Dactyloidae/devtools/server/actors/highlighters/eye-dropper.js

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";

// Eye-dropper tool. This is implemented as a highlighter so it can be displayed in the
// content page.
// It basically displays a magnifier that tracks mouse moves and shows a magnified version
// of the page. On click, it samples the color at the pixel being hovered.

const {Ci, Cc} = require("chrome");
const {CanvasFrameAnonymousContentHelper, createNode} = require("./utils/markup");
const Services = require("Services");
const EventEmitter = require("devtools/shared/event-emitter");
const {rgbToHsl, rgbToColorName} = require("devtools/shared/css/color").colorUtils;
const {getCurrentZoom, getFrameOffsets} = require("devtools/shared/layout/utils");

loader.lazyGetter(this, "clipboardHelper",
  () => Cc["@mozilla.org/widget/clipboardhelper;1"].getService(Ci.nsIClipboardHelper));
loader.lazyGetter(this, "l10n",
  () => Services.strings.createBundle("chrome://devtools/locale/eyedropper.properties"));

const ZOOM_LEVEL_PREF = "devtools.eyedropper.zoom";
const FORMAT_PREF = "devtools.defaultColorUnit";
// Width of the canvas.
const MAGNIFIER_WIDTH = 96;
// Height of the canvas.
const MAGNIFIER_HEIGHT = 96;
// Start position, when the tool is first shown. This should match the top/left position
// defined in CSS.
const DEFAULT_START_POS_X = 100;
const DEFAULT_START_POS_Y = 100;
// How long to wait before closing after copy.
const CLOSE_DELAY = 750;

/**
 * The EyeDropper is the class that draws the gradient line and
 * color stops as an overlay on top of a linear-gradient background-image.
 */
function EyeDropper(highlighterEnv) {
  EventEmitter.decorate(this);

  this.highlighterEnv = highlighterEnv;
  this.markup = new CanvasFrameAnonymousContentHelper(this.highlighterEnv,
                                                      this._buildMarkup.bind(this));

  // Get a couple of settings from prefs.
  this.format = Services.prefs.getCharPref(FORMAT_PREF);
  this.eyeDropperZoomLevel = Services.prefs.getIntPref(ZOOM_LEVEL_PREF);
}

EyeDropper.prototype = {
  typeName: "EyeDropper",

  ID_CLASS_PREFIX: "eye-dropper-",

  get win() {
    return this.highlighterEnv.window;
  },

  _buildMarkup() {
    // Highlighter main container.
    let container = createNode(this.win, {
      attributes: {"class": "highlighter-container"}
    });

    // Wrapper element.
    let wrapper = createNode(this.win, {
      parent: container,
      attributes: {
        "id": "root",
        "class": "root",
        "hidden": "true"
      },
      prefix: this.ID_CLASS_PREFIX
    });

    // The magnifier canvas element.
    createNode(this.win, {
      parent: wrapper,
      nodeType: "canvas",
      attributes: {
        "id": "canvas",
        "class": "canvas",
        "width": MAGNIFIER_WIDTH,
        "height": MAGNIFIER_HEIGHT
      },
      prefix: this.ID_CLASS_PREFIX
    });

    // The color label element.
    let colorLabelContainer = createNode(this.win, {
      parent: wrapper,
      attributes: {"class": "color-container"},
      prefix: this.ID_CLASS_PREFIX
    });
    createNode(this.win, {
      nodeType: "div",
      parent: colorLabelContainer,
      attributes: {"id": "color-preview", "class": "color-preview"},
      prefix: this.ID_CLASS_PREFIX
    });
    createNode(this.win, {
      nodeType: "div",
      parent: colorLabelContainer,
      attributes: {"id": "color-value", "class": "color-value"},
      prefix: this.ID_CLASS_PREFIX
    });

    return container;
  },

  destroy() {
    this.hide();
    this.markup.destroy();
  },

  getElement(id) {
    return this.markup.getElement(this.ID_CLASS_PREFIX + id);
  },

  /**
   * Show the eye-dropper highlighter.
   * @param {DOMNode} node The node which document the highlighter should be inserted in.
   * @param {Object} options The options object may contain the following properties:
   * - {Boolean} copyOnSelect Whether selecting a color should copy it to the clipboard.
   */
  show(node, options = {}) {
    if (this.highlighterEnv.isXUL) {
      return false;
    }

    this.options = options;

