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.nio.FloatBuffer;
  import java.util.List;
  
  import static org.lwjgl.opengl.GL11C.GL_FLOAT;
  import static org.lwjgl.opengl.GL15.GL_ARRAY_BUFFER;
  import static org.lwjgl.opengl.GL15.GL_STATIC_DRAW;
  import static org.lwjgl.opengl.GL15.glBindBuffer;
  import static org.lwjgl.opengl.GL15.glBufferData;
  import static org.lwjgl.opengl.GL15.glGenBuffers;
  import static org.lwjgl.opengl.GL20C.glEnableVertexAttribArray;
  import static org.lwjgl.opengl.GL20C.glVertexAttribPointer;
  import static org.lwjgl.opengl.GL33.glVertexAttribDivisor;
  
  import org.lwjgl.system.MemoryUtil;
  
  /**
   * Represents a Vertex Buffer Object (VBO)
   * A VBO stores vertex data on the GPU
   */
  public class VertexBuffer {
  	private static final int SIZE_OF_FLOAT_BYTES = 4;
  
  	private final List<VertexAttribute> attributes;
  	private FloatBuffer dataBuffer;
  	// Distance between the same attribute for consecutive vertices (= vertex size in bytes)
  	private final int stride;
  	private final int numberOfVertices;
  	private final int handle;
  
  	public VertexBuffer(final int numberOfVertices, final List<VertexAttribute> attributes) {
  		this.attributes = attributes;
  		this.numberOfVertices = numberOfVertices;
  		final int floatComponentsPerVertex = getFloatComponentsPerVertex(attributes);
  		this.stride = floatComponentsPerVertex * SIZE_OF_FLOAT_BYTES;
  		this.dataBuffer = MemoryUtil.memAllocFloat(numberOfVertices * floatComponentsPerVertex);
  		this.handle = glGenBuffers();
  	}
  
  	private static int getFloatComponentsPerVertex(final List<VertexAttribute> attributes) {
  		return attributes.stream().mapToInt(VertexAttribute::getNumberOfFloatComponents).sum();
  	}
  
  	public void setVertexData(final float[] vertexData) {
  		dataBuffer.put(vertexData).flip();
  	}
  
  	public void bind() {
  		glBindBuffer(GL_ARRAY_BUFFER, handle);
  		glBufferData(GL_ARRAY_BUFFER, dataBuffer, GL_STATIC_DRAW);
  
  		int offset = 0;
  		for (VertexAttribute attribute : attributes) {
  			glVertexAttribPointer(
  					attribute.getLocation(),
  					attribute.getNumberOfFloatComponents(),
  					GL_FLOAT,
  					false,
  					stride,
  					offset);
  			glEnableVertexAttribArray(attribute.getLocation());
  			glVertexAttribDivisor(
  					attribute.getLocation(),
  					attribute.getDivisor());
  			offset += attribute.getNumberOfFloatComponents() * SIZE_OF_FLOAT_BYTES;
  		}
  
  		glBindBuffer(GL_ARRAY_BUFFER, 0);
  	}
  
  	public void freeBufferData() {
  		if (dataBuffer != null) {
  			MemoryUtil.memFree(dataBuffer);
  		}
  	}
  }
  