How to set up vertex attributes in OpenGL?

问题:

I am trying to create a VBO for a simple rectangle. The GL is set up to use the core profile (GL: 3.2, GLSL: 1.5, inside an NSView in Cocoa).

I spent hours trying to figure out how to draw a simple rectangle in OpenGL. It seems really hard to find any decent tutorials on the core profile. The best I could find was this tutorial.

I adapted it to my needs and came up with the following code:

GLfloat vertices[] = { 1.0, -1.0, 1.0,
                       1.0,  1.0, 1.0,
                      -1.0,  1.0, -1.0,
                      -1.0, -1.0, -1.0 };
glGenBuffers(1, &vertexVBO);
glBindBuffer(GL_ARRAY_BUFFER, vertexVBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*3*4, vertices, GL_STATIC_DRAW);
glVertexAttribPointer(VERTEX_POS, 3, GL_FLOAT, GL_FALSE, 0, 0); // VERTEX_POS = 0
glEnableVertexAttribArray(VERTEX_POS); // fails

However, this is throwing an error when calling glEnableVertexAttribArray: INVALID_OPERATION. The documentation suggests that this error is produced if the aforementioned call is made between a glBegin and glEnd. This is not the case. I mean, as far as I know, glBegin and glEnd are not even supported in the core profile.

Thus, I am at a loss. How can I draw this stupid rectangle (or at least initialize it)?

回答1:

You need to bind a VAO before setting attribute pointers.

GLuint vao_name;
glGenVertexArrays(1, &vao_name);
glBindVertexArray(vao_name);
// ...
glVertexAttribPointer(...);
glEnableVertexAttribArray(...);

Also, the documentation you're linking to is outdated — use this one instead.