01shader_vbo2.cpp

/* OpenGL example code - Tesselation
 * 
 * This example shows the setup and usage of shaders and a vbo+vao
 * In this example the attrbute locations are set via BindAttribLocation
 * instead of layout qualifiers in the shaders
 * 
 * Autor: Jakob Progsch
 */

#include <GLXW/glxw.h>
#include <GLFW/glfw3.h>

#include <iostream>
#include <string>
#include <vector>

// helper to check and display for shader compiler errors
bool check_shader_compile_status(GLuint obj) {
    GLint status;
    glGetShaderiv(obj, GL_COMPILE_STATUS, &status);
    if(status == GL_FALSE) {
        GLint length;
        glGetShaderiv(obj, GL_INFO_LOG_LENGTH, &length);
        std::vector<char> log(length);
        glGetShaderInfoLog(obj, length, &length, &log[0]);
        std::cerr << &log[0];
        return false;
    }
    return true;
}

// helper to check and display for shader linker error
bool check_program_link_status(GLuint obj) {
    GLint status;
    glGetProgramiv(obj, GL_LINK_STATUS, &status);
    if(status == GL_FALSE) {
        GLint length;
        glGetProgramiv(obj, GL_INFO_LOG_LENGTH, &length);
        std::vector<char> log(length);
        glGetProgramInfoLog(obj, length, &length, &log[0]);
        std::cerr << &log[0];
        return false;   
    }
    return true;
}

int main() {
    int width = 640;
    int height = 480;
    
    if(glfwInit() == GL_FALSE) {
        std::cerr << "failed to init GLFW" << std::endl;
        return 1;
    }

    // select opengl version
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
 
    // create a window
    GLFWwindow *window;
    if((window = glfwCreateWindow(width, height, "01shader_vbo2", 0, 0)) == 0) {
        std::cerr << "failed to open window" << std::endl;
        glfwTerminate();
        return 1;
    }
    
    glfwMakeContextCurrent(window);

    if(glxwInit()) {
        std::cerr << "failed to init GL3W" << std::endl;
        glfwDestroyWindow(window);
        glfwTerminate();
        return 1;
    }

    // shader source code
    std::string vertex_source =
        "#version 330\n"
        "in vec4 vposition;\n"
        "in vec4 vcolor;\n"
        "out vec4 fcolor;\n"
        "void main() {\n"
        "   fcolor = vcolor;\n"
        "   gl_Position = vposition;\n"
        "}\n";
        
    std::string fragment_source =
        "#version 330\n"
        "in vec4 fcolor;\n"
        "out vec4 FragColor;\n"
        "void main() {\n"
        "   FragColor = fcolor;\n"
        "}\n";

    // program and shader handles
    GLuint shader_program, vertex_shader, fragment_shader;
    
    // we need these to properly pass the strings
    const char *source;
    int length;

    // create and compiler vertex shader
    vertex_shader = glCreateShader(GL_VERTEX_SHADER);
    source = vertex_source.c_str();
    length = vertex_source.size();
    glShaderSource(vertex_shader, 1, &source, &length); 
    glCompileShader(vertex_shader);
    if(!check_shader_compile_status(vertex_shader)) {
        glfwDestroyWindow(window);
        glfwTerminate();
        return 1;
    }
 
    // create and compiler fragment shader
    fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
    source = fragment_source.c_str();
    length = fragment_source.size();
    glShaderSource(fragment_shader, 1, &source, &length);   
    glCompileShader(fragment_shader);
    if(!check_shader_compile_status(fragment_shader)) {
        glfwDestroyWindow(window);
        glfwTerminate();
        return 1;
    }    
    // create program
    shader_program = glCreateProgram();
    
    // attach shaders
    glAttachShader(shader_program, vertex_shader);
    glAttachShader(shader_program, fragment_shader);

    // bind the attribute locations (inputs)
    glBindAttribLocation(shader_program, 0, "vposition");
    glBindAttribLocation(shader_program, 1, "vcolor");
    
    // bind the FragDataLocation (output)
    glBindFragDataLocation(shader_program, 0, "FragColor");
    
    // link the program and check for errors
    glLinkProgram(shader_program);
    check_program_link_status(shader_program);
    
    // vao and vbo handle
    GLuint vao, vbo;
 
    // generate and bind the vao
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    
    // generate and bind the buffer object
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
            
    // data for a fullscreen quad
    GLfloat vertexData[] = {
    //  X     Y     Z           R     G     B
       1.0f, 1.0f, 0.0f,       1.0f, 0.0f, 0.0f, // vertex 0
      -1.0f, 1.0f, 0.0f,       0.0f, 1.0f, 0.0f, // vertex 1
       1.0f,-1.0f, 0.0f,       0.0f, 0.0f, 1.0f, // vertex 2
       1.0f,-1.0f, 0.0f,       0.0f, 0.0f, 1.0f, // vertex 3
      -1.0f, 1.0f, 0.0f,       0.0f, 1.0f, 0.0f, // vertex 4
      -1.0f,-1.0f, 0.0f,       1.0f, 0.0f, 0.0f, // vertex 5
    }; // 6 vertices with 6 components (floats) each
    
    // fill with data
    glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*6*6, vertexData, GL_STATIC_DRAW);
           
    // set up generic attrib pointers
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6*sizeof(GLfloat), (char*)0 + 0*sizeof(GLfloat));

    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6*sizeof(GLfloat), (char*)0 + 3*sizeof(GLfloat));
    
    while(!glfwWindowShouldClose(window)) {
        glfwPollEvents();
        
        // clear first
        glClear(GL_COLOR_BUFFER_BIT);
        
        // use the shader program
        glUseProgram(shader_program);
        
        // bind the vao
        glBindVertexArray(vao);

        // draw
        glDrawArrays(GL_TRIANGLES, 0, 6);
       
        // check for errors
        GLenum error = glGetError();
        if(error != GL_NO_ERROR) {
            std::cerr << error << std::endl;
            break;
        }
        
        // finally swap buffers
        glfwSwapBuffers(window);      
    }

    // delete the created objects
    
    glDeleteVertexArrays(1, &vao);
    glDeleteBuffers(1, &vbo);
    
    glDetachShader(shader_program, vertex_shader);	
    glDetachShader(shader_program, fragment_shader);
    glDeleteShader(vertex_shader);
    glDeleteShader(fragment_shader);
    glDeleteProgram(shader_program);
    
    glfwDestroyWindow(window);
    glfwTerminate();
    return 0;
}