Simple Opengl Triangle on mavericks - macos

Question

I am new at opengl. I am starting with a simple triangle using GLFW , but I dont get anything drawn.
My system is :
OSX Mavericks 10.9.2 Intel HD 4000
compilation cmd line:
g++ main.cpp -o Test -I/usr/local/include -L/usr/local/lib -lglfw -framework Opengl
First thing I noticed odd was, on compilation , it did not identify
glGenVertexArrays , and suggested: glGenVertexArraysAPPLE same for:glBindVertexArray and suggested: glBindVertexArrayAPPLE
On using APPLE ext , didnt draw anything.
What am I missing here?
#include <iostream>
#include <OpenGL/gl.h>
#include <GLFW/glfw3.h>
#include <string.h>
GLuint vao=0;
GLuint shader_programme;
void CheckGLErrors(std::string str)
{
int errCount = 0;
GLenum currError = glGetError();
if(currError != GL_NO_ERROR)
{
//Do something with `currError`.
std::cout<<"\n"<<str<<" Error raised:"<<currError<<"\n";
}
}
void initVertex()
{
float points[] = {
0.0f, 0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
-0.5f, -0.5f, 0.0f
};
static const float colors[] =
{
1.0, 0.0, 0.0, 1.0,
0.0, 1.0, 0.0, 1.0,
0.0, 0.0, 1.0, 1.0
};
glGenVertexArraysAPPLE(1, &vao);
glBindVertexArrayAPPLE (vao);
GLuint vbo = 0;
glGenBuffers (1, &vbo);
glBindBuffer (GL_ARRAY_BUFFER, vbo);
glBufferData (GL_ARRAY_BUFFER, 9 * sizeof (float), points, GL_STATIC_DRAW);
glEnableVertexAttribArray (0);
glVertexAttribPointer (0, 3, GL_FLOAT, GL_FALSE, 0, NULL);
const char* vertex_shader =
"#version 400\n"
"in vec3 vp;"
"void main () {"
" gl_Position = vec4 (vp, 1.0);"
"}";
const char* fragment_shader =
"#version 400\n"
"out vec4 frag_colour;"
"void main () {"
" frag_colour = vec4 (0.5, 0.0, 0.5, 1.0);"
"}";
GLuint vs = glCreateShader (GL_VERTEX_SHADER);
glShaderSource (vs, 1, &vertex_shader, NULL);
glCompileShader (vs);
GLint status = GL_TRUE;
glGetShaderiv(vs, GL_COMPILE_STATUS, &status);
if(status != GL_TRUE) std::cout<<"VS FAILED\n";
GLuint fs = glCreateShader (GL_FRAGMENT_SHADER);
glShaderSource (fs, 1, &fragment_shader, NULL);
glCompileShader (fs);
status = GL_TRUE;
glGetShaderiv(fs, GL_COMPILE_STATUS, &status);
if(status != GL_TRUE) std::cout<<"PS FAILED\n";
shader_programme = glCreateProgram ();
glAttachShader (shader_programme, fs);
glAttachShader (shader_programme, vs);
glLinkProgram (shader_programme);
}
int main(int argc, char * argv[])
{
GLFWwindow* window;
int ver[3];
glfwGetVersion(&ver[0], &ver[1], &ver[2]);
std::cout << "major " <<ver[0] <<"minor: "<<ver[1]<<" ver: "<<ver[2];
/* Initialize the library */
if (!glfwInit())
{
std::cout << "Error";
return -1;
}
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
std::cout << "Create window Error";
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
std::cout<<"Version: " << glGetString(GL_VERSION);;
initVertex();
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glPointSize(40.0f);
glClearColor(0.0f,1.0f,0.0f,0.0f);
glUseProgram(shader_programme);
glBindVertexArrayAPPLE(vao);
glDrawArrays(GL_TRIANGLE, 0, 3);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwTerminate();
return 0;
}

Answer 1

On the missing declaration for glGenVertexArrays(), you need to include gl3.h instead of gl.h to get GL3 level functionality:
#include <OpenGL/gl3.h>
One problem I see in your code is that you use vertex attribute location 0 for setting up your coordinates. The attribute location is the first argument to glEnableVertexAttribArray() and glVertexAttribPointer(). But you don't really know that the location of vp in your shader program is 0. The easiest way to ensure this is that you specify it directly in your shader code by extending the declaration of vp:
layout(location = 0) in vec3 vp;
This works with GL 3.3 and higher. An alternative with older GL versions is to make the following API call before the glLinkProgram() call:
glBindAttribLocation(shader_programme, 0, "vp");