
;;;; ---------------------------------------------------------------------
   Particle Demo : a simple SDL demo using common lisp .
   Copyright ( C ) 2007     <  >
;;;;
;;;;  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 </>.
;;;; ---------------------------------------------------------------------

(in-package #:sdl-examples)

;;; ----------------------------------------------------------------------
;;;  Parameters of the demo.
;;; ----------------------------------------------------------------------
(defparameter *screen-width* 800)
(defparameter *screen-height* 600)
(defparameter *particle-speed-min* 120.0)
(defparameter *particle-speed-max* 200.0)
(defparameter *particle-count* 200)
(defparameter *increment* 100)
(defparameter *frames-p* (every-n-frames 200))

;;; ----------------------------------------------------------------------
;;;  Global variables.
;;; ----------------------------------------------------------------------
(defvar *particle-img* nil)
(defvar *particles* nil)

(defvar *font-large* nil)
(defvar *font-small* nil)

(defvar *mouse-x* (/ *screen-width* 2))
(defvar *mouse-y* (/ *screen-height* 2))

;;; ----------------------------------------------------------------------
;;;  Functions for rendering the current FPS to the screen.
;;; ----------------------------------------------------------------------
(defun draw-cached-string (string x y font surface render-p)
  ;; Create a new FPS string when render-p is T
  (when render-p
    (sdl:render-string-solid string :color sdl:*white* :font font :cache t :free t))
  ;; Draw the string each frame
  (sdl:draw-font-at-* x y :font font :surface surface))

;;; ----------------------------------------------------------------------
;;;  Generate a random number in the range [a, b].
;;; ----------------------------------------------------------------------
(defun rand-range (a b)
  (+ (* (random 1.0) (- b a)) a))

;;; ----------------------------------------------------------------------
;;;  A 2D vector.
;;; ----------------------------------------------------------------------

(defun make-vec2 (&key x y) (vector x y))

(defun vec2-x (vec) (svref vec 0))
(defun vec2-y (vec) (svref vec 1))

(defun (setf vec2-x) (val self)
  (setf (svref self 0) val))
(defun (setf vec2-y) (val self)
  (setf (svref self 1) val))

;;; ----------------------------------------------------------------------
;;;  Normalize a 2D vector.
;;; ----------------------------------------------------------------------
(defun vec2-normalize (v)
  (let ((n (sqrt (+ (* (vec2-x v) (vec2-x v))
                    (* (vec2-y v) (vec2-y v))))))
    (when (not (zerop n))
      (setf (vec2-x v) (/ (vec2-x v) n))
   (setf (vec2-y v) (/ (vec2-y v) n)))))

;;; ----------------------------------------------------------------------
;;;  A particle.
;;; ----------------------------------------------------------------------
(defstruct particle
  pos velocity)

;;; ----------------------------------------------------------------------
   Initialize a particle , position it to the center of the screen ,
;;;  and give it a random velocity.
;;; ----------------------------------------------------------------------
(defun init-particle (p)
  (let ((hx (- *mouse-x* (/ (sdl:width *particle-img*) 2)))
        (hy (- *mouse-y* (/ (sdl:height *particle-img*) 2))))
    (let ((vel (make-vec2 :x (rand-range -2.0 2.0) :y (rand-range -2.0 2.0))))
      (vec2-normalize vel)
      (let ((sp (rand-range *particle-speed-min* *particle-speed-max*)))
        (setf (vec2-x vel) (* (vec2-x vel) sp)
              (vec2-y vel) (* (vec2-y vel) sp))
        (setf (particle-pos p) (make-vec2 :x hx :y hy))
        (setf (particle-velocity p) vel))))
  p)

;;; ----------------------------------------------------------------------
;;;  Update the position of a particle.
;;; ----------------------------------------------------------------------
(defun update-particle (p ftime)
  (let ((vel (particle-velocity p)))
    (incf (vec2-x (particle-pos p)) (* (vec2-x vel) ftime))
    (incf (vec2-y (particle-pos p)) (* (vec2-y vel) ftime)))
  (let ((pos (particle-pos p)))
    (when (or (< (vec2-x pos) (- 0 (sdl:width *particle-img*)))
              (< (vec2-y pos) (- 0 (sdl:height *particle-img*)))
              (> (vec2-x pos) (sdl:width sdl:*default-display*))
              (> (vec2-y pos) (sdl:height sdl:*default-display*)))
      ;; The particle is out of screen, re-init it
      (init-particle p)))
  p)

;;; ----------------------------------------------------------------------
;;;  Add and remove particles.
;;; ----------------------------------------------------------------------
(defun add-particles ()
  (dotimes (i *increment*)
    (push (init-particle (make-particle))
	  *particles*))
  (incf *particle-count* *increment*))

