OpenGL Alpha混合

//红宝书---Alpha分量混合P158
#include<GL\freeglut.h>

static int leftFirst = GL_TRUE;
void init(void)
{
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);//设置以【源像素的Alpha*目标像素+(1-源像素的Alpha)*源像素】的混合方式
	glShadeModel(GL_FLAT);
	glClearColor(0.0,0.0,0.0,0.0);
}

void drawLeftTriangle(void)
{
	glBegin(GL_TRIANGLES);
		glColor4f(1.0,1.0,0.0,0.75);
		glVertex3f(0.1,0.9,0.0);
		glVertex3f(0.1,0.1,0.0);
		glVertex3f(0.7,0.5,0.0);
	glEnd();
}

void drawRightTriangle(void)
{
	glBegin(GL_TRIANGLES);
		glColor4f(0.0,1.0,1.0,0.75);
		glVertex3f(0.9,0.9,0.0);
		glVertex3f(0.3,0.5,0.0);
		glVertex3f(0.9,0.1,0.0);
	glEnd();
}

void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT);

	if(leftFirst)
	{
		drawLeftTriangle();//左边的三角形为目标像素
		drawRightTriangle();//右边的三角形为源像素，用其Alpha分量与目标像素相乘+（1-Alpha分量）*源像素——————>帧缓冲区
	}
	else
	{
		drawRightTriangle();
		drawLeftTriangle();
	}

	glFlush();
}

void reshape(int w,int h)
{
	glViewport(0,0,(GLsizei)w,(GLsizei)h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	if(w <= h)
		gluOrtho2D(0.0,1.0,0.0,1.0*(GLfloat)h/(GLfloat)w);
	else
		gluOrtho2D(0.0,1.0*(GLfloat)w/(GLfloat)h,0.0,1.0);
}

void keyboard(unsigned char key,int x,int y)
{
	switch(key)
	{
	case 't':case 'T':
		leftFirst = !leftFirst;
		glutPostRedisplay();
		break;
	case 27:
		exit(0);
		break;
	default:
		break;
	}
}

int main(int argc,char **argv)
{
	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
	glutInitWindowSize(500,500);
	glutCreateWindow(argv[0]);
	init();
	glutReshapeFunc(reshape);
	glutKeyboardFunc(keyboard);
	glutDisplayFunc(display);
	glutMainLoop();
	return 0;
}