // bushes/boulders
  '#CC2255': function( ctx ) {
    ctx.fillStyle = '#C90';
    ctx.save();
    ctx.beginPath();
    ctx.arc( 0.5, 0.5, 0.45, TAU * 3/8, TAU*9/8 );
    ctx.fill();
    ctx.closePath();
    ctx.restore();
  }

};

function circle( ctx, x, y, radius ) {
  ctx.beginPath();
  ctx.arc( x, y, radius, 0, TAU );
  ctx.fill();
  ctx.closePath();
}

function emptyDot( ctx, x, y ) {
  if ( Math.random() > 0.0 ) {
    circle( ctx, x, y, 0.125 );
  }
}


for ( var tileY = 0; tileY < height; tileY += 10 ) {
  for ( var tileX = 0; tileX < width; tileX += 10 ) {
    renderOverworldTile( tileX, tileY );
  }
}

function renderOverworldTile( tileX, tileY ) {
  var canvas = document.createElement('canvas');
  var ctx = canvas.getContext('2d');
  var tw = canvas.width = scale * 10;
  var th = canvas.height = scale * 10;

  ctx.fillStyle = '#FED';
  ctx.fillRect( 0, 0, tw, th );
  ctx.scale( scale, scale );

  // console.log('render tile', tileX, tileY);

  for ( var y=0; y<10; y++ ) {
    for ( var x=0; x<10; x++ ) {
      var x2 = tileX + x;
      var y2 = tileY + y;
      // console.log( x2, y2 );
      var i = ( y2*width + x2 ) * 4;
      var color = [ imgData[i], imgData[i+1], imgData[i+2] ];
      var hex = rgb2hex( color );
      var renderer = colorRenderers[ hex ];
      if ( renderer ) {
        ctx.save();
        ctx.translate( x, y );
        renderer( ctx );
        ctx.restore();
      }
    }
  }

  document.body.appendChild( canvas );
}


document.body.insertBefore( previewCanvas, container );

function renderForest() {
  curlyWalk({
    color: '#8C8',
    length: 200,
    angleVelocitySize: 1.5,
    walkSize: 2,
    minBrushSize: 2,
    maxBrushSize: 10,
    startBrushSize: 4,
    brushStepSize: 2,
  });
}

function renderTallGrass() {
  curlyWalk({
    color: '#CEB',
    maxBrushSize: 7,
    startBrushSize: 3,
    brushStepSize: 2,
    // angleVelocitySize: 1.5,
    // walkSize: 2,
    // minBrushSize: 1,
    // maxBrushSize: 3,
  });
}

function renderBushes() {
  curlyWalk({
    color: '#C25',
    walkSize: 2,
    minBrushSize: 1,
    maxBrushSize: 3,
    startBrushSize: 1,
    brushStepSize: 1,
  });
}

function renderMountainRange() {

  curlyWalk({
    color: '#C50',
    angleVelocitySize: 2,
    walkSize: 3,
    minBrushSize: 4,
    maxBrushSize: 12,
    startBrushSize: 4,
    brushStepSize: 2,
  });


}

function renderRiver() {

  var startTheta = Math.random() * TAU;

  var walkerX = Math.cos( startTheta ) * 80;
  var walkerY = Math.sin( startTheta ) * 80;

  var flowAngle = startTheta + TAU/2;
  var angle = flowAngle;
  var rSize = 3;

  pctx.fillStyle = '#19F';

  for ( var i=0; i < 400; i++ ) {
    // angleVelocity = (Math.random() - 0.5) * (Math.random() - 0.5) * 3;
    if ( Math.random() > 0.7 ) {
      angle = flowAngle + ( Math.random()*2 - 1 ) * TAU/4;
    }
    walkerX += Math.cos( angle );
    walkerY += Math.sin( angle );

    var rRand = Math.random();
    if ( rRand > 0.82 ) {
      rSize += 1;
    } else if ( rRand > 0.62 ) {
      rSize -= 1;
    }
    rSize = Math.max( 2, Math.min( rSize, 8 ) );
    var size = rSize;

    var x = Math.round( width/2 + walkerX - size/2 );
    var y = Math.round( height/2 + walkerY - size/2 );

    pctx.fillRect( x, y, size, size );
  }


}


function curlyWalk( props ) {

  props = extend({
    startSize: 30,
    length: 300,
    color: '#888',
    angleVelocitySize: 1.5,
    walkSize: 1,
    minBrushSize: 1,
    maxBrushSize: 5,
    brushStepSize: 1,
    startBrushSize: 1,
  }, props );

  var wx = ( Math.random()*2 - 1 ) * props.startSize;
  var wy = ( Math.random()*2 - 1 ) * props.startSize;

  var angleVelocity = 0;
  var angle = 0;

  pctx.fillStyle = props.color;

  for ( var i=0; i < props.length; i++ ) {

    angleVelocity = ( Math.random()*2 - 1 ) * props.angleVelocitySize;
    angle += angleVelocity;

    wx += Math.cos( angle ) * props.walkSize;
    wy += Math.sin( angle ) * props.walkSize;

    var rSize = props.startBrushSize;
    var rRand = Math.random();
    if ( rRand > 0.82 ) {
      rSize += props.brushStepSize;
    } else if ( rRand > 0.62 ) {
      rSize -= props.brushStepSize;
    }
    rSize = Math.max( props.minBrushSize, Math.min( rSize, props.maxBrushSize ) );

    var x = Math.round( width/2 + wx - rSize/2 );
    var y = Math.round( height/2 + wy - rSize/2 );

    pctx.fillRect( x, y, rSize, rSize );

  }

}


function extend( a, b ) {
  for ( var prop in b ) {
    a[ prop ] = b[ prop ];
  }
  return a;
}


function rgb2hex( rgb ) {
  var hex = rgb.map( function( value ) {
    var hexNum = value.toString(16).toUpperCase();
    // left pad 0
    hexNum = hexNum.length < 2 ? '0' + hexNum : hexNum;
    return hexNum;
  });

  return '#' + hex.join('');
}
!
999px

Console