(defun remove-particles ()
  (when *particles*
    (dotimes (i *increment*)
      (pop *particles*))
    (if (< (decf *particle-count* *increment*) 0)
	(setf *particle-count* 0))))

;;; ----------------------------------------------------------------------
;;;  Define the callback to be used in the event filter.
;;; ----------------------------------------------------------------------
(defun resize-screen (sdl-event)
  (sdl:resize-window (sdl::video-resize-w sdl-event)
                     (sdl::video-resize-h sdl-event))
  t)

;;; ----------------------------------------------------------------------
;;;  Toggles fullescreen/window mode.
;;; ----------------------------------------------------------------------
(let ((currently-fullscreen? nil))
  (defun toggle-fullscreen ()
    (if currently-fullscreen?
      (sdl:resize-window *screen-width* *screen-height* :sw t :resizable t)
      (sdl:resize-window *screen-width* *screen-height* :sw t :fullscreen t))
    (setf currently-fullscreen? (if currently-fullscreen? nil t))))

;;; ----------------------------------------------------------------------
   ' Builing an executable in  ' function .
;;; ----------------------------------------------------------------------

;;; ----------------------------------------------------------------------
;;;  'Main' function.
;;; ----------------------------------------------------------------------
(defun particles (&optional (frame-rate nil))
  (sdl:load-library)
  (sdl:with-init ()
    ;; Create a window
    (unless (sdl:window *screen-width* *screen-height*
                        :title-caption "Particles Demo"
                        :icon-caption "Particles Demo"
                        :sw t :resizable t
                        :fps (make-instance 'sdl:fps-fixed))
      (error "~&Unable to create a SDL window~%"))

    ;; Enable event filters using the specified callback.
    (sdl:enable-event-filters)
    (sdl:remove-all-event-filters)
    (sdl::set-event-filter :video-resize-event #'resize-screen)

    ;; Fix the framerate
    (setf (sdl:frame-rate) frame-rate)
    ;; Enable key repeat. Set to default values.
    (sdl:enable-key-repeat nil nil)
  Load images . Convert the 24 - bit particle surface into a 32bpp
    ;; surface with an alpha component
    (setf *particle-img* (sdl::convert-to-display-format :surface (sdl:load-image (sdl:create-path
                                                                                  "particle.bmp"
                                                                                  sdl:*default-asset-path*))
                                                        :inherit nil
                                                        :pixel-alpha t
                                                        :free t))
( setf * particle - img * ( sdl : load - image ( sdl : create - path
    ;;                                      "particle.bmp"
    ;;                                      sdl:*default-asset-path*)))

    ;;(format t "surface-info: ~A~%" (sdl:surface-info *particle-img*))

    ;; Replace the alpha channel of *particle-img* with
    ;; the alpha map in particle-alpha.bmp
    (sdl:with-surface (alpha (sdl:load-image (sdl:create-path "particle-alpha.bmp"
                                                              sdl:*default-asset-path*)))
      (sdl:copy-channel-to-alpha *particle-img* alpha :channel :r))


( setf * particle - img * ( sdl : copy - surface : surface * particle - img * : inherit nil : rle - accel t : free t : fill nil ) )

    ;; (format t "surface-info: ~A~%" (sdl:surface-info *particle-img*))

    ;; Load the bitmap fonts
    (setf *font-large* (sdl:initialise-font sdl:*font-8x13*))
    (setf *font-small* (sdl:initialise-font sdl:*font-7x14*))

    ;; Render the initial text.
    ;; We cache the rendered string in the FONT object.
    ;; Drawing the font to the display then involves a fast blit.
    (draw-cached-string (format nil "{ESC} = Exit, {P} Add 100 Particles, {L} Remove 100 Particles, {SPACE} = Toggle Fullscreen.")
                        5 5 *font-large* sdl:*default-display* t)
    (draw-cached-string (format nil "Particles: ~d, Framerate: Calculating...."
                                *particle-count*)
                        5 35 *font-small* sdl:*default-display* t)

    ;; Create the particles
    (setf *particles* nil)
    (dotimes (i *particle-count*)
      (push (init-particle (make-particle)) *particles*))

    ;; Event loop
    (sdl:with-events ()
      ;; A key was pressed
      (:key-down-event (:key k)
       (cond
        ;; Escape
        ((sdl:key= k :sdl-key-escape)
         (sdl:push-quit-event))
        ;; Add particle
        ((sdl:key= k :sdl-key-p)
         (add-particles))
        ;; Remove particle
        ((sdl:key= k :sdl-key-l)
         (remove-particles))
        ((sdl:key= k :sdl-key-space)
         (toggle-fullscreen))))

