;;; Chickadee Game Toolkit
;;; Copyright © 2016 David Thompson <dthompson2@worcester.edu>
;;;
;;; Licensed under the Apache License, Version 2.0 (the "License");
;;; you may not use this file except in compliance with the License.
;;; You may obtain a copy of the License at
;;;
;;;    http://www.apache.org/licenses/LICENSE-2.0
;;;
;;; Unless required by applicable law or agreed to in writing, software
;;; distributed under the License is distributed on an "AS IS" BASIS,
;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
;;; See the License for the specific language governing permissions and
;;; limitations under the License.

(define-module (chickadee math)
  #:export (pi
            pi/2
            tau
            cotan
            clamp
            min
            max
            lerp
            degrees->radians
            radians->degrees)
  #:replace (min max))

(define pi 3.1415926535897932)
(define pi/2 1.5707963267948966)
(define tau 6.283185307179586) ;; AKA 2pi

(define-inlinable (cotan z)
  "Return the cotangent of Z."
  (/ 1.0 (tan z)))

(define-inlinable (clamp min max x)
  "Restrict X to the range defined by MIN and MAX. Assumes that MIN is
actually less than MAX."
  (cond ((< x min) min)
        ((> x max) max)
        (else x)))

;; Some macro trickery to inline calls to min/max with 2 arguments.
;; We often call min/max on floating point values, so inlining such
;; calls allows the compiler to unbox many of these operations,
;; reducing allocation.
(define-syntax min
  (syntax-rules ()
    ((_ a b)
     (if (< a b) a b))
    ((_ a b ...)
     (let ((m (min b ...)))
       (if (< a m) a m)))))

(define-syntax max
  (syntax-rules ()
    ((_ a b) (if (> a b) a b))
    ((_ a b ...)
     (let ((m (max b ...)))
       (if (> a m) a m)))))

(define-inlinable (lerp start end alpha)
  (+ (* start (- 1.0 alpha))
     (* end alpha)))

(define-inlinable (degrees->radians degrees)
  (/ (* pi degrees) 180.0))

(define-inlinable (radians->degrees radians)
  (/ (* 180.0 radians) pi))