OpenGL笔记：绘制的四边形不断缩小时，一会消失，一会出现

问题

图中两根红线用四边形模拟，绿线为GL_LINES，均在同一平面上绘制。不断缩小图形，红线会消失，一会又会出现，缩小到一定程度，就全部消失了，但绿色线一直都在。

测试代码

#define FREEGLUT_STATIC

#include "gl/freeglut.h"
#include <cmath>
#include <iostream>
#include <iomanip>
#include <gemat3d.h>



#define MY_PI (3.1415926535f)
GLfloat g_dApectRadio = 1.0;
GLfloat g_CurScale = 1.0;



void OnDisplay()
{
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  double fRange = 2000 * g_CurScale; //正交投影，通过投影矩阵来达到缩放的效果
  if (g_dApectRadio > 1.0)
  {
    glOrtho(-fRange*g_dApectRadio, fRange * g_dApectRadio, -fRange, fRange, -2000, 2000);
  }
  else
  {
    glOrtho(-fRange, fRange, -fRange / g_dApectRadio, fRange * g_dApectRadio, -2000, 2000);
  }

  //俯视
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  gluLookAt(1000, 210, 0, 1000, 210, -1, 0, 1, 0);

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  glColor3d(1.0, 0.0, 0.0);
  glBegin(GL_QUADS);
  glVertex3d(0, 0, 0);
  glVertex3d(2000, 0, 0);
  glVertex3d(2000, 20, 0);
  glVertex3d(0, 20, 0);

  glVertex3d(0, 400, 0);
  glVertex3d(2000, 400, 0);
  glVertex3d(2000, 420, 0);
  glVertex3d(0, 420, 0);
  glEnd();

  glColor3f(0.0, 1.0, 0.0);
  glBegin(GL_LINES);
  glVertex3d(0, 400, 0);
  glVertex3d(2000, 20, 0);
  glEnd();


  glFlush();
}


void OnReSize(int w, int h)
{
  glViewport(0, 0, w, h);

  if (h <= 0) h = 1;
  g_dApectRadio = 1.0 * w / h;
}

void OnSpecialKey(GLint key, GLint x, GLint y)
{
  GLfloat fStep = 0.2;
  if (key == GLUT_KEY_UP)
  {
    g_CurScale *= (1.0 + fStep); //缩小

  }
  else if (key == GLUT_KEY_DOWN)
  {
    g_CurScale *= (1.0 - fStep); //放大
  }

  glutPostRedisplay();
}


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

  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowSize(600, 600);

  double fWidths[2] = { 0 };
  glGetDoublev(GL_LINE_WIDTH_RANGE, fWidths);

  GLfloat fWidthStep = 0;
  glGetFloatv(GL_LINE_WIDTH_GRANULARITY, &fWidthStep);

  glutCreateWindow("Ortho3D");


  glutDisplayFunc(OnDisplay);
  glutReshapeFunc(OnReSize);
  glutSpecialFunc(OnSpecialKey);

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



  glutMainLoop();

  return 0;
}

解决方案

开启多边形反走样或反锯齿，即可解决

glEnable(GL_POLYGON_SMOOTH);