      (:mouse-motion-event (:x x :y y)
       (setf *mouse-x* x
             *mouse-y* y))

      ;; Application is quitting
      (:quit-event () t)

      ;; Redraw display
      (:video-expose-event () (sdl:update-display))

      ;; Idle work
      (:idle
       ;; Clear screen
       (sdl:clear-display sdl:*black*)

       ;; Update/Draw the particles
       (dolist (p *particles*)
         (update-particle p (sdl:time-scale))
         (let ((pos (particle-pos p)))
           (sdl:draw-surface-at-* *particle-img*
                                  (round (vec2-x pos)) (round (vec2-y pos)))))
       ;; Display text.
       (draw-cached-string "" 5 5 *font-large* sdl:*default-display* nil)

       (if (funcall *frames-p*)
         (draw-cached-string (format nil "Particles: ~d, Framerate: ~f, timescale: ~f"
                                     *particle-count* (truncate (sdl:average-fps)) (sdl:time-scale))
                             5 35 *font-small* sdl:*default-display* t)
         (draw-cached-string nil 5 35 *font-small* sdl:*default-display* nil))

       ;; Flip back/front buffers
       (sdl:update-display)))))


(defun particles-timestep (&optional (frame-rate nil))
  (sdl:with-init ()
    ;; Create a window
    (unless (sdl:window *screen-width* *screen-height*
                        :title-caption "Particles Demo"
                        :icon-caption "Particles Demo"
                        :flags '(sdl:sdl-sw-surface sdl:sdl-resizable)
                        :fps (make-instance 'sdl:fps-mixed))
      (error "~&Unable to create a SDL window~%"))

    ;; Fix the framerate
    (setf (sdl:frame-rate) frame-rate)

    ;; Enable event filters.
    (sdl:enable-event-filters)
    ;; Remove any existing filters.
    (sdl:remove-all-event-filters)
    ;; Handle the :video-resize-event
    (sdl::set-event-filter :video-resize-event #'resize-screen)

    ;; Enable key repeat. Set to default values.
    (sdl:enable-key-repeat nil nil)

  Load images . Convert the 24 - bit particle surface into a 32bpp
    ;; surface with an alpha component
    (setf *particle-img* (sdl::convert-to-display-format :surface (sdl:load-image (sdl:create-path
                                                                                   "particle.bmp"
                                                                                   sdl:*default-asset-path*))
                                                         :inherit nil
                                                         :pixel-alpha t
                                                         :free t))

    ;; Replace the alpha channel of *particle-img* with
    ;; the alpha map in particle-alpha.bmp
    (sdl:with-surface (alpha (sdl:load-image (sdl:create-path "particle-alpha.bmp"
                                                              sdl:*default-asset-path*)))
      (sdl:copy-channel-to-alpha *particle-img* alpha :channel :r))

    ;; Load the bitmap fonts
    (setf *font-large* (sdl:initialise-font sdl:*font-8x13*))
    (setf *font-small* (sdl:initialise-font sdl:*font-7x14*))

    ;; Render the initial text.
    ;; We cache the rendered string in the FONT object.
    ;; Drawing the font to the display then involves a fast blit.
    (draw-cached-string (format nil "{ESC} = Exit, {P} Add 100 Particles, {L} Remove 100 Particles, {SPACE} = Toggle Fullscreen.")
                        5 5 *font-large* sdl:*default-display* t)
    (draw-cached-string (format nil "Particles: ~d, Framerate: Calculating...."
                                *particle-count*)
                        5 35 *font-small* sdl:*default-display* t)

    ;; Create the particles
    (setf *particles* nil)
    (dotimes (i *particle-count*)
      (push (init-particle (make-particle)) *particles*))

    ;; Event loop
    (sdl:with-events ()
      ;; A key was pressed
      (:key-down-event (:key k)
       (cond
        ;; Escape
        ((sdl:key= k :sdl-key-escape)
         (sdl:push-quit-event))
        ;; Add particle
        ((sdl:key= k :sdl-key-p)
         (add-particles))
        ;; Remove particle
        ((sdl:key= k :sdl-key-l)
         (remove-particles))
        ((sdl:key= k :sdl-key-space)
         (toggle-fullscreen))))

      (:mouse-motion-event (:x x :y y)
       (setf *mouse-x* x
             *mouse-y* y))

      ;; Application is quitting
      (:quit-event () t)

      ;; Redraw display
      (:video-expose-event () (sdl:update-display))

      ;; Idle work
      (:idle
       ;; Clear screen
       (sdl:clear-display sdl:*black*)

