math.lisp

;;; math.lisp --- math and geometry routines

;; Copyright (C) 2008  David O'Toole

;; Author: David O'Toole <dto@gnu.org>
;; Keywords: 

;; 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, either version 3 of the License, or
;; (at your option) any later version.

;; 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.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;;; Code:

(in-package :xe2)

;;; Probability

(defmacro percent-of-time (percent &body body)
  `(when (< (random 100) ,percent)
     ,@body))

(defun roll (rolls &optional (sides 6) (adds 0))
  "Total ROLLS rolls of a SIDES-sided die, then add ADDS.
So 2d6+2 would be (roll 2 6 2)."
  (let ((total 0))
    (+ adds
       (dotimes (r rolls total)
	 (incf total (+ 1 (random sides)))))))

(defun roll-under (n sides)
  (< n (random sides)))

;;; Space

(defun distance (x1 y1 x2 y2) 
 "Compute the distance between the points X1,Y1 and X2,Y2."
  (declare (integer x1 y1 x2 y2) (optimize (safety 0) (speed 3)))
  (let ((delta-x (- x2 x1))
	(delta-y (- y2 y1)))
    (sqrt (+ (* delta-x delta-x) (* delta-y delta-y)))))

(defvar *compass-directions* (list :north :south :east :west
				   :northeast :southeast
				   :northwest :southwest :here)
  "List of keywords representing the eight compass directions, plus :here.")

(defvar *compass-opposites* (list :north :south
				  :south :north
				  :east :west
				  :west :east
				  :northeast :southwest
				  :southwest :northeast
				  :southeast :northwest
				  :northwest :southeast
				  :here :here)
  "Property list mapping direction keywords to their 180-degree
opposites.")

(defparameter *left-turn* 
  '(:north :northwest
    :northwest :west
    :west :southwest
    :southwest :south
    :south :southeast
    :southeast :east
    :east :northeast
    :northeast :north))

(defparameter *right-turn*
  '(:north :northeast
    :northeast :east
    :east :southeast
    :southeast :south
    :south :southwest
    :southwest :west
    :west :northwest
    :northwest :north))

(defun opposite-direction (direction)
  "Return the direction keyword that is the opposite direction from
DIRECTION."
  (getf *compass-opposites* direction))

(defun random-direction ()
  (nth (random (length *compass-directions*))
       *compass-directions*))

(defun step-in-direction (row column direction &optional (n 1))
  "Return the point ROW, COLUMN moved by n squares in DIRECTION."
  ;; (when (minusp n)
  ;;   (setf n (abs n))
  ;;   (setf direction (opposite-direction direction)))
  (ecase direction
    (:here (values row column))
    (:north (values (- row n) column))
    (:south (values (+ row n) column))
    (:east  (values row (+ column n)))
    (:west  (values row (- column n)))
    (:northeast (values (- row n) (+ column n)))
    (:northwest (values (- row n) (- column n)))
    (:southeast (values (+ row n) (+ column n)))
    (:southwest (values (+ row n) (- column n)))))

(defun direction-to (r1 c1 r2 c2)
  "Return general direction of the ray from R1,C1 to R2,C2."
  (if (or (some #'null (list r1 c1 r2 c2))
	  (and (= r1 r2) (= c1 c2)))
      :here
      (if (< r1 r2) ; definitely to the south
	  (if (< c1 c2)
	      :southeast
	      (if (> c1 c2)
		  :southwest
		  :south))
	  (if (> r1 r2) ;; definitely to the north
	      (if (< c1 c2)
		  :northeast
		  (if (> c1 c2)
		      :northwest
		      :north))
	      ;; rows are equal; it's either east or west
	      (if (< c1 c2)
		  :east
		  :west)))))

(defun within-extents (x y x0 y0 x1 y1)
  (and (>= x x0) 
       (<= x x1)
       (>= y y0)
       (<= y y1)))

;;; Functions that trace out shapes

(defun trace-rectangle (trace-function row column height width &optional fill)
  "Call TRACE-FUNCTION for each point on the rectangle of HEIGHT and
WIDTH with top left corner at ROW COLUMN. When FILL is non-nil, fill
the rectangle."
  (block tracing
    (dotimes (r height)
      ;; Are we painting a full horizontal? (always the case when filling)
      (if (or fill (equal r 0) (equal r (- height 1)))
	  (dotimes (c width)
	    (if (funcall trace-function (+ r row) (+ c column))
		(return-from tracing)))
	  ;; no, it's a row with only verticals. just paint the left and right.
	  (if (or (funcall trace-function (+ r row) column)
		  (funcall trace-function (+ r row) (+ width column -1)))
	      (return-from tracing))))))