    // Get the page's current zoom level.
    this.pageZoom = getCurrentZoom(this.win);

    // Take a screenshot of the viewport. This needs to be done first otherwise the
    // eyedropper UI will appear in the screenshot itself (since the UI is injected as
    // native anonymous content in the page).
    // Once the screenshot is ready, the magnified area will be drawn.
    this.prepareImageCapture();

    // Start listening for user events.
    let {pageListenerTarget} = this.highlighterEnv;
    pageListenerTarget.addEventListener("mousemove", this);
    pageListenerTarget.addEventListener("click", this, true);
    pageListenerTarget.addEventListener("keydown", this);
    pageListenerTarget.addEventListener("DOMMouseScroll", this);
    pageListenerTarget.addEventListener("FullZoomChange", this);

    // Show the eye-dropper.
    this.getElement("root").removeAttribute("hidden");

    // Prepare the canvas context on which we're drawing the magnified page portion.
    this.ctx = this.getElement("canvas").getCanvasContext();
    this.ctx.imageSmoothingEnabled = false;

    this.magnifiedArea = {width: MAGNIFIER_WIDTH, height: MAGNIFIER_HEIGHT,
                          x: DEFAULT_START_POS_X, y: DEFAULT_START_POS_Y};

    this.moveTo(DEFAULT_START_POS_X, DEFAULT_START_POS_Y);

    // Focus the content so the keyboard can be used.
    this.win.focus();

    return true;
  },

  /**
   * Hide the eye-dropper highlighter.
   */
  hide() {
    if (this.highlighterEnv.isXUL) {
      return;
    }

    this.pageImage = null;

    let {pageListenerTarget} = this.highlighterEnv;
    pageListenerTarget.removeEventListener("mousemove", this);
    pageListenerTarget.removeEventListener("click", this, true);
    pageListenerTarget.removeEventListener("keydown", this);
    pageListenerTarget.removeEventListener("DOMMouseScroll", this);
    pageListenerTarget.removeEventListener("FullZoomChange", this);

    this.getElement("root").setAttribute("hidden", "true");
    this.getElement("root").removeAttribute("drawn");

    this.emit("hidden");
  },

  prepareImageCapture() {
    // Get the image data from the content window.
    let imageData = getWindowAsImageData(this.win);

    // We need to transform imageData to something drawWindow will consume. An ImageBitmap
    // works well. We could have used an Image, but doing so results in errors if the page
    // defines CSP headers.
    this.win.createImageBitmap(imageData).then(image => {
      this.pageImage = image;
      // We likely haven't drawn anything yet (no mousemove events yet), so start now.
      this.draw();

      // Set an attribute on the root element to be able to run tests after the first draw
      // was done.
      this.getElement("root").setAttribute("drawn", "true");
    });
  },

  /**
   * Get the number of cells (blown-up pixels) per direction in the grid.
   */
  get cellsWide() {
    // Canvas will render whole "pixels" (cells) only, and an even number at that. Round
    // up to the nearest even number of pixels.
    let cellsWide = Math.ceil(this.magnifiedArea.width / this.eyeDropperZoomLevel);
    cellsWide += cellsWide % 2;

    return cellsWide;
  },

  /**
   * Get the size of each cell (blown-up pixel) in the grid.
   */
  get cellSize() {
    return this.magnifiedArea.width / this.cellsWide;
  },

  /**
   * Get index of cell in the center of the grid.
   */
  get centerCell() {
    return Math.floor(this.cellsWide / 2);
  },

  /**
   * Get color of center cell in the grid.
   */
  get centerColor() {
    let pos = (this.centerCell * this.cellSize) + (this.cellSize / 2);
    let rgb = this.ctx.getImageData(pos, pos, 1, 1).data;
    return rgb;
  },

  draw() {
    // If the image of the page isn't ready yet, bail out, we'll draw later on mousemove.
    if (!this.pageImage) {
      return;
    }

    let {width, height, x, y} = this.magnifiedArea;

    let zoomedWidth = width / this.eyeDropperZoomLevel;
    let zoomedHeight = height / this.eyeDropperZoomLevel;

    let sx = x - (zoomedWidth / 2);
    let sy = y - (zoomedHeight / 2);
    let sw = zoomedWidth;
    let sh = zoomedHeight;

    this.ctx.drawImage(this.pageImage, sx, sy, sw, sh, 0, 0, width, height);