       (sdl:with-timestep ()
         ;; Update the particles
         (dolist (p *particles*)
           (update-particle p (/ (sdl::dt) 1000))))

       ;; Update the particles
       (dolist (p *particles*)
         (sdl:draw-surface-at-* *particle-img*
                                (round (vec2-x (particle-pos p)))
                                (round (vec2-y (particle-pos p)))))
       ;; Display text.
       (draw-cached-string nil 5 5 *font-large* sdl:*default-display* nil)

       (if (funcall *frames-p*)
         (draw-cached-string (format nil "Particles: ~d, Framerate: ~f, timescale: ~f, dt: ~f"
                                     *particle-count* (truncate (sdl:average-fps)) (sdl:time-scale) (sdl:dt))
                             5 35 *font-small* sdl:*default-display* t)
         (draw-cached-string nil 5 35 *font-small* sdl:*default-display* nil))

       ;; Flip back/front buffers
       (sdl:update-display)))))

(defun particles-event-loop (&optional (frame-rate nil))
  (sdl:with-init ()
    ;; Create a window
    (unless (sdl:window *screen-width* *screen-height*
                        :title-caption "Particles Demo"
                        :icon-caption "Particles Demo"
                        :flags '(sdl:sdl-sw-surface sdl:sdl-resizable)
                        :fps (make-instance 'sdl:fps-mixed)
                        :position 'center)
      (error "~&Unable to create a SDL window~%"))

    ;; Fix the framerate
    (setf (sdl:frame-rate) frame-rate)

    ;; Enable event filters.
    (sdl:enable-event-filters)
    ;; Remove any existing filters.
    (sdl:remove-all-event-filters)
    ;; Handle the :video-resize-event
    (sdl::set-event-filter :video-resize-event #'resize-screen)

    ;; Enable key repeat. Set to default values.
    (sdl:enable-key-repeat nil nil)

  Load images . Convert the 24 - bit particle surface into a 32bpp
    ;; surface with an alpha component
    (setf *particle-img* (sdl::convert-to-display-format :surface (sdl:load-image (sdl:create-path
                                                                                   "particle.bmp"
                                                                                   sdl:*default-asset-path*))
                                                         :inherit nil
                                                         :pixel-alpha t
                                                         :free t))

    ;; Replace the alpha channel of *particle-img* with
    ;; the alpha map in particle-alpha.bmp
    (sdl:with-surface (alpha (sdl:load-image (sdl:create-path "particle-alpha.bmp"
                                                              sdl:*default-asset-path*)))
      (sdl:copy-channel-to-alpha *particle-img* alpha :channel :r))

    ;; Load the bitmap fonts
    (setf *font-large* (sdl:initialise-font sdl:*font-8x13*))
    (setf *font-small* (sdl:initialise-font sdl:*font-7x14*))

    ;; Render the initial text.
    ;; We cache the rendered string in the FONT object.
    ;; Drawing the font to the display then involves a fast blit.
    (draw-cached-string (format nil "{ESC} = Exit, {P} Add 100 Particles, {L} Remove 100 Particles, {SPACE} = Toggle Fullscreen.")
                        5 5 *font-large* sdl:*default-display* t)
    (draw-cached-string (format nil "Particles: ~d, Framerate: Calculating...."
                                *particle-count*)
                        5 35 *font-small* sdl:*default-display* t)

    ;; Create the particles
    (setf *particles* nil)
    (dotimes (i *particle-count*)
      (push (init-particle (make-particle)) *particles*))

    ;; Event loop
    (loop with event* = (sdl:new-event)
          for event = (sdl::get-event event*) then (sdl::get-event event*)
          while event do
          (case (sdl:event-type event)
            (:idle
             (sdl:update-input-util (sdl:frame-time))
             (sdl:with-frame-rate ()
               ;; Clear screen
               (sdl:clear-display sdl:*black*)

               (sdl:with-timestep ()
                 ;; Update the particles
                 (dolist (p *particles*)
                   (update-particle p (/ (sdl::dt) 1000))))

               ;; Update the particles
               (dolist (p *particles*)
                 (sdl:draw-surface-at-* *particle-img*
                                        (round (vec2-x (particle-pos p)))
                                        (round (vec2-y (particle-pos p)))))
               ;; Display text.
               (draw-cached-string nil 5 5 *font-large* sdl:*default-display* nil)

               (if (funcall *frames-p*)
                 (draw-cached-string (format nil "Particles: ~d, Framerate: ~f, timescale: ~f, dt: ~f"
                                             *particle-count* (truncate (sdl:average-fps)) (sdl:time-scale) (sdl:dt))
                                     5 35 *font-small* sdl:*default-display* t)
                 (draw-cached-string nil 5 35 *font-small* sdl:*default-display* nil))

