diff -r 000000000000 -r 6474c204b198 browser/devtools/shared/widgets/CSSTransformPreviewer.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/shared/widgets/CSSTransformPreviewer.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,389 @@
+/* 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";
+
+/**
+ * The CSSTransformPreview module displays, using a <canvas> a rectangle, with
+ * a given width and height and its transformed version, given a css transform
+ * property and origin. It also displays arrows from/to each corner.
+ *
+ * It is useful to visualize how a css transform affected an element. It can
+ * help debug tricky transformations. It is used today in a tooltip, and this
+ * tooltip is shown when hovering over a css transform declaration in the rule
+ * and computed view panels.
+ *
+ * TODO: For now, it multiplies matrices itself to calculate the coordinates of
+ * the transformed box, but that should be removed as soon as we can get access
+ * to getQuads().
+ */
+
+const HTML_NS = "http://www.w3.org/1999/xhtml";
+
+/**
+ * The TransformPreview needs an element to output a canvas tag.
+ *
+ * Usage example:
+ *
+ * let t = new CSSTransformPreviewer(myRootElement);
+ * t.preview("rotate(45deg)", "top left", 200, 400);
+ * t.preview("skew(19deg)", "center", 100, 500);
+ * t.preview("matrix(1, -0.2, 0, 1, 0, 0)");
+ * t.destroy();
+ *
+ * @param {nsIDOMElement} parentEl
+ *        Where the canvas will go
+ */
+function CSSTransformPreviewer(parentEl) {
+  this.parentEl = parentEl;
+  this.doc = this.parentEl.ownerDocument;
+  this.canvas = null;
+  this.ctx = null;
+}
+
+module.exports.CSSTransformPreviewer = CSSTransformPreviewer;
+
+CSSTransformPreviewer.prototype = {
+  /**
+   * The preview look-and-feel can be changed using these properties
+   */
+  MAX_DIM: 250,
+  PAD: 5,
+  ORIGINAL_FILL: "#1F303F",
+  ORIGINAL_STROKE: "#B2D8FF",
+  TRANSFORMED_FILL: "rgba(200, 200, 200, .5)",
+  TRANSFORMED_STROKE: "#B2D8FF",
+  ARROW_STROKE: "#329AFF",
+  ORIGIN_STROKE: "#329AFF",
+  ARROW_TIP_HEIGHT: 10,
+  ARROW_TIP_WIDTH: 8,
+  CORNER_SIZE_RATIO: 6,
+
+  /**
+   * Destroy removes the canvas from the parentelement passed in the constructor
+   */
+  destroy: function() {
+    if (this.canvas) {
+      this.parentEl.removeChild(this.canvas);
+    }
+    if (this._hiddenDiv) {
+      this.parentEl.removeChild(this._hiddenDiv);
+    }
+    this.parentEl = this.canvas = this.ctx = this.doc = null;
+  },
+
+  _createMarkup: function() {
+    this.canvas = this.doc.createElementNS(HTML_NS, "canvas");
+
+    this.canvas.setAttribute("id", "canvas");
+    this.canvas.setAttribute("width", this.MAX_DIM);
+    this.canvas.setAttribute("height", this.MAX_DIM);
+    this.canvas.style.position = "relative";
+    this.parentEl.appendChild(this.canvas);
+
+    this.ctx = this.canvas.getContext("2d");
+  },
+
+  _getComputed: function(name, value, width, height) {
+    if (!this._hiddenDiv) {
+      // Create a hidden element to apply the style to
+      this._hiddenDiv = this.doc.createElementNS(HTML_NS, "div");
+      this._hiddenDiv.style.visibility = "hidden";
+      this._hiddenDiv.style.position = "absolute";
+      this.parentEl.appendChild(this._hiddenDiv);
+    }
+
+    // Camelcase the name
+    name = name.replace(/-([a-z]{1})/g, (m, letter) => letter.toUpperCase());
+
+    // Apply width and height to make sure computation is made correctly
+    this._hiddenDiv.style.width = width + "px";
+    this._hiddenDiv.style.height = height + "px";
+
+    // Show the hidden div, apply the style, read the computed style, hide the
+    // hidden div again
+    this._hiddenDiv.style.display = "block";
+    this._hiddenDiv.style[name] = value;
+    let computed = this.doc.defaultView.getComputedStyle(this._hiddenDiv);
+    let computedValue = computed[name];
+    this._hiddenDiv.style.display = "none";
+
+    return computedValue;
+  },
+
+  _getMatrixFromTransformString: function(transformStr) {
+    let matrix = transformStr.substring(0, transformStr.length - 1).
