OpenGL：在图像表面上绘制的污点

Question

我正在尝试编写一个魔方的接口。

但是，当我绘制它时，立方体的表面上有污迹：

这是注释良好的代码。有人可以帮助我，或许可以运行代码并告诉我哪里可能出错了？

#include <GL/glut.h>
#include <stdlib.h>

#include <stdio.h>

void init() {

  glClearColor(1.0f, 0.0f, 1.0f, 1.0f);

  glEnable(GL_DEPTH_TEST);

}

static float x_degs = 0.0f;
static float y_degs = 0.0f;

void keyboard(unsigned char key, int x, int y) {

  switch (key) {

    case 'q':

      exit(EXIT_SUCCESS);

    case 'h':

      y_degs -= 1.0f;

      glutPostRedisplay();

      glutSwapBuffers();

      break;

    case 'j':

      x_degs -= 1.0f;

      glutPostRedisplay();

      glutSwapBuffers();

      break;

    case 'k':

      x_degs += 1.0f;

      glutPostRedisplay();

      glutSwapBuffers();

      break;

    case 'l':

      y_degs += 1.0f;

      glutPostRedisplay();

      glutSwapBuffers();

      break;

  }

}

// half the length of one card

static const float card_half_size = 1.0f;

// half the space between cards

static const float space_half_size = 0.1f;

// number of cards per face

static const int NUM_CARDS_PER_FACE = 4;
/*
// start position of center of top left card 

const float start = - 3 * (card_half_size + space_half_size);

// increment between center of cards

const float incr = 2 * (card_half_size + space_half_size);

// half the size of a cube face

const float cube_half_size = 4 * (card_half_size + space_half_size);
*/
// draw a card centered at the origin

void draw_card() {

  glBegin(GL_QUADS);
    glVertex3f(- card_half_size, - card_half_size, 0.0f);
    glVertex3f(- card_half_size, card_half_size, 0.0f);
    glVertex3f(card_half_size, card_half_size, 0.0f);
    glVertex3f(card_half_size, - card_half_size, 0.0f);
  glEnd();

}

// draw a cube face made up of cards

void draw_card_face() {

  const float cube_half_size = 4 * (card_half_size + space_half_size);
  const float start = - 3 * (card_half_size + space_half_size);
  const float incr = 2 * (card_half_size + space_half_size);

  glColor3f(0.0f, 1.0f, 1.0f);

  glBegin(GL_QUADS);
    glVertex3f(- cube_half_size, - cube_half_size, -0.001f);
    glVertex3f(- cube_half_size, cube_half_size, -0.001f);
    glVertex3f(cube_half_size, cube_half_size, -0.001f);
    glVertex3f(cube_half_size, - cube_half_size, -0.001f);
  glEnd();

  glColor3f(1.0f, 1.0f, 1.0f);

  for (int i = 0; i < NUM_CARDS_PER_FACE; i++)

    for (int j = 0; j < NUM_CARDS_PER_FACE; j++) {

      glPushMatrix();
        glTranslatef(start + i * incr, start + j * incr, 0.0f);
        draw_card();
      glPopMatrix();

    }

}

// draw a cube made up of cards

void draw_card_cube() {

  const float cube_half_size = 4 * (card_half_size + space_half_size);

  // front face

  glPushMatrix();
    glTranslatef(0.0f, 0.0f, cube_half_size);
    draw_card_face();
  glPopMatrix();

  // back face

  glPushMatrix();
    glTranslatef(0.0f, 0.0f, - cube_half_size);
    glRotatef(180.0f, 0.0f, 1.0f, 0.0f);
    draw_card_face();
  glPopMatrix();

  // right face

  glPushMatrix();
    glTranslatef(cube_half_size, 0.0f, 0.0f);
    glRotatef(90.0f, 0.0f, 1.0f, 0.0f);
    draw_card_face();
  glPopMatrix();

