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An output pane is a pane whose display and input behavior can be controlled by the programmer.









A function called to redisplay the pane.


A keyword controlling quality of drawing, especially anti-aliasing of text.


A platform-specific plist of options controlling how graphics are drawn.


A boolean controlling whether output is buffered, on Microsoft Windows and Motif.


A list of input specifications, otherwise known as a command table.


A function called when the pane is scrolled, or nil. The default is nil.


A generalized boolean specifying whether the pane itself is responsible for drawing into the visible area.


A function called when the pane gets or loses the input focus, or nil. The default is nil.


A function called when the pane is resized, or nil. The default is nil.


A function called just after the pane is created.


A function called just before the pane is destroyed.


Controls whether to use native input method to interpret keyboard input. Currently this has an effect only on GTK+.


This is called for various events related to composition, which here means composing input characters into other characters by an input method.






The class output-pane is a subclass of gp:graphics-port-mixin which means that it supports the graphics ports drawing operations such as draw-image, draw-string and draw-path.

When the CAPI needs to redisplay a region of the output pane, the display-callback gets called with the output-pane and the x , y , width and height of the region that needs redrawing. The display-callback should then use Graphics Ports functions to redisplay that area. To force an area to be re-displayed, use the function invalidate-rectangle.

Note: if you need to temporarily prevent the display-callback from running, for example because it is slow, then use the Cached Display interface so that the pane still redraws. See output-pane-cache-display for the details.

drawing-mode should be either :compatible which causes drawing to be the same as in LispWorks 6.0, or :quality which causes all the drawing to be transformed properly, and allows control over anti-aliasing on Microsoft Windows and GTK+. The default value of drawing-mode is :quality.

For more information about drawing-mode , see The drawing mode and anti-aliasing.

graphics-options is currently only used by the Mac OS X Cocoa implementation. The single option defined is :text-rendering, with allowed values:


Draw glyphs directly using Core Graphics. This only draws characters with glyphs in the chosen font.


Draw using ATSUI APIs where possible.This is slower but can handle more characters.

When draw-with-buffer is true, display of the output-pane (that is drawing the background and calling the display-callback ) is done by first drawing to a pixmap buffer, and then drawing from that buffer. This is useful to avoid flickering if the display is complex. The default value of draw-with-buffer is nil.

The input-model provides a means to get callbacks on mouse and keyboard gestures. An input-model is a list of mappings from gesture to callback, where each mapping is a list

( gesture callback . extra-callback-args )

gesture specifies the type of gesture, which can be Gesture Spec (representing keyboard input), character, mouse button (including multiple clicks made in quick succession), modifier change, key, command or cursor motion. On Microsoft Windows and Cocoa gesture can also specify multi-touch gestures that come from trackpad or touchscreen devices, including zoom, rotate, pan and more.

gesture can match specific input such as uppercase A with the Control key pressed, or a general class of input such as any character.

input-model can be set before the pane is displayed, but changes after that are ignored. cl:initialize-instance is the natural place for subclasses to modify the existing input-model , using the output-pane accessor output-pane-input-model. Note that since the mappings are processed in order, prepending to an existing input-model overrides it when there are clashes, while appending affects only gestures for which the original input-model did not have a match.

For all the details of input-model syntax and the precedence and interpretation of the various gesture types, see Detailed description of the input model.

If pane-can-scroll is true then the pane is responsible for handling scrolling, by redrawing. It should draw into the visible area according to the scroll parameters. This is known as internal scrolling and an example is editor-pane. If pane-can-scroll is nil, then the CAPI is responsible for scrolling over the data range. The default value is nil. This is known as ordinary scrolling and there is an example in output-panes/scroll-test.lisp.

When the output pane is scrolled, the CAPI calls the scroll-callback if this is non-nil. The arguments of the scroll callback are the output-pane, the direction (:vertical, :horizontal or :pan), the scroll operation (:move, :drag, :step or :page), the amount of scrolling (an integer), and a keyword argument :interactive. This has value t if the scroll was invoked interactively, and value nil if the scroll was programmatic, such as via the function scroll. In the Mac OS X Cocoa implementation the direction is always :pan. See the following CAPI example files:


focus-callback , if non-nil, is a function of two arguments. The first argument is the output-pane itself, and the second is a boolean. When the output-pane gets the focus, focus-callback is called with second argument t, and when the output-pane loses the focus, focus-callback is called with second argument nil.

resize-callback , if non-nil, is a function of five arguments called when the output-pane is resized. The first argument is the output-pane itself, and the rest are its new geometry: x , y , width and height .

create-callback , if non-nil, is a function of one argument which is called just after the pane is created (but before it becomes visible). The argument is the pane itself. This function can perform initialization such as loading images.

destroy-callback , if non-nil, is a function of one argument which is called just before the pane is destroyed, for example when the window is closed or the pane is removed from its layout. The argument is the pane itself. This function can perform cleanup operations (though note that images associated with the pane are automatically freed).

use-native-input-method should be nil, t or :default. If use-native-input-method is not supplied, or is :default, the default is used, which is controlled by set-default-use-native-input-method. The default setting is always to use native input methods.

composition-callback is a function with signature

composition-callback pane what

where pane is the output pane and what can be one of:


The composition operation is starting.


The composition ends.

