From a5b656e44e7205b38dff45b06ece5832bc724cb2 Mon Sep 17 00:00:00 2001
From: mikolalysenko <mikolalysenko@gmail.com>
Date: Sun, 11 Sep 2016 10:55:57 -0400
Subject: [PATCH 1/2] test case for new elements constructor

---
 test/elements-length.js | 32 ++++++++++++++++++++++++++++++++
 test/util/index.js      |  1 +
 2 files changed, 33 insertions(+)
 create mode 100644 test/elements-length.js

diff --git a/test/elements-length.js b/test/elements-length.js
new file mode 100644
index 00000000..f7b47647
--- /dev/null
+++ b/test/elements-length.js
@@ -0,0 +1,32 @@
+var tape = require('tape')
+var createContext = require('./util/create-context')
+var createREGL = require('../regl')
+
+tape('elements - length', function (t) {
+  var gl = createContext(5, 5)
+  var regl = createREGL(gl)
+
+  var N = 5
+
+  var cellsBuffer = regl.elements({
+    type: 'uint16',
+    usage: 'dynamic',
+    primitive: 'triangles',
+    count: N * 3
+  })
+
+  t.equals(cellsBuffer._elements.buffer.byteLength, N * 3 * 2, 'count')
+
+  var cells2Buffer = regl.elements({
+    type: 'uint16',
+    usage: 'dynamic',
+    primitive: 'triangles',
+    length: N * 2 * 3
+  })
+
+  t.equals(cells2Buffer._elements.vertCount, N * 3, 'count')
+
+  regl.destroy()
+  createContext.destroy(gl)
+  t.end()
+})
diff --git a/test/util/index.js b/test/util/index.js
index 6a37813b..b9d0dd6d 100644
--- a/test/util/index.js
+++ b/test/util/index.js
@@ -60,3 +60,4 @@ require('../attribute-constants')
 require('../attributes-nested')
 require('../buffer-update')
 require('../elements-update')
+require('../elements-length')

From e407d227dd4b0911235fd5ee1b555702f5e270a3 Mon Sep 17 00:00:00 2001
From: mikolalysenko <mikolalysenko@gmail.com>
Date: Sun, 11 Sep 2016 10:56:09 -0400
Subject: [PATCH 2/2] infer length and count for elements

---
 lib/elements.js | 78 +++++++++++++++++++++++++------------------------
 1 file changed, 40 insertions(+), 38 deletions(-)

diff --git a/lib/elements.js b/lib/elements.js
index 45d5bee2..5a7ee740 100644
--- a/lib/elements.js
+++ b/lib/elements.js
@@ -75,21 +75,29 @@ module.exports = function wrapElementsState (gl, extensions, bufferState, stats)
     count,
     byteLength,
     type) {
-    var predictedType = type
-    if (!type && (
-        !isTypedArray(data) ||
-       (isNDArrayLike(data) && !isTypedArray(data.data)))) {
-      predictedType = extensions.oes_element_index_uint
-        ? GL_UNSIGNED_INT
-        : GL_UNSIGNED_SHORT
-    }
     elements.buffer.bind()
-    bufferState._initBuffer(
-      elements.buffer,
-      data,
-      usage,
-      predictedType,
-      3)
+    if (data) {
+      var predictedType = type
+      if (!type && (
+          !isTypedArray(data) ||
+         (isNDArrayLike(data) && !isTypedArray(data.data)))) {
+        predictedType = extensions.oes_element_index_uint
+          ? GL_UNSIGNED_INT
+          : GL_UNSIGNED_SHORT
+      }
+      bufferState._initBuffer(
+        elements.buffer,
+        data,
+        usage,
+        predictedType,
+        3)
+    } else {
+      gl.bufferData(GL_ELEMENT_ARRAY_BUFFER, byteLength, usage)
+      elements.buffer.dtype = dtype || GL_UNSIGNED_BYTE
+      elements.buffer.usage = usage
+      elements.buffer.dimension = 3
+      elements.buffer.byteLength = byteLength
+    }
 
     var dtype = type
     if (!type) {
@@ -212,9 +220,6 @@ module.exports = function wrapElementsState (gl, extensions, bufferState, stats)
               'invalid vertex count for elements')
             vertCount = options.count | 0
           }
-          if ('length' in options) {
-            byteLength = options.length | 0
-          }
           if ('type' in options) {
             check.parameter(
               options.type,
@@ -222,28 +227,25 @@ module.exports = function wrapElementsState (gl, extensions, bufferState, stats)
               'invalid buffer type')
             dtype = elementTypes[options.type]
           }
+          if ('length' in options) {
+            byteLength = options.length | 0
+          } else {
+            byteLength = vertCount
+            if (dtype === GL_UNSIGNED_SHORT || dtype === GL_SHORT) {
+              byteLength *= 2
+            } else if (dtype === GL_UNSIGNED_INT || dtype === GL_INT) {
+              byteLength *= 4
+            }
+          }
         }
-        if (data) {
-          initElements(
-            elements,
-            data,
-            usage,
-            primType,
-            vertCount,
-            byteLength,
-            dtype)
-        } else {
-          var _buffer = elements.buffer
-          _buffer.bind()
-          gl.bufferData(GL_ELEMENT_ARRAY_BUFFER, byteLength, usage)
-          _buffer.dtype = dtype || GL_UNSIGNED_BYTE
-          _buffer.usage = usage
-          _buffer.dimension = 3
-          _buffer.byteLength = byteLength
-          elements.primType = primType < 0 ? GL_TRIANGLES : primType
-          elements.vertCount = vertCount < 0 ? 0 : vertCount
-          elements.type = _buffer.dtype
-        }
+        initElements(
+          elements,
+          data,
+          usage,
+          primType,
+          vertCount,
+          byteLength,
+          dtype)
       }
 
       return reglElements