4. Draw a red triangle and a yellow square on the screen. Triangle in the back, small; Square in front, big. Using the fusion technology, the triangle can be seen through the square, and the source an

#include "windows.h"
#include <gl/glut.h>
#include "math.h"
GLint mixMode[] = { GL_ZERO,GL_ONE,GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA };
int m=2, n=3;
// initialization OpenGL
void init(void)
{
	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);// Set the background color 
	glShadeModel(GL_SMOOTH);// Set shading , There are two selection modes ：GL_FLAT（ No gradients ） and GL_SMOOTH（ Gradient transition ）
}
// The main drawing process 
void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// Clear color cache     
	glLoadIdentity();
	glEnable(GL_DEPTH_TEST);

	// Draw the first quadrilateral 
	glPushMatrix();
	glTranslatef(-1, -1, -6.0);
	glShadeModel(GL_FLAT);
	glEnable(GL_TEXTURE_2D);
	glColor3f(1, 0, 0);
	glBegin(GL_TRIANGLES);
	 glVertex3f(0.0, 0.0, 0.0);
	 glVertex3f(2.0, 0.0, 0.0);
	glVertex3f(2.0, 2.0, 0.0);
	
	glEnd();
	glPopMatrix();

	// Draw the second quadrilateral 
	glLoadIdentity();
	glPushMatrix();
	glTranslatef(0.0, 0, -4.0);
	glEnable(GL_BLEND);
	glDisable(GL_DEPTH_TEST);
	glColor4f(1.0, 1.0, 0.0, 0.5);
	glBlendFunc(mixMode[m], mixMode[n]);
	glBegin(GL_QUADS);
	glVertex3f(0.0, 0.0, 0.0);
	glVertex3f(2.0, 0.0, 0.0);
	glVertex3f(2.0, 2.0, 0.0);
	glVertex3f(0.0, 2.0, 0.0);
	glEnd();
	glEnable(GL_DEPTH_TEST);
	glDisable(GL_BLEND);
	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) {
	case 27://esc Key to exit 
		exit(0);
		break;
	case 's':
	case 'S':
		m = 2;
		n = 3;
		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 	
}