blockly/core/workspace_drag_surface_svg.js

/**
 * @license
 * Copyright 2016 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @fileoverview An SVG that floats on top of the workspace.
 * Blocks are moved into this SVG during a drag, improving performance.
 * The entire SVG is translated using CSS translation instead of SVG so the
 * blocks are never repainted during drag improving performance.
 */

'use strict';

/**
 * An SVG that floats on top of the workspace.
 * Blocks are moved into this SVG during a drag, improving performance.
 * The entire SVG is translated using CSS translation instead of SVG so the
 * blocks are never repainted during drag improving performance.
 * @class
 */
goog.module('Blockly.WorkspaceDragSurfaceSvg');

const dom = goog.require('Blockly.utils.dom');
const svgMath = goog.require('Blockly.utils.svgMath');
/* eslint-disable-next-line no-unused-vars */
const {Coordinate} = goog.requireType('Blockly.utils.Coordinate');
const {Svg} = goog.require('Blockly.utils.Svg');


/**
 * Blocks are moved into this SVG during a drag, improving performance.
 * The entire SVG is translated using CSS transforms instead of SVG so the
 * blocks are never repainted during drag improving performance.
 * @param {!Element} container Containing element.
 * @constructor
 * @alias Blockly.WorkspaceDragSurfaceSvg
 */
const WorkspaceDragSurfaceSvg = function(container) {
  this.container_ = container;
  this.createDom();
};

/**
 * The SVG drag surface. Set once by WorkspaceDragSurfaceSvg.createDom.
 * @type {SVGElement}
 * @private
 */
WorkspaceDragSurfaceSvg.prototype.SVG_ = null;

/**
 * Containing HTML element; parent of the workspace and the drag surface.
 * @type {Element}
 * @private
 */
WorkspaceDragSurfaceSvg.prototype.container_ = null;

/**
 * Create the drag surface and inject it into the container.
 */
WorkspaceDragSurfaceSvg.prototype.createDom = function() {
  if (this.SVG_) {
    return;  // Already created.
  }

  /**
   * Dom structure when the workspace is being dragged. If there is no drag in
   * progress, the SVG is empty and display: none.
   * <svg class="blocklyWsDragSurface" style=transform:translate3d(...)>
   *   <g class="blocklyBlockCanvas"></g>
   *   <g class="blocklyBubbleCanvas">/g>
   * </svg>
   */
  this.SVG_ = dom.createSvgElement(
      Svg.SVG, {
        'xmlns': dom.SVG_NS,
        'xmlns:html': dom.HTML_NS,
        'xmlns:xlink': dom.XLINK_NS,
        'version': '1.1',
        'class': 'blocklyWsDragSurface blocklyOverflowVisible',
      },
      null);
  this.container_.appendChild(this.SVG_);
};

/**
 * Translate the entire drag surface during a drag.
 * We translate the drag surface instead of the blocks inside the surface
 * so that the browser avoids repainting the SVG.
 * Because of this, the drag coordinates must be adjusted by scale.
 * @param {number} x X translation for the entire surface
 * @param {number} y Y translation for the entire surface
 * @package
 */
WorkspaceDragSurfaceSvg.prototype.translateSurface = function(x, y) {
  // This is a work-around to prevent a the blocks from rendering
  // fuzzy while they are being moved on the drag surface.
  const fixedX = x.toFixed(0);
  const fixedY = y.toFixed(0);

  this.SVG_.style.display = 'block';
  dom.setCssTransform(
      this.SVG_, 'translate3d(' + fixedX + 'px, ' + fixedY + 'px, 0)');
};

/**
 * Reports the surface translation in scaled workspace coordinates.
 * Use this when finishing a drag to return blocks to the correct position.
 * @return {!Coordinate} Current translation of the surface
 * @package
 */
WorkspaceDragSurfaceSvg.prototype.getSurfaceTranslation = function() {
  return svgMath.getRelativeXY(/** @type {!SVGElement} */ (this.SVG_));
};

/**
 * Move the blockCanvas and bubbleCanvas out of the surface SVG and on to
 * newSurface.
 * @param {SVGElement} newSurface The element to put the drag surface contents
 *     into.
 * @package
 */
WorkspaceDragSurfaceSvg.prototype.clearAndHide = function(newSurface) {
  if (!newSurface) {
    throw Error(
        'Couldn\'t clear and hide the drag surface: missing new surface.');
  }
  const blockCanvas = /** @type {!Element} */ (this.SVG_.childNodes[0]);
  const bubbleCanvas = /** @type {!Element} */ (this.SVG_.childNodes[1]);
  if (!blockCanvas || !bubbleCanvas ||
      !dom.hasClass(blockCanvas, 'blocklyBlockCanvas') ||
      !dom.hasClass(bubbleCanvas, 'blocklyBubbleCanvas')) {
    throw Error(
        'Couldn\'t clear and hide the drag surface. A node was missing.');
  }

  // If there is a previous sibling, put the blockCanvas back right afterwards,
  // otherwise insert it as the first child node in newSurface.
  if (this.previousSibling_ !== null) {
    dom.insertAfter(blockCanvas, this.previousSibling_);
  } else {
    newSurface.insertBefore(blockCanvas, newSurface.firstChild);
  }

  // Reattach the bubble canvas after the blockCanvas.
  dom.insertAfter(bubbleCanvas, blockCanvas);
  // Hide the drag surface.
  this.SVG_.style.display = 'none';
  if (this.SVG_.childNodes.length) {
    throw Error('Drag surface was not cleared.');
  }
  dom.setCssTransform(this.SVG_, '');
  this.previousSibling_ = null;
};

/**
 * Set the SVG to have the block canvas and bubble canvas in it and then
 * show the surface.
 * @param {!SVGElement} blockCanvas The block canvas <g> element from the
 *     workspace.
 * @param {!SVGElement} bubbleCanvas The <g> element that contains the bubbles.
 * @param {Element} previousSibling The element to insert the block canvas and
       bubble canvas after when it goes back in the DOM at the end of a drag.
 * @param {number} width The width of the workspace SVG element.
 * @param {number} height The height of the workspace SVG element.
 * @param {number} scale The scale of the workspace being dragged.
 * @package
 */
WorkspaceDragSurfaceSvg.prototype.setContentsAndShow = function(
    blockCanvas, bubbleCanvas, previousSibling, width, height, scale) {
  if (this.SVG_.childNodes.length) {
    throw Error('Already dragging a block.');
  }
  this.previousSibling_ = previousSibling;
  // Make sure the blocks and bubble canvas are scaled appropriately.
  blockCanvas.setAttribute('transform', 'translate(0, 0) scale(' + scale + ')');
  bubbleCanvas.setAttribute(
      'transform', 'translate(0, 0) scale(' + scale + ')');
  this.SVG_.setAttribute('width', width);
  this.SVG_.setAttribute('height', height);
  this.SVG_.appendChild(blockCanvas);
  this.SVG_.appendChild(bubbleCanvas);
  this.SVG_.style.display = 'block';
};

exports.WorkspaceDragSurfaceSvg = WorkspaceDragSurfaceSvg;