1 files changed, 134 insertions, 0 deletions
diff --git a/devtools/client/memory/components/tree-map/canvas-utils.js b/devtools/client/memory/components/tree-map/canvas-utils.js
new file mode 100644
index 000000000..c7d67a0bf
--- /dev/null
+++ b/devtools/client/memory/components/tree-map/canvas-utils.js
@@ -0,0 +1,134 @@
+/* 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/. */
+
+/* eslint-env browser */
+
+"use strict";
+
+/**
+ * Create 2 canvases and contexts for drawing onto, 1 main canvas, and 1 zoom
+ * canvas. The main canvas dimensions match the parent div, but the CSS can be
+ * transformed to be zoomed and dragged around (potentially creating a blurry
+ * canvas once zoomed in). The zoom canvas is a zoomed in section that matches
+ * the parent div's dimensions and is kept in place through CSS. A zoomed in
+ * view of the visualization is drawn onto this canvas, providing a crisp zoomed
+ * in view of the tree map.
+ */
+const { debounce } = require("sdk/lang/functional");
+const EventEmitter = require("devtools/shared/event-emitter");
+
+const HTML_NS = "http://www.w3.org/1999/xhtml";
+const FULLSCREEN_STYLE = {
+  width: "100%",
+  height: "100%",
+  position: "absolute",
+};
+
+/**
+ * Create the canvases, resize handlers, and return references to them all
+ *
+ * @param  {HTMLDivElement} parentEl
+ * @param  {Number} debounceRate
+ * @return {Object}
+ */
+function Canvases(parentEl, debounceRate) {
+  EventEmitter.decorate(this);
+  this.container = createContainingDiv(parentEl);
+
+  // This canvas contains all of the treemap
+  this.main = createCanvas(this.container, "main");
+  // This canvas contains only the zoomed in portion, overlaying the main canvas
+  this.zoom = createCanvas(this.container, "zoom");
+
+  this.removeHandlers = handleResizes(this, debounceRate);
+}
+
+Canvases.prototype = {
+
+  /**
+   * Remove the handlers and elements
+   *
+   * @return {type}  description
+   */
+  destroy : function () {
+    this.removeHandlers();
+    this.container.removeChild(this.main.canvas);
+    this.container.removeChild(this.zoom.canvas);
+  }
+};
+
+module.exports = Canvases;
+
+/**
+ * Create the containing div
+ *
+ * @param  {HTMLDivElement} parentEl
+ * @return {HTMLDivElement}
+ */
+function createContainingDiv(parentEl) {
+  let div = parentEl.ownerDocument.createElementNS(HTML_NS, "div");
+  Object.assign(div.style, FULLSCREEN_STYLE);
+  parentEl.appendChild(div);
+  return div;
+}
+
+/**
+ * Create a canvas and context
+ *
+ * @param  {HTMLDivElement} container
+ * @param  {String} className
+ * @return {Object} { canvas, ctx }
+ */
+function createCanvas(container, className) {
+  let window = container.ownerDocument.defaultView;
+  let canvas = container.ownerDocument.createElementNS(HTML_NS, "canvas");
+  container.appendChild(canvas);
+  canvas.width = container.offsetWidth * window.devicePixelRatio;
+  canvas.height = container.offsetHeight * window.devicePixelRatio;
+  canvas.className = className;
+
+  Object.assign(canvas.style, FULLSCREEN_STYLE, {
+    pointerEvents: "none"
+  });
+
+  let ctx = canvas.getContext("2d");
+
+  return { canvas, ctx };
+}
+
+/**
+ * Resize the canvases' resolutions, and fires out the onResize callback
+ *
+ * @param  {HTMLDivElement} container
+ * @param  {Object} canvases
+ * @param  {Number} debounceRate
+ */
+function handleResizes(canvases, debounceRate) {
+  let { container, main, zoom } = canvases;
+  let window = container.ownerDocument.defaultView;
+
+  function resize() {
+    let width = container.offsetWidth * window.devicePixelRatio;
+    let height = container.offsetHeight * window.devicePixelRatio;
+
+    main.canvas.width = width;
+    main.canvas.height = height;
+    zoom.canvas.width = width;
+    zoom.canvas.height = height;
+
+    canvases.emit("resize");
+  }
+
+  // Tests may not need debouncing
+  let debouncedResize = debounceRate > 0
+    ? debounce(resize, debounceRate)
+    : resize;
+
+  window.addEventListener("resize", debouncedResize, false);
+  resize();
+
+  return function removeResizeHandlers() {
+    window.removeEventListener("resize", debouncedResize, false);
+  };
+}