code: /*
   * Copyright (c) 2021 Callum Newlands
   *
   *     This program is free software: you can redistribute it and/or modify
   *     it under the terms of the GNU General Public License as published by
   *     the Free Software Foundation, either version 3 of the License, or
   *     (at your option) any later version.
   *
   *     The additional term of 7.b applies: Requiring preservation of specified
   *     reasonable legal notices or author attributions in that material or in the
   *     Appropriate Legal Notices displayed by works containing it
   *
   *     This program is distributed in the hope that it will be useful,
   *     but WITHOUT ANY WARRANTY; without even the implied warranty of
   *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *     GNU General Public License for more details.
   *
   *     You should have received a copy of the GNU General Public License
   *     along with this program.  If not, see <https://www.gnu.org/licenses/>.
   */
  
  package modeldata.meshdata;
  
  import java.util.List;
  
  import static org.lwjgl.opengl.GL11C.GL_TRIANGLES;
  import static org.lwjgl.opengl.GL11C.GL_UNSIGNED_INT;
  import static org.lwjgl.opengl.GL11C.glDrawElements;
  import static org.lwjgl.opengl.GL30.glBindVertexArray;
  import static org.lwjgl.opengl.GL30.glGenVertexArrays;
  import static org.lwjgl.opengl.GL31.glDrawElementsInstanced;
  
  import lombok.Setter;
  
  /**
   * Represents a Vertex Array Object (VAO)
   * A VAO stores references to VBOs and EBOs
   */
  public class VertexArray {
  
  	private final int handle;
  	private final int numberOfVertices;
  	private final int numberOfIndices;
  	@Setter
  	private boolean isInstanced;
  
  	public VertexArray(final float[] vertices, final int numberOfVertices, final int[] indices, final List<VertexAttribute> attributes) {
  
  		handle = glGenVertexArrays();
  
  		this.numberOfVertices = numberOfVertices;
  		VertexBuffer vertexBuffer = new VertexBuffer(numberOfVertices, attributes);
  		vertexBuffer.setVertexData(vertices);
  		bindVertexBuffer(vertexBuffer);
  
  		glBindVertexArray(handle);
  		this.numberOfIndices = indices.length;
  		ElementBuffer elementBuffer = new ElementBuffer(indices.length);
  		elementBuffer.setIndexData(indices);
  		elementBuffer.bind();
  
  		glBindVertexArray(0);
  
  		isInstanced = attributes.contains(VertexAttribute.INSTANCE_MODEL.get(0));
  	}
  
  	public void bindVertexBuffer(VertexBuffer vertexBuffer) {
  		glBindVertexArray(handle);
  
  		vertexBuffer.bind();
  		vertexBuffer.freeBufferData();
  		glBindVertexArray(0);
  	}
  
  	public void draw() {
  		glBindVertexArray(handle);
  		if (isInstanced) {
  			draw(1);
  		} else {
  			glDrawElements(GL_TRIANGLES, numberOfIndices, GL_UNSIGNED_INT, 0);
  		}
  		glBindVertexArray(0);
  	}
  
  	public void draw(int numberOfInstances) {
  		glBindVertexArray(handle);
  		if (isInstanced) {
  			glDrawElementsInstanced(GL_TRIANGLES, numberOfIndices, GL_UNSIGNED_INT, 0, numberOfInstances);
  		} else {
  			throw new RuntimeException("draw() called with int parameter for non-instanced VAO");
  		}
  		glBindVertexArray(0);
  	}
  }