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7.5.2 With Object Sets Example

This example involves more work, but you get a little more for your effort. It defines two objects, input-box and slider, and establishes a :key-press handler for each object, key-pressed and slider-pressed. We have two object sets because we handle events on the windows manifesting these objects differently, but the events come over the same display connection.

(in-package "SERVER-EXAMPLE")

(defstruct (input-box (:print-function print-input-box)
                      (:constructor make-input-box (display window)))
  "Our program knows about input-boxes, and it doesn't care how they
   are implemented."
  display        ; The CLX display on which my input-box is displayed.
  window)        ; The CLX window in which the user types.
;;;
(defun print-input-box (object stream n)
  (declare (ignore n))
  (format stream "#<Input-Box ~S>" (input-box-display object)))

(defvar *input-box-windows*
        (system:make-object-set "Input Box Windows"
                                #'ext:default-clx-event-handler))

(defun key-pressed (input-box event-key event-window root child
                    same-screen-p x y root-x root-y modifiers time
                    key-code send-event-p)
  "This is our :key-press event handler."
  (declare (ignore event-key root child same-screen-p x y
                   root-x root-y time send-event-p))
  (format t "KEY-PRESSED (Window = ~D) = ~S.~%"
          (xlib:window-id event-window)
          ;; See Hemlock Command Implementor's Manual for convenient
          ;; input mapping function.
          (ext:translate-character (input-box-display input-box)
                                     key-code modifiers)))
;;;
(ext:serve-key-press *input-box-windows* #'key-pressed)
(defstruct (slider (:print-function print-slider)
                   (:include input-box)
                   (:constructor %make-slider
                                    (display window window-width max)))
  "Our program knows about sliders too, and these provide input values
   zero to max."
  bits-per-value  ; bits per discrete value up to max.
  max)            ; End value for slider.
;;;
(defun print-slider (object stream n)
  (declare (ignore n))
  (format stream "#<Slider ~S  0..~D>"
          (input-box-display object)
          (1- (slider-max object))))
;;;
(defun make-slider (display window max)
  (%make-slider display window
                  (truncate (xlib:drawable-width window) max)
                max))

(defvar *slider-windows*
        (system:make-object-set "Slider Windows"
                                #'ext:default-clx-event-handler))

(defun slider-pressed (slider event-key event-window root child
                       same-screen-p x y root-x root-y modifiers time
                       key-code send-event-p)
  "This is our :key-press event handler for sliders.  Probably this is
   a mouse thing, but for simplicity here we take a character typed."
  (declare (ignore event-key root child same-screen-p x y
                   root-x root-y time send-event-p))
  (format t "KEY-PRESSED (Window = ~D) = ~S  -->  ~D.~%"
          (xlib:window-id event-window)
          ;; See Hemlock Command Implementor's Manual for convenient
          ;; input mapping function.
          (ext:translate-character (input-box-display slider)
                                     key-code modifiers)
          (truncate x (slider-bits-per-value slider))))
;;;
(ext:serve-key-press *slider-windows* #'slider-pressed)
(defun server-example ()
  "An example of using the SYSTEM:SERVE-EVENT function and object sets to
   handle CLX events."
  (let* ((display (ext:open-clx-display))
         (screen (display-default-screen display))
         (black (screen-black-pixel screen))
         (white (screen-white-pixel screen))
         (iwindow (create-window :parent (screen-root screen)
                                 :x 0 :y 0 :width 200 :height 200
                                 :background white :border black
                                 :border-width 2
                                 :event-mask
                                 (xlib:make-event-mask :key-press)))
         (swindow (create-window :parent (screen-root screen)
                                 :x 0 :y 300 :width 200 :height 50
                                 :background white :border black
                                 :border-width 2
                                 :event-mask
                                 (xlib:make-event-mask :key-press)))
         (input-box (make-input-box display iwindow))
         (slider (make-slider display swindow 15)))
    ;; Wrap code in UNWIND-PROTECT, so we clean up after ourselves.
    (unwind-protect
        (progn
          ;; Enable event handling on the display.
          (ext:enable-clx-event-handling display
                                         #'ext:object-set-event-handler)
          ;; Add the windows to the appropriate object sets.
          (system:add-xwindow-object iwindow input-box
                                       *input-box-windows*)
          (system:add-xwindow-object swindow slider
                                       *slider-windows*)
          ;; Map the windows to the screen.
          (map-window iwindow)
          (map-window swindow)
          ;; Make sure we send all our requests.
          (display-force-output display)
          ;; Call server for 100,000 events or immediate timeouts.
          (dotimes (i 100000) (system:serve-event)))
      ;; Disable event handling on this display.
      (ext:disable-clx-event-handling display)
      (delete-window iwindow display)
      (delete-window swindow display)
      ;; Close the display.
      (xlib:close-display display))))
(defun delete-window (window display)
  ;; Remove the windows from the object sets before destroying them.
  (system:remove-xwindow-object window)
  ;; Destroy the window.
  (destroy-window window)
  ;; Pick off any events the X server has already queued for our
  ;; windows, so we don't choke since SYSTEM:SERVE-EVENT is no longer
  ;; prepared to handle events for us.
  (loop
   (unless (deleting-window-drop-event display window)
     (return))))

(defun deleting-window-drop-event (display win)
  "Check for any events on win.  If there is one, remove it from the
   event queue and return t; otherwise, return nil."
  (xlib:display-finish-output display)
  (let ((result nil))
    (xlib:process-event
     display :timeout 0
     :handler #'(lambda (&key event-window &allow-other-keys)
                  (if (eq event-window win)
                      (setf result t)
                      nil)))
    result))

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