do not create WebGL ctx in 'pick' canvas on graphs w/o parcoords

- so that we create two (not three) contexts in scattergl graph
  as we in versions before 1.36.0

Author: etpinard

src/lib/prepare_regl.js

@@ -23,8 +23,12 @@ var createRegl = require('regl');
  * @param {array} extensions : list of extension to pass to createRegl
  */
 module.exports = function prepareRegl(gd, extensions) {
-    gd._fullLayout._glcanvas.each(function(d) {
+    var fullLayout = gd._fullLayout;
+
+    fullLayout._glcanvas.each(function(d) {
         if(d.regl) return;
+        // only parcoords needs pick layer
+        if(d.pick && !fullLayout._has('parcoords')) return;
 
         d.regl = createRegl({
             canvas: this,

test/jasmine/tests/gl2d_plot_interact_test.js

@@ -948,6 +948,20 @@ describe('@gl Test gl2d plots', function() {
         .catch(failTest)
         .then(done);
     });
+
+    it('should create two WebGL context per graph', function(done) {
+        var fig = Lib.extendDeep({}, require('@mocks/gl2d_stacked_subplots.json'));
+
+        Plotly.plot(gd, fig).then(function() {
+            var cnt = 0;
+            d3.select(gd).selectAll('canvas').each(function(d) {
+                if(d.regl) cnt++;
+            });
+            expect(cnt).toBe(2);
+        })
+        .catch(failTest)
+        .then(done);
+    });
 });
 
 describe('Test scattergl autorange:', function() {

test/jasmine/tests/parcoords_test.js

@@ -770,8 +770,8 @@ describe('@gl parcoords Lifecycle methods', function() {
 });
 
 describe('@gl parcoords basic use', function() {
-    var mockCopy,
-        gd;
+    var mockCopy;
+    var gd;
 
     beforeEach(function(done) {
         mockCopy = Lib.extendDeep({}, mock);
@@ -789,6 +789,14 @@ describe('@gl parcoords basic use', function() {
 
     afterAll(purgeGraphDiv);
 
+    it('should create three WebGL context per graph', function() {
+        var cnt = 0;
+        d3.select(gd).selectAll('canvas').each(function(d) {
+            if(d.regl) cnt++;
+        });
+        expect(cnt).toBe(3);
+    });
+
     it('`Plotly.plot` should have proper fields on `gd.data` on initial rendering', function() {
 
         expect(gd.data.length).toEqual(1);