               ;; Flip back/front buffers
               (sdl:update-display)))

            (:key-down-event
             (sdl:with-key-down-event ((k :key)) event
               (case k
                 (:sdl-key-escape (sdl:push-quit-event))
                 (:sdl-key-p (add-particles))
                 (:sdl-key-l (remove-particles))
                 (:sdl-key-space (toggle-fullscreen)))))

            (:mouse-motion-event
             (sdl:with-mouse-motion-event ((x :x) (y :y)) event
               (setf *mouse-x* x
                     *mouse-y* y)))

            (:video-expose-event (sdl:update-display))

            (:quit-event (loop-finish)))
          finally (sdl:free-event event*))))

 ---------------------------------------------------------------------

  This program is free software: you can redistribute it and/or modify
  (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.

  along with this program. If not, see </>.
 ---------------------------------------------------------------------
 ----------------------------------------------------------------------
  Parameters of the demo.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  Global variables.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  Functions for rendering the current FPS to the screen.
 ----------------------------------------------------------------------
 Create a new FPS string when render-p is T
 Draw the string each frame
 ----------------------------------------------------------------------
  Generate a random number in the range [a, b].
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  A 2D vector.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  Normalize a 2D vector.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  A particle.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  and give it a random velocity.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  Update the position of a particle.
 ----------------------------------------------------------------------
 The particle is out of screen, re-init it
 ----------------------------------------------------------------------
  Add and remove particles.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  Define the callback to be used in the event filter.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  Toggles fullescreen/window mode.
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
 ----------------------------------------------------------------------
  'Main' function.
 ----------------------------------------------------------------------
 Create a window
 Enable event filters using the specified callback.
 Fix the framerate
 Enable key repeat. Set to default values.
 surface with an alpha component
                                      "particle.bmp"
                                      sdl:*default-asset-path*)))
(format t "surface-info: ~A~%" (sdl:surface-info *particle-img*))
 Replace the alpha channel of *particle-img* with
 the alpha map in particle-alpha.bmp
 (format t "surface-info: ~A~%" (sdl:surface-info *particle-img*))
 Load the bitmap fonts
 Render the initial text.
 We cache the rendered string in the FONT object.
 Drawing the font to the display then involves a fast blit.
 Create the particles
 Event loop
 A key was pressed
 Escape
 Add particle
 Remove particle
 Application is quitting
 Redraw display
 Idle work
 Clear screen
 Update/Draw the particles
 Display text.
 Flip back/front buffers
 Create a window
 Fix the framerate
 Enable event filters.
 Remove any existing filters.
 Handle the :video-resize-event
 Enable key repeat. Set to default values.
 surface with an alpha component
 Replace the alpha channel of *particle-img* with
 the alpha map in particle-alpha.bmp
 Load the bitmap fonts
 Render the initial text.
 We cache the rendered string in the FONT object.
 Drawing the font to the display then involves a fast blit.
 Create the particles
 Event loop
 A key was pressed
 Escape
 Add particle
 Remove particle
 Application is quitting
 Redraw display
 Idle work
 Clear screen
 Update the particles
 Update the particles
 Display text.
 Flip back/front buffers
 Create a window
 Fix the framerate
 Enable event filters.
 Remove any existing filters.
 Handle the :video-resize-event
 Enable key repeat. Set to default values.
 surface with an alpha component
 Replace the alpha channel of *particle-img* with
 the alpha map in particle-alpha.bmp
 Load the bitmap fonts
 Render the initial text.
 We cache the rendered string in the FONT object.
 Drawing the font to the display then involves a fast blit.
 Create the particles
 Event loop
 Clear screen
 Update the particles
 Update the particles
 Display text.
 Flip back/front buffers

   Particle Demo : a simple SDL demo using common lisp .
   Copyright ( C ) 2007     <  >
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation , either version 3 of the License , or
   You should have received a copy of the GNU General Public License

(in-package #:sdl-examples)

(defparameter *screen-width* 800)
(defparameter *screen-height* 600)
(defparameter *particle-speed-min* 120.0)
(defparameter *particle-speed-max* 200.0)
(defparameter *particle-count* 200)
(defparameter *increment* 100)
(defparameter *frames-p* (every-n-frames 200))

(defvar *particle-img* nil)
(defvar *particles* nil)

(defvar *font-large* nil)
(defvar *font-small* nil)

(defvar *mouse-x* (/ *screen-width* 2))
(defvar *mouse-y* (/ *screen-height* 2))

(defun draw-cached-string (string x y font surface render-p)
  (when render-p
    (sdl:render-string-solid string :color sdl:*white* :font font :cache t :free t))
  (sdl:draw-font-at-* x y :font font :surface surface))

