#55 Create shader loader system.

shaders/README.md

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+All game shaders are placed in this directory.
+
+Only `.vert` and `.frag` files are loaded; all other extensions are ignored.
+
+Shader language used: GLSL ES2.
+
+Usage:
+```js
+import getShader from './shaders';
+const shader = getShader('shaderName');
+console.log(shader);
+// { vertex: '...', fragment: '...' }
+```
+
+References:
+ * https://www.khronos.org/files/opengles_shading_language.pdf
+ * https://www.khronos.org/opengl/wiki/Shader
+ * https://www.khronos.org/opengl/wiki/Vertex_Shader
+ * https://www.khronos.org/opengl/wiki/Fragment_Shader

shaders/index.js

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+import fs from 'fs';
+
+// All loaded shaders are stored here.
+const shader = {};
+// Amount of files that need to be loaded / skipped.
+let shadersToLoad = null;
+// If true, all shaders have been loaded.
+let discoveryComplete = false;
+// Used as keys in `shader`.
+const term = {
+  vert: 'vertexShader',
+  frag: 'fragmentShader',
+}
+
+// Counts the amount of shaders loaded. Calls 'onComplete' if loaded shader
+// count equals initial total count.
+function checkAllComplete (onComplete) {
+  if (!--shadersToLoad) {
+    discoveryComplete = true;
+    onComplete();
+  }
+}
+
+function discoverShaders(onComplete=()=>{}) {
+  if (discoveryComplete) {
+    return onComplete();
+  }
+  fs.readdir('./shaders', (error, files) => {
+    if (error) {
+      discoveryComplete = true;
+      console.error('Could not read shader directory.');
+      return onComplete();
+    }
+
+    shadersToLoad = files.length;
+    for (let i = 0, len = files.length; i < len; i++) {
+      const file = files[i];
+      if (!file.includes('.vert') && !file.includes('.frag')) {
+        // We currently support .vert and .frag. This also weeds out .js.
+        checkAllComplete(onComplete);
+        continue;
+      }
+
+      fs.readFile('./shaders/' + file, (error, data) => {
+        if (error) {
+          console.error(`Could not read shader '${file}':`, error);
+          return checkAllComplete(onComplete);
+        }
+
+        const baseName = file.replace(/\.[^/.]+$/, '');
+        const shaderType = term[file.split('.').pop()];
+
+        if (!shader[baseName]) {
+          shader[baseName] = {};
+        }
+        shader[baseName][shaderType] = data.toString();
+        checkAllComplete(onComplete);
+      });
+    }
+  });
+}
+
+function getShader(name) {
+  return shader[name];
+}
+
+export {
+  discoverShaders,
+  getShader,
+}