OpenGL: Unprojecting a point

[hopestar]

I've been searching around the internet for a while now and I'm not finding the answer to my question so I thought I'd give this a whirl...

All I want to do is click on a point in my application's window and have the app draw a dot at that point. My problem comes in when I use the coordinates I get from unprojecting the mouse click to draw the point. The window size is 600 x 600 but my viewing area is set up as glOrtho(-30, 30, -30, 30, -10, 10)

Is there a way to unproject the mouse click to the glOrtho coordinates? If there is, does it lose too much accuracy?

Thanks for any help!!

[Zeeshan]

Take a look at this.

// draw point on mouse click
#include <GL/glut.h>

/* to remove Console Window */
#pragma comment(linker, "/subsystem:windows")
#pragma comment(linker, "/entry:mainCRTStartup")

GLint g_iHeight = 500;
GLint g_iWidth = 500;

void display()
{
	glClearColor(1.0, 1.0, 1.0, 1.0);	/* set current color to white */
	glClear(GL_COLOR_BUFFER_BIT);		/* clear the display */
	glFlush();
}

void drawPoint(int x, int y)
{
	glPointSize(3);
	glColor3f(0.0, 0.0, 1.0);
	glBegin(GL_POINTS);
		glVertex2i(x, g_iHeight - y);
	glEnd();
	glFlush();
}

void mouse(int button, int state, int x, int y)
{
	switch (button)
	{
	case GLUT_LEFT_BUTTON:

		if (GLUT_DOWN == state)
		{
			drawPoint(x, y);
		}
		break;
	}
}

void reshape(GLint width, GLint height)
{
	/* update the value of variable whenever window resize */
	g_iWidth = width;
	g_iHeight = height;
	//gluOrtho2D(0, 0 + g_iWidth, 0, 0 + g_iHeight);
}

int main(int argc, char *argv[])
{
	/* initialize GLUT system */
	glutInit(&argc, argv);

	/* initilise it to use double buffer */
	glutInitDisplayMode(GLUT_RGB);

	/* width=500 pixels height=500 pixels */
	glutInitWindowSize(g_iWidth, g_iHeight);

	/* set window position to 100, 100 */
	glutInitWindowPosition(100, 100);

	/* create window */
	glutCreateWindow("GL Test");

	/* how object is mapped to window */
	gluOrtho2D(0, 0 + g_iWidth, 0, 0 + g_iHeight);

	/* register mouse function */
	glutMouseFunc(mouse);
	
	/* register function when window resize */
	glutReshapeFunc(reshape);

	/* register window display function */
	glutDisplayFunc(display);

	/* start processing events */
	glutMainLoop();
	return 0;
}

Hope it helps.