openlayers/src/ol/renderer/canvas/intermediatecanvas.js

Build tools and sources for developing OpenLayers based mapping applications

goog.provide('ol.renderer.canvas.IntermediateCanvas');

goog.require('ol');
goog.require('ol.coordinate');
goog.require('ol.dom');
goog.require('ol.renderer.canvas.Layer');
goog.require('ol.transform');


/**
 * @constructor
 * @extends {ol.renderer.canvas.Layer}
 * @param {ol.layer.Layer} layer Layer.
 */
ol.renderer.canvas.IntermediateCanvas = function(layer) {

  ol.renderer.canvas.Layer.call(this, layer);

  /**
   * @protected
   * @type {ol.Transform}
   */
  this.coordinateToCanvasPixelTransform = ol.transform.create();

  /**
   * @private
   * @type {CanvasRenderingContext2D}
   */
  this.hitCanvasContext_ = null;

  /**
   * @protected
   * @type {number}
   */
  this.renderedResolution;

};
ol.inherits(ol.renderer.canvas.IntermediateCanvas, ol.renderer.canvas.Layer);


/**
 * @inheritDoc
 */
ol.renderer.canvas.IntermediateCanvas.prototype.composeFrame = function(frameState, layerState, context) {

  this.preCompose(context, frameState);

  var image = this.getImage();
  if (image) {

    // clipped rendering if layer extent is set
    var extent = layerState.extent;
    var clipped = extent !== undefined;
    if (clipped) {
      this.clip(context, frameState, /** @type {ol.Extent} */ (extent));
    }

    var imageTransform = this.getImageTransform();
    // for performance reasons, context.save / context.restore is not used
    // to save and restore the transformation matrix and the opacity.
    // see http://jsperf.com/context-save-restore-versus-variable
    var alpha = context.globalAlpha;
    context.globalAlpha = layerState.opacity;

    // for performance reasons, context.setTransform is only used
    // when the view is rotated. see http://jsperf.com/canvas-transform
    var dx = imageTransform[4];
    var dy = imageTransform[5];
    var dw = image.width * imageTransform[0];
    var dh = image.height * imageTransform[3];
    context.drawImage(image, 0, 0, +image.width, +image.height,
        Math.round(dx), Math.round(dy), Math.round(dw), Math.round(dh));
    context.globalAlpha = alpha;

    if (clipped) {
      context.restore();
    }
  }

  this.postCompose(context, frameState, layerState);
};


/**
 * @abstract
 * @return {HTMLCanvasElement|HTMLVideoElement|Image} Canvas.
 */
ol.renderer.canvas.IntermediateCanvas.prototype.getImage = function() {};


/**
 * @abstract
 * @return {!ol.Transform} Image transform.
 */
ol.renderer.canvas.IntermediateCanvas.prototype.getImageTransform = function() {};


/**
 * @inheritDoc
 */
ol.renderer.canvas.IntermediateCanvas.prototype.forEachFeatureAtCoordinate = function(coordinate, frameState, hitTolerance, callback, thisArg) {
  var layer = this.getLayer();
  var source = layer.getSource();
  var resolution = frameState.viewState.resolution;
  var rotation = frameState.viewState.rotation;
  var skippedFeatureUids = frameState.skippedFeatureUids;
  return source.forEachFeatureAtCoordinate(
      coordinate, resolution, rotation, hitTolerance, skippedFeatureUids,
      /**
       * @param {ol.Feature|ol.render.Feature} feature Feature.
       * @return {?} Callback result.
       */
      function(feature) {
        return callback.call(thisArg, feature, layer);
      });
};


/**
 * @inheritDoc
 */
ol.renderer.canvas.IntermediateCanvas.prototype.forEachLayerAtCoordinate = function(coordinate, frameState, callback, thisArg) {
  if (!this.getImage()) {
    return undefined;
  }

  if (this.getLayer().getSource().forEachFeatureAtCoordinate !== ol.nullFunction) {
    // for ImageVector sources use the original hit-detection logic,
    // so that for example also transparent polygons are detected
    return ol.renderer.canvas.Layer.prototype.forEachLayerAtCoordinate.apply(this, arguments);
  } else {
    var pixel = ol.transform.apply(this.coordinateToCanvasPixelTransform, coordinate);
    ol.coordinate.scale(pixel, frameState.viewState.resolution / this.renderedResolution);

    if (!this.hitCanvasContext_) {
      this.hitCanvasContext_ = ol.dom.createCanvasContext2D(1, 1);
    }

    this.hitCanvasContext_.clearRect(0, 0, 1, 1);
    this.hitCanvasContext_.drawImage(this.getImage(), pixel[0], pixel[1], 1, 1, 0, 0, 1, 1);

    var imageData = this.hitCanvasContext_.getImageData(0, 0, 1, 1).data;
    if (imageData[3] > 0) {
      return callback.call(thisArg, this.getLayer(),  imageData);
    } else {
      return undefined;
    }
  }
};