13.9.9 Creating external images from Graphics Ports operations

To create an external-image object from an on-screen window, use with-pixmap-graphics-port as in this example:

(defun record-picture (output-pane)

  (gp:with-pixmap-graphics-port

      (port output-pane

            400 400

            :clear t

            :background :red)

    (gp:draw-rectangle port 0 0 200 200

                       :filled t

                       :foreground :blue)

    (let ((image (gp:make-image-from-port port)))

      (gp:externalize-image port image))))

Here output-pane must be a displayed instance of capi:output-pane (or a subclass). The code does not affect the displayed pane.

If you do not already display a suitable output pane, you can create an invisible one like this:

(defun record-picture-1 ()

  (let* ((pl (make-instance 'capi:pinboard-layout))

         (win (capi:display

               (make-instance 'capi:interface

                              :display-state :hidden

                              :layout pl))))

    (prog1 (record-picture pl)

      (capi:destroy win))))

Note: There is no reason to create and destroy the invisible interface each time a new picture is recorded, so for efficiency you could cache the interface object and use it repeatedly.

CAPI User Guide (Unix version) - 30 Aug 2011