OpenGL多边形z缓冲区问题

Question

这是一个快速而肮脏的基于 GLUT 的 C++ 程序，用于在平坦的红色背景上绘制两个矩形，蓝色和绿色。按“a”或“z”使它们沿 X 轴在任一方向运行。我的问题是，如果我启用 GL_DEPTH_TEST，它有时会绘制一个矩形，有时会绘制两个或有时只是背景，但永远不会正确地使用较近的多边形遮挡较远的多边形的部分或全部部分。不设置 GL_DEPTH_TEST 只会使多边形出现在绘制顺序中。

下面的代码有什么问题？

#include <windows.h>

#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

#include <cmath>

#pragma comment(lib, "opengl32.lib")
#pragma comment(lib, "glu32.lib")

int angle = 0;

void oglDraw()
{
    angle += 360;
    angle %= 360;
    float fAngle = angle / (180 / 3.14159);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    gluPerspective(90, 1, 0, 10);
    gluLookAt(0, 0, -1, 0, 0, 1, 0, 1, 0);

    float yFactor = 1;
    float zFactor = 1; 
    float y = yFactor * sin(fAngle);
    float z = 1 + zFactor - cos(fAngle) * zFactor;

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 

    glClearColor(1, 0, 0, 1);

    glPolygonMode(GL_FRONT, GL_FILL);

    glBegin(GL_POLYGON);
    glColor4f(0, 0, 1, 1);
    glVertex3f(-1.0, y-1.0, z);
    glVertex3f(+1.0, y-1.0, z);
    glVertex3f(+1.0, y+1.0, z);
    glVertex3f(-1.0, y+1.0, z);
    glEnd();

    fAngle = (180 - angle) / (180 / 3.14159);
    y = -yFactor * sin(fAngle);
    z = 1 + zFactor - cos(fAngle) * zFactor;

    glBegin(GL_POLYGON);
    glColor4f(0, 1, 0, 1);
    glVertex3f(-1.0, y-1.0, z);
    glVertex3f(+1.0, y-1.0, z);
    glVertex3f(+1.0, y+1.0, z);
    glVertex3f(-1.0, y+1.0, z);
    glEnd();

    glFlush();
    glutSwapBuffers();
}
//////////////////////////////////////////////////////////////////////////

void oglKeyboard(byte ch, int x, int y)
{
    if(ch == 'z')
    {
        angle++;

        glutPostRedisplay();

    }
    else
    if(ch == 'a')
    {
        angle--;

        glutPostRedisplay();
    }
}
//////////////////////////////////////////////////////////////////////////

int main(int argc, char **argv)
{
    glutInit(&argc, argv);

    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH );
    glutInitWindowSize(1024, 768);
    glutCreateWindow("OGL test");
    gluOrtho2D(0, 1024, 768, 0);

    glEnable(GL_DEPTH_TEST);
    glutDisplayFunc(oglDraw);
    glutKeyboardFunc(oglKeyboard);

    glutMainLoop();
}

Answer 1

为gluPerspective() 的zNear 传递大于零的值：

gluPerspective(90, 1, 0.1, 10);