Draw a circle and a square on the screen. The square is in front and the circle is behind. You can move the square through the keyboard. In the following cases, the square can only move within the cir

/* Draw a square on the screen , use ice.bmp Texture map the square ; Draw a yellow teapot behind the square , Suppose the square is transparent , Draw the mixing effect of teapot and square ; adopt A,D,W and K Press the key to adjust the teapot in X Axis and Y Position of the shaft , As follows ：[1] A：x Value reduction on axis ;
[2] D：x The value on the axis increases ;[3] W：y The value on the axis increases ; [4] K：y Value reduction on axis . Add a template cache to the program so that the teapot can only move in a square area .
*/
#define GLUT_DISABLE_ATEXIT_HACK

#include "windows.h"
#include <gl/glut.h>
#include "math.h"
float alpha = 0.5;
float p1=0.0;
float p2=0.0;


// initialization OpenGL
void init(void)
{
	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);// Set the background color 


	glClearStencil(1);
	glClearDepth(1.0f);
	

}
// The main drawing process 
void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// Clear color cache     
	glLoadIdentity();
	glEnable(GL_DEPTH_TEST);

	
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_ALWAYS, 0x01, 0xFFFFFFFF);
glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);//
	
    // Draw a teapot 
	glLoadIdentity();
	glPushMatrix();


	glTranslatef(0.0, 0.0, -6.0);
	glColor3f(1, 1, 0);
	//glBlendFunc(GL_ZERO, GL_ONE);
    glutSolidSphere(2, 36, 36);

	glEnable(GL_DEPTH_TEST);
	glDisable(GL_BLEND);
	glPopMatrix();


glStencilFunc(GL_NOTEQUAL, 0x00, 0xFFFFFFFF);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

	// Draw irregular quadrilateral 
	glPushMatrix();
	glEnable(GL_BLEND);
	glDisable(GL_DEPTH_TEST);
	glTranslatef(-1+p1, -1+p2, -4.0);
	glShadeModel(GL_FLAT);
	//glEnable(GL_TEXTURE_2D);
	glColor3f(1.0, 0.0, 0.0);

	glBegin(GL_QUADS);
    glVertex3f(0.0, 0.0, 0.0);
    glVertex3f(1.0, 0.0, 0.0);
	glVertex3f(1.0, 1.0, 0.0);
	glVertex3f(0.0, 1.0, 0.0);
	glEnd();
	glPopMatrix();




	glFlush();
	glutSwapBuffers();
}
// Call when the window changes size 
void reshape(int w, int h) {
	glViewport(0, 0, w, h);// Set up the viewport 
	glMatrixMode(GL_PROJECTION);// Set the current projection transformation mode 
	glLoadIdentity();// Replace the current transformation matrix with the identity matrix 
	gluPerspective(90, (float)w / h, 4, 10.0);// Set the orthographic projection body 
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	gluLookAt(0.0, 0.0, 4.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
}
// Dealing with keyboards 
void keyboard(unsigned char key, int x, int y) {
	switch (key) {
	//	[1] A：x Value reduction on axis ;[2] D：x The value on the axis increases ;[3] W：y The value on the axis increases ; [4] K：y Value reduction on axis .
	case 27://esc Key to exit 
		exit(0);
		break;
	case 'a':
	case 'A':
		p1=p1-1;
		
		glutPostRedisplay();
		break;
	case 'd':
	case 'D':
		p1=p1+1;
		glutPostRedisplay();
		break;

	case 'w':
	case 'W':
		p2=p2+1;
		glutPostRedisplay();
		break;

	case 'k':
	case 'K':
		p2=p2-1;
		glutPostRedisplay();
		break;
	default:
		break;
	}
}
int main(int argc, char* argv[])							// The main function :  The number of arguments & Parameter values 
{
	glutInit(&argc, argv);
	glutInitWindowSize(640, 480);
	glutCreateWindow("Basic");// Set the window title 
	init();// initialization OpenGL
	glutDisplayFunc(display);// Set display callback function  
	glutReshapeFunc(reshape);// Set up reshape Callback function 
	glutKeyboardFunc(keyboard);// Set the keyboard callback function 
	glutMainLoop();// Enter the main loop 	
}