openlayers/src/ol/render/canvas/hitdetect.js

/**
 * @module ol/render/canvas/hitdetet
 */

import CanvasImmediateRenderer from './Immediate.js';
import {createCanvasContext2D} from '../../dom.js';
import {Icon} from '../../style.js';
import IconAnchorUnits from '../../style/IconAnchorUnits.js';
import GeometryType from '../../geom/GeometryType.js';
import {intersects} from '../../extent.js';
import {numberSafeCompareFunction} from '../../array.js';

/**
 * @param {import("../../size.js").Size} size Canvas size in css pixels.
 * @param {Array<import("../../transform.js").Transform>} transforms Transforms
 * for rendering features to all worlds of the viewport, from coordinates to css
 * pixels.
 * @param {Array<import("../../Feature.js").FeatureLike>} features
 * Features to consider for hit detection.
 * @param {import("../../style/Style.js").StyleFunction|undefined} styleFunction
 * Layer style function.
 * @param {import("../../extent.js").Extent} extent Extent.
 * @param {number} resolution Resolution.
 * @param {number} rotation Rotation.
 * @return {ImageData} Hit detection image data.
 */
export function createHitDetectionImageData(size, transforms, features, styleFunction, extent, resolution, rotation) {
  const width = size[0] / 2;
  const height = size[1] / 2;
  const context = createCanvasContext2D(width, height);
  context.imageSmoothingEnabled = false;
  const canvas = context.canvas;
  const renderer = new CanvasImmediateRenderer(context, 0.5, extent, null, rotation);
  const featureCount = features.length;
  // Stretch hit detection index to use the whole available color range
  const indexFactor = Math.floor((256 * 256 * 256 - 1) / featureCount);
  const featuresByZIndex = {};
  for (let i = 1; i <= featureCount; ++i) {
    const feature = features[i - 1];
    const featureStyleFunction = feature.getStyleFunction() || styleFunction;
    if (!styleFunction) {
      continue;
    }
    let styles = featureStyleFunction(feature, resolution);
    if (!styles) {
      continue;
    }
    if (!Array.isArray(styles)) {
      styles = [styles];
    }
    const index = i * indexFactor;
    const color = '#' + ('000000' + index.toString(16)).slice(-6);
    for (let j = 0, jj = styles.length; j < jj; ++j) {
      const originalStyle = styles[j];
      const style = originalStyle.clone();
      const fill = style.getFill();
      if (fill) {
        fill.setColor(color);
      }
      const stroke = style.getStroke();
      if (stroke) {
        stroke.setColor(color);
      }
      style.setText(undefined);
      const image = originalStyle.getImage();
      if (image) {
        const imgSize = image.getImageSize();
        if (!imgSize) {
          continue;
        }

        const canvas = document.createElement('canvas');
        canvas.width = imgSize[0];
        canvas.height = imgSize[1];
        const imgContext = canvas.getContext('2d', {alpha: false});
        imgContext.fillStyle = color;
        const img = imgContext.canvas;
        imgContext.fillRect(0, 0, img.width, img.height);
        const width = imgSize ? imgSize[0] : img.width;
        const height = imgSize ? imgSize[1] : img.height;
        const iconContext = createCanvasContext2D(width, height);
        iconContext.drawImage(img, 0, 0);
        style.setImage(new Icon({
          img: img,
          imgSize: imgSize,
          anchor: image.getAnchor(),
          anchorXUnits: IconAnchorUnits.PIXELS,
          anchorYUnits: IconAnchorUnits.PIXELS,
          offset: image.getOrigin(),
          size: image.getSize(),
          opacity: image.getOpacity(),
          scale: image.getScale(),
          rotation: image.getRotation(),
          rotateWithView: image.getRotateWithView()
        }));
      }
      const zIndex = Number(style.getZIndex());
      let byGeometryType = featuresByZIndex[zIndex];
      if (!byGeometryType) {
        byGeometryType = {};
        featuresByZIndex[zIndex] = byGeometryType;
        byGeometryType[GeometryType.POLYGON] = [];
        byGeometryType[GeometryType.CIRCLE] = [];
        byGeometryType[GeometryType.LINE_STRING] = [];
        byGeometryType[GeometryType.POINT] = [];
      }
      const geometry = style.getGeometryFunction()(feature);
      if (geometry && intersects(extent, geometry.getExtent())) {
        byGeometryType[geometry.getType().replace('Multi', '')].push(geometry, style);
      }
    }
  }

  const zIndexKeys = Object.keys(featuresByZIndex).map(Number).sort(numberSafeCompareFunction);
  for (let i = 0, ii = zIndexKeys.length; i < ii; ++i) {
    const byGeometryType = featuresByZIndex[zIndexKeys[i]];
    for (const type in byGeometryType) {
      const geomAndStyle = byGeometryType[type];
      for (let j = 0, jj = geomAndStyle.length; j < jj; j += 2) {
        renderer.setStyle(geomAndStyle[j + 1]);
        for (let k = 0, kk = transforms.length; k < kk; ++k) {
          renderer.setTransform(transforms[k]);
          renderer.drawGeometry(geomAndStyle[j]);
        }
      }
    }
  }
  return context.getImageData(0, 0, canvas.width, canvas.height);
}

/**
 * @param {import("../../pixel").Pixel} pixel Pixel coordinate on the hit
 * detection canvas in css pixels.
 * @param {Array<import("../../Feature").FeatureLike>} features Features. Has to
 * match the `features` array that was passed to `createHitDetectionImageData()`.
 * @param {ImageData} imageData Hit detection image data generated by
 * `createHitDetectionImageData()`.
 * @return {Array<import("../../Feature").FeatureLike>} features Features.
 */
export function hitDetect(pixel, features, imageData) {
  const resultFeatures = [];
  if (imageData) {
    const index = (Math.round(pixel[0] / 2) + Math.round(pixel[1] / 2) * imageData.width) * 4;
    const r = imageData.data[index];
    const g = imageData.data[index + 1];
    const b = imageData.data[index + 2];
    const i = b + (256 * (g + (256 * r)));
    const indexFactor = Math.floor((256 * 256 * 256 - 1) / features.length);
    if (i && i % indexFactor === 0) {
      resultFeatures.push(features[i / indexFactor - 1]);
    }
  }
  return resultFeatures;
}