Use mock canvas object replacing `canvas` (#3518)

* Use mock canvas object replacing `canvas`

Fixes #3515.

A mock canvas object is added to the unit tests, which makes usage of module `canvas` voluntary.

The issue with `canvas` is that it requires an external dependency to `cairo`. This complicates setting up a develop environment for `vis.js`

- Removed `canvas` from `package.json`
- Added section to README.md with instructions on how to install `canvas` instead.

* Removed debugger statements

* Updates for review

* Fixes for review

README.md

@@ -36,6 +36,16 @@ Link via cdnjs: http://cdnjs.com
 Or download the library from the github project:
 [https://github.com/almende/vis.git](https://github.com/almende/vis.git).
 
+
+### Installing module `canvas`
+
+Module `canvas` is only required if you need to run `vis.js` on `node.js` and require actual output. It is not required for regular usage in a browser.
+
+Currently, the unit tests use a mock object for canvas which has limited but adequate functionality. If `canvas` is installed, that will be used silently in place of the mock object.
+
+The issue with `canvas` is that it has an external dependency to `cairo`. This needs to be installed outside of the regular install as done by `npm`. Please consult [`node-canvas` github page](https://github.com/Automattic/node-canvas/wiki#desktop) for the correct installation procecure your platform
+
+
 ## Load
 
 To use a component, include the javascript and css files of vis in your web page:
@@ -322,6 +332,9 @@ module: {
 
 There is also an [demo-project](https://github.com/mojoaxel/vis-webpack-demo) showing the integration of vis.js using webpack.
 
+
+
+
 ## Test
 
 To test the library, install the project dependencies once:

package.json

@@ -34,29 +34,28 @@
   },
   "dependencies": {
     "emitter-component": "^1.1.1",
-    "moment": "^2.18.1",
-    "propagating-hammerjs": "^1.4.6",
     "hammerjs": "^2.0.8",
-    "keycharm": "^0.2.0"
+    "keycharm": "^0.2.0",
+    "moment": "^2.18.1",
+    "propagating-hammerjs": "^1.4.6"
   },
   "devDependencies": {
     "async": "^2.5.0",
     "babel-core": "^6.25.0",
     "babel-loader": "^7.1.1",
-    "babel-polyfill": "^6.23.0",
     "babel-plugin-transform-es3-member-expression-literals": "^6.22.0",
     "babel-plugin-transform-es3-property-literals": "^6.22.0",
     "babel-plugin-transform-runtime": "^6.23.0",
+    "babel-polyfill": "^6.23.0",
     "babel-preset-es2015": "^6.24.1",
     "babel-runtime": "^6.23.0",
     "babelify": "^7.3.0",
-    "canvas": "^1.6.5",
     "clean-css": "^4.1.7",
     "eslint": "^4.3.0",
     "gulp": "^3.9.1",
-    "gulp-eslint": "^4.0.0",
     "gulp-clean-css": "^3.7.0",
     "gulp-concat": "^2.6.1",
+    "gulp-eslint": "^4.0.0",
     "gulp-rename": "^1.2.2",
     "gulp-util": "^3.0.8",
     "jsdom": "9.12.0",

test/Graph3d.test.js

@@ -2,6 +2,7 @@ var assert = require('assert');
 var vis = require('../dist/vis');
 var Graph3d = vis.Graph3d;
 var jsdom_global = require('jsdom-global');
+var canvasMockify = require('./canvas-mock');
 var stdout = require('test-console').stdout;
 var Validator = require("./../lib/shared/Validator").default;
 //var {printStyle} = require('./../lib/shared/Validator');
@@ -16,6 +17,7 @@ describe('Graph3d', function () {
       "<div id='mygraph'></div>",
       { skipWindowCheck: true}
     );
+    canvasMockify(window);
     this.container = document.getElementById('mygraph');
   });
 

test/Label.test.js

@@ -13,6 +13,7 @@ var Label = require('../lib/network/modules/components/shared/Label').default;
 var NodesHandler = require('../lib/network/modules/NodesHandler').default;
 var util = require('../lib/util');
 var jsdom_global = require('jsdom-global');
+var canvasMockify = require('./canvas-mock');
 var vis = require('../dist/vis');
 var Network = vis.network;
 
