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+# -*- encoding: utf-8 -*-
+##
+## Copyright (C) 2013 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published
+## by the Free Software Foundation; version 3 only.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+
+from math import radians
+from libc.math cimport tan
+
+from .matrix cimport Matrix
+from .vector import Vector, normalize, cross, dot
+
+
+cpdef ortho_2d(left, right, bottom, top):
+    mat = Matrix()
+    data = mat.data
+    data[0][0] = 2 / (right - left)
+    data[1][1] = 2 / (top - bottom)
+    data[2][2] = -1
+    data[3][0] = -(right + left) / (right - left)
+    data[3][1] = -(top + bottom) / (top - bottom)
+    return mat
+
+
+cpdef look_at(eye, center, up):
+    eye = Vector(eye)
+    center = Vector(center)
+    up = Vector(up)
+
+    f = normalize(center - eye)
+    u = normalize(up)
+    s = normalize(cross(f, u))
+    u = cross(s, f)
+
+    return Matrix([[s[0], u[0], -f[0], 0],
+                   [s[1], u[1], -f[1], 0],
+                   [s[2], u[2], -f[2], 0],
+                   [-dot(s, eye), -dot(u, eye), dot(f, eye), 1]])
+
+
+cpdef perspective(fovy, aspect, z_near, z_far):
+    top = tan(radians(fovy / 2)) * z_near
+    bottom = -top
+    left = -top * aspect
+    right = top * aspect
+
+    mat = Matrix()
+    data = mat.data
+    data[0][0] = (2 * z_near) / (right - left)
+    data[1][1] = (2 * z_near) / (top - bottom)
+    data[2][2] = -(z_far + z_near) / (z_far - z_near)
+    data[2][3] = -1
+    data[3][2] = -(2 * z_far * z_near) / (z_far - z_near)
+    data[3][3] = 0
+    return mat
+
+
+cpdef setup_camera(dx, dy, dz):
+    # Some explanations on the magic constants:
+    # 192. = 384. / 2. = width / 2.
+    # 224. = 448. / 2. = height / 2.
+    # 835.979370 = 224./math.tan(math.radians(15)) = (height/2.)/math.tan(math.radians(fov/2))
+    # This is so that objects on the (O, x, y) plane use pixel coordinates
+    return look_at((192., 224., - 835.979370 * dz),
+                   (192. + dx, 224. - dy, 0.), (0., -1., 0.))