  // left face

  glPushMatrix();
    glTranslatef(- cube_half_size, 0.0f, 0.0f);
    glRotatef(- 90.0f, 0.0f, 1.0f, 0.0f);
    draw_card_face();
  glPopMatrix();

  // top face

  glPushMatrix();
    glTranslatef(0.0f, cube_half_size, 0.0f);
    glRotatef(90.0f, 1.0f, 0.0f, 0.0f);
    draw_card_face();
  glPopMatrix();

  // bottom face

  glPushMatrix();
    glTranslatef(0.0f, - cube_half_size, 0.0f);
    glRotatef(- 90.0f, 1.0f, 0.0f, 0.0f);
    draw_card_face();
  glPopMatrix();


}

void display() {

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glLoadIdentity();

  glRotatef(x_degs, 1.0f, 0.0f, 0.0f);
  glRotatef(y_degs, 0.0f, 1.0f, 0.0f);

  gluLookAt(-0.6f, 0.6f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);
  draw_card_cube();
  glutSwapBuffers();

}

void reshape(int w, int h) {

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-15.0f, 15.0f, -15.0f, 15.0f, -15.0f, 15.0f);
  glViewport(0, 0, w, h);
  glMatrixMode(GL_MODELVIEW);

}

int main(int argc, char **argv) {

  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
  glutCreateWindow(argv[0]);
  init();
  glutKeyboardFunc(keyboard);
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutMainLoop();
  return 0;

}

好的，我已经修改了代码，以便我在后面绘制青色矩形 0.01f 单位而不是 0.001f 单位，这似乎已经修复了 z-fighting。但是我本来想使用 glPolygonOffset(factor, units) 来解决这个问题，但我无法做到，因为以下 原因：

1. 我不知道如何设置因子和单位（我都试过 1.0）。
2. 我尝试了不同的值，但没有结果。

这是没有流血/缝合/z-fighting的代码：

#include <GL/glut.h>
#include <stdlib.h>

#include <stdio.h>

void init() {

  glClearColor(1.0f, 0.0f, 1.0f, 1.0f);

  glEnable(GL_DEPTH_TEST);

}

static float x_degs = 0.0f;
static float y_degs = 0.0f;

void keyboard(unsigned char key, int x, int y) {

  switch (key) {

    case 'q':

      exit(EXIT_SUCCESS);

    case 'h':

      y_degs -= 1.0f;

      glutPostRedisplay();

      glutSwapBuffers();

      break;

    case 'j':

      x_degs -= 1.0f;

      glutPostRedisplay();

      glutSwapBuffers();

      break;

    case 'k':

      x_degs += 1.0f;

      glutPostRedisplay();

      glutSwapBuffers();

      break;

    case 'l':

      y_degs += 1.0f;

      glutPostRedisplay();

      glutSwapBuffers();

      break;

  }

}

// half the length of one card

static const float card_half_size = 1.0f;

// half the space between cards

static const float space_half_size = 0.1f;

// number of cards per face

static const int NUM_CARDS_PER_FACE = 4;
/*
// start position of center of top left card 

const float start = - 3 * (card_half_size + space_half_size);

// increment between center of cards

const float incr = 2 * (card_half_size + space_half_size);

// half the size of a cube face

const float cube_half_size = 4 * (card_half_size + space_half_size);
*/
// draw a card centered at the origin

void draw_card() {

  glBegin(GL_QUADS);
    glVertex3f(- card_half_size, - card_half_size, 0.0f);
    glVertex3f(- card_half_size, card_half_size, 0.0f);
    glVertex3f(card_half_size, card_half_size, 0.0f);
    glVertex3f(card_half_size, - card_half_size, 0.0f);
  glEnd();

