/* *  shadow.c *  This program draws a polygon and its shadow. */
/* E. Angel, Interactive Computer Graphics */
/* A Top-Down Approach with OpenGL, Third Edition */
/* Addison-Wesley Longman, 2003 */
#include <stdlib.h>           #include <GL/glut.h>              /* glut.h */   GLfloat theta=0.0;void display(void){/* set clear color to white and clear window */	GLfloat light[3]={0.0, 10.0, 0.0};	GLfloat m[16];	double sin(), cos();	int i;	for(i=0;i<16;i++) m[i]=0.0;	light[0]=10.0*sin((6.28/180.0)*theta);	light[2]=10.0*cos((6.28/180.0)*theta);	m[0]=m[5]=m[10]=1.0;	m[7]=-1.0/light[1];	glClearColor (1.0, 1.0, 1.0, 0.0);	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);/* set drawing/fill  color to red */	glColor3f(1.0, 0.0, 0.0);/* set up standard orthogonal view with clipping *//* box as cube of side 2 centered at origin */	glMatrixMode (GL_PROJECTION);	glLoadIdentity ();	glOrtho(-2.0, 2.0, -2.0, 2.0, -5.0, 5.0); 	glMatrixMode(GL_MODELVIEW);	glLoadIdentity();	gluLookAt(1.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0);/* define unit square polygon */	glBegin(GL_POLYGON);	 	glVertex3f(-0.5, 0.5, -0.5);	 	glVertex3f(-0.5, 0.5, 0.5);	 	glVertex3f(0.5, 0.5, 0.5);	 	glVertex3f(0.5, 0.5, -0.5);	glEnd();	glPushMatrix();	glTranslatef(light[0], light[1],light[2]);	glMultMatrixf(m);	glTranslatef(-light[0], -light[1],-light[2]);	glColor3f(0.0,0.0,0.0);	glBegin(GL_POLYGON);	 	glVertex3f(-0.5, 0.5, -0.5);	 	glVertex3f(-0.5, 0.5, 0.5);	 	glVertex3f(0.5, 0.5, 0.5);	 	glVertex3f(0.5, 0.5, -0.5);	glEnd();	glPopMatrix();/* Swap buffers */	glutSwapBuffers();}void myidle(){   theta+=2.0;   if(theta>360.0) theta-=360;   glutPostRedisplay();}int main(int argc, char** argv){/* Initialize mode and open a window in upper left corner of screen *//* Window title is name of program (arg[0]) */	glutInit(&argc,argv);	glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB |GLUT_DEPTH); 	glutInitWindowSize(500,500);	glutInitWindowPosition(0,0);	glutCreateWindow("shadow");	glutDisplayFunc(display);	glEnable(GL_DEPTH_TEST);	glutIdleFunc(myidle);	glutMainLoop();}