[Open GL] LearnOpenGL hello_triangle_exercise 1, 2, 3

LearnOpenGL의 hello_triangle_exercise 1,2,3를 간단하게 분석해보는 포스팅입니다.

버텍스 쉐이더의 in 데이터인 버텍스 배열의 합체 혹은 분리,

여러 프레그먼트 쉐이더를 사용해보는 기법을 배울 수 있는 파트입니다.

 

관련 docs : https://learnopengl.com/Getting-started/Hello-Triangle

LearnOpenGL - Hello Triangle

 

1.  hello_triangle_exercise 1 VS 2

hello_triangle_exercise1과 hello_triangle_exercise2의 렌더링 차이점은 없어보인다.

다만 인풋 버텍스 입력과 그 처리를 위한 과정이 바뀜으로써 코드에 많은 변화가 생겼다.

exercise1에서는 하나의 vertices 안에서 모든 삼각형 버텍스를 다 그려주었고,

exercise2에서는 두개로 분리하여 VBO와 VAO역시 배열형으로 선언한 후 각종 generate와 bind처리를 두번씩하였다.

exercise1 코드

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }


    // build and compile our shader program
    // ------------------------------------
    // vertex shader
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // fragment shader
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // link shaders
    unsigned int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    // check for linking errors
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    // add a new set of vertices to form a second triangle (a total of 6 vertices); the vertex attribute configuration remains the same (still one 3-float position vector per vertex)
    float vertices[] = {
        // first triangle
        -0.9f, -0.5f, 0.0f,  // left 
        -0.0f, -0.5f, 0.0f,  // right
        -0.45f, 0.5f, 0.0f,  // top 
        // second triangle
         0.0f, -0.5f, 0.0f,  // left
         0.9f, -0.5f, 0.0f,  // right
         0.45f, 0.5f, 0.0f   // top 
    }; 

    unsigned int VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    // bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

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

    // note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
    glBindBuffer(GL_ARRAY_BUFFER, 0); 

    // You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
    // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
    glBindVertexArray(0); 


    // uncomment this call to draw in wireframe polygons.
    //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // draw our first triangle
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
        glDrawArrays(GL_TRIANGLES, 0, 6); // set the count to 6 since we're drawing 6 vertices now (2 triangles); not 3!
        // glBindVertexArray(0); // no need to unbind it every time 
 
        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteProgram(shaderProgram);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

exercise2 코드

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }


    // build and compile our shader program
    // ------------------------------------
    // vertex shader
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // fragment shader
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // link shaders
    unsigned int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    // check for linking errors
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float firstTriangle[] = {
        -0.9f, -0.5f, 0.0f,  // left 
        -0.0f, -0.5f, 0.0f,  // right
        -0.45f, 0.5f, 0.0f,  // top 
    };
    float secondTriangle[] = {
        0.0f, -0.5f, 0.0f,  // left
        0.9f, -0.5f, 0.0f,  // right
        0.45f, 0.5f, 0.0f   // top 
    };
    unsigned int VBOs[2], VAOs[2];
    glGenVertexArrays(2, VAOs); // we can also generate multiple VAOs or buffers at the same time
    glGenBuffers(2, VBOs);
    // first triangle setup
    // --------------------
    glBindVertexArray(VAOs[0]);
    glBindBuffer(GL_ARRAY_BUFFER, VBOs[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(firstTriangle), firstTriangle, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);	// Vertex attributes stay the same
    glEnableVertexAttribArray(0);
    // glBindVertexArray(0); // no need to unbind at all as we directly bind a different VAO the next few lines
    // second triangle setup
    // ---------------------
    glBindVertexArray(VAOs[1]);	// note that we bind to a different VAO now
    glBindBuffer(GL_ARRAY_BUFFER, VBOs[1]);	// and a different VBO
    glBufferData(GL_ARRAY_BUFFER, sizeof(secondTriangle), secondTriangle, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0); // because the vertex data is tightly packed we can also specify 0 as the vertex attribute's stride to let OpenGL figure it out
    glEnableVertexAttribArray(0);
    // glBindVertexArray(0); // not really necessary as well, but beware of calls that could affect VAOs while this one is bound (like binding element buffer objects, or enabling/disabling vertex attributes)


    // uncomment this call to draw in wireframe polygons.
    //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shaderProgram);
        // draw first triangle using the data from the first VAO
        glBindVertexArray(VAOs[0]);
        glDrawArrays(GL_TRIANGLES, 0, 3);
        // then we draw the second triangle using the data from the second VAO
        glBindVertexArray(VAOs[1]);
        glDrawArrays(GL_TRIANGLES, 0, 3);
 
        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(2, VAOs);
    glDeleteBuffers(2, VBOs);
    glDeleteProgram(shaderProgram);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

2. hello_triangle_exercise 3

렌더링 결과를 보자마자 오른쪽 삼각형 프레그먼트 쉐이더에 변화가 생겼음을 짐작할 수 있다.