}

// draw a cube face made up of cards

void draw_card_face() {

  const float cube_half_size = 4 * (card_half_size + space_half_size);
  const float start = - 3 * (card_half_size + space_half_size);
  const float incr = 2 * (card_half_size + space_half_size);

  glColor3f(0.0f, 1.0f, 1.0f);

  glBegin(GL_QUADS);
    glVertex3f(- cube_half_size, - cube_half_size, -0.001f);
    glVertex3f(- cube_half_size, cube_half_size, -0.001f);
    glVertex3f(cube_half_size, cube_half_size, -0.001f);
    glVertex3f(cube_half_size, - cube_half_size, -0.001f);
  glEnd();

  glColor3f(1.0f, 1.0f, 1.0f);

  for (int i = 0; i < NUM_CARDS_PER_FACE; i++)

    for (int j = 0; j < NUM_CARDS_PER_FACE; j++) {

      glPushMatrix();
        glTranslatef(start + i * incr, start + j * incr, 0.0f);
        draw_card();
      glPopMatrix();

    }

}

// draw a cube made up of cards

void draw_card_cube() {

  const float cube_half_size = 4 * (card_half_size + space_half_size);

  // front face

  glPushMatrix();
    glTranslatef(0.0f, 0.0f, cube_half_size);
    draw_card_face();
  glPopMatrix();

  // back face

  glPushMatrix();
    glTranslatef(0.0f, 0.0f, - cube_half_size);
    glRotatef(180.0f, 0.0f, 1.0f, 0.0f);
    draw_card_face();
  glPopMatrix();

  // right face

  glPushMatrix();
    glTranslatef(cube_half_size, 0.0f, 0.0f);
    glRotatef(90.0f, 0.0f, 1.0f, 0.0f);
    draw_card_face();
  glPopMatrix();

  // left face

  glPushMatrix();
    glTranslatef(- cube_half_size, 0.0f, 0.0f);
    glRotatef(- 90.0f, 0.0f, 1.0f, 0.0f);
    draw_card_face();
  glPopMatrix();

  // top face

  glPushMatrix();
    glTranslatef(0.0f, cube_half_size, 0.0f);
    glRotatef(90.0f, 1.0f, 0.0f, 0.0f);
    draw_card_face();
  glPopMatrix();

  // bottom face

  glPushMatrix();
    glTranslatef(0.0f, - cube_half_size, 0.0f);
    glRotatef(- 90.0f, 1.0f, 0.0f, 0.0f);
    draw_card_face();
  glPopMatrix();


}

void display() {

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glLoadIdentity();

  glRotatef(x_degs, 1.0f, 0.0f, 0.0f);
  glRotatef(y_degs, 0.0f, 1.0f, 0.0f);

  gluLookAt(-0.6f, 0.6f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);
  draw_card_cube();
  glutSwapBuffers();

}

void reshape(int w, int h) {

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-15.0f, 15.0f, -15.0f, 15.0f, -15.0f, 15.0f);
  glViewport(0, 0, w, h);
  glMatrixMode(GL_MODELVIEW);

}

int main(int argc, char **argv) {

  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
  glutCreateWindow(argv[0]);
  init();
  glutKeyboardFunc(keyboard);
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutMainLoop();
  return 0;

}

Answer 1

我认为您将棋子绘制为主立方体面的共面四边形；如果是这样的话，你遇到的问题就叫做“z打架”。

您可以查看点 12.040 深度缓冲似乎有效，但多边形似乎会通过它们前面的多边形流血。发生了什么事？ 这里： http://www.opengl.org/resources/faq/technical/depthbuffer.htm

基本上，您的深度缓冲区没有足够的精度来解决为每个像素显示哪个四边形，从而导致问题。

您可以手动向棋盘四边形添加偏移量，以将它们从立方体上移开；或通过glPolygonOffset 使用深度偏差来解决问题。

Answer 2

我认为您正在尝试进行共面渲染。查看glPolygonOffset()，而不是像您那样使用小 Z 偏移。

Answer 3

这是我从你的代码中得到的，用gcc -std=c99 -lGL -lGLU -lglut a.c 编译：没有污迹。可以发你的吗？ （Ubuntu 11.10，英特尔 GPU）