(defun rand-range (a b)
  (+ (* (random 1.0) (- b a)) a))


(defun make-vec2 (&key x y) (vector x y))

(defun vec2-x (vec) (svref vec 0))
(defun vec2-y (vec) (svref vec 1))

(defun (setf vec2-x) (val self)
  (setf (svref self 0) val))
(defun (setf vec2-y) (val self)
  (setf (svref self 1) val))

(defun vec2-normalize (v)
  (let ((n (sqrt (+ (* (vec2-x v) (vec2-x v))
                    (* (vec2-y v) (vec2-y v))))))
    (when (not (zerop n))
      (setf (vec2-x v) (/ (vec2-x v) n))
   (setf (vec2-y v) (/ (vec2-y v) n)))))

(defstruct particle
  pos velocity)

   Initialize a particle , position it to the center of the screen ,
(defun init-particle (p)
  (let ((hx (- *mouse-x* (/ (sdl:width *particle-img*) 2)))
        (hy (- *mouse-y* (/ (sdl:height *particle-img*) 2))))
    (let ((vel (make-vec2 :x (rand-range -2.0 2.0) :y (rand-range -2.0 2.0))))
      (vec2-normalize vel)
      (let ((sp (rand-range *particle-speed-min* *particle-speed-max*)))
        (setf (vec2-x vel) (* (vec2-x vel) sp)
              (vec2-y vel) (* (vec2-y vel) sp))
        (setf (particle-pos p) (make-vec2 :x hx :y hy))
        (setf (particle-velocity p) vel))))
  p)

(defun update-particle (p ftime)
  (let ((vel (particle-velocity p)))
    (incf (vec2-x (particle-pos p)) (* (vec2-x vel) ftime))
    (incf (vec2-y (particle-pos p)) (* (vec2-y vel) ftime)))
  (let ((pos (particle-pos p)))
    (when (or (< (vec2-x pos) (- 0 (sdl:width *particle-img*)))
              (< (vec2-y pos) (- 0 (sdl:height *particle-img*)))
              (> (vec2-x pos) (sdl:width sdl:*default-display*))
              (> (vec2-y pos) (sdl:height sdl:*default-display*)))
      (init-particle p)))
  p)

(defun add-particles ()
  (dotimes (i *increment*)
    (push (init-particle (make-particle))
	  *particles*))
  (incf *particle-count* *increment*))

(defun remove-particles ()
  (when *particles*
    (dotimes (i *increment*)
      (pop *particles*))
    (if (< (decf *particle-count* *increment*) 0)
	(setf *particle-count* 0))))

(defun resize-screen (sdl-event)
  (sdl:resize-window (sdl::video-resize-w sdl-event)
                     (sdl::video-resize-h sdl-event))
  t)

(let ((currently-fullscreen? nil))
  (defun toggle-fullscreen ()
    (if currently-fullscreen?
      (sdl:resize-window *screen-width* *screen-height* :sw t :resizable t)
      (sdl:resize-window *screen-width* *screen-height* :sw t :fullscreen t))
    (setf currently-fullscreen? (if currently-fullscreen? nil t))))

   ' Builing an executable in  ' function .

(defun particles (&optional (frame-rate nil))
  (sdl:load-library)
  (sdl:with-init ()
    (unless (sdl:window *screen-width* *screen-height*
                        :title-caption "Particles Demo"
                        :icon-caption "Particles Demo"
                        :sw t :resizable t
                        :fps (make-instance 'sdl:fps-fixed))
      (error "~&Unable to create a SDL window~%"))

    (sdl:enable-event-filters)
    (sdl:remove-all-event-filters)
    (sdl::set-event-filter :video-resize-event #'resize-screen)

    (setf (sdl:frame-rate) frame-rate)
    (sdl:enable-key-repeat nil nil)
  Load images . Convert the 24 - bit particle surface into a 32bpp
    (setf *particle-img* (sdl::convert-to-display-format :surface (sdl:load-image (sdl:create-path
                                                                                  "particle.bmp"
                                                                                  sdl:*default-asset-path*))
                                                        :inherit nil
                                                        :pixel-alpha t
                                                        :free t))
( setf * particle - img * ( sdl : load - image ( sdl : create - path


    (sdl:with-surface (alpha (sdl:load-image (sdl:create-path "particle-alpha.bmp"
                                                              sdl:*default-asset-path*)))
      (sdl:copy-channel-to-alpha *particle-img* alpha :channel :r))


( setf * particle - img * ( sdl : copy - surface : surface * particle - img * : inherit nil : rle - accel t : free t : fill nil ) )


