Use an index buffer instead

src/OpenGL.cake

@@ -85,24 +85,31 @@ void main()\n
       (glDeleteShader vertex-shader)
       (glDeleteShader fragment-shader)))
 
-    (var triangle-array-object gl-id)
-    (glGenVertexArrays 1 (addr triangle-array-object))
-    (var start-triangles int 0)
-    (var num-triangles int 3)
+    (var mesh-array-object gl-id)
+    (glGenVertexArrays 1 (addr mesh-array-object))
+    (var start-indices int 0)
+    (var num-indices int 3)
     (scope
+     (var-static vertices ([] float)
+       (array
+        0.25f 0.25f 0.25f
+        0.75f 0.25f 0.25f
+        0.75f 0.75f 0.25f
+        0.25f 0.75f 0.25f))
+     (var-static indices ([] int)
+       (array 0 1 3
+              1 2 3))
+
+     (set num-indices (array-size indices))
+
      ;; From this point on, configuration will be saved in the vertex array object
-     (glBindVertexArray triangle-array-object)
+     (glBindVertexArray mesh-array-object)
 
      ;; Make our triangle vertex array
      (var vertex-buffer-id gl-id)
      (glGenBuffers 1 (addr vertex-buffer-id))
      (glBindBuffer GL_ARRAY_BUFFER vertex-buffer-id)
 
-     (var-static vertices ([] float)
-       (array
-        0.25f 0.25f 0.25f
-        0.5f 0.25f 0.25f
-        0.5f 0.75f 0.25f))
      (glBufferData GL_ARRAY_BUFFER (sizeof vertices) vertices GL_STATIC_DRAW)
 
      (var layout-location int 0) ;; Should match vertex shader layout
@@ -112,7 +119,14 @@ void main()\n
                             (* 3 (sizeof float))
                             ;; Buffer start offset
                             (type-cast 0 (* void)))
-     (glEnableVertexAttribArray layout-location))
+     (glEnableVertexAttribArray layout-location)
+
+     ;; Make our index buffer array
+     (var index-buffer-id gl-id)
+     (glGenBuffers 1 (addr index-buffer-id))
+     (glBindBuffer GL_ELEMENT_ARRAY_BUFFER index-buffer-id)
+
+     (glBufferData GL_ELEMENT_ARRAY_BUFFER (sizeof indices) indices GL_STATIC_DRAW))
 
     (var exit-reason (* (const char)) null)
     (while (not exit-reason)
@@ -128,8 +142,10 @@ void main()\n
       (glClear GL_COLOR_BUFFER_BIT)
 
       (glUseProgram shader-program)
-      (glBindVertexArray triangle-array-object)
-      (glDrawArrays GL_TRIANGLES start-triangles num-triangles)
+      (glBindVertexArray mesh-array-object)
+      (glDrawElements GL_TRIANGLES num-indices GL_UNSIGNED_INT
+                      (type-cast 0 (* void)))
+      (glBindVertexArray 0) ;; Unbind
 
       (SDL_GL_SwapWindow window))