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field.lisp
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(in-package :option-9)
#+option-9-debug (declaim (optimize (safety 3) (space 0) (speed 0) (debug 3)))
(defun euclidean-distance (fx fy tx ty)
(let ((factor-1 (- tx fx))
(factor-2 (- ty fy)))
(let ((ndist (+ (* factor-1 factor-1)
(* factor-2 factor-2))))
(values (sqrt ndist) ndist))))
(defun unit-vector (from tx ty)
(with-pvec-accessors (o (matrix-translate-get (world-basis from)))
(multiple-value-bind (dist ndist)
(euclidean-distance ox oy tx ty)
(values (/ (- tx ox) dist)
(/ (- ty oy) dist)
ndist))))
(defun e-field-one-point (from tx ty)
(multiple-value-bind (ux uy ndist)
(unit-vector from tx ty)
(let ((c (/ (charge from) ndist)))
(values (* c ux)
(* c uy)))))
(defun e-field (charges tx ty)
(let* ((const (/ 1.0 (* 4.0 pi 8.854187817e-12)))
(nx 0) (ny 0))
(dolist (q charges)
;; Since this is so expensive, ensure to only do it for things that
;; are actually alive at the computation of this field.
(when (alivep q)
(with-pvec-accessors (o (matrix-translate-get (world-basis q)))
(if (< (euclidean-distance ox oy tx ty)
(radius q))
(return-from e-field (values :collision 0 0 q))
(multiple-value-bind (qx qy)
(e-field-one-point q tx ty)
(incf nx qx)
(incf ny qy))))))
(values :tracing (* const nx) (* const ny) nil)))
(defun normalize-vector (dx dy)
(let ((dist (euclidean-distance 0 0 dx dy)))
(if (= dist 0)
(values 0 0)
(values (/ dx dist) (/ dy dist)))))
(defun e-field-direction (dx dy)
(normalize-vector dx dy))
;; This is a random dumping ground for the field and tesla-field class until
;; I figure out exactly how these verbs work.
;; This will help us keep up to date numerous portions of the
;; telsa-field when the range for the tesla field changes.
(defmethod (setf power-range) (range (tf tesla-field))
(assert (> range 0))
;; The power range of the tesla-field can range from 1 to 7
(setf (slot-value tf '%power-range) (min range 7))
;; Now we regenerate all of the internals.
;; First we figure out the real range of the traces, capped at 2^7 for
;; efficiency (otherwise we could waste 25% of our time in oscillations
;; or other integration foibles when computing the trace).
(setf (range tf) (min (expt 2 (power-range tf))
(expt 2 7)))
;; Remake the paths array
(setf (paths tf) (gen-paths (num-paths tf) (range tf)))
;; Clear out the contacts hash since it is now invalid
(setf (entity-contacts tf) (make-hash-table :test #'equal))
range)
;; Allocate the whole array which could hold up to 'steps' locations.
(defun gen-path (steps)
(make-array (list steps)
:initial-contents
(loop repeat steps collecting (make-instance 'location))))
;; When we construct a fieldpath class, we initially set up all of the
;; memory we'll need to deal with it. Since we'll compute a fair
;; amount of information per frame, we don't want to generate too much
;; garbage.
(defun make-fieldpath (max-steps)
(make-instance 'fieldpath :path (gen-path max-steps)))
(defun make-pathcontact ()
(make-instance 'pathcontact))
(defun gen-paths (num-paths steps)
(make-array (list num-paths)
:initial-contents
(loop repeat num-paths collecting
(make-fieldpath steps))))
;; Return true if c1 and c2 are both positive, or both negative, charges
(defun same-polarityp (c1 c2)
(or (and (> (charge c1) 0) (> (charge c2) 0))
(and (< (charge c1) 0) (< (charge c2) 0))))
;; This will help us keep up to date numerous portions of the
;; telsa-field when the density (or number of path lines in the field
;; we will be tracing) for the tesla field changes.
(defmethod (setf power-lines) (lines (tf tesla-field))
(assert (> lines 0))
(setf (slot-value tf '%power-lines) (min lines 4))
(setf (num-paths tf) (expt 2 (power-lines tf)))
(setf (paths tf) (gen-paths (num-paths tf) (range tf)))
(setf (entity-contacts tf) (make-hash-table :test #'equal))
lines)
(defmethod power-range-maxp ((tf tesla-field))
(if (= (power-range tf) 7)
t
nil))
(defmethod power-density-maxp ((tf tesla-field))
(if (= (power-lines tf) 4)
t
nil))
(defmethod increase-range ((tf tesla-field))
(unless (power-range-maxp tf)
(incf (power-range tf))))
(defmethod increase-density ((tf tesla-field))
(unless (power-density-maxp tf)
(incf (power-lines tf))))
;; Starting at x,y trace a field line until we get close to a charge
;; which is not q1 or we go out of bounds.
