glVertexAttribPointer causing Invalid Operation OpenGL error in D - opengl

Question

I have a simple D application using DerelictGL3 and DerelictSDL2. I am trying to render a red triangle using vertex buffer objects however whenever I run glVertexAttribPointer(position, 2, GL_FLOAT, GL_FALSE, float.sizeof * 2, null);, glGetError() returns 1282 (Invalid Operation). The code is as follows...
app.d
import std.string;
import std.conv;
import std.stdio;
import std.file;
import std.c.stdlib;
import derelict.opengl3.gl3;
import derelict.sdl2.sdl;
void main() {
DerelictSDL2.load();
DerelictGL3.load();
assert(SDL_Init(SDL_INIT_VIDEO) >= 0);
auto vertex_shader = (cast(string) read("shaders/minimal.vert")).toStringz;
auto fragment_shader = (cast(string) read("shaders/minimal.frag")).toStringz;
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
auto final_param = SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN;
auto window = SDL_CreateWindow("Triangle", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, final_param);
assert(window);
SDL_GL_CreateContext(window);
DerelictGL3.reload();
GLfloat[] vertices = [1, 1, 1, -1, -1, 1, -0.8, -1, 1];
uint vbo;
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, vertices.length * float.sizeof, vertices.ptr, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
auto program = glCreateProgram();
auto vshader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vshader, 1, &vertex_shader, null);
glCompileShader(vshader);
glAttachShader(program, vshader);
auto fshader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fshader, 1, &fragment_shader, null);
glCompileShader(fshader);
glAttachShader(program, fshader);
glLinkProgram(program);
glUseProgram(program);
auto position = glGetAttribLocation(program, "position");
auto close = false;
check();
while(!close) {
SDL_Event event;
while(SDL_PollEvent(&event)) {
if(event.type == SDL_QUIT) close = true;
}
glClearColor(1, 0.4, 0.4, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glEnableVertexAttribArray(position);
check("before"); // Does not return error.
glVertexAttribPointer(position, 2, GL_FLOAT, GL_FALSE, float.sizeof * 2, null); // <- Causing Invalid Operation GL error.
check("after"); // Returns error.
glDrawArrays(GL_TRIANGLES, 0, 3);
SDL_GL_SwapWindow(window);
}
}
void check(string msg="") {
auto error = glGetError();
assert(error == 0, msg ~ ":" ~ to!string(error));
}
shaders/minimal.vert
#version 120
attribute vec2 position;
void main(void) {
gl_Position = vec4(position, 0, 1);
}
shaders/minimal.frag
#version 120
void main(void) {
gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}
When ignoring the error, a red rectangle is rendered in the top right corner of the screen.

Answer 1

You're missing a VAO which is required in OpenGL 3.2. You can create it before other buffers like this:
GLuint vao;
glGenVertexArrays(1,&vao);
glBindVertexArray(vao);

Answer 2

What might help is enabling OpenGL debug logging, you can do it like this: https://github.com/d-gamedev-team/gfm/blob/master/opengl/gfm/opengl/opengl.d#L419
Some drivers like the NVIDIA one provide extensive warning when something go wrong, the problem might not be where you think it is.