Question

Just trying to get a triangle to draw to the screen, following a c++ tutorial. Tried to run the program and I get a NullPointerException on all Opengl calls. Also, I’m following a tutorial for opengl 3 although most of my calls are for earlier versions, is this just how lwjgl is set up, with the functions residing in the version where they originated from?

package examples;

import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.*;

import java.nio.*;

public class Triangle
{
// An array of 3 vectors which represents 3 vertices
static final float vertexData[] = {
   -1.0f, -1.0f, 0.0f,
   1.0f, -1.0f, 0.0f,
   0.0f,  1.0f, 0.0f,
};

// This will identify our vertex buffer
int vertexBufferID;

public static void main(String[] args)
{
    new Triangle();
}

public Triangle()
{
    // Allocate floatBuffer to hold vertex data
    FloatBuffer vertexBuffer = FloatBuffer.allocate(9);
    // Put float data into buffer and position ready to read
    vertexBuffer.put(vertexData).position(0);

    // Generate 1 buffer, put the resulting identifier in vertexbuffer
    IntBuffer buffers  = IntBuffer.allocate(1); // allocate
    GL15.glGenBuffers(buffers);
    vertexBufferID = buffers.get(0);

    // Binds a buffer to the ARRAY_BUFFER(target)   (1 at a time) (breaks other bonds)
    GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vertexBufferID);

    // Give our vertices to OpenGL. (creates store for data bound to target(above))
    GL15.glBufferData(GL15.GL_ARRAY_BUFFER, vertexBuffer,GL15.GL_STATIC_DRAW);

    try {
        Display.setDisplayMode(new DisplayMode(800,600));
        Display.create();
    } catch (LWJGLException e) {
        e.printStackTrace();
        System.exit(0);
    }

    while(!Display.isCloseRequested())
    {
        // Render
        // 1st attribute buffer : vertices
        GL20.glEnableVertexAttribArray(0); // enable vertex attribute index: 0
        GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vertexBufferID);

        // Specify location of vertex data for index 0
        GL33.glVertexAttribP1ui(0, GL11.GL_FLOAT, false, 0);

        // Draw the triangle!
        GL11.glDrawArrays(GL11.GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle

        GL20.glDisableVertexAttribArray(0);
    }

}
}

Answer 1

I think that the problem is you have to create the Display before any openGl call.
Try to move

   try {
        Display.setDisplayMode(new DisplayMode(800,600));
        Display.create();
    } catch (LWJGLException e) {
        e.printStackTrace();
        System.exit(0);
    }

at the top of the Triangle constructor.