아예 프레그먼트 쉐이더를 하나 더 만들어서 붙여주는 식으로 코드가 작성되어 있다.

 

 

3 코드

const char *vertexShaderSource = "#version 330 core\n"
    "layout (location = 0) in vec3 aPos;\n"
    "void main()\n"
    "{\n"
    "   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
    "}\0";
const char *fragmentShader1Source = "#version 330 core\n"
    "out vec4 FragColor;\n"
    "void main()\n"
    "{\n"
    "   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
    "}\n\0";
const char *fragmentShader2Source = "#version 330 core\n"
    "out vec4 FragColor;\n"
    "void main()\n"
    "{\n"
    "   FragColor = vec4(1.0f, 1.0f, 0.0f, 1.0f);\n"
    "}\n\0";


int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }


    // build and compile our shader program
    // ------------------------------------
    // we skipped compile log checks this time for readability (if you do encounter issues, add the compile-checks! see previous code samples)
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    unsigned int fragmentShaderOrange = glCreateShader(GL_FRAGMENT_SHADER); // the first fragment shader that outputs the color orange
    unsigned int fragmentShaderYellow = glCreateShader(GL_FRAGMENT_SHADER); // the second fragment shader that outputs the color yellow
    unsigned int shaderProgramOrange = glCreateProgram();
    unsigned int shaderProgramYellow = glCreateProgram(); // the second shader program
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    glShaderSource(fragmentShaderOrange, 1, &fragmentShader1Source, NULL);
    glCompileShader(fragmentShaderOrange);
    glShaderSource(fragmentShaderYellow, 1, &fragmentShader2Source, NULL);
    glCompileShader(fragmentShaderYellow);
    // link the first program object
    glAttachShader(shaderProgramOrange, vertexShader);
    glAttachShader(shaderProgramOrange, fragmentShaderOrange);
    glLinkProgram(shaderProgramOrange);
    // then link the second program object using a different fragment shader (but same vertex shader)
    // this is perfectly allowed since the inputs and outputs of both the vertex and fragment shaders are equally matched.
    glAttachShader(shaderProgramYellow, vertexShader);
    glAttachShader(shaderProgramYellow, fragmentShaderYellow);
    glLinkProgram(shaderProgramYellow);

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float firstTriangle[] = {
        -0.9f, -0.5f, 0.0f,  // left 
        -0.0f, -0.5f, 0.0f,  // right
        -0.45f, 0.5f, 0.0f,  // top 
    };
    float secondTriangle[] = {
        0.0f, -0.5f, 0.0f,  // left
        0.9f, -0.5f, 0.0f,  // right
        0.45f, 0.5f, 0.0f   // top 
    };
    unsigned int VBOs[2], VAOs[2];
    glGenVertexArrays(2, VAOs); // we can also generate multiple VAOs or buffers at the same time
    glGenBuffers(2, VBOs);
    // first triangle setup
    // --------------------
    glBindVertexArray(VAOs[0]);
    glBindBuffer(GL_ARRAY_BUFFER, VBOs[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(firstTriangle), firstTriangle, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);	// Vertex attributes stay the same
    glEnableVertexAttribArray(0);
    // glBindVertexArray(0); // no need to unbind at all as we directly bind a different VAO the next few lines
    // second triangle setup
    // ---------------------
    glBindVertexArray(VAOs[1]);	// note that we bind to a different VAO now
    glBindBuffer(GL_ARRAY_BUFFER, VBOs[1]);	// and a different VBO
    glBufferData(GL_ARRAY_BUFFER, sizeof(secondTriangle), secondTriangle, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0); // because the vertex data is tightly packed we can also specify 0 as the vertex attribute's stride to let OpenGL figure it out
    glEnableVertexAttribArray(0);
    // glBindVertexArray(0); // not really necessary as well, but beware of calls that could affect VAOs while this one is bound (like binding element buffer objects, or enabling/disabling vertex attributes)


    // uncomment this call to draw in wireframe polygons.
    //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // now when we draw the triangle we first use the vertex and orange fragment shader from the first program
        glUseProgram(shaderProgramOrange);
        // draw the first triangle using the data from our first VAO
        glBindVertexArray(VAOs[0]);
        glDrawArrays(GL_TRIANGLES, 0, 3);	// this call should output an orange triangle
        // then we draw the second triangle using the data from the second VAO
        // when we draw the second triangle we want to use a different shader program so we switch to the shader program with our yellow fragment shader.
        glUseProgram(shaderProgramYellow);
        glBindVertexArray(VAOs[1]);
        glDrawArrays(GL_TRIANGLES, 0, 3);	// this call should output a yellow triangle

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(2, VAOs);
    glDeleteBuffers(2, VBOs);
    glDeleteProgram(shaderProgramOrange);
    glDeleteProgram(shaderProgramYellow);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}