Improve avatar resampling of non-animated canvas

app/assets/javascripts/components/components/avatar.jsx

@@ -1,5 +1,91 @@
 import PureRenderMixin from 'react-addons-pure-render-mixin';
 
+// From: http://stackoverflow.com/a/18320662
+const resample = (canvas, width, height, resize_canvas) => {
+  let width_source  = canvas.width;
+  let height_source = canvas.height;
+  width  = Math.round(width);
+  height = Math.round(height);
+
+  let ratio_w      = width_source / width;
+  let ratio_h      = height_source / height;
+  let ratio_w_half = Math.ceil(ratio_w / 2);
+  let ratio_h_half = Math.ceil(ratio_h / 2);
+
+  let ctx   = canvas.getContext("2d");
+  let img   = ctx.getImageData(0, 0, width_source, height_source);
+  let img2  = ctx.createImageData(width, height);
+  let data  = img.data;
+  let data2 = img2.data;
+
+  for (let j = 0; j < height; j++) {
+    for (let i = 0; i < width; i++) {
+      let x2            = (i + j * width) * 4;
+      let weight        = 0;
+      let weights       = 0;
+      let weights_alpha = 0;
+      let gx_r          = 0;
+      let gx_g          = 0;
+      let gx_b          = 0;
+      let gx_a          = 0;
+      let center_y      = (j + 0.5) * ratio_h;
+      let yy_start      = Math.floor(j * ratio_h);
+      let yy_stop       = Math.ceil((j + 1) * ratio_h);
+
+      for (let yy = yy_start; yy < yy_stop; yy++) {
+        let dy       = Math.abs(center_y - (yy + 0.5)) / ratio_h_half;
+        let center_x = (i + 0.5) * ratio_w;
+        let w0       = dy * dy; //pre-calc part of w
+        let xx_start = Math.floor(i * ratio_w);
+        let xx_stop  = Math.ceil((i + 1) * ratio_w);
+
+        for (let xx = xx_start; xx < xx_stop; xx++) {
+          let dx = Math.abs(center_x - (xx + 0.5)) / ratio_w_half;
+          let w  = Math.sqrt(w0 + dx * dx);
+
+          if (w >= 1) {
+            // pixel too far
+            continue;
+          }
+
+          // hermite filter
+          weight    = 2 * w * w * w - 3 * w * w + 1;
+          let pos_x = 4 * (xx + yy * width_source);
+
+          // alpha
+          gx_a          += weight * data[pos_x + 3];
+          weights_alpha += weight;
+
+          // colors
+          if (data[pos_x + 3] < 255)
+            weight = weight * data[pos_x + 3] / 250;
+
+          gx_r    += weight * data[pos_x];
+          gx_g    += weight * data[pos_x + 1];
+          gx_b    += weight * data[pos_x + 2];
+          weights += weight;
+        }
+      }
+
+      data2[x2]     = gx_r / weights;
+      data2[x2 + 1] = gx_g / weights;
+      data2[x2 + 2] = gx_b / weights;
+      data2[x2 + 3] = gx_a / weights_alpha;
+    }
+  }
+
+  // clear and resize canvas
+  if (resize_canvas === true) {
+    canvas.width  = width;
+    canvas.height = height;
+  } else {
+    ctx.clearRect(0, 0, width_source, height_source);
+  }
+
+  // draw
+  ctx.putImageData(img2, 0, 0);
+};
+
 const Avatar = React.createClass({
 
   propTypes: {
@@ -25,7 +111,11 @@ const Avatar = React.createClass({
   },
 
   handleLoad () {
-    this.canvas.getContext('2d').drawImage(this.image, 0, 0, this.props.size * window.devicePixelRatio, this.props.size * window.devicePixelRatio);
+    this.canvas.width  = this.image.naturalWidth;
+    this.canvas.height = this.image.naturalHeight;
+    this.canvas.getContext('2d').drawImage(this.image, 0, 0);
+
+    resample(this.canvas, this.props.size * window.devicePixelRatio, this.props.size * window.devicePixelRatio, true);
   },
 
   setImageRef (c) {
@@ -42,7 +132,7 @@ const Avatar = React.createClass({
     return (
       <div onMouseEnter={this.handleMouseEnter} onMouseLeave={this.handleMouseLeave} style={{ ...this.props.style, width: `${this.props.size}px`, height: `${this.props.size}px`, position: 'relative' }}>
         <img ref={this.setImageRef} onLoad={this.handleLoad} src={this.props.src} width={this.props.size} height={this.props.size} alt='' style={{ position: 'absolute', top: '0', left: '0', visibility: hovering ? 'visible' : 'hidden', borderRadius: '4px' }} />
-        <canvas ref={this.setCanvasRef} width={this.props.size * window.devicePixelRatio} height={this.props.size * window.devicePixelRatio} style={{ borderRadius: '4px', width: this.props.size, height: this.props.size }} />
+        <canvas ref={this.setCanvasRef} style={{ borderRadius: '4px', width: this.props.size, height: this.props.size, visibility: hovering ? 'hidden' : 'visible' }} />
       </div>
     );
   }