Question

I tried to use this tutorial with Golang: http://www.opengl-tutorial.org/beginners-tutorials/tutorial-2-the-first-triangle/
The go-version opens the window and makes the background blue, but it doesn’t show the triangle. The c-version does show it.
This is the code in Go:

err := glfw.Init()
if err != nil {
    log.Fatal("Failed to init GLFW: " + err.Error())
}

err = glfw.OpenWindow(1024, 768, 0,0,0,0, 32,0, glfw.Windowed)
if err != nil {
    log.Fatal("Failed to open GLFW window: " + err.Error())
}

if gl.Init() != 0 {
    log.Fatal("Failed to init GL")
}

gl.ClearColor(0.0, 0.0, 0.3, 0.0)

// create vertexbuffer
gVertexBufferData := []float32{-1.0,-1.0,0.0, 1.0,-1.0,0.0, 0.0,1.0,0.0}
vertexBuffer := gl.GenBuffer()
vertexBuffer.Bind(gl.ARRAY_BUFFER)
gl.BufferData(gl.ARRAY_BUFFER, len(gVertexBufferData), gVertexBufferData, gl.STATIC_DRAW)

for {
    // clear screen
    gl.Clear(gl.COLOR_BUFFER_BIT)

    // first attribute buffer: vertices
    var vertexAttrib gl.AttribLocation = 0
    vertexAttrib.EnableArray()
    vertexBuffer.Bind(gl.ARRAY_BUFFER)
    var f float32 = 0.0
    vertexAttrib.AttribPointer(
        3,     // size
        false, // normalized?
        0,     // stride
        &f) // array buffer offset

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

    vertexAttrib.DisableArray()

    glfw.SwapBuffers()
}

And this is the code in c which works:

if(!glfwInit())
    return -1;

if(!glfwOpenWindow( 1024, 768, 0,0,0,0, 32,0, GLFW_WINDOW ))
    return -1;

if(glewInit() != GLEW_OK)
    return -1;

glClearColor(0.0f, 0.0f, 0.3f, 0.0f);

GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);

static const GLfloat g_vertex_buffer_data[] = { 
    -1.0f, -1.0f, 0.0f,
    1.0f, -1.0f, 0.0f,
    0.0f,  1.0f, 0.0f,
};
GLuint vertexbuffer;
glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

while(1) {
    glClear( GL_COLOR_BUFFER_BIT );

    // 1rst attribute buffer : vertices
    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    glVertexAttribPointer(
        0,
        3, // size
        GL_FLOAT, // type
        GL_FALSE, // normalized?
        0, // stride
        (void*)0 // array buffer offset
    );

    // Draw the triangle !
    glDrawArrays(GL_TRIANGLES, 0, 3); // From index 0 to 3 -> 1 triangle

    glDisableVertexAttribArray(0);

    // Swap buffers
    glfwSwapBuffers();
}

Maybe I give vertexAttrib.AttribPointer() the wrong arguments, because I’m not sure what to give it instead of (void*)0. I tried nil, but that caused the application to crash. &gVertexBufferData[0] doesn’t work either.

I’m using github.com/banthar/gl as glew-wrapper, go 1.0.2 and ubuntu 12.04 amd64.

EDIT update:

glGetError doesn’t give any errors

Answer 1

I had the same problem and I managed to fix it after looking at your post, so first of all thanks a lot.

I managed to display a triangle by using the work branch of banthar bindings with this call to AttribPointer:

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

and by passing the size in bytes to BufferData.

[...]
data := []float32{0, 1, 0, -1, -1, 0, 1, -1, 0}
[...]
gl.BufferData(gl.ARRAY_BUFFER, len(data)*4, data, gl.STATIC_DRAW)
[...]

There is probably a better way to pass the right length.