小白学opengl之gluLookAt函数例子

时间：2022-09-10 21:23:05
#include <stdlib.h>
#include <stdio.h>
#include <GL/glut.h>
#include <GL/glu.h>

using namespace std;

GLdouble wx,wy,wz;/*returned world x,y,z coords */  
void init(void)
{
	glClearColor(0,0,0,0);
	glShadeModel(GL_FLAT);
}

void display(void)
{
	//printf("use display\n");

	glClear(GL_COLOR_BUFFER_BIT);
	// float mat[16];
	// glGetFloatv(GL_MODELVIEW_MATRIX, mat);
	// glColor3f(1,1,0);
	// glPointSize(10);
	// glVertex2f(0.1,0.1);
	// for(int i=0;i<16;++i)
	// {
	// 	printf("%f ",mat[i]);
	// }
	// printf("\n");
	//glGetFloatv(GL_PROJECTION_MATRIX, mat);
	// for(int i=0;i<16;++i)
	// {
	// 	printf("%f ",mat[i]);
	// }
	// printf("\n");
	//glTranslatef(-0.5f,-0.5f,-1.0f);  
	glColor3f(0,1,0);  
	glPointSize(5);
	glBegin(GL_POINTS);
	glVertex3f(0,1.1,0);//任意一个>1的分量都不会被显示
	glEnd();


	glutSwapBuffers();

}

void reshape(int w,int h)
{
	//printf("use reshape\n");
	glViewport(0,0,(GLsizei)w,(GLsizei)h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();//如果注释，每次调用reshape都会累加结果
	//gluPerspective( 45.0, (GLfloat)w/(GLfloat)h, 0.1, 100.0 );  

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();//如果注释，每次调用reshape都会累加结果
	gluLookAt(0,0,0,0,1.1,0,0,1,0);

}


// void mouse(int button, int state, int x, int y)
// { 
// 	GLint viewport [4];  
// 	GLdouble mvmatrix [16],projmatrix [16];  
// 	GLint realy;/*OpenGL y coordinate position */  

// 	switch (button)
// 	{  
// 		case GLUT_LEFT_BUTTON: 
// 		{
// 			if (state == GLUT_DOWN) 
// 			{
// 				glGetDoublev(GL_MODELVIEW_MATRIX,mvmatrix);  
// 				glGetDoublev(GL_PROJECTION_MATRIX,projmatrix); 
// 				glGetIntegerv(GL_VIEWPORT,viewport);  
// 				note viewport [3] is height of window in pixels   
// 				realy =viewport [3] -(GLint)y -1;  
// 				printf("Coordinates at cursor are (%4d,%4d)\n " , x,realy);  
// 				gluUnProject((GLdouble)x,(GLdouble)realy,0.1,  
// 				mvmatrix,projmatrix,viewport,&wx,&wy,&wz); 
// 				printf("World coords at z=0.0 are (%f,%f,%f)\n ",  
// 				wx,wy,wz); 



// 			}
// 			break;
// 		} 

// 		// Start of drag.  


// 	} 

// 	// redraw.
// 	glutPostRedisplay();
// }

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

	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
	glutInitWindowSize(500,500);
	glutInitWindowPosition(100,100);//(0,0)表示窗口的左上角对齐屏幕的左上角，（0，100）窗会向下移100
	glutCreateWindow("test");
	init();

	glutDisplayFunc(display);
	glutReshapeFunc(reshape);
	//glutMouseFunc(mouse);
	glutMainLoop();

	return 0;
}

////////////////////////////////////////////////////////////////////////////////////////

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

using namespace std;
GLdouble mvmatrix [16],projmatrix [16];  

GLdouble wx,wy,wz;/*returned world x,y,z coords */  
void init(void)
{
	glClearColor(0,0,0,0);
	glShadeModel(GL_FLAT);
}

void display(void)
{
	//printf("use display\n");

	glClear(GL_COLOR_BUFFER_BIT);
	float mat[16];
	glGetFloatv(GL_MODELVIEW_MATRIX, mat);


	for(int i=0;i<16;++i)
	{
		printf("%f ",mat[i]);
	}
	printf("\n");
	glGetFloatv(GL_PROJECTION_MATRIX, mat);
	for(int i=0;i<16;++i)
	{
		printf("%f ",mat[i]);
	}
	printf("\n");

	glColor3f(0,1,0);  
	glPointSize(5);
	glBegin(GL_POINTS);
	glVertex3f(0,0.5,0.5);//任意一个>1的分量都不会被显示

	glColor3f(1,1,0);
	glPointSize(10);
	glVertex3f(0,1,-1);
	glEnd();


	glutSwapBuffers();

}

void reshape(int w,int h)
{
	//printf("use reshape\n");
	glViewport(0,0,(GLsizei)w,(GLsizei)h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();//如果注释，每次调用reshape都会累加结果
	glOrtho(-1,1,-1,1,-1,1);//照相机在坐标原点时默认的视景体


	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();//如果注释，每次调用reshape都会累加结果
	gluLookAt(0,0,0,0,1,0,0,1,0);
}


// void mouse(int button, int state, int x, int y)
// { 
// 	GLint viewport [4];  
// 	GLdouble mvmatrix [16],projmatrix [16];  
// 	GLint realy;/*OpenGL y coordinate position */  

// 	switch (button)
// 	{  
// 		case GLUT_LEFT_BUTTON: 
// 		{
// 			if (state == GLUT_DOWN) 
// 			{
// 				glGetDoublev(GL_MODELVIEW_MATRIX,mvmatrix);  
// 				glGetDoublev(GL_PROJECTION_MATRIX,projmatrix); 
// 				glGetIntegerv(GL_VIEWPORT,viewport);  
// 				note viewport [3] is height of window in pixels   
// 				realy =viewport [3] -(GLint)y -1;  
// 				printf("Coordinates at cursor are (%4d,%4d)\n " , x,realy);  
// 				gluUnProject((GLdouble)x,(GLdouble)realy,0.1,  
// 				mvmatrix,projmatrix,viewport,&wx,&wy,&wz); 
// 				printf("World coords at z=0.0 are (%f,%f,%f)\n ",  
// 				wx,wy,wz); 



// 			}
// 			break;
// 		} 

// 		// Start of drag.  


// 	} 

// 	// redraw.
// 	glutPostRedisplay();
// }

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

	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
	glutInitWindowSize(500,500);
	glutInitWindowPosition(100,100);//(0,0)表示窗口的左上角对齐屏幕的左上角，（0，100）窗会向下移100
	glutCreateWindow("test");
	init();

	glutDisplayFunc(display);
	glutReshapeFunc(reshape);
	//glutMouseFunc(mouse);
	glutMainLoop();

	return 0;
}

得到 投影矩阵和模型视图矩阵后  算出两者乘积 {(0,0,0,0),(0,0,-1,0),(0,0,0,0),(0,0,0,1)} ，取空间任意两点的 与 这个矩阵相乘  ，得到的列向量 第一个分量和第三个分量都是0，此时与镜头朝向(0,1,0)在同一直线上，打印到屏幕上显示 两个点的位置重合 只能看到一个点

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