Constraining aspect ratios of images

by Admiral Potato

HTML

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/vue.js"></script>
<div id="app">
  <form id="size">
    <div>
      <label for="maxHeight">maxHeight</label>
      <input id="maxHeight" v-model="maxHeight" />
    </div>
    <div>
      <label for="x">x</label>
      <input id="x" v-model="imageSize.x" />
    </div>
    <div>
      <label for="y">y</label>
      <input id="y" v-model="imageSize.y" />
    </div>
  </form>
  <div
       class="aspectre"
       :style="instanceStyles"
  >
    <div 
         class="ratio"
         :style="ratio"
         ></div>
    <canvas
            ref="canvas"
            :width="imageSize.x"
            :height="imageSize.y"
            ></canvas>
    <span
          class="aspect-label"
          >{{imageSize.x + ' x ' + imageSize.y}}</span>
  </div>
</div>

CSS

* {
  font-family: monospace;
  color: #ddd;
}

body {
  background-color: #262626;
}

form#size {
  position: fixed;
  top: 10px;
  left: 10px;
  z-index: 10;
}

form#size label,
form#size input {
  border: 1px solid #666;
  background-color: #262626;
  padding: 2px;
}
form#size label {
  display: inline-block;
  width: 96px;
  text-align: right;
}

.aspectre {
  margin: auto;
  position: relative;
  background-color: #000;
  border: 1px solid #f00;
}

.aspectre .ratio {
  position: relative;
}

.aspectre canvas,
.aspectre .aspect-label {
  position: absolute;
  display: block;
  margin: auto;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: #333;
}

.aspectre canvas {
  min-width: 100%;
  max-width: 100%;
  height: auto;
}

.aspectre .aspect-label {
  position: absolute;
  width: 128px;
  height: 32px;
}

JavaScript

var app = new Vue({
	el: '#app',
	data: {
	  maxHeight: 400,
  	imageSize: {
    	x: 15,
      y: 20
    }
  },
  computed: {
  	aspect: function () {
    	return this.imageSize.y / this.imageSize.x
    },
  	ratio: function () {
    	return {
      	paddingBottom: (this.aspect * 100) + '%'
      }
    },
    instanceStyles: function () {
    	return {
      	maxHeight: this.maxHeight + 'px',
        maxWidth: (this.maxHeight / this.aspect) + 'px'
      }
    },
  },
  mounted: function () {
	  this.generateImage()
  },
  updated: function () {
	  this.generateImage()
  },
  methods: {
  	generateImage: function () {
      var canvas = this.$refs.canvas
      var ctx = canvas.getContext('2d')
      var grd = ctx.createLinearGradient(
      	0,
        0,
        this.imageSize.x,
        this.imageSize.y,
      );
      
      // Add colors
      grd.addColorStop(0.000, 'rgba(0, 255, 255, 1)');
      grd.addColorStop(1.000, 'rgba(127, 255, 0, 1)');
      
      // Fill with gradient
      ctx.fillStyle = grd;
      ctx.fillRect(0, 0, this.imageSize.x, this.imageSize.y);
    }
  }
})