無法更改 OpenGL 中的背景顏色

Question

我剛剛開始試驗 OpenGL（使用 freeglut 和 GLEW）。 我可以彈出一個 window ，但什么都沒有吸引到它，我什至不能讓它改變背景顏色。

這是主要的 function 的樣子：

int
main(int argc, char **argv)
{ 
  GLenum err;

  /* Initialize GLUT library */
  glutInit(&argc, argv);

  /* Set window mode */
  glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);

  /* Choose OpenGL version */
  glutInitContextVersion(3, 3);

  /* Choose OpenGL profile */
  glutInitContextFlags(GLUT_CORE_PROFILE);

  /* Create a GLUT window */
  glutCreateWindow("OpenGL 2D");

  /* Initialize GLEW library */
  glewExperimental = GL_TRUE;
  err = glewInit();
  if(err != GLEW_OK) {
    printf("Cannot initialize GLEW: %s\n",
       glewGetErrorString(err));
    return 1;
  }

  /* WORKAROUND: Ignore all GLEW errors */
  while(glGetError() != GL_NO_ERROR)
    ;

  (void) printf("OpenGL vendor: \"%s\"\n"
        "       renderer: \"%s\"\n"
        "       version: \"%s\"\n"
        "       SL version: \"%s\"\n",
        glGetString(GL_VENDOR),
        glGetString(GL_RENDERER),
        glGetString(GL_VERSION),
        glGetString(GL_SHADING_LANGUAGE_VERSION));

  /* Set up callback function for "reshape" event */
  printf("Setting callback functions\n");
  glutReshapeFunc(canvas_reshape);

  /* Set up callback function for "display" event */
  glutDisplayFunc(canvas_display);

  /* Set up callback function for "keyboard" event */
  glutKeyboardFunc(canvas_keyboard);

  /* Set up callback function for "timer" event */
  glutTimerFunc(30, canvas_timer, 0);

  /* Initialize OpenGL */
  init();

  /* Choose the window's position */
  glutPositionWindow(100, 100);

  /* Choose the window's size */
  glutReshapeWindow(800, 600);

  /* Start main loop */
  printf("Entering main loop\n");
  glutMainLoop();

  return 0;
}

這是初始化的樣子：

init()
{
  const GLchar *vertex_shader_source[] = {
    "#version 330 core\n",
    "\n",
    "layout(location=0) in vec4 position;\n",
    "out vec4 color;\n",
    "uniform mat4 viewtrans;\n",
    "\n",
    "void\n",
    "main()\n",
    "{\n",
    "  gl_Position = viewtrans * position;\n"
    "  color =  vec4(1.0, 1.0, 1.0, 1.0);\n"
    "}\n" };
  const GLchar *fragment_shader_source[] = {
    "#version 330 core\n",
    "in vec4 color;\n",
    "layout(location=0) out vec4 fcolor;\n",
    "void\n",
    "main()\n",
    "{\n",
    "  fcolor = color;\n",
    "}\n" };
  char compiler_log[LOGSIZE];

  /* Obtain an unused name for our vertex array */
  printf("Creating vertex array\n");
  glGenVertexArrays(1, &vertex_array);
  check_error("glGenVertexArrays");

  /* Tell OpenGL to use the new vertex array */
  glBindVertexArray(vertex_array);
  check_error("glBindVertexArray");

  /* Obtain an unused name for our vertex buffer */
  printf("Creating vertex buffer\n");
  glGenBuffers(1, &vertex_buffer);
  check_error("glGenBuffers");

  /* Tell OpenGL to use the new vertex buffer as the
   * vertex array */
  glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
  check_error("glBindBuffer");

  /* We want to get two coordinates from the vertex buffer and
   * feed them as the first parameter to the vertex shader */
  glEnableVertexAttribArray(0);
  glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 2, 0);

  /* Create vertex shader */
  printf("Creating vertex shader\n");
  vertex_shader = glCreateShader(GL_VERTEX_SHADER);
  check_error("glCreateShader");

  /* Assign vertex shader source code */
  glShaderSource(vertex_shader, sizeof(vertex_shader_source) / sizeof(GLchar *),
         vertex_shader_source, 0);
  check_error("glShaderSource");

  /* Compile vertex shader */
  glCompileShader(vertex_shader);
  check_error("glCompileShader");

