Shit WORKS

Pendulum/Pendulum.js

@@ -32,17 +32,7 @@ var PEN_LENGTH = 0.8;
 // Rotation angle (degrees/second)
 var A_VELOCITY = 45.0;
 
-// Common functions:
+
-//  acquire_buffer: Get a vertex buffer object from gl
-function acquire_buffer(gl) {
-  // Create a buffer object
-  var vertexBuffer = gl.createBuffer();
-  if (!vertexBuffer) {
-    console.log('Failed to create the buffer object');
-    return -1;
-  }
-  return vertexBuffer;
-}
 
 function main() {
   // Retrieve <canvas> element

Pendulum/PendulumComponents.js

@@ -1,9 +1,32 @@
 // PendulumComponents.js
 // John Breaux  2022-06-30
-// Classes and data structures for Pendulum.js
+// Classes, functions, and data structures for Pendulum.js
 
 "use strict"
 
+// Common functions:
+//  acquire_buffer: Get a vertex buffer object from gl
+function acquire_buffer(gl) {
+   // Create a buffer object
+   var vertexBuffer = gl.createBuffer();
+   if (!vertexBuffer) {
+      console.log('Failed to create the buffer object');
+      return -1;
+   }
+   return vertexBuffer;
+}
+
+function acquire_VAO(gl, name, size, type) {
+   // Acquire a reference to named attr
+   var ret = gl.getAttribLocation(gl.program, name);
+   if (ret < 0) {
+      console.log(`Failed to get the storage location of ${name}`);
+      return -1;
+   }
+   gl.vertexAttribPointer(ret, size, type, false, 0, 0);
+   return ret;
+}
+
 // Classes
 //   homo2: Stores a 2d vector or point in homog. coords
 class homog2 {
@@ -76,17 +99,6 @@ class Anchor {
       gl.bindBuffer(gl.ARRAY_BUFFER, this.vertexBuffer);
       gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);
 
-      // Acquire a reference to a_Position
-      var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
-      if (a_Position < 0) {
-         console.log('Failed to get the storage location of a_Position');
-         return -1;
-      }
-      gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
-
-      // Enable the assignment to a_Position variable
-      gl.enableVertexAttribArray(a_Position);
-
       // Write date into the buffers
       gl.bufferData(gl.ARRAY_BUFFER, this.vertex_array(), gl.STATIC_DRAW);
       gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, this.index_array(), gl.STATIC_DRAW);
@@ -96,6 +108,12 @@ class Anchor {
       // Bind the buffers
       gl.bindBuffer(gl.ARRAY_BUFFER, this.vertexBuffer);
       gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);
+
+      // get a_Position
+      var a_Position = acquire_VAO(gl, 'a_Position', 2, gl.FLOAT);
+      // Enable the assignment to a_Position variable
+      gl.enableVertexAttribArray(a_Position);
+
       // Pass the rotation matrix to the vertex shader
       gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements);
       // Draw the Anchor
@@ -147,25 +165,21 @@ class Polygon {
       gl.bindBuffer(gl.ARRAY_BUFFER, this.vertexBuffer);
       gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);
 
-      // Acquire a reference to a_Position
-      var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
-      if (a_Position < 0) {
-         console.log('Failed to get the storage location of a_Position');
-         return -1;
-      }
-      gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
-
-      // Enable the assignment to a_Position variable
-      gl.enableVertexAttribArray(a_Position);
-
       // Write date into the buffers
       gl.bufferData(gl.ARRAY_BUFFER, this.vertex_array(), gl.STATIC_DRAW);
       gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, this.index_array(), gl.STATIC_DRAW);
    }
 
    draw(gl, modelMatrix, u_ModelMatrix) {
+      // Bind the buffers
       gl.bindBuffer(gl.ARRAY_BUFFER, this.vertexBuffer);
       gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);
+
+      // get a_Position
+      var a_Position = acquire_VAO(gl, 'a_Position', 2, gl.FLOAT);
+      // Enable the assignment to a_Position variable
+      gl.enableVertexAttribArray(a_Position);
+
       // Pass the rotation matrix to the vertex shader
       gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements);
       // Draw the shape