glvertexattribtest.cpp

#include <stdio.h>
#include <stdlib.h>
#include <string>

#define GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>
#include <glm/gtx/transform.hpp>

#include "../common/shader.h"


const GLfloat reticle_vertices[] =
{
    -1.0f, -1.0f, 0.0f,
    1.0f, -1.0f, 0.0f,
    0.0f, 1.0f, 0.0f
};


glm::mat4 MVP;
glm::mat4 vp;


const char *vertexSource =
    "#version 150\n"
    "layout(location = 0) in vec3 position;"
    "layout(location = 1) in vec3 color;"
    "out vec3 fragColor;"
    "uniform mat4 MVP;"
    "void main() {"
    "gl_Position = MVP * vec4(position, 1.0);"
    "fragColor = color;"
    "}";

const char *fragmentSource =
    "#version 150\n"
    "in vec3 fragColor;"
    "out vec4 outColor;"
    "void main() {"
    "outColor = vec4(fragColor, 1.0);"
    "}";


// Key callback: exit on ESCAPE
static void key_callback(GLFWwindow *window, int key, int scancode, int action, int mods)
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GL_TRUE);
}


// Initialize and return a window with GLFW
GLFWwindow *initGLWindow(int width, int height, int samples, const char *title, GLFWkeyfun keycb)
{
    if (!glfwInit())
    {
        fprintf(stderr, "Failed to initialize GLFW\n");
        return NULL;
    }
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_SAMPLES, samples);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow *w = glfwCreateWindow(width, height, title, NULL, NULL);
    if (!w)
    {
        glfwTerminate();
        return NULL;
    }

    glfwMakeContextCurrent(w);
    glfwSetKeyCallback(w, keycb);

    glewExperimental = true;
    if (glewInit() != GLEW_OK)
    {
        fprintf(stderr, "Failed to initialize GLEW\n");
        return NULL;
    }

    return w;
}


int main()
{
    // Initialize the OpenGL window
    GLFWwindow *window = initGLWindow(1024, 768, 2, "Schnuff", key_callback);

    // Load and use the shaders
    GLuint programID = LoadShaders(vertexSource, fragmentSource);
    glUseProgram(programID);

    // Get the attribute locations
    GLuint posAttrib = glGetAttribLocation(programID, "position");
    printf("posAttrib = %d\n", posAttrib);
    GLuint colAttrib = glGetAttribLocation(programID, "color");
    printf("colAttrib = %d\n", colAttrib);
    //GLint normAttrib = glGetAttribLocation(programID, "normal");
    //printf("normAttrib = %d\n", normAttrib);
    GLuint mvpID = glGetUniformLocation(programID, "MVP");

    // Vertex array object
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    // Vertex buffer object
    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(reticle_vertices), reticle_vertices, GL_STATIC_DRAW);

    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);

    // Hide the cursor
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_HIDDEN);

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);
    glEnable(GL_CULL_FACE);

    glClearColor(0.0f, 0.0f, 0.2f, 1.0f);
    glm::mat4 m = glm::mat4(1.0f);

    // Main loop
    do
    {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glUniformMatrix4fv(mvpID, 1, GL_FALSE, &m[0][0]);
        glVertexAttrib3f(colAttrib, 1.0f, 0.0f, 0.0f);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    while (!glfwWindowShouldClose(window));

    glDeleteProgram(programID);
    glfwDestroyWindow(window);
    glfwTerminate();
    return 0;
}