    // Draw the grid on top, but only at 3x or more, otherwise it's too busy.
    if (this.eyeDropperZoomLevel > 2) {
      this.drawGrid();
    }

    this.drawCrosshair();

    // Update the color preview and value.
    let rgb = this.centerColor;
    this.getElement("color-preview").setAttribute("style",
      `background-color:${toColorString(rgb, "rgb")};`);
    this.getElement("color-value").setTextContent(toColorString(rgb, this.format));
  },

  /**
   * Draw a grid on the canvas representing pixel boundaries.
   */
  drawGrid() {
    let {width, height} = this.magnifiedArea;

    this.ctx.lineWidth = 1;
    this.ctx.strokeStyle = "rgba(143, 143, 143, 0.2)";

    for (let i = 0; i < width; i += this.cellSize) {
      this.ctx.beginPath();
      this.ctx.moveTo(i - .5, 0);
      this.ctx.lineTo(i - .5, height);
      this.ctx.stroke();

      this.ctx.beginPath();
      this.ctx.moveTo(0, i - .5);
      this.ctx.lineTo(width, i - .5);
      this.ctx.stroke();
    }
  },

  /**
   * Draw a box on the canvas to highlight the center cell.
   */
  drawCrosshair() {
    let pos = this.centerCell * this.cellSize;

    this.ctx.lineWidth = 1;
    this.ctx.lineJoin = "miter";
    this.ctx.strokeStyle = "rgba(0, 0, 0, 1)";
    this.ctx.strokeRect(pos - 1.5, pos - 1.5, this.cellSize + 2, this.cellSize + 2);

    this.ctx.strokeStyle = "rgba(255, 255, 255, 1)";
    this.ctx.strokeRect(pos - 0.5, pos - 0.5, this.cellSize, this.cellSize);
  },

  handleEvent(e) {
    switch (e.type) {
      case "mousemove":
        // We might be getting an event from a child frame, so account for the offset.
        let [xOffset, yOffset] = getFrameOffsets(this.win, e.target);
        let x = xOffset + e.pageX - this.win.scrollX;
        let y = yOffset + e.pageY - this.win.scrollY;
        // Update the zoom area.
        this.magnifiedArea.x = x * this.pageZoom;
        this.magnifiedArea.y = y * this.pageZoom;
        // Redraw the portion of the screenshot that is now under the mouse.
        this.draw();
        // And move the eye-dropper's UI so it follows the mouse.
        this.moveTo(x, y);
        break;
      case "click":
        this.selectColor();
        break;
      case "keydown":
        this.handleKeyDown(e);
        break;
      case "DOMMouseScroll":
        // Prevent scrolling. That's because we only took a screenshot of the viewport, so
        // scrolling out of the viewport wouldn't draw the expected things. In the future
        // we can take the screenshot again on scroll, but for now it doesn't seem
        // important.
        e.preventDefault();
        break;
      case "FullZoomChange":
        this.hide();
        this.show();
        break;
    }
  },

  moveTo(x, y) {
    let root = this.getElement("root");
    root.setAttribute("style", `top:${y}px;left:${x}px;`);

    // Move the label container to the top if the magnifier is close to the bottom edge.
    if (y >= this.win.innerHeight - MAGNIFIER_HEIGHT) {
      root.setAttribute("top", "");
    } else {
      root.removeAttribute("top");
    }

    // Also offset the label container to the right or left if the magnifier is close to
    // the edge.
    root.removeAttribute("left");
    root.removeAttribute("right");
    if (x <= MAGNIFIER_WIDTH) {
      root.setAttribute("right", "");
    } else if (x >= this.win.innerWidth - MAGNIFIER_WIDTH) {
      root.setAttribute("left", "");
    }
  },

  /**
   * Select the current color that's being previewed. Depending on the current options,
   * selecting might mean copying to the clipboard and closing the
   */
  selectColor() {
    let onColorSelected = Promise.resolve();
    if (this.options.copyOnSelect) {
      onColorSelected = this.copyColor();
    }

    this.emit("selected", toColorString(this.centerColor, this.format));
    onColorSelected.then(() => this.hide(), e => console.error(e));
  },

