OpenGL convert mouse position to world coordinates without gluUnproject in Python?

Question

EDIT: I changed the bottom left to -1,-1 and the top right to 1,1, and while I can draw objects within this range, I cannot map the mouse x,y to the world space.

I have been trying to learn OpenGL and my current goal is to move a circle on mouse drag. I have created the circle, but I cannot seem to be able to map my mouse coordinates to the world coordinates using glOrtho. I also set the initial window position to 100, 100, I don't know if that is relevant to the issue though.

For reference this is my init code:

def init():
    # select clearing color
    glClearColor(0.0, 0.0, 0.0, 0.0)

    # initialize viewing values
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0)

I know that the glOrtho takes the left, right, bottom, top, near and far values, but when I try to convert to world space coordinates from mouse position(since I only need the x and y so I can calculate distance from the circle's origin) I end up with coordinates in the range 0.0 - 1.25, which makes no sense to me at all, because it should be 0.0 - 1.0.

This is my glutMotionFunc:

def click(x, y):
    global current_circle

    nx = float(x * SCREEN_SIZE / SCREEN_SIZE)
    ny = float(y * SCREEN_SIZE / SCREEN_SIZE)

    print("Mouse click", nx, ny)

    for circle in circles:
        print("Circle center", circle.cx, circle.cy)
        if (np.square(nx - circle.cx) + np.square(ny - circle.cy)) <= np.square(circle.r * (SCREEN_SIZE / 10)):
            current_circle = circle
            current_circle.set_position(nx, ny)

            glutPostRedisplay()

Also, why is my window 300x300 when it should be 250x250? I don't set the window size anywhere but the above init function.

Answer 1

I figured out my issues:

1. First off, I need to set the window size before I create it.
2. I was not using normalized device coordinates.
3. I found the simple equation to convert my mouse position to device coordinates: new_x = glut_mouse_x / (SCREEN_SIZE/2) - 1.0 new_y = -1 * (glut_mouse_y / (SCREEN_SIZE/2) - 1.0)