+      substring(transformStr.indexOf("(") + 1).split(",");
+
+    matrix.forEach(function(value, index) {
+      matrix[index] = parseFloat(value, 10);
+    });
+
+    let transformMatrix = null;
+
+    if (matrix.length === 6) {
+      // 2d transform
+      transformMatrix = [
+        [matrix[0], matrix[2], matrix[4], 0],
+        [matrix[1], matrix[3], matrix[5], 0],
+        [0,     0,     1,     0],
+        [0,     0,     0,     1]
+      ];
+    } else {
+      // 3d transform
+      transformMatrix = [
+        [matrix[0], matrix[4], matrix[8],  matrix[12]],
+        [matrix[1], matrix[5], matrix[9],  matrix[13]],
+        [matrix[2], matrix[6], matrix[10], matrix[14]],
+        [matrix[3], matrix[7], matrix[11], matrix[15]]
+      ];
+    }
+
+    return transformMatrix;
+  },
+
+  _getOriginFromOriginString: function(originStr) {
+    let offsets = originStr.split(" ");
+    offsets.forEach(function(item, index) {
+      offsets[index] = parseInt(item, 10);
+    });
+
+    return offsets;
+  },
+
+  _multiply: function(m1, m2) {
+    let m = [];
+    for (let m1Line = 0; m1Line < m1.length; m1Line++) {
+      m[m1Line] = 0;
+      for (let m2Col = 0; m2Col < m2.length; m2Col++) {
+        m[m1Line] += m1[m1Line][m2Col] * m2[m2Col];
+      }
+    }
+    return [m[0], m[1]];
+  },
+
+  _getTransformedPoint: function(matrix, point, origin) {
+    let pointMatrix = [point[0] - origin[0], point[1] - origin[1], 1, 1];
+    return this._multiply(matrix, pointMatrix);
+  },
+
+  _getTransformedPoints: function(matrix, rect, origin) {
+    return rect.map(point => {
+      let tPoint = this._getTransformedPoint(matrix, [point[0], point[1]], origin);
+      return [tPoint[0] + origin[0], tPoint[1] + origin[1]];
+    });
+  },
+
+  /**
+   * For canvas to avoid anti-aliasing
+   */
+  _round: x => Math.round(x) + .5,
+
+  _drawShape: function(points, fillStyle, strokeStyle) {
+    this.ctx.save();
+
+    this.ctx.lineWidth = 1;
+    this.ctx.strokeStyle = strokeStyle;
+    this.ctx.fillStyle = fillStyle;
+
+    this.ctx.beginPath();
+    this.ctx.moveTo(this._round(points[0][0]), this._round(points[0][1]));
+    for (var i = 1; i < points.length; i++) {
+      this.ctx.lineTo(this._round(points[i][0]), this._round(points[i][1]));
+    }
+    this.ctx.lineTo(this._round(points[0][0]), this._round(points[0][1]));
+    this.ctx.fill();
+    this.ctx.stroke();
+
+    this.ctx.restore();
+  },
+
+  _drawArrow: function(x1, y1, x2, y2) {
+    // do not draw if the line is too small
+    if (Math.abs(x2-x1) < 20 && Math.abs(y2-y1) < 20) {
+      return;
+    }
+
+    this.ctx.save();
+
+    this.ctx.strokeStyle = this.ARROW_STROKE;
+    this.ctx.fillStyle = this.ARROW_STROKE;
+    this.ctx.lineWidth = 1;
+
+    this.ctx.beginPath();
+    this.ctx.moveTo(this._round(x1), this._round(y1));
+    this.ctx.lineTo(this._round(x2), this._round(y2));
+    this.ctx.stroke();
+
+    this.ctx.beginPath();
+    this.ctx.translate(x2, y2);
+    let radians = Math.atan((y1 - y2) / (x1 - x2));
+    radians += ((x1 >= x2) ? -90 : 90) * Math.PI / 180;
+    this.ctx.rotate(radians);
+    this.ctx.moveTo(0, 0);
+    this.ctx.lineTo(this.ARROW_TIP_WIDTH / 2, this.ARROW_TIP_HEIGHT);
+    this.ctx.lineTo(-this.ARROW_TIP_WIDTH / 2, this.ARROW_TIP_HEIGHT);
+    this.ctx.closePath();
+    this.ctx.fill();
+
+    this.ctx.restore();
+  },
+
+  _drawOrigin: function(x, y) {
+    this.ctx.save();
+
+    this.ctx.strokeStyle = this.ORIGIN_STROKE;
+    this.ctx.fillStyle = this.ORIGIN_STROKE;
+
+    this.ctx.beginPath();
+    this.ctx.arc(x, y, 4, 0, 2 * Math.PI, false);
+    this.ctx.stroke();
+    this.ctx.fill();
+
+    this.ctx.restore();
+  },
+
+  /**
+   * Computes the largest width and height of all the given shapes and changes
+   * all of the shapes' points (by reference) so they fit into the configured
+   * MAX_DIM - 2*PAD area.