  /**
   * Handler for the keydown event. Either select the color or move the panel in a
   * direction depending on the key pressed.
   */
  handleKeyDown(e) {
    // Bail out early if any unsupported modifier is used, so that we let
    // keyboard shortcuts through.
    if (e.metaKey || e.ctrlKey || e.altKey) {
      return;
    }

    if (e.keyCode === e.DOM_VK_RETURN) {
      this.selectColor();
      e.preventDefault();
      return;
    }

    if (e.keyCode === e.DOM_VK_ESCAPE) {
      this.emit("canceled");
      this.hide();
      e.preventDefault();
      return;
    }

    let offsetX = 0;
    let offsetY = 0;
    let modifier = 1;

    if (e.keyCode === e.DOM_VK_LEFT) {
      offsetX = -1;
    } else if (e.keyCode === e.DOM_VK_RIGHT) {
      offsetX = 1;
    } else if (e.keyCode === e.DOM_VK_UP) {
      offsetY = -1;
    } else if (e.keyCode === e.DOM_VK_DOWN) {
      offsetY = 1;
    }

    if (e.shiftKey) {
      modifier = 10;
    }

    offsetY *= modifier;
    offsetX *= modifier;

    if (offsetX !== 0 || offsetY !== 0) {
      this.magnifiedArea.x = cap(this.magnifiedArea.x + offsetX,
                                 0, this.win.innerWidth * this.pageZoom);
      this.magnifiedArea.y = cap(this.magnifiedArea.y + offsetY, 0,
                                 this.win.innerHeight * this.pageZoom);

      this.draw();

      this.moveTo(this.magnifiedArea.x / this.pageZoom,
                  this.magnifiedArea.y / this.pageZoom);

      e.preventDefault();
    }
  },

  /**
   * Copy the currently inspected color to the clipboard.
   * @return {Promise} Resolves when the copy has been done (after a delay that is used to
   * let users know that something was copied).
   */
  copyColor() {
    // Copy to the clipboard.
    let color = toColorString(this.centerColor, this.format);
    clipboardHelper.copyString(color);

    // Provide some feedback.
    this.getElement("color-value").setTextContent(
      "✓ " + l10n.GetStringFromName("colorValue.copied"));

    // Hide the tool after a delay.
    clearTimeout(this._copyTimeout);
    return new Promise(resolve => {
      this._copyTimeout = setTimeout(resolve, CLOSE_DELAY);
    });
  }
};

exports.EyeDropper = EyeDropper;

/**
 * Draw the visible portion of the window on a canvas and get the resulting ImageData.
 * @param {Window} win
 * @return {ImageData} The image data for the window.
 */
function getWindowAsImageData(win) {
  let canvas = win.document.createElementNS("http://www.w3.org/1999/xhtml", "canvas");
  let scale = getCurrentZoom(win);
  let width = win.innerWidth;
  let height = win.innerHeight;
  canvas.width = width * scale;
  canvas.height = height * scale;
  canvas.mozOpaque = true;

  let ctx = canvas.getContext("2d");

  ctx.scale(scale, scale);
  ctx.drawWindow(win, win.scrollX, win.scrollY, width, height, "#fff");

  return ctx.getImageData(0, 0, canvas.width, canvas.height);
}

/**
 * Get a formatted CSS color string from a color value.
 * @param {array} rgb Rgb values of a color to format.
 * @param {string} format Format of string. One of "hex", "rgb", "hsl", "name".
 * @return {string} Formatted color value, e.g. "#FFF" or "hsl(20, 10%, 10%)".
 */
function toColorString(rgb, format) {
  let [r, g, b] = rgb;

  switch (format) {
    case "hex":
      return hexString(rgb);
    case "rgb":
      return "rgb(" + r + ", " + g + ", " + b + ")";
    case "hsl":
      let [h, s, l] = rgbToHsl(rgb);
      return "hsl(" + h + ", " + s + "%, " + l + "%)";
    case "name":
      let str;
      try {
        str = rgbToColorName(r, g, b);
      } catch (e) {
        str = hexString(rgb);
      }
      return str;
    default:
      return hexString(rgb);
  }
}

/**
 * Produce a hex-formatted color string from rgb values.
 * @param {array} rgb Rgb values of color to stringify.
 * @return {string} Hex formatted string for color, e.g. "#FFEE00".
 */
function hexString([r, g, b]) {
  let val = (1 << 24) + (r << 16) + (g << 8) + (b << 0);
  return "#" + val.toString(16).substr(-6).toUpperCase();
}

function cap(value, min, max) {
  return Math.max(min, Math.min(value, max));
}