  /* Get compiler log *//* Set up callback function for "timer" event */
  glGetShaderInfoLog(vertex_shader, LOGSIZE, 0, compiler_log);
  printf("  Compiler log: \"%s\"\n", compiler_log);

  /* Create fragment shader */
  printf("Creating fragment shader\n");
  fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
  check_error("glCreateShader");

  /* Assign fragment shader source code */
  glShaderSource(fragment_shader, sizeof(fragment_shader_source) / sizeof(GLchar *),
         fragment_shader_source, 0);
  check_error("glShaderSource");

  /* Compile fragment shader */
  glCompileShader(fragment_shader);
  check_error("glCompileShader");

  /* Get compiler log */
  glGetShaderInfoLog(fragment_shader, LOGSIZE, 0, compiler_log);
  printf("  Compiler log: \"%s\"\n", compiler_log);

  /* Create shader program */
  printf("Creating shader program\n");
  shader_program = glCreateProgram();
  check_error("glCreateProgram");

  /* Attach vertex shader */
  glAttachShader(shader_program, vertex_shader);
  check_error("glAttachShader");

  /* Attach fragment shader */
  glAttachShader(shader_program, fragment_shader);
  check_error("glAttachShader");

  /* Link shader program */
  glLinkProgram(shader_program);
  check_error("glLinkProgram");

  /* Get linker log */
  glGetProgramInfoLog(shader_program, LOGSIZE, 0, compiler_log);
  printf("  Linker log: \"%s\"\n", compiler_log);

  /* Get location of "viewtrans" matrix */
  viewtrans = glGetUniformLocation(shader_program, "viewtrans");
  check_error("glGetUniformLocation");

  /* Tell OpenGL to use the new shader program */
  glUseProgram(shader_program);

  /* Choose background color */
  glClearColor(1.0, 0.0, 1.0, 0.0);
}

這是我用來畫的：

static void
canvas_display()
{
  glClearColor(0.0, 0.0, 0.0, 0.0);

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}

這一切都基於一個教程。 實際發生的情況類似於 300 x 300 白色 window 出現，被重新塑造成 800 x 600 黑色 window，但中間或角落仍然有 300 x 300 白色方塊，其像素（部分）變為黑色調整 window 的大小，使（部分）正方形消失（手動或通過代碼）。 我還編寫了繪制三角形的代碼，但這也不起作用，正如人們所期望的那樣。 但無論如何，這是代碼：

static void
canvas_display()
{
    glClearColor(0.0, 0.0, 0.0, 0.0);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    GLfloat vertices[] =
    { 0.0, 0.0,
      0.5, 0.5,
      0.5, 0.0 };

    glGenVertexArrays(1, &vertex_array);
    glBindVertexArray(vertex_array);

    glGenBuffers(1, &vertex_buffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(GL_FLOAT) * 2, vertices);

    glDrawArrays(GL_TRIANGLES, 0, 3);
}

Answer 1

不要連續指定新的頂點數組對象。 在初始化時創建 1 個頂點數組 Object 。 頂點數組包含在頂點緩沖區 Object中。 當命名緩沖區 object 綁定到ARRAY_BUFFER目標時， glVertexAttribPointer的最后一個參數被視為緩沖區對象數據存儲的字節偏移量。 因此偏移量必須是NULL ：

void init()
{
    // [...]

    GLfloat vertices[] =
    { 0.0, 0.0,
      0.5, 0.5,
      0.5, 0.0 };

    glGenVertexArrays(1, &vertex_array);
    glBindVertexArray(vertex_array);

    glGenBuffers(1, &vertex_buffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(GL_FLOAT) * 2, NULL);
}

確保在繪制幾何圖形時安裝了程序並綁定了 VAO。 默認情況下，制服的值初始化為零。 至少您必須設置Identity 矩陣，然后設置矩陣統一viewtrans 。
由於您使用雙緩沖（ GLUT_DOUBLE ），因此您必須在通過glutSwapBuffers繪制所有幾何圖形后交換當前 window 的緩沖區

void canvas_display()
{
    glClearColor(1.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glUseProgram(shader_program);
    GLfloat identity_mat[] = { 1,0,0,0,  0,1,0,0, 0,0,1,0, 0,0,0,1 };
    glUniformMatrix4fv(viewtrans, 1, GL_FALSE, identity_mat);

    glBindVertexArray(vertex_array);
    glDrawArrays(GL_TRIANGLES, 0, 3);

    glutSwapBuffers();
    glutPostRedisplay();
}