Why doesn't this OpenGL program draw a triangle?

Question

I am trying to learn modern OpenGL and want to draw a triangle like this:

I am following this tutorial: www.opengl-tutorial.org/beginners-tutorials/tutorial-2-the-first-triangle/, but all I get is the dark blue background (clear color). What could be wrong with this code?

I am writing this in Go and tried to run it on Ubuntu and OS X. Note: I am using the glfw 3 library instead of glfw 2.7 that is used in the tutorial.

I think the relevant parts are:

func setup() {
    gl.ClearColor(0.0, 0.0, 0.4, 0.0)

    makeProgram(vertexShaderSource,fragmentShaderSource)

    vertexBufferData := []float32{
        -1,-1,0,
         1,-1,0,
         0, 1,0,
    }

    vertexBuffer = gl.GenBuffer()
    vertexBuffer.Bind(gl.ARRAY_BUFFER)
    gl.BufferData(gl.ARRAY_BUFFER, len(vertexBufferData)*4, vertexBufferData, gl.STATIC_DRAW)
}

func draw() {
    gl.Clear(gl.COLOR_BUFFER_BIT)

    program.Use()
    // first attribute buffer: vertices
    var vertexAttrib = program.GetAttribLocation("vertexPosition_modelspace")
    vertexAttrib.EnableArray()
    vertexBuffer.Bind(gl.ARRAY_BUFFER)
    var f float32 = 0.0

    vertexAttrib.AttribPointer(
        3,     // size
        gl.FLOAT, // type
        false, // normalized
        0,     // stride
        &f) // array buffer offset

    // draw the triangle
    gl.DrawArrays(gl.TRIANGLES, 0, 3)

    vertexAttrib.DisableArray()

}

Link to the full code: https://gist.github.com/mbertschler/8672365

I already tried to debug this with OpenGL Profiler on OSX, but it shows me no errors so far.

Answer 1

The error was in:

var f float32 = 0.0

vertexAttrib.AttribPointer(
    3,     // size
    gl.FLOAT, // type
    false, // normalized
    0,     // stride
    &f) // array buffer offset

Although it seemed to work for the OP of this question: OpenGL Vertex Buffer doesn't draw anything in golang it doesn't with my program. The accepted answer had the right version of this call. It works with nil as array buffer offset.

Working Code:

(At least for github.com/go-gl/gl bindings)

vertexAttrib.AttribPointer(
    3,     // size
    gl.FLOAT, // type
    false, // normalized
    0,     // stride
    nil) // array buffer offset