fix: #396 by changing documentation and adding unit test

Author: robertleeplummerjr

README.md

@@ -505,15 +505,15 @@ Sometimes you want to do multiple math operations on the gpu without the round t
 _**Note:**_ Kernels can have different output sizes.
 ```js
 const add = gpu.createKernel(function(a, b) {
-  return a + b;
+  return a[this.thread.x] + b[this.thread.x];
 }).setOutput([20]);
 
 const multiply = gpu.createKernel(function(a, b) {
-  return a * b;
+  return a[this.thread.x] * b[this.thread.x];
 }).setOutput([20]);
 
 const superKernel = gpu.combineKernels(add, multiply, function(a, b, c) {
-  return multiply(add(a[this.thread.x], b[this.thread.x]), c[this.thread.x]);
+  return multiply(add(a, b), c);
 });
 
 superKernel(a, b, c);

test/all.html

@@ -153,6 +153,7 @@
 <script type="module" src="issues/359-addfunction-params-wrong.js"></script>
 <script type="module" src="issues/382-bad-constant.js"></script>
 <script type="module" src="issues/390-thread-assignment.js"></script>
+<script type="module" src="issues/396-combine-kernels-example.js"></script>
 <script type="module" src="issues/399-double-definition.js"></script>
 <script type="module" src="issues/401-cpu-canvas-check.js"></script>
 <script type="module" src="issues/422-warnings.js"></script>

test/issues/396-combine-kernels-example.js

@@ -0,0 +1,52 @@
+const { assert, skip, test, module: describe } = require('qunit');
+const { GPU } = require('../../src');
+
+describe('issues #396 - combine kernels example');
+
+function combineKernelsExample(mode) {
+  const gpu = new GPU({ mode });
+  const add = gpu.createKernel(function(a, b) {
+    return a[this.thread.x] + b[this.thread.x];
+  }).setOutput([5]);
+
+  const multiply = gpu.createKernel(function(a, b) {
+    return a[this.thread.x] * b[this.thread.x];
+  }).setOutput([5]);
+
+  const superKernel = gpu.combineKernels(add, multiply, function(a, b, c) {
+    return multiply(add(a, b), c);
+  });
+
+  const result = superKernel([1,2,3,4,5],[1,2,3,4,5],[1,2,3,4,5]);
+  assert.deepEqual(Array.from(result), [2,
+    8,
+    18,
+    32,
+    50
+  ]);
+  gpu.destroy();
+}
+
+test('auto', () => {
+  combineKernelsExample();
+});
+
+test('gpu', () => {
+  combineKernelsExample('gpu');
+});
+
+(GPU.isWebGLSupported ? test : skip)('webgl', () => {
+  combineKernelsExample('webgl');
+});
+
+(GPU.isWebGL2Supported ? test : skip)('webgl2', () => {
+  combineKernelsExample('webgl2');
+});
+
+(GPU.isHeadlessGLSupported ? test : skip)('headlessgl', () => {
+  combineKernelsExample('headlessgl');
+});
+
+test('cpu', () => {
+  combineKernelsExample('cpu');
+});