So I am working through the tutorials here: http://arcsynthesis.org/gltut/Basics/Tut01%20Making%20Shaders.html, and I don’t fully understand something. Here is the lwjgl port which someone posted in another thread someplace.
package rosick.mckesson.I.tut01;
import static org.lwjgl.opengl.GL11.*;
import static org.lwjgl.opengl.GL15.*;
import static org.lwjgl.opengl.GL20.*;
import static org.lwjgl.opengl.GL30.*;
import static org.lwjgl.opengl.GL32.*;
import java.nio.FloatBuffer;
import java.util.ArrayList;
import org.lwjgl.BufferUtils;
import rosick.LWJGLWindow;
/**
* Visit https://github.com/rosickteam/OpenGL for project info, updates and license terms.
*
* I. The Basics
* Chapter 1. Hello, Triangle!
* http://www.arcsynthesis.org/gltut/Basics/Tutorial%2001.html
* @author integeruser
*/
public class HelloTriangle01 extends LWJGLWindow {
public static void main(String[] args) {
new HelloTriangle01().start();
}
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
private final float vertexPositions[] = {
0.75f, 0.75f, 0.0f, 1.0f,
0.75f, -0.75f, 0.0f, 1.0f,
-0.75f, -0.75f, 0.0f, 1.0f
};
private final String strVertexShader =
"#version 330 \n" +
"\n" +
"layout(location = 0) in vec4 position;\n" +
"void main()\n" +
"{\n" +
" gl_Position = position;\n" +
"}";
private final String strFragmentShader =
"#version 330\n" +
"\n" +
"out vec4 outputCol;\n" +
"void main()\n" +
"{\n" +
" outputCol = vec4(1.0f, 1.0f, 1.0f, 1.0f);\n" +
"}";
private int theProgram;
private int positionBufferObject;
private int vao;
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
private void initializeProgram() {
ArrayList<Integer> shaderList = new ArrayList<>();
shaderList.add(createShader(GL_VERTEX_SHADER, strVertexShader));
shaderList.add(createShader(GL_FRAGMENT_SHADER, strFragmentShader));
theProgram = createProgram(shaderList);
for (Integer shader : shaderList) {
glDeleteShader(shader);
}
}
private void initializeVertexBuffer() {
FloatBuffer vertexPositionsBuffer = BufferUtils.createFloatBuffer(vertexPositions.length);
vertexPositionsBuffer.put(vertexPositions);
vertexPositionsBuffer.flip();
positionBufferObject = glGenBuffers();
glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject);
glBufferData(GL_ARRAY_BUFFER, vertexPositionsBuffer, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
@Override
protected void init() {
initializeProgram();
initializeVertexBuffer();
vao = glGenVertexArrays();
glBindVertexArray(vao);
}
@Override
protected void display() {
glClearColor(0f, 0f, 0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(theProgram);
glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 4, GL_FLOAT, false, 0, 0);
glDrawArrays(GL_TRIANGLES, 0, 3);
glDisableVertexAttribArray(0);
glUseProgram(0);
}
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
private int createShader(int eShaderType, String strShaderFile) {
int shader = glCreateShader(eShaderType);
glShaderSource(shader, strShaderFile);
glCompileShader(shader);
int status = glGetShader(shader, GL_COMPILE_STATUS);
if (status == 0) {
int infoLogLength = glGetShader(shader, GL_INFO_LOG_LENGTH);
String strInfoLog = glGetShaderInfoLog(shader, infoLogLength);
String strShaderType = null;
switch (eShaderType) {
case GL_VERTEX_SHADER:
strShaderType = "vertex";
break;
case GL_GEOMETRY_SHADER:
strShaderType = "geometry";
break;
case GL_FRAGMENT_SHADER:
strShaderType = "fragment";
break;
}
System.err.printf("Compile failure in %s shader:\n%s\n", strShaderType, strInfoLog);
}
return shader;
}
private int createProgram(ArrayList<Integer> shaderList) {
int program = glCreateProgram();
for (Integer shader : shaderList) {
glAttachShader(program, shader);
}
glLinkProgram(program);
int status = glGetProgram(program, GL_LINK_STATUS);
if (status == 0) {
int infoLogLength = glGetProgram(program, GL_INFO_LOG_LENGTH);
String strInfoLog = null;
strInfoLog = glGetProgramInfoLog(program, infoLogLength);
System.err.printf("Linker failure: %s\n", strInfoLog);
}
for (Integer shader : shaderList) {
glDetachShader(program, shader);
}
return program;
}
}
I understand what everything does except for this one bit of code:
vao = glGenVertexArrays();
glBindVertexArray(vao);
I don’t see “vao” referenced anywhere else in the program and when I comment these lines out the program still runs perfectly fine. Can anyone either help me understand this or point me in the right direction. I have been looking on google and whatnot for quite some time and still don’t really see what’s going on.
Thanks!
