Make sure gl.vertexAttribDivisor exists

Previously, this would have failed on WebGL1.

Author: dominicprior

src/attributes.js

@@ -198,8 +198,7 @@ function makeTypedArray(array, name) {
  * @property {boolean} [normalize] whether or not to normalize the data. Default = false
  * @property {number} [offset] offset into buffer in bytes. Default = 0
  * @property {number} [stride] the stride in bytes per element. Default = 0
- * @property {number} [divisor] the divisor in instances. Default = 0
- *    where as anything else = do call it with this value
+ * @property {number} [divisor] the divisor in instances. Default = 0.  Requires WebGL2 or the ANGLE_instanced_arrays extension.
  * @property {WebGLBuffer} buffer the buffer that contains the data for this attribute
  * @property {number} [drawType] the draw type passed to gl.bufferData. Default = gl.STATIC_DRAW
  * @memberOf module:twgl
@@ -221,8 +220,7 @@ function makeTypedArray(array, name) {
  * @property {boolean} [normalize] normalize for `vertexAttribPointer`. Default is true if type is `Int8Array` or `Uint8Array` otherwise false.
  * @property {number} [stride] stride for `vertexAttribPointer`. Default = 0
  * @property {number} [offset] offset for `vertexAttribPointer`. Default = 0
- * @property {number} [divisor] divisor for `vertexAttribDivisor`. Default = 0
- *    where as anything else = do call it with this value
+ * @property {number} [divisor] divisor for `vertexAttribDivisor`. Default = 0.  Requires WebGL2 or the ANGLE_instanced_arrays extension.
  * @property {string} [attrib] name of attribute this array maps to. Defaults to same name as array prefixed by the default attribPrefix.
  * @property {string} [name] synonym for `attrib`.
  * @property {string} [attribName] synonym for `attrib`.

src/programs.js

@@ -395,7 +395,9 @@ function floatAttribSetter(gl, index) {
       gl.enableVertexAttribArray(index);
       gl.vertexAttribPointer(
           index, b.numComponents || b.size, b.type || FLOAT, b.normalize || false, b.stride || 0, b.offset || 0);
-      gl.vertexAttribDivisor(index, b.divisor || 0);
+      if (gl.vertexAttribDivisor) {
+        gl.vertexAttribDivisor(index, b.divisor || 0);
+      }
     }
   };
 }
@@ -414,7 +416,9 @@ function intAttribSetter(gl, index) {
       gl.enableVertexAttribArray(index);
       gl.vertexAttribIPointer(
           index, b.numComponents || b.size, b.type || INT, b.stride || 0, b.offset || 0);
-      gl.vertexAttribDivisor(index, b.divisor || 0);
+      if (gl.vertexAttribDivisor) {
+        gl.vertexAttribDivisor(index, b.divisor || 0);
+      }
     }
   };
 }
@@ -433,7 +437,9 @@ function uintAttribSetter(gl, index) {
       gl.enableVertexAttribArray(index);
       gl.vertexAttribIPointer(
           index, b.numComponents || b.size, b.type || UNSIGNED_INT, b.stride || 0, b.offset || 0);
-      gl.vertexAttribDivisor(index, b.divisor || 0);
+      if (gl.vertexAttribDivisor) {
+        gl.vertexAttribDivisor(index, b.divisor || 0);
+      }
     }
   };
 }
@@ -456,7 +462,9 @@ function matAttribSetter(gl, index, typeInfo) {
       gl.enableVertexAttribArray(index + i);
       gl.vertexAttribPointer(
           index + i, size, type, normalize, stride, offset + rowOffset * i);
-      gl.vertexAttribDivisor(index + i, b.divisor || 0);
+      if (gl.vertexAttribDivisor) {
+        gl.vertexAttribDivisor(index + i, b.divisor || 0);
+      }
     }
   };
 }