[PoC] bypass ax.d2c for typedArray during ax.makeCalcdata

... and use typed array 'subarray' to slice coordinate arrays
    to series length

Author: etpinard

src/lib/index.js

@@ -28,7 +28,8 @@ lib.relinkPrivateKeys = require('./relink_private');
 lib.ensureArray = require('./ensure_array');
 
 var isArrayModule = require('./is_array');
-lib.isArrayOrTypedArray = isArrayModule.isArrayOrTypedArray
+lib.isTypedArray = isArrayModule.isTypedArray;
+lib.isArrayOrTypedArray = isArrayModule.isArrayOrTypedArray;
 
 var coerceModule = require('./coerce');
 lib.valObjectMeta = coerceModule.valObjectMeta;

src/lib/is_array.js

@@ -13,6 +13,8 @@ var ab = (typeof ArrayBuffer === 'undefined' || !ArrayBuffer.isView) ?
     {isView: function() { return false; }} :
     ArrayBuffer;
 
+exports.isTypedArray = ab.isView;
+
 exports.isArrayOrTypedArray = function(a) {
     return Array.isArray(a) || ab.isView(a);
 };

src/plots/cartesian/set_convert.js

@@ -405,10 +405,15 @@ module.exports = function setConvert(ax, fullLayout) {
         if(axLetter in trace) {
             arrayIn = trace[axLetter];
             len = trace._length || arrayIn.length;
-            arrayOut = new Array(len);
 
-            for(i = 0; i < len; i++) {
-                arrayOut[i] = ax.d2c(arrayIn[i], 0, cal);
+            if(ax.type === 'linear' && Lib.isTypedArray(arrayIn) && arrayIn.subarray) {
+                arrayOut = arrayIn.subarray(0, len);
+            } else {
+                arrayOut = new Array(len);
+
+                for(i = 0; i < len; i++) {
+                    arrayOut[i] = ax.d2c(arrayIn[i], 0, cal);
+                }
             }
         }
         else {

test/jasmine/tests/is_array_test.js

@@ -41,3 +41,45 @@ describe('isArrayOrTypedArray', function() {
         });
     });
 });
+
+describe('isTypedArray', function() {
+    function A() {}
+
+    var shouldPass = [
+        new Float32Array(1),
+        new Int32Array([1, 2, 3])
+    ];
+
+    var shouldFail = [
+        new Array(10),
+        [],
+        A,
+        new A(),
+        document,
+        window,
+        null,
+        undefined,
+        'string',
+        true,
+        false,
+        NaN,
+        Infinity,
+        /foo/,
+        '\n',
+        new Date(),
+        new RegExp('foo'),
+        new String('string')
+    ];
+
+    shouldPass.forEach(function(obj) {
+        it('treats ' + JSON.stringify(obj) + ' as an array', function() {
+            expect(Lib.isTypedArray(obj)).toBe(true);
+        });
+    });
+
+    shouldFail.forEach(function(obj) {
+        it('treats ' + JSON.stringify(obj !== window ? obj : 'window') + ' as NOT an array', function() {
+            expect(Lib.isTypedArray(obj)).toBe(false);
+        });
+    });
+});