Modify canvas on the fly

[talamask]

I kind of cannot understand why given example does not ends up with red texture.

function modify(width, pixelSize) {
   let existingImage = this.textures.get("dude").getSourceImage();
   let context = existingImage.getContext("2d");

   for (var y = 0; y < width; y++) {
      for (var x = 0; x < width; x++) {
         context.fillStyle = "#f00";
         context.fillRect(x * pixelSize, y * pixelSize, pixelSize, pixelSize);
      }
   }
}

I have checked that existingImage and context variables are populated ok, but calling this function does not produce desired result.

Please assist.