如何使OpenGL光定向？

Posted 2023-02-16

【中文标题】如何使OpenGL光定向？

【英文标题】：How to make OpenGl Light Directional?

【发布时间】：2021-01-14 02:29:59

【问题描述】：

我编写这段代码是为了在 y 方向上发出红灯。我希望它看起来像聚光灯。它是红色的，但它无处不在，而不仅仅是 y 方向。知道要改变什么让它看起来像聚光灯吗？

glEnable(GL_LIGHT1);
GLfloat ambient1[] =  0.7f, 0.0f, 0.0f, 1.0f ;
glLightfv(GL_LIGHT1, GL_AMBIENT, ambient1);

GLfloat diffuse1[] =  1.0, 0.0, 0.0, 1.0 ;
glLightfv(GL_LIGHT1, GL_DIFFUSE, diffuse1);

GLfloat specular1[] =  1.0f, 1.0f, 1.0f, 1.0f ;
glLightfv(GL_LIGHT1, GL_SPECULAR, specular1);

GLfloat light_position1[] =  0.0f, 0.0f, 0.2f, 0.0f ;
glLightfv(GL_LIGHT1, GL_POSITION, light_position1);

GLfloat spotCUtOff[] =  10.0f ;
glLightfv(GL_LIGHT1, GL_SPOT_CUTOFF, spotCUtOff);

GLfloat SPOTDIRECTION[] =  0.0f, 2.0f, 0.0f ;
glLightfv(GL_LIGHT1, GL_SPOT_DIRECTION, SPOTDIRECTION);

GLfloat SPOTEXPONENT[] =  2.0f ;
glLightfv(GL_LIGHT1, GL_SPOT_EXPONENT, SPOTEXPONENT);

【参考方案1】：

您的指数和截止值太低。 GL_SPOT_CUTOFF 指定光线分布的角度，GL_SPOT_EXPONENT 指定截止后光线消散的强度。

为了获得合理的聚光灯效果，您应该尝试提高这些值：

  GLfloat spotExp = 20.0;
  glLightf(GL_LIGHT1, GL_SPOT_EXPONENT, spotExp);
  GLfloat spotCutoff = 60.0;
  glLightf(GL_LIGHT1, GL_SPOT_CUTOFF, spotCutoff);

这是一个改编自 Mark J. Kilgard here 的示例的 MCVE：

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

static void
Init(void)

  glMatrixMode(GL_PROJECTION);
  glFrustum(-1, 1, -1, 1, 2, 6);

  glMatrixMode(GL_MODELVIEW);
  glTranslatef(0.0, 0.0, -3.0);
  glRotatef(45.0, 1, 0, 0);

  glEnable(GL_LIGHTING);
  glEnable(GL_LIGHT1);
  GLfloat ambient1[] =  0.7f, 0.0f, 0.0f, 1.0f ;
  glLightfv(GL_LIGHT1, GL_AMBIENT, ambient1);
  GLfloat diffuse1[] =  1.0, 0.0, 0.0, 1.0 ;
  glLightfv(GL_LIGHT1, GL_DIFFUSE, diffuse1);
  GLfloat specular1[] =  1.0f, 1.0f, 1.0f, 1.0f ;
  glLightfv(GL_LIGHT1, GL_SPECULAR, specular1);
  GLfloat light_position1[] =  0.0f, 0.0f, 0.2f, 0.0f ;
  glLightfv(GL_LIGHT1, GL_POSITION, light_position1);
  GLfloat spotExp = 20.0;
  glLightf(GL_LIGHT1, GL_SPOT_EXPONENT, spotExp);
  GLfloat spotCutoff = 60.0;
  glLightf(GL_LIGHT1, GL_SPOT_CUTOFF, spotCutoff);


static void
drawPlane(int w, int h)

  int i, j;
  float dw = 1.0 / w;
  float dh = 1.0 / h;

  glNormal3f(0.0, 0.0, 1.0);
  for (j = 0; j < h; ++j) 
    glBegin(GL_TRIANGLE_STRIP);
    for (i = 0; i <= w; ++i) 
      glVertex2f(dw * i, dh * (j + 1));
      glVertex2f(dw * i, dh * j);
    
    glEnd();
  


static void
Draw(void)

  glClearColor(0.0, 0.0, 0.0, 1.0);
  glClear(GL_COLOR_BUFFER_BIT);

  glPushMatrix();
  glTranslatef(0,1.25,0);
  float light_pos[4] = 0,0,0,1;
  glLightfv(GL_LIGHT1, GL_POSITION, light_pos);
  float light_dir[3] = 0,-1,0;
  glLightfv(GL_LIGHT1, GL_SPOT_DIRECTION, light_dir);
  glPopMatrix();

  glPushMatrix();
  glRotatef(-90.0, 1, 0, 0);
  glScalef(1.9, 1.9, 1.0);
  glTranslatef(-0.5, -0.5, 0.0);
  drawPlane(16, 16);
  glPopMatrix();
  glFlush();


int
main(int argc, char **argv)

  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE);
  glutCreateWindow("spotlight");
  Init();
  glutDisplayFunc(Draw);
  glutMainLoop();
  return 0;