Hello OpenGL

main.c

#include <GL/glew.h>
#define GLFW_DLL
#include <GLFW/glfw3.h>
#include <stdio.h>

int main(int argc, char* argv[])
{
    // start GL context and OS window using GLFW
    if (!glfwInit()) {
	fprintf(stderr, "ERROR: could not start GLFW3\n");
	return 1;
    }
    
    GLFWwindow* window = glfwCreateWindow(640, 480, "Hello Triangle", NULL, NULL);
    if (!window) {
	fprintf(stderr, "ERROR: could not open window\n");
	glfwTerminate();
	return 1;
    }
    glfwMakeContextCurrent(window);
    
    // start GLEW extension handler
    glewExperimental = GL_TRUE;
    glewInit();
    
    // get version info
    const GLubyte* renderer = glGetString(GL_RENDERER);
    const GLubyte* version = glGetString(GL_VERSION);
    printf("Renderer: %s\n", renderer);
    printf("OpenGL version: %s\n", version);
    
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);

    /* OTHER STUFF GOES HERE NEXT */
    float points[] = {
	 0.0f,  0.5f, 0.0f,
	 0.5f, -0.5f, 0.0f,
	-0.5f, -0.5f, 0.0f
    };
    
    // Vertex Buffer Object
    GLuint vbo = 0;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(float), points, GL_STATIC_DRAW);
    
    // Vertex Attribute Object
    GLuint vao = 0;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);

    // Define shaders
    /* http://en.wikipedia.org/wiki/OpenGL_Shading_Language */
    const char* vertex_shader =
	"#version 130\n" /* 400 for OpenGL 4, 150 for OpenGL 3 */
	"in vec3 vp;"
	"void main() {"
	"  gl_Position = vec4(vp, 1.0);"
	"}";
    
    const char* fragment_shader =
	"#version 130\n"
	"out vec4 frag_colour;"
	"void main() {"
	"  frag_colour = vec4(0.5, 0.0, 0.5, 1.0);"
	"}";
    
    // Compile shaders
    GLuint vs = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vs, 1, &vertex_shader, NULL);
    glCompileShader(vs);
    GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fs, 1, &fragment_shader, NULL);
    glCompileShader(fs);
    
    // Create Shader Program
    GLuint shader_programme = glCreateProgram();
    glAttachShader(shader_programme, fs);
    glAttachShader(shader_programme, vs);
    glLinkProgram(shader_programme);
    
    // Draw loop
    while (!glfwWindowShouldClose(window)) {
	// wipe the drawing surface
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glUseProgram(shader_programme);
	glBindVertexArray(vao);
	// draw points 0-3 from the currently bound VAO with shaders
	glDrawArrays(GL_TRIANGLES, 0, 3);
	// update other events like input handling
	glfwPollEvents();
	// put the stuff we've been drawing on the display
	glfwSwapBuffers(window);
    }
    
    // close GL context and any other GLFW resources
    glfwTerminate();
    return 0;
}

Makefile

all: hellogl

hellogl: main.c
	clang -o hellogl main.c -lglfw -lGL -lGLEW