Application of OpenGL gllightfv function and related knowledge of light source

First introduced OpenGL Simple lighting model , Its reflected light can be divided into three components ： Ambient reflected light , Diffuse light , The mirror reflects light . Is that you want to achieve a lighting effect , These three components need to be set , The sum of the three reaches the lighting effect you want .

1. The ambient light , Simply put, it is light in the environment , It seems to come from all directions

2. Diffuse reflection , From one direction , Light shines on objects , It radiates evenly in all directions , No matter where the viewpoint is , Objects are all equally bright .

3. Specular light , From a particular direction , And reflect it in the other direction .

glLightfv The function prototype ：void glLightfv( Light source name , type , assignment );

There are four main types ： The color of the light source ---AMBIENT、DIFFUSE、SPECULAR And light source location ---POSITION

among DIFFUSE The parameters of are closely related to the color of the light source , Generally, simple lighting models only set DIFFUSE It's enough

GLfloat light0_diffuse[]= { 1.0, 0.0, 0, 1.0};
glLightfv(GL_LIGHT0, GL_DIFFUSE, light0_diffuse);

The following is the code of assignment ：

GLfloat light0_ambient[]= { 0.2, 0.2, 0.2, 1.0 };
GLfloat light0_diffuse[]= { 1.0, 0.0, 0, 1.0};
GLfloat light0_specular[] = { 1.0, 0, 0, 1.0 };
glLightfv(GL_LIGHT0, GL_AMBIENT, light0_ambient);
glLightfv(GL_LIGHT0, GL_DIFFUSE, light0_diffuse);
glLightfv(GL_LIGHT0, GL_SPECULAR,light0_specular);

Set the light source position

GLfloat light0_position[] = { 1.0, 1.0, 1.0, 0.0 };
 
glLightfv(GL_LIGHT0, GL_POSITION,light0_position);

Turn on the light source  

glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_DEPTH_TEST);

glEnable(GL_LIGHTING); Indicates the main switch for starting the lighting  glEnable(GL_LIGHT0);// open 0 Signal light source

glEnable(GL_DEPTH_TEST);// Open depth buffer , draw 3D When using images

Complete code

 

 
#include "stdafx.h"
#include <GL/glut.h>
#include "math.h"
void reshape(int w,int h)
{
	glViewport(0,0,(GLsizei)w,(GLsizei)h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	if(w<h)
	glOrtho(-1.5, 1.5, -1.5,1.5 * (GLfloat)h / (GLfloat)w, -1.5,1.5);
	else
		glOrtho(-1.5* (GLfloat)w / (GLfloat)h, 1.5, -1.5,1.5, -1.5,1.5 );
		glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();
}
 
void init ()
{
glClearColor(1.0,1.0,1.0,0.0);
glColor3f(1.0,1.0,0.0);
GLfloat light0_ambient[]= { 0.2, 0.2, 0.2, 1.0 };
GLfloat light0_diffuse[]= { 1.0, 0.0, 0, 1.0};// Red point light source 
GLfloat light0_specular[] = { 1.0, 0, 0, 1.0 };
GLfloat light0_position[] = { 1.0, 1.0, 1.0, 0.0 };
glLightfv(GL_LIGHT0, GL_AMBIENT, light0_ambient);
glLightfv(GL_LIGHT0, GL_DIFFUSE, light0_diffuse);
glLightfv(GL_LIGHT0, GL_SPECULAR,light0_specular);
glLightfv(GL_LIGHT0, GL_POSITION,light0_position);
glShadeModel(GL_SMOOTH);// Smooth coloring , Transition color effect 
glEnable(GL_LIGHTING);// Start lighting , Main switch 
glEnable(GL_LIGHT0);// open 0 Signal light source 
glEnable(GL_DEPTH_TEST);
 
}
void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
	glutSolidTeapot(0.5);
	glFlush();
}
int main(int argc, char* argv[])
{
	glutInit(&argc,argv);
	glutInitWindowPosition(200,200);
    glutInitWindowSize(500,500);
	glutCreateWindow("001");
	init();
	glutDisplayFunc(display);
	glutReshapeFunc(reshape);
	glutMainLoop();
	return 0;
}
 

Running results

  We found that the color of the teapot was covered by the set light , Its own color （ yellow ） It doesn't show . Here we introduce a new function --- Color material function glEnable(GL_COLOR_MATERIAL); It ensures that the graphic color can be preserved after the light effect is turned on . Put it in init Function .

