#!python
# -*- mode: python; Encoding: utf-8; coding: utf-8 -*-
# Last updated: <2020/04/23 15:00:16 +0900>
"""
Calc camera fov area.

* +x : right, +y : top, +z : front

Windows10 x64 1909 + Python 3.7.7 64bit
"""

import math

def get_rot_pos(x, y, ang):
    a = math.radians(ang)
    xr = x * math.cos(a) - y * math.sin(a)
    yr = x * math.sin(a) + y * math.cos(a)
    return xr, yr

def dump_pos(p, s):
    print("%s = (%f, %f, %f)" % (s, p[0], p[1], p[2]))

def get_fov_area(cx, cy, cz, cxrot, fov, w, h):
    print("Camera pos = (%f, %f, %f)" % (cx, cy, cz))
    print("Camera x rot = %f" % cxrot)
    print("Camera fov = %f" % fov)
    print("Window size = %d x %d" % (w, h))
    
    d = (h/2) / math.tan(math.radians(fov/2))
    p1 = (-w/2, h/2, -d)
    p2 = (w/2, -h/2, -d)
    
    # Rotate by Camera angle
    z, y = get_rot_pos(p1[2], p1[1], -cxrot)
    p1r = (p1[0], y, z)
    z, y = get_rot_pos(p2[2], p2[1], -cxrot)
    p2r = (p2[0], y, z)
    
    y = -cy
    xr, yr, zr = p1r
    z = y * zr / yr + cz
    x = y * xr / yr
    topleft = (x, 0, z)

    xr, yr, zr = p2r
    z = y * zr / yr + cz
    x = y * xr / yr
    bottomright = (x, 0, z)

    dump_pos(p1, "p1")
    dump_pos(p2, "p2")
    dump_pos(p1r, "p1r")
    dump_pos(p2r, "p2r")
    dump_pos(topleft, "topleft")
    dump_pos(bottomright, "bottomright")

get_fov_area(0, 40, 12, -65, 60, 1280, 720)