RasterSource

• inputs align with the sources order and hold Uint8ClampedArray RGBA pixels of equal length.
• The operation must return arrays of the same length; multiple arrays become output bands.
• beforeoperations and afteroperations events expose inputs, resolutions and returned data.

var red = new ol.source.XYZ({ url: '/tiles/red/{z}/{x}/{y}.png' });
var nir = new ol.source.XYZ({ url: '/tiles/nir/{z}/{x}/{y}.png' });

var ndvi = new ol.source.Raster({
  sources: [red, nir],
  operationType: 'pixel',
  threads: 2,
  operation: function (inputs, data) {
    var r = inputs[0];
    var n = inputs[1];
    var out = new Uint8ClampedArray(r.length);

    for (var i = 0; i < r.length; i += 4) {
      var redValue = r[i];
      var nirValue = n[i];
      var index = (nirValue - redValue) / (nirValue + redValue + 1e-6);
      var v = Math.round(((index + 1) / 2) * 255);
      out[i] = v;
      out[i + 1] = 255 - v;
      out[i + 2] = 90;
      out[i + 3] = r[i + 3];
    }

    data.max = 1;
    return [out];
  }
});

var layer = new ol.layer.Image({ source: ndvi });

• Unapproved cross-origin source images taint the canvas and turn the whole result blank; set crossOrigin anonymous.
• The operation is serialized into workers, so closure variables fail; put helpers in lib and constants in data.