The effect of adding tea pot is as follows

 

In fact, the light source is the basis of all lighting effects , Nothing can be said without a light source .OpenGL We can set up ８ A light source , Their numbers are GL_LIGHT0、GL_LIGHT1、……、GL_LIGHT7. It is equivalent to having ８ The SUNS , But the position of each sun 、 The direction and the light it emits can be completely different . therefore ,OpenGL When we set the light source , The main thing is to set its color 、 Location 、 Direction and other properties . in addition ,OpenGL Any light source in the can emit ambient light of different intensity 、 Scattered light 、 The mirror reflects light , These aspects together determine the color of the light source .

We go through glLightfv（ Light source number , Light source characteristics , Parameter data ） To set the light source . among , The light source number can be GL_LIGHT0、GL_LIGHT1、……、GL_LIGHT7 common 8 It's worth . Light source characteristics are mainly desirable GL_AMBIENT（ Set the ambient light properties of the light source , The default value is (0,0,0,1)）、GL_DIFFUSE（ Set the scattered light attribute of the light source , The default value is (1,1,1,1)）、GL_SPECULAR（ Set the specular light properties of the light source , The default value is (1,1,1,1)）、GL_POSITION（ Set the position of the light source , The default value is (0,0,1,0)）. The format of parameter data should be array , That is, the vector form in Mathematics .

The following code , We will completely set the properties of a light source ：

GLfloat Va[]={0.4,0.4,0.4,1};           // Light source ambient light intensity array   
GLfloat Vd[]={0.6,0.6,0.6,1};           // Light source scattered light intensity array   
GLfloat Vs[]={0.6,0.6,0.6,1};           // Light source specular light intensity array   
GLfloat Vp[]={1,1,1,1};             // Array of light source positions   
glLightfv(GL_LIGHT0,GL_AMBIENT,Va); // Set up 0 Ambient light properties of No. 1 light source   
glLightfv(GL_LIGHT0,GL_DIFFUSE,Vd); // Set up 0 Scattered light attribute of No. 1 light source   
glLightfv(GL_LIGHT0,GL_SPECULAR,Vs);    // Set up 0 Specular light attribute of No. 1 light source   
glLightfv(GL_LIGHT0,GL_POSITION,Vp);    // Set up 0 The position attribute of the light source   

The property of the light source is set , And call glEnable(GL_LIGHT0) To turn on the light . It's equivalent to buying a flashlight 、 Install the battery （ Set light source ）, But if you don't turn on the switch （ Turn on the power ）, Flashlights don't work .

in addition , about GL_POSITION, Its position array (x,y,z,w) Defines the position of the light source in space . But why three-dimensional space is needed 4 How much is it ？ In fact, homogeneous coordinates are used here , When w≠0 when , It means that the light source is in space (x,y,z) It's about , The light source at this time is called a fixed-point light source ; When w＝0 when , According to the properties of homogeneous coordinates , It means that the light source is located at infinity , At this time, the light source is called a directional light source , All the lights are almost equal to each other , Like the sun . Its light direction is from point （x,y,z） Point to (0,0,0).