    (setf *font-large* (sdl:initialise-font sdl:*font-8x13*))
    (setf *font-small* (sdl:initialise-font sdl:*font-7x14*))

    (draw-cached-string (format nil "{ESC} = Exit, {P} Add 100 Particles, {L} Remove 100 Particles, {SPACE} = Toggle Fullscreen.")
                        5 5 *font-large* sdl:*default-display* t)
    (draw-cached-string (format nil "Particles: ~d, Framerate: Calculating...."
                                *particle-count*)
                        5 35 *font-small* sdl:*default-display* t)

    (setf *particles* nil)
    (dotimes (i *particle-count*)
      (push (init-particle (make-particle)) *particles*))

    (sdl:with-events ()
      (:key-down-event (:key k)
       (cond
        ((sdl:key= k :sdl-key-escape)
         (sdl:push-quit-event))
        ((sdl:key= k :sdl-key-p)
         (add-particles))
        ((sdl:key= k :sdl-key-l)
         (remove-particles))
        ((sdl:key= k :sdl-key-space)
         (toggle-fullscreen))))

      (:mouse-motion-event (:x x :y y)
       (setf *mouse-x* x
             *mouse-y* y))

      (:quit-event () t)

      (:video-expose-event () (sdl:update-display))

      (:idle
       (sdl:clear-display sdl:*black*)

       (dolist (p *particles*)
         (update-particle p (sdl:time-scale))
         (let ((pos (particle-pos p)))
           (sdl:draw-surface-at-* *particle-img*
                                  (round (vec2-x pos)) (round (vec2-y pos)))))
       (draw-cached-string "" 5 5 *font-large* sdl:*default-display* nil)

       (if (funcall *frames-p*)
         (draw-cached-string (format nil "Particles: ~d, Framerate: ~f, timescale: ~f"
                                     *particle-count* (truncate (sdl:average-fps)) (sdl:time-scale))
                             5 35 *font-small* sdl:*default-display* t)
         (draw-cached-string nil 5 35 *font-small* sdl:*default-display* nil))

       (sdl:update-display)))))


(defun particles-timestep (&optional (frame-rate nil))
  (sdl:with-init ()
    (unless (sdl:window *screen-width* *screen-height*
                        :title-caption "Particles Demo"
                        :icon-caption "Particles Demo"
                        :flags '(sdl:sdl-sw-surface sdl:sdl-resizable)
                        :fps (make-instance 'sdl:fps-mixed))
      (error "~&Unable to create a SDL window~%"))

    (setf (sdl:frame-rate) frame-rate)

    (sdl:enable-event-filters)
    (sdl:remove-all-event-filters)
    (sdl::set-event-filter :video-resize-event #'resize-screen)

    (sdl:enable-key-repeat nil nil)

  Load images . Convert the 24 - bit particle surface into a 32bpp
    (setf *particle-img* (sdl::convert-to-display-format :surface (sdl:load-image (sdl:create-path
                                                                                   "particle.bmp"
                                                                                   sdl:*default-asset-path*))
                                                         :inherit nil
                                                         :pixel-alpha t
                                                         :free t))

    (sdl:with-surface (alpha (sdl:load-image (sdl:create-path "particle-alpha.bmp"
                                                              sdl:*default-asset-path*)))
      (sdl:copy-channel-to-alpha *particle-img* alpha :channel :r))

    (setf *font-large* (sdl:initialise-font sdl:*font-8x13*))
    (setf *font-small* (sdl:initialise-font sdl:*font-7x14*))

    (draw-cached-string (format nil "{ESC} = Exit, {P} Add 100 Particles, {L} Remove 100 Particles, {SPACE} = Toggle Fullscreen.")
                        5 5 *font-large* sdl:*default-display* t)
    (draw-cached-string (format nil "Particles: ~d, Framerate: Calculating...."
                                *particle-count*)
                        5 35 *font-small* sdl:*default-display* t)

    (setf *particles* nil)
    (dotimes (i *particle-count*)
      (push (init-particle (make-particle)) *particles*))

    (sdl:with-events ()
      (:key-down-event (:key k)
       (cond
        ((sdl:key= k :sdl-key-escape)
         (sdl:push-quit-event))
        ((sdl:key= k :sdl-key-p)
         (add-particles))
        ((sdl:key= k :sdl-key-l)
         (remove-particles))
        ((sdl:key= k :sdl-key-space)
         (toggle-fullscreen))))

      (:mouse-motion-event (:x x :y y)
       (setf *mouse-x* x
             *mouse-y* y))

      (:quit-event () t)

      (:video-expose-event () (sdl:update-display))