(defun trace-octagon (trace-function center-row center-column radius &optional thicken )
  "Call TRACE-FUNCTION for each point on the octagon of radius RADIUS
centered at row ROW, column COLUMN. When THICKEN is non-nil, thicken
the diagonals of the rectangle in order to facilitate raycasting.
It's an ugly hack, but it helps reduce artifacts."
  ;; calculate
  (let* ((origin-row (- center-row radius))
	 (origin-column (- center-column radius))
	 (side-length radius)
	 (angle-length (floor (/ (float radius) 2.0)))
	 (starting-x (+ 1 angle-length)))
    ;; draw top line
    (dotimes (i side-length)
      (funcall trace-function
	       origin-row
	       (+ origin-column starting-x i)))
    ;; draw top angles
    (dotimes (i angle-length)
      ;; left side
      (funcall trace-function
	       (+ 1 origin-row i)
	       (- center-column angle-length i 1))
      ;; right side
      (funcall trace-function
	       (+ 1 origin-row i)
	       (+ center-column angle-length i 1))
      ;;
      (when thicken
	;; left side
	(funcall trace-function
		 (+ 1 origin-row i)
		 (- center-column angle-length i))
	;; right side
	(funcall trace-function
		 (+ 1 origin-row i)
		 (+ center-column angle-length i))))
    ;; fill in diagonal points that are along the sides
    (when thicken
      ;; left side
      (funcall trace-function
	       (+ 1 origin-row angle-length)
	       (+ origin-column 1))
      ;; right side
      (funcall trace-function
	       (+ 1 origin-row angle-length)
	       (+ center-column side-length -1)))
    ;; draw side lines
    (dotimes (i side-length)
      ;; leftside
      (funcall trace-function
	       (+ 1 origin-row angle-length i)
	       origin-column)
      ;; right side
      (funcall trace-function
	       (+ 1 origin-row angle-length i)
	       (+ origin-column (* 2 side-length))))
    ;; fill in diagonal points that are along the sides
    (when thicken
	  ;; left side
	  (funcall trace-function
		   (+ origin-row side-length angle-length)
		   (+ origin-column 1))
	  ;; right side
	  (funcall trace-function
		   (+ origin-row side-length angle-length)
		   (+ center-column side-length -1)))
    ;; draw bottom angles
    (dotimes (i angle-length)
      ;; left side
      (funcall trace-function
	       (+ 1 origin-row angle-length side-length i)
	       (- center-column angle-length (- angle-length i)))
      ;; right side
      (funcall trace-function
	       (+ 1 origin-row angle-length side-length i)
	       (+ center-column angle-length (- angle-length i)))
      (when thicken
	;; left side
	(funcall trace-function
		 (+ 1 origin-row angle-length side-length i)
		 (+ 1 (- center-column angle-length (- angle-length i))))
	;; right side
	(funcall trace-function
		 (+ 1 origin-row angle-length side-length i)
		 (+ center-column angle-length (- angle-length i 1)))))
    ;; draw bottom line
    (dotimes (i side-length)
      (funcall trace-function
	       (+ 1 origin-row side-length (* 2 angle-length))
	       (+ origin-column starting-x i)))))

;;; Line of sight and lighting

;; <: lighting :>

;; We use Bresenham's line algorithm to trace out the player's field
;; of vision and determine which squares are lit.

;; See also http://en.wikipedia.org/wiki/Bresenham's\_line\_algorithm

(defun trace-column (trace-function column y0 y1)
  (let* ((diff (- y1 y0))
	 (fact (if (minusp diff) 1 -1)))
    (dotimes (n (abs diff))
      (funcall trace-function (+ y1 (* n fact)) column))))
  ;; (dotimes (n (abs (- y1 y0)))
  ;;   (funcall trace-function x (+ y0 n))))

(defun trace-row (trace-function row x0 x1)
  (let* ((diff (- x1 x0))
	 (fact (if (minusp diff) 1 -1)))
    (dotimes (n (abs diff))
      (funcall trace-function row (+ x1 (* n fact))))))

(defun trace-line (trace-function x0 y0 x1 y1)
  "Trace a line between X0,Y0 and X1,Y1.
calling TRACE-FUNCTION at each point of the line."
  ;; analyze coordinates and prepare them for bresenham's
  (let ((steep (> (abs (- y1 y0))
		  (abs (- x1 x0)))))
    ;; reflect steep lines through line y=x
    (when steep
      (rotatef x0 y0)
      (rotatef x1 y1))
    ;; swap points if line is backwards
    (let ((flipped (> x0 x1)))
      (when flipped
	(rotatef x0 x1)
	(rotatef y0 y1))
      (values flipped 
	(if (= x1 x0)
	    ;; just trace a vertical line.
	    (if flipped
		(trace-column trace-function x1 y0 y1)
		(trace-column trace-function x1 y1 y0))
	    ;; ok, use bresenham's
	    (let* ((delta-x (- x1 x0))
		   (delta-y (abs (- y1 y0)))
		   (err 0.0)
		   (delta-err (/ (float delta-y) (float delta-x)))
		   (y y0)
		   (x x0)
		   (step-y (if (< y0 y1) 1 -1)))
	      ;; main loop
	      (block tracing
		(loop while (/= x x1) do
		  ;; call the supplied trace function.
		  ;; note that trace functions get args in order (row column).
		  ;; terminate with result = nil if it returns non-nil.
		  (when (if steep
			    (funcall trace-function x y)
			    (funcall trace-function y x))
		    (return-from tracing t))
		  (incf err delta-err)
		  (when (>= err 0.5)
		    (incf y step-y)
		    (decf err 1.0))
		  ;; for next iteration
		  (incf x)))))))))

