wanderlust: hook for modifying buffer *WL:Message* as it is being accessed

Question

I want to optionally perform some functions on the data in buffer *WL:Message* right after I access and view it.

For example, when first viewing a new message in the *WL:Message* buffer via wl-summary-read or wl-summary-enter-handler, I'd like to perform the following logic (pseudo-code) ...

Enter the *WL:Message* buffer
IF *WL:Message* buffer contains images
THEN
   Scroll down to the first image
   Do a (recenter 1) to position this image at the top of the window
ENDIF

I know how to write the elisp code to do all of this. The problem is knowing when to issue this code. I haven't been able to find a hook that runs right as the *WL:Message* buffer is being displayed.

I tried to use advice around various existing wanderlust wl-summary and wl-message functions, but I haven't found a reliable way to do what I want. Sometimes (seemingly at random), the wl-message-buffer variable is not set, or that buffer's window is not live (it needs to be a live window in order for (recenter 1) to work).

Does anyone know of the proper place I can insert my code so that it always reliably runs whenever I first view a new message in the *WL:Message* buffer?

Answer 1

Thanks to the help from lawlist, I figured out the solution.

I'm pretty sure I had tried wl-message-redisplay-hook, but I was incorrectly trying to use the variable wl-message-buffer to get the current *WL:Message* buffer. However, in that hook (and in many other places in the wanderlust code), that variable's value is set to nil. In general, I believe we cannot ever reliably use the wl-message-buffer variable.

However, in wl-message-redisplay-hook, the (current-buffer) function will correctly return a reference to a live *WL:Message* buffer instance containing the new message. I can then do whatever I want within that buffer.

Here's my code for performing the function I described above ...

(defun my-redisplay-func ()
  ;; As long as this function is run as a
  ;; wl-message-redisplay-hook, (current-buffer)
  ;; will return an instance of a live *WL:Message*
  ;; buffer.
  (let ((win (get-buffer-window (current-buffer))))
    (when win
      (with-selected-window win
        (let ((cur (point-min))
              (end (point-max))
              (image-pos))
          ;; Get the position of the first displayed
          ;; image, if there is one.
          (while (and (not image-pos) (<= cur end))
            (when (get-char-property cur 'display)
              (setq image-pos cur))
            (setq cur (1+ cur)))
          (when image-pos
            ;; Scroll to the first image row and reposition
            ;; it to the bottom of the window.
            (goto-char image-pos)
            (next-line)
            (recenter -1)
            (goto-char image-pos)))))))
(add-hook 'wl-message-redisplay-hook 'my-redisplay-func)