(defmethod trace-field-line ((f field) path-num tx ty q1 charges)
(labels ((determine-field-line-direction (vx vy dx dy q)
(with-pvec-accessors (qo (matrix-translate-get (world-basis q)))
(multiple-value-bind (dx dy)
(e-field-direction dx dy)
;; than vx vy is by itself, return -1, otherwise 1
(let ((nx (+ vx (* .1 dx)))
(ny (+ vy (* .1 dy))))
(if (< (euclidean-distance qox qoy nx ny)
(euclidean-distance qox qoy vx vy))
-1.0
1.0)))))
(store-contact (f path-id entity-id xl yl)
(declare (ignorable xl yl))
(multiple-value-bind (path-contact presentp)
(gethash entity-id (entity-contacts f))
;; Is there a better idiom for this?
(unless presentp
(let ((pc (make-pathcontact)))
(setf (gethash entity-id (entity-contacts f)) pc)
(setf path-contact pc)))
(incf (number-of-contacts path-contact))
(push path-id (path-ids path-contact)))))
(with-accessors ((fp-steps steps) (fp-path path))
(svref (paths f) path-num)
(setf fp-steps 0)
(let ((vx tx) (vy ty) (sum 0))
;; First, we compute the field direction at the initial point, if
;; by following that vector, we get closer to q1, we'll reverse
(when (or (< vx 0.0)
(> vx (game-width *game*))
(< vy 0.0)
(> vy (game-height *game*)))
(return-from trace-field-line))
;; direction and follow the stream backwards.
(multiple-value-bind (classification ex ey cent)
(e-field charges vx vy)
(declare (ignorable cent))
;; XXX For traced paths which START in a colliding
;; situation, we ignore them. This might be bad and needs
;; revisiting.
(when (eq classification :tracing)
(multiple-value-bind (dx dy) (e-field-direction ex ey)
(let ((dir (determine-field-line-direction vx vy dx dy q1)))
;; Now, we begin storing the line strip moving the
;; test charge from the start point to wherever it ends up
;; ensuring it goes in the right direction.
;; Keep walking the field line until we are done. We
;; bound it to (range f) to keep the oscillations from
;; the gross integration from overwhelming the
;; computation.
(when
(dotimes (index (range f) t)
(when (or (< vx 0.0)
(> vx (game-width *game*))
(< vy 0.0)
(> vy (game-height *game*)))
;; we went off the screen, so no contact.
(return t))
(multiple-value-bind (classification ex ey cent)
(e-field charges vx vy)
;; If we collide and the entity we collided with
;; is of an opposite charge, we're done.
(when (and (eq classification :collision)
(not (same-polarityp q1 cent)))
(setf (x (svref fp-path index)) vx
(y (svref fp-path index)) vy)
(incf fp-steps)
;; Associate the contacting path-num with
;; the id of to whom it collided and where.
(store-contact f path-num (id cent) vx vy)
(return nil))
;; otherwise we keep tracing the path
(multiple-value-bind (dx dy)
(e-field-direction ex ey)
(setf (x (svref fp-path index)) vx
(y (svref fp-path index)) vy
(dx (svref fp-path index)) dx
(dy (svref fp-path index)) dy)
(incf fp-steps)
;; No direction guarantees that we loop
;; until done with no path movement, so we
;; bail.
(when (and (= dx 0) (= dy 0))
;; we died in a saddle point, no contact.
(return t))
;; Stepping to the next point is a little
;; interesting. We use a quadratic function
;; near the field generator to increase the
;; resolution of the field lines. As we go
;; farther away from the generator, we then
;; fixate the resolution to a ad hoc number
;; which looked good and was cheap to
;; compute for game play. This allows for us
;; to decrease the ugly oscillations right
;; nearby the ship, but not have to pay for
;; that oscillation reduction farther away
;; where oscillations are less likely to
;; happen. This equation to compute the
;; incremental was pulled out of my butt.
(let* ((delta (/ (+ index 25.0) 450.0))
(incremental (if (< sum 2.0)
;; the 100.0 is
;; there because
;; this value is
;; resized according
;; to the raw size
;; of the world
;; which is (0,0) to
;; (100,100).
(* delta delta 100.0)
1.5)))
(incf sum incremental)
(setf vx (+ vx (* dx incremental dir))
vy (+ vy (* dy incremental dir)))))))
;; If the dotimes returned true, it meant that the
;; path did not collide with any game entity but
;; instead ran out of range, got clipped, or
;; whatever. So it gets a special designation in the
;; entity-contacts table.
(store-contact f path-num :no-collision vx vy))))))))))
;; Starting at slightly more than radius from the object in world
;; space, trace each field-line whose number depends upon the charge.
(defmethod trace-field-lines ((f field) q1 charges)
;; we're going to circle around the charge in even increments according
;; to num-paths
(let* ((num-paths (num-paths f))
(delta (/ (* 2.0 pi) num-paths)))
(flet ((start-point (x y path-num)
(values (+ x (* (+ (radius q1) .1) (sin (* path-num delta))))
(+ y (* (+ (radius q1) .1) (cos (* path-num delta)))))))
(dotimes (path-num num-paths)
(with-pvec-accessors (o (matrix-translate-get (world-basis q1)))
(multiple-value-bind (nx ny)
(start-point ox oy path-num)
(trace-field-line f path-num nx ny q1 charges)))))))
;; return the path-contact instance if the entity was contacted by any
;; field paths, otherwise nil.
(defmethod contacts ((f tesla-field) (e entity))
(multiple-value-bind (path-contact presentp)
(gethash (id e) (entity-contacts f))
(when presentp
path-contact)))