Will be the first 2 Make the following modifications to the cube example in Chapter . The modified void __fastcall TForm1::OpenGL1 GLPaint(TObject *Sender) The code at is as follows （ The rest is the same ）：

void __fastcall TForm1::OpenGL1GLPaint(TObject *Sender)  
{  
  glEnable(GL_DEPTH_TEST);          // Hidden surface elimination   
  glClear(GL_DEPTH_BUFFER_BIT); // Clear window color   
 
  const GLfloat glfLightAmbient1[4] = {0.1, 0.1, 0.1, 1.0};  
  const GLfloat glfLightAmbient2[4] = {0.4, 0.4, 0.4, 1.0};  
  const GLfloat glfLightDiffuse1[4] = {0, 0.8, 0.8, 1.0};  
  const GLfloat glfLightDiffuse2[4] = {0.8, 0.8, 0.8, 1.0};  
  const GLfloat glfLightSpecular1[4] = {0, 0.8, 0.8, 1.0};  
  const GLfloat glfLightSpecular2[4] = {0.8, 0.8, 0.8, 1.0};  
  const GLfloat glPosition1[4]={0,0,1,0};  
  const GLfloat glPosition2[4]={0.6,0.6,-0.6,1};  
  glLightfv(GL_LIGHT0, GL_AMBIENT,  glfLightAmbient1);  
  glLightfv(GL_LIGHT0, GL_DIFFUSE,  glfLightDiffuse1);  
  glLightfv(GL_LIGHT0, GL_SPECULAR, glfLightSpecular1);  
  glLightfv(GL_LIGHT0,GL_POSITION,glPosition1);  
  glLightfv(GL_LIGHT1, GL_AMBIENT,  glfLightAmbient2);  
  glLightfv(GL_LIGHT1, GL_DIFFUSE,  glfLightDiffuse2);  
  glLightfv(GL_LIGHT1, GL_SPECULAR, glfLightSpecular2);  
  glLightfv(GL_LIGHT1,GL_POSITION,glPosition2);  
  glLightModeli(GL_LIGHT_MODEL_TWO_SIDE,GL_TRUE);// Light on both sides   
      glEnable(GL_LIGHTING);// Turn on lighting   
      glEnable(GL_LIGHT0);  
      glEnable(GL_LIGHT1);// Turn on the light   
      glEnable(GL_COLOR_MATERIAL);// Enable color tracking   
      glColorMaterial(GL_FRONT,GL_AMBIENT_AND_DIFFUSE);  
// The material environment color and scattering color of the front of the object , track glColor Set the color （ Relatively awkward ,
 In fact, it's about making OpenGL according to glColor The set color automatically sets the reflection intensity of the object ）  
 
  glShadeModel(GL_FLAT);// Set the color fill mode   
   glBegin(GL_QUAD_STRIP) ;  
     glVertex3f(i,-i,i);  
     glVertex3f(i,-i,-i);  
     glColor3f(1,0,0);  
     glVertex3f(-i,-i,i);  
     glVertex3f(-i,-i,-i);  
     glColor3f(0,1,0);  
     glVertex3f(-i,i,i);  
     glVertex3f(-i,i,-i);  
     glColor3f(0,0,1);  
     glVertex3f(i,i,i);  
     glVertex3f(i,i,-i);  
     glColor3f(1,1,0);  
     glVertex3f(i,-i,i);  
     glVertex3f(i,-i,-i);  
   glEnd();  
   glBegin(GL_QUADS);  
     glVertex3f(i,-i,i);  
     glVertex3f(-i,-i,i);  
     glVertex3f(-i,i,i);  
     glColor3f(1,0,1);  
     glVertex3f(i,i,i);  
 
     glVertex3f(i,-i,-i);  
     glVertex3f(-i,-i,-i);  
     glVertex3f(-i,i,-i);  
     glColor3f(0,1,1);  
     glVertex3f(i,i,-i);  
   glEnd();  
 
      glDisable(GL_LIGHTING);// Turn off the light   
      glDisable(GL_LIGHT0);// close ０ Signal light source   
      glDisable(GL_LIGHT1); // close １ Signal light source   
}