A list

A plist describing the "preedit" string, which is a string containing the partial input that should be displayed while the composition is ongoing. These calls with a plist occur only when the underlying system does not display the partial input itself. Currently on Microsoft Windows the system always displays the preedit string itself, so these calls occur only on GTK+ and Cocoa.

During composition there will be repeated calls with a list, in general each time that the preedit string changes. Each call is a complete description of what needs to be displayed. The data from previous calls should be ignored.

The keys that can appear in the plist are currently:


The value is a list where each element is itself a list, where the first element is a string and the second a plist describing a face (a face plist). The strings are the strings that need to be displayed, and the face plist describing the face that the underlying GUI thinks that each string needs to be displayed. The face plist may contain any of the following keywords: :foreground, :background, :font, :bold-p, :italic-p, :underline-p. The argument string-face-lists may be nil, which means display nothing.


The argument is an integer describing where the "cursor" should be displayed. The index is into the string that is concatenation of the strings in string-face-lists .


If present, the value specifies the selected range as a cons of start and length in characters. The start is an index into the string that is a concatenation of the strings in the string-face-lists .


A boolean specifying whether the selected-range should have a different face to the unselected range.

The editor uses the :start call to position the composition window at the cursor by using set-composition-placement and the calls with a list to display the partial composition string.

  1. A composition session is initiated and managed by the underlying windowing system (not CAPI) when it is set to use input method which needs to compose characters from several keyboard gestures (mostly input methods for east Asian languages). Keyboard gestures that are used by the composition session are not visible to the application, but some keyboard gestures, typically gestures with modifiers, may be passed through.
  2. When the user commits the composition session, the user callbacks from the input-model are called on each character in the resulting string (as if the user typed each of these characters). The call to composition-callback with :start should typically use set-composition-placement to tell the system where the interaction should happen. The calls to composition-callback with a list do not always happen, the underlying system may do it all itself.
  3. You can stop an ongoing composition session by calling output-pane-stop-composition. That is useful for gestures like mouse clicks that may change the interaction such that it does not make sense to continue the composition.
  4. draw-with-buffer is typically useful for a pinboard-layout with large number of pinboard objects, or any other feature that may cause it to flicker.
  5. The GTK+ and Cocoa libraries always buffer, so draw-with-buffer is ignored on these platforms.
  6. In GTK+ versions before 2.12 the :start and :end calls are not reliable.

Firstly, here is an example that draws a circle in an output pane.

(defun display-circle (self x y width height)
  (declare (ignore x y width height))
  (gp:draw-circle self 200 200 200 :filled t))
(capi:contain (make-instance
               :display-callback 'display-circle)
              :best-width 200 :best-height 200)

Here is an example that shows how to use a button gesture.

(defun test-callback (self x y)
   "Pressed button 1 at (~S,~S) in ~S" x y self))
  :title "Press button 1:"
  :input-model `(((:button-1 :press)
 :best-width 200 :best-height 200)

This example illustrates Gesture Spec mappings.

(defun draw-input (self x y gspec)
  (let ((data (sys:gesture-spec-data gspec))
        (mods (sys:gesture-spec-modifiers gspec)))
     (with-output-to-string (ss) 
        gspec ss :force-shift-for-upcase nil))
     x y)))
  :title "Press keys in the pane..."
  :input-model '((:gesture-spec
 :best-width 200 :best-height 200)
  :title "Press Control-a in the pane..."
  :input-model '(((:gesture-spec "Control-a")
 :best-width 200 :best-height 200)

Here is a simple example that draws the character typed at the cursor point.

(defun draw-character (self x y character)
  (gp:draw-character self character x y))
  :title "Press keys in the pane..."
  :input-model '((:character draw-character)))
 :best-width 200 :best-height 200)

This example shows how to use the motion gesture.

(defun draw-red-blob (self x y)
  (gp:draw-circle self x y 3 
                  :filled t 
                  :foreground :red))
  :title "Drag button-1 across this pane."
  :input-model '(((:button-1 :motion)
                 ((:button-1 :motion :control)
 :best-width 200 :best-height 200)

This example illustrates the use of focus-callback :

  #'(lambda (x y)
      (format t 
              "Pane ~a ~:[lost~;got~] the focus~%" 
              x y))))

This example illustrates the use of graphics-options to specify ATSUI drawing on Cocoa:

(defvar *string* 
  (coerce (loop for i from 0 below 60
                collect (code-char (* 5 i))) 
 (make-instance 'capi:output-pane 
                :visible-min-width 400 
                :visible-max-height 50
                #'(lambda (pane x y w h)  
                    (gp:draw-string pane 
                                    10 10)) 
                '(:text-rendering :atsui)))

This example illustrates some effects of drawing-mode :

(example-edit-file "capi/graphics/catherine-wheel")

This example shows how to draw a rectangle indicating selection of objects in response to mouse movement:

(example-edit-file "capi/graphics/highlight-rectangle")

These two examples illustrate drawing the results of dynamic computation:

(example-edit-file "capi/graphics/plot-directly") (example-edit-file "capi/graphics/plot-offline")

There are further examples here:

(example-edit-file "capi/output-panes/")

See also Self-contained examples.

See also

Programming with CAPI Windows
Popup menus for panes
Creating Panes with Your Own Drawing and Input
Drawing - Graphics Ports
Rendering of colors
Printing from the CAPI—the Hardcopy API
Drag and Drop

CAPI User Guide and Reference Manual (Windows version) - 25 Feb 2015