;;; Tracing macros

(defmacro with-trace-line ((row-sym col-sym) x0 y0 x1 y1 &rest body)
  (let ((tracer-sym (gensym)))
    `(labels ((,tracer-sym ,(list row-sym col-sym)
		,@body))
       (trace-line #',tracer-sym ,x0 ,y0 ,x1 ,y1))))

;; Try macroexpanding: 
;; (with-trace-line (r c) x0 y0 x1 y1 (plot r c))

(defmacro with-trace-rectangle ((row-sym col-sym)
				row column height width &rest body)
  (let ((tracer-sym (gensym)))
    `(labels ((,tracer-sym ,(list row-sym col-sym)
		,@body))
       (trace-rectangle #',tracer-sym ,row ,column ,height ,width))))

(defmacro with-trace-octagon ((row-sym col-sym) center-row center-column 
			      radius thicken-p &rest body)
  (let ((tracer-sym (gensym)))
    `(labels ((,tracer-sym ,(list row-sym col-sym)
		,@body))
       (trace-octagon #',tracer-sym ,center-row ,center-column ,radius ,thicken-p))))

;;; Random midpoint displacement fractals, a.k.a. plasma

;; The following routines create random midpoint displacement fractals
;; on a grid. This is useful for natural-looking world generation.
;; See also http://en.wikipedia.org/wiki/Diamond-square_algorithm

;; My implementation is slow and needs to be improved.

;; First comes the midpoint formula.
;; http://en.wikipedia.org/wiki/Midpoint

(defun midpoint (A B)
  (list (truncate (/ (+ (first A) (first B)) 2))
	(truncate (/ (+ (second A) (second B)) 2))))

;; We need an representation for a rectangle that is appropriate to
;; our problem. Then we must allow recursive subdivision of
;; rectangles.

(defstruct plasma-rect
  A B C D)

(defun subdivide-rect (R)
  "Subdivide rectangle R into four rectangles joined at the
center point of the original R, and return the list of four
rectangles, or NIL if they would be smaller than one pixel."
  (let* ((A (plasma-rect-A R))
	 (B (plasma-rect-B R))
	 (C (plasma-rect-C R))
	 (D (plasma-rect-D R)))
    ;; are they too small?
    (if (> 2 (abs (- (first C) (first A))))
	nil
	(let
	    ((R1 (make-plasma-rect :A A
				   :B (midpoint A B)
				   :C (midpoint A C)
				   :D (midpoint A D)))
	     ;;
	     (R2 (make-plasma-rect :A (midpoint A B)
				   :B B
				   :C (midpoint B C)
				   :D (midpoint B D)))
	     ;;
	     (R3 (make-plasma-rect :A (midpoint A C)
				   :B (midpoint B C)
				   :C C
				   :D (midpoint C D)))
	     ;;
	     (R4 (make-plasma-rect :A (midpoint A D)
				   :B (midpoint B D)
				   :C (midpoint C D)
				   :D D)))
	  (list R1 R2 R3 R4)))))

(defun render-plasma (height width &key (graininess 1.0) array)
  (let* ((grid (or array (make-array (list height width))))
	 (A (list 0 0))
	 (B (list 0 (- height 1)))
	 (C (list (- width 1) 0))
	 (D (list (- width 1) (- height 1)))
	 (Rs (list (make-plasma-rect :A A :B B :C C :D D)))
	 (Ss nil)
	 (S nil)
	 (R nil)
	 (rect-width nil))
    ;; assign random values to corners of grid to prime the algorithm
    (dolist (P (list A B C D))
      (setf (aref grid (second P) (first P)) (random graininess)))
    ;; begin processing rectangles and painting plasma
    (loop while (setf R (pop Rs))
       do
       ;; subdivide rectangle R and push results onto the rectangle list Rs
	 (setf Ss (subdivide-rect R))
	 (if Ss
	     (loop while (setf S (pop Ss)) do
		  (push S Rs)))
       ;; calculate values for midpoints and center of current rectangle R
	 (setf A (plasma-rect-A R))
	 (setf B (plasma-rect-B R))
	 (setf C (plasma-rect-C R))
	 (setf D (plasma-rect-D R))
	 (setf rect-width (abs (- -1 (first C) (first A))))
       ;; do for all edge midpoints and center:
	 (dolist (pair (list (list A B) (list A C)
			     (list B D) (list C D) (list A D)))
	   (let* ((P1 (first pair))
		  (P2 (second pair))
		  (M (midpoint P1 P2))
		  (V (+
		      ;; average value of values at P1 and P2
		      (* 0.5
			 (+ (aref grid (second P1) (first P1))
			    (aref grid (second P2) (first P2))
			    ;; random part smaller as rects get smaller
			    (* graininess (- 0.5 (random 1.0))
			       (sqrt (float rect-width))))))))
	     ;; paint the point
	     (setf (aref grid (second M) (first M)) V))))
    grid))

;;; Cellular automata



;;; math.lisp ends here