OpenGL does not render my Mesh

Question

Using LWJGL I tried to render to render a simple Mesh on screen, but OpenGL decided to instead do nothing. :(

So I have a mesh class which creates a VBO. I can add some vertices which then are supposed to be drawn on screen.

public class Mesh {

    private int vbo;
    private int size = 0;

    public Mesh() {
        vbo = glGenBuffers();
    }

    public void addVertices(Vertex[] vertices) {
        size = vertices.length;

        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        glBufferData(GL_ARRAY_BUFFER, Util.createFlippedBuffer(vertices), GL_STATIC_DRAW);
    }

    public void draw() {
        glEnableVertexAttribArray(0);

        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        glVertexAttribPointer(0, 3, GL_FLOAT, false, Vertex.SIZE * 4, 0);

        glDrawArrays(GL_TRIANGLES, 0, size);

        glDisableVertexAttribArray(0);
    }

}

Here is how I add vertices to my mesh:

mesh = new Mesh();

Vertex[] vertices = new Vertex[] { new Vertex(new Vector3f(-1, -1, 0)),
                                   new Vertex(new Vector3f(-1, 1, 0)),
                                   new Vertex(new Vector3f(0, 1, 0)) };

mesh.addVertices(vertices);

I am pretty sure I added them in the correct (clock-wise) order.

And my OpenGL setup:

glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

glFrontFace(GL_CW);
glCullFace(GL_BACK);
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);

Calling glGetError() returns no error (0).

EDIT:

Well I found out that macs are little weird when it comes to OpenGL. I needed to use a VAO along with the VBO. Now it works fine. Thanks anyway!

addVertices is a misnomer, it replaces the existing vertices, setVertices would be a more accurate name. — ratchet freak
I know, but thanks for pointing it out. I only add them once. — user1734282

Jherico Jherico · Accepted Answer · 2014-07-15T19:26:30

I don't see anywhere you're specifying either a shader for output or a color, or a vertex array. Depending on which profile you're using you need to be doing one or more of these.

I would suggest checking / setting the following

Disable face culling to ensure that regardless of the winding you should see something
If you're requesting a core profile, you'll need a shader and quite possibly a vertex array object
If you're instead using a compatibility profile you should call glColor3f(1, 1, 1) in your draw call to ensure you're not drawing a black triangle
Are you clearing the color and depth framebuffers before your render?

OpenGL does not render my Mesh

2 Answers