#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <glut.h>

GLboolean doubleBuffer;

void draw_background()
{
	//big blue square
	glColor3ub(0,255,255);
	glBegin(GL_POLYGON);
	glVertex3i(5, 5, 0);
	glVertex3i(-5, 5, 0);
	glVertex3i(-5, -5, 0);
	glVertex3i(5, -5, 0);
	glEnd();
}
void draw_trangle()
{
	/* transparent triangle */
	glColor4ub(255, 0, 0, 0);
	glBegin(GL_POLYGON);
	glVertex3i(-4, -4, 0);
	glVertex3i(4, -4, 0);
	glVertex3i(0, 4, 0);
	glEnd();
}
void draw_blue_square()
{
	/* blue square */
	glColor3ub(0, 0, 200);
	glBegin(GL_POLYGON);
	glVertex3i(3, 3, 0);
	glVertex3i(-3, 3, 0);
	glVertex3i(-3, -3, 0);
	glVertex3i(3, -3, 0);
	glEnd();
}

/* ARGSUSED1 */
static void
Key(unsigned char key, int x, int y)
{
	switch (key) {
		case 27:
			exit(0);
	}
}

static void
Draw(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

	//big blue square
	glColor3ub(0,255,255);
	glBegin(GL_POLYGON);
	glVertex3i(5, 5, 0);
	glVertex3i(-5, 5, 0);
	glVertex3i(-5, -5, 0);
	glVertex3i(5, -5, 0);
	glEnd();

	glStencilFunc(GL_ALWAYS, 1, 1);
	glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);

	glPushMatrix();
	/* transparent triangle */
	glScalef(0.5f, 0.5f, 0.0f);
	glColor4ub(0.0f, 0.0f, 0.0f, 0.0f);
	glBegin(GL_POLYGON);
	glVertex3i(-4, -4, 0);
	glVertex3i(4, -4, 0);
	glVertex3i(0, 4, 0);
	glEnd();
	glPopMatrix();

//	glStencilFunc(GL_EQUAL, 1, 1);
//	glStencilOp(GL_INCR, GL_KEEP, GL_DECR);

	glStencilFunc(GL_EQUAL, 2, 1);
	glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

	/* blue square */
	glColor3ub(0, 0, 200);
	glBegin(GL_POLYGON);
	glVertex3i(3, 3, 0);
	glVertex3i(-3, 3, 0);
	glVertex3i(-3, -3, 0);
	glVertex3i(3, -3, 0);
	glEnd();

	if (doubleBuffer) {
		glutSwapBuffers();
	} else {
		glFlush();
	}
}

static void
Args(int argc, char **argv)
{
	GLint i;

	doubleBuffer = GL_TRUE;
	for (i = 1; i < argc; i++) {
		if (strcmp(argv[i], "-sb") == 0) {
			doubleBuffer = GL_FALSE;
		} else if (strcmp(argv[i], "-db") == 0) {
			doubleBuffer = GL_TRUE;
		}
	}
}

int
main(int argc, char **argv)
{
	GLenum type;

	glutInit(&argc, argv);
	Args(argc, argv);

	type = GLUT_RGB | GLUT_STENCIL;

	type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
	glutInitDisplayMode(type);
	glutCreateWindow("Stencil Test");

	glClearColor(0.0, 0.0, 0.0, 0.0);
	glClearStencil(0);
	glStencilMask(1);
	glEnable(GL_STENCIL_TEST);

	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glEnable(GL_BLEND);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-4, 4, -4, 4, -0.1, 0.1);
	glMatrixMode(GL_MODELVIEW);

	glutKeyboardFunc(Key);
	glutDisplayFunc(Draw);
	glutMainLoop();
	return 0;
}