@@ -324,6 +325,7 @@ describe('Network Label', function() {
       "<div id='mynetwork'></div>",
       { skipWindowCheck: true}
     );
+    canvasMockify(window);
     this.container = document.getElementById('mynetwork');
   });
 

test/Network.test.js

@@ -14,9 +14,10 @@ var fs = require('fs');
 var assert = require('assert');
 var vis = require('../dist/vis');
 var Network = vis.network;
-var jsdom_global = require('jsdom-global');
 var stdout = require('test-console').stdout;
 var Validator = require("./../lib/shared/Validator").default;
+var jsdom_global = require('jsdom-global');
+var canvasMockify = require('./canvas-mock');
 var {allOptions, configureOptions} = require('./../lib/network/options.js');
 //var {printStyle} = require('./../lib/shared/Validator');
 
@@ -222,6 +223,8 @@ function checkFontProperties(fontItem, checkStrict = true) {
 
 
 
+
+
 describe('Network', function () {
 
   before(function() {
@@ -229,6 +232,7 @@ describe('Network', function () {
       "<div id='mynetwork'></div>",
       { skipWindowCheck: true}
     );
+    canvasMockify(window);
     this.container = document.getElementById('mynetwork');
   });
 
@@ -324,6 +328,7 @@ describe('Network', function () {
    * The real deterrent is eslint rule 'guard-for-in`.
    */
   it('can deal with added fields in Array.prototype', function (done) {
+    var canvas = window.document.createElement('canvas');
     Array.prototype.foo = 1;  // Just add anything to the prototype
     Object.prototype.bar = 2; // Let's screw up hashes as well
 
@@ -688,7 +693,6 @@ describe('Edge', function () {
 
 describe('Clustering', function () {
 
-
   it('properly handles options allowSingleNodeCluster', function() {
     var [network, data, numNodes, numEdges] = createSampleNetwork();
 		data.edges.update({from: 1, to: 11,});

test/canvas-mock.js

@@ -0,0 +1,90 @@
+/**
+ * Set up mock 2D context, for usage in unit tests.
+ *
+ * Adapted from: https://github.com/Cristy94/canvas-mock
+ */
+
+var canvasMock;  // Use one canvas instance for all calls to createElement('canvas');
+
+
+function replaceCanvasContext (el) {
+  el.getContext = function() {
+    return {
+      fillRect: function() {},
+      clearRect: function(){},
+      getImageData: function(x, y, w, h) {
+        return  {
+          data: new Array(w*h*4)
+        };
+      },
+      putImageData: function() {},
+      createImageData: function(){ return []},
+      setTransform: function(){},
+      drawImage: function(){},
+      save: function(){},
+      fillText: function(){},
+      restore: function(){},
+      beginPath: function(){},
+      moveTo: function(){},
+      lineTo: function(){},
+      closePath: function(){},
+      stroke: function(){},
+      translate: function(){},
+      scale: function(){},
+      rotate: function(){},
+      arc: function(){},
+      fill: function(){},
+
+      //
+      // Following added for vis.js unit tests
+      //
+
+      measureText: function(text) {
+        return {
+          width: 12*text.length,
+          height: 14
+        };
+      },
+    };
+  }
+};
+
+
+/**
+ * Overrides document.createElement(), in order to supply a custom canvas element.
+ *
+ * In the canvas element, getContext() is overridden in order to supply a simple 
+ * mock object for the 2D context. For all other elements, the call functions unchanged.
+ *
+ * The override is only done if there is no 2D context already present.
+ * This allows for normal running in a browser, and for node.js the usage of 'canvas'.
+ *
+ * @param {object} the current global window object. This can possible come from module 'jsdom',
+ *                 when running under node.js.
+ */
+function mockify(window) {
+  var d = window.document;
+  var f = window.document.createElement;
+
+  // Check if 2D context already present. That happens either when running in a browser,
+  // or this is node.js with 'canvas' installed. 
+  var ctx = d.createElement('canvas').getContext('2d');
+  if (ctx !== null && ctx !== undefined) {
+    //console.log('2D context is present, no need to override');
+    return;
+  }
+
+  window.document.createElement = function(param) {
+    if (param === 'canvas') {
+      if (canvasMock === undefined) {
+        canvasMock = f.call(d, 'canvas');
+        replaceCanvasContext(canvasMock);
+      }
+      return canvasMock;
+    } else {
+      return f.call(d, param);
+    }
+  };
+}
+
+module.exports = mockify;