      (:idle
       (sdl:clear-display sdl:*black*)

       (sdl:with-timestep ()
         (dolist (p *particles*)
           (update-particle p (/ (sdl::dt) 1000))))

       (dolist (p *particles*)
         (sdl:draw-surface-at-* *particle-img*
                                (round (vec2-x (particle-pos p)))
                                (round (vec2-y (particle-pos p)))))
       (draw-cached-string nil 5 5 *font-large* sdl:*default-display* nil)

       (if (funcall *frames-p*)
         (draw-cached-string (format nil "Particles: ~d, Framerate: ~f, timescale: ~f, dt: ~f"
                                     *particle-count* (truncate (sdl:average-fps)) (sdl:time-scale) (sdl:dt))
                             5 35 *font-small* sdl:*default-display* t)
         (draw-cached-string nil 5 35 *font-small* sdl:*default-display* nil))

       (sdl:update-display)))))

(defun particles-event-loop (&optional (frame-rate nil))
  (sdl:with-init ()
    (unless (sdl:window *screen-width* *screen-height*
                        :title-caption "Particles Demo"
                        :icon-caption "Particles Demo"
                        :flags '(sdl:sdl-sw-surface sdl:sdl-resizable)
                        :fps (make-instance 'sdl:fps-mixed)
                        :position 'center)
      (error "~&Unable to create a SDL window~%"))

    (setf (sdl:frame-rate) frame-rate)

    (sdl:enable-event-filters)
    (sdl:remove-all-event-filters)
    (sdl::set-event-filter :video-resize-event #'resize-screen)

    (sdl:enable-key-repeat nil nil)

  Load images . Convert the 24 - bit particle surface into a 32bpp
    (setf *particle-img* (sdl::convert-to-display-format :surface (sdl:load-image (sdl:create-path
                                                                                   "particle.bmp"
                                                                                   sdl:*default-asset-path*))
                                                         :inherit nil
                                                         :pixel-alpha t
                                                         :free t))

    (sdl:with-surface (alpha (sdl:load-image (sdl:create-path "particle-alpha.bmp"
                                                              sdl:*default-asset-path*)))
      (sdl:copy-channel-to-alpha *particle-img* alpha :channel :r))

    (setf *font-large* (sdl:initialise-font sdl:*font-8x13*))
    (setf *font-small* (sdl:initialise-font sdl:*font-7x14*))

    (draw-cached-string (format nil "{ESC} = Exit, {P} Add 100 Particles, {L} Remove 100 Particles, {SPACE} = Toggle Fullscreen.")
                        5 5 *font-large* sdl:*default-display* t)
    (draw-cached-string (format nil "Particles: ~d, Framerate: Calculating...."
                                *particle-count*)
                        5 35 *font-small* sdl:*default-display* t)

    (setf *particles* nil)
    (dotimes (i *particle-count*)
      (push (init-particle (make-particle)) *particles*))

    (loop with event* = (sdl:new-event)
          for event = (sdl::get-event event*) then (sdl::get-event event*)
          while event do
          (case (sdl:event-type event)
            (:idle
             (sdl:update-input-util (sdl:frame-time))
             (sdl:with-frame-rate ()
               (sdl:clear-display sdl:*black*)

               (sdl:with-timestep ()
                 (dolist (p *particles*)
                   (update-particle p (/ (sdl::dt) 1000))))

               (dolist (p *particles*)
                 (sdl:draw-surface-at-* *particle-img*
                                        (round (vec2-x (particle-pos p)))
                                        (round (vec2-y (particle-pos p)))))
               (draw-cached-string nil 5 5 *font-large* sdl:*default-display* nil)

               (if (funcall *frames-p*)
                 (draw-cached-string (format nil "Particles: ~d, Framerate: ~f, timescale: ~f, dt: ~f"
                                             *particle-count* (truncate (sdl:average-fps)) (sdl:time-scale) (sdl:dt))
                                     5 35 *font-small* sdl:*default-display* t)
                 (draw-cached-string nil 5 35 *font-small* sdl:*default-display* nil))

               (sdl:update-display)))

            (:key-down-event
             (sdl:with-key-down-event ((k :key)) event
               (case k
                 (:sdl-key-escape (sdl:push-quit-event))
                 (:sdl-key-p (add-particles))
                 (:sdl-key-l (remove-particles))
                 (:sdl-key-space (toggle-fullscreen)))))

            (:mouse-motion-event
             (sdl:with-mouse-motion-event ((x :x) (y :y)) event
               (setf *mouse-x* x
                     *mouse-y* y)))

            (:video-expose-event (sdl:update-display))

            (:quit-event (loop-finish)))
          finally (sdl:free-event event*))))