+   * @return {Object} A {w, h} giving the size the canvas should be
+   */
+  _fitAllShapes: function(allShapes) {
+    let allXs = [], allYs = [];
+    for (let shape of allShapes) {
+      for (let point of shape) {
+        allXs.push(point[0]);
+        allYs.push(point[1]);
+      }
+    }
+    let minX = Math.min.apply(Math, allXs);
+    let maxX = Math.max.apply(Math, allXs);
+    let minY = Math.min.apply(Math, allYs);
+    let maxY = Math.max.apply(Math, allYs);
+
+    let spanX = maxX - minX;
+    let spanY = maxY - minY;
+    let isWide = spanX > spanY;
+
+    let cw = isWide ? this.MAX_DIM :
+      this.MAX_DIM * Math.min(spanX, spanY) / Math.max(spanX, spanY);
+    let ch = !isWide ? this.MAX_DIM :
+      this.MAX_DIM * Math.min(spanX, spanY) / Math.max(spanX, spanY);
+
+    let mapX = x => this.PAD + ((cw - 2 * this.PAD) / (maxX - minX)) * (x - minX);
+    let mapY = y => this.PAD + ((ch - 2 * this.PAD) / (maxY - minY)) * (y - minY);
+
+    for (let shape of allShapes) {
+      for (let point of shape) {
+        point[0] = mapX(point[0]);
+        point[1] = mapY(point[1]);
+      }
+    }
+
+    return {w: cw, h: ch};
+  },
+
+  _drawShapes: function(shape, corner, transformed, transformedCorner) {
+    this._drawOriginal(shape);
+    this._drawOriginalCorner(corner);
+    this._drawTransformed(transformed);
+    this._drawTransformedCorner(transformedCorner);
+  },
+
+  _drawOriginal: function(points) {
+    this._drawShape(points, this.ORIGINAL_FILL, this.ORIGINAL_STROKE);
+  },
+
+  _drawTransformed: function(points) {
+    this._drawShape(points, this.TRANSFORMED_FILL, this.TRANSFORMED_STROKE);
+  },
+
+  _drawOriginalCorner: function(points) {
+    this._drawShape(points, this.ORIGINAL_STROKE, this.ORIGINAL_STROKE);
+  },
+
+  _drawTransformedCorner: function(points) {
+    this._drawShape(points, this.TRANSFORMED_STROKE, this.TRANSFORMED_STROKE);
+  },
+
+  _drawArrows: function(shape, transformed) {
+    this._drawArrow(shape[0][0], shape[0][1], transformed[0][0], transformed[0][1]);
+    this._drawArrow(shape[1][0], shape[1][1], transformed[1][0], transformed[1][1]);
+    this._drawArrow(shape[2][0], shape[2][1], transformed[2][0], transformed[2][1]);
+    this._drawArrow(shape[3][0], shape[3][1], transformed[3][0], transformed[3][1]);
+  },
+
+  /**
+   * Draw a transform preview
+   *
+   * @param {String} transform
+   *        The css transform value as a string, as typed by the user, as long
+   *        as it can be computed by the browser
+   * @param {String} origin
+   *        Same as above for the transform-origin value. Defaults to "center"
+   * @param {Number} width
+   *        The width of the container. Defaults to 200
+   * @param {Number} height
+   *        The height of the container. Defaults to 200
+   * @return {Boolean} Whether or not the preview could be created. Will return
+   *         false for instance if the transform is invalid
+   */
+  preview: function(transform, origin="center", width=200, height=200) {
+    // Create/clear the canvas
+    if (!this.canvas) {
+      this._createMarkup();
+    }
+    this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
+
+    // Get computed versions of transform and origin
+    transform = this._getComputed("transform", transform, width, height);
+    if (transform && transform !== "none") {
+      origin = this._getComputed("transform-origin", origin, width, height);
+
+      // Get the matrix, origin and width height data for the previewed element
+      let originData = this._getOriginFromOriginString(origin);
+      let matrixData = this._getMatrixFromTransformString(transform);
+
+      // Compute the original box rect and transformed box rect
+      let shapePoints = [
+        [0, 0],
+        [width, 0],
+        [width, height],
+        [0, height]
+      ];
+      let transformedPoints = this._getTransformedPoints(matrixData, shapePoints, originData);
+
+      // Do the same for the corner triangle shape
+      let cornerSize = Math.min(shapePoints[2][1] - shapePoints[1][1],
+        shapePoints[1][0] - shapePoints[0][0]) / this.CORNER_SIZE_RATIO;
+      let cornerPoints = [
+        [shapePoints[1][0], shapePoints[1][1]],
+        [shapePoints[1][0], shapePoints[1][1] + cornerSize],
+        [shapePoints[1][0] - cornerSize, shapePoints[1][1]]
+      ];
+      let transformedCornerPoints = this._getTransformedPoints(matrixData, cornerPoints, originData);
+
+      // Resize points to fit everything in the canvas
+      let {w, h} = this._fitAllShapes([
+        shapePoints,
+        transformedPoints,
+        cornerPoints,
+        transformedCornerPoints,
+        [originData]
+      ]);
+
+      this.canvas.setAttribute("width", w);
+      this.canvas.setAttribute("height", h);
+
+      this._drawShapes(shapePoints, cornerPoints, transformedPoints, transformedCornerPoints)
+      this._drawArrows(shapePoints, transformedPoints);
+      this._drawOrigin(originData[0], originData[1]);
+
+      return true;
+    } else {
+      return false;
+    }
+  }
+};