Add some comments to Mesh class

engine/src/main/java/com/bartlomiejpluta/base/engine/core/gl/object/mesh/Mesh.java

@@ -20,6 +20,16 @@ import static org.lwjgl.opengl.GL20.*;
 import static org.lwjgl.opengl.GL30.*;
 
 public class Mesh implements Renderable, Disposable {
+   // default.vs: layout(location=0) in vec2 position;
+   //                             ^        ^
+   private static final int POSITION_VECTOR_LAYOUT_INDEX = 0;
+   private static final int POSITION_VECTOR_LENGTH = 2;
+
+   // default.vs: layout(location=1) in vec2 texCoord;
+   //                             ^        ^
+   private static final int TEX_COORDS_VECTOR_LAYOUT_INDEX = 1;
+   private static final int TEX_COORDS_VECTOR_LENGTH = 2;
+
    private final int vaoId;
    private final List<Integer> vboIds = new ArrayList<>(2);
    private final int elementsCount;
@@ -43,14 +53,14 @@ public class Mesh implements Renderable, Disposable {
          vboIds.add(vboId);
          glBindBuffer(GL_ARRAY_BUFFER, vboId);
          glBufferData(GL_ARRAY_BUFFER, stack.mallocFloat(vertices.length).put(vertices).flip(), GL_STATIC_DRAW);
-         glVertexAttribPointer(0, 2, GL_FLOAT, false, 0, 0);
+         glVertexAttribPointer(POSITION_VECTOR_LAYOUT_INDEX, POSITION_VECTOR_LENGTH, GL_FLOAT, false, 0, 0);
 
          // Texture Coordinates VBO
          vboId = glGenBuffers();
          vboIds.add(vboId);
          glBindBuffer(GL_ARRAY_BUFFER, vboId);
          glBufferData(GL_ARRAY_BUFFER, stack.mallocFloat(texCoords.length).put(texCoords).flip(), GL_STATIC_DRAW);
-         glVertexAttribPointer(1, 2, GL_FLOAT, false, 0, 0);
+         glVertexAttribPointer(TEX_COORDS_VECTOR_LAYOUT_INDEX, TEX_COORDS_VECTOR_LENGTH, GL_FLOAT, false, 0, 0);
 
          // Elements VBO
          vboId = glGenBuffers();
@@ -122,16 +132,53 @@ public class Mesh implements Renderable, Disposable {
    }
 
    public static Mesh quad(float width, float height, float originX, float originY) {
-      var vertices = new float[] {
+      //  1 ----------- 2
-         -originX, -originY,
+      //  |             |
-         -originX, height - originY,
+      //  |             |
-         width - originX, height - originY,
+      //  |             |
-         width - originX, - originY
+      //  |             |
+      //  |             |
+      //  0 ----------- 3
+      var vertices = new float[]{
+            -originX, -originY,                   // 0 - bottom left
+            -originX, height - originY,           // 1 - top left
+            width - originX, height - originY,    // 2 - top right
+            width - originX, -originY             // 3 - bottom right
       };
 
-      var texCoords = new float[] { 0, 0, 0, 1, 1, 1, 1, 0 };
+      // Texture:           Quad:
+      // (0,1) ---- (1,1)    1 ----------- 2
+      // |          |        |             |
+      // |          |  =>    |   TEKSTURA  |
+      // |          |        |             |
+      // (0,0) ---- (1,0)    0 ----------- 3
+      var texCoords = new float[]{
+            0, 0,  // 0 - bottom left
+            0, 1,  // 1 - top left
+            1, 1,  // 2 - top right
+            1, 0   // 3 - bottom right
+      };
 
-      var elements = new int[] { 0, 1, 2, 2, 3, 0 };
+
+      var elements = new int[]{
+            // First triangle: indices 0-1-2
+            // 1 ----------- 2
+            // |XXXXXXXXXXX╱ |
+            // |XXXXXXXX╱    |
+            // |XXXXX╱       |
+            // |XX╱          |
+            // 0 ----------- 3
+            0, 1, 2,
+
+            // Second triangle: indices 2-3-0
+            // 1 ----------- 2
+            // |           ╱X|
+            // |        ╱XXXX|
+            // |     ╱XXXXXXX|
+            // |  ╱XXXXXXXXXX|
+            // 0 ----------- 3
+            2, 3, 0
+      };
 
       return new Mesh(vertices, texCoords, elements);
    }