why is switch-to-buffer effect not visible immediately when called in a list with other functions?

Question

I have a key bound to some program which prepares a buffer, switches to it via switch-to-buffer and afterwards calls some function which modifies the buffer (and can take a few seconds to execute).

When pressing the key, this modifying function is executed before the buffer is actually switched (noticeable by a considerable lag), although it appears after switch-to-buffer.

Can somebody please explain why this is the case?

Here are full details, although I don't think these are relevant for my problem:

I'm using elfeed and have set elfeed-entry-switch, which by default is just #'switch-to-buffer, to #'my-elfeed-entry-switch, where

(defun my-elfeed-entry-switch (buffer)
    (with-current-buffer buffer
      (switch-to-buffer buffer)
      (org-latex-preview)))

The computationally intensive function therefore is org-latex-preview, which renders and displays inline latex code and, like I wrote, sometimes takes several seconds to complete.

When trying to switch to an entry which contains a lot of latex code, I have to wait for a second or so before the buffer becomes visible.

What I actually expect is that the buffer first becomes visible (with unrendered latex code) and then org-latex-preview starts its work, which it does if called interactively.

UPDATE As suggested below, removing with-current-buffer does not solve the problem, i.e.

(defun my-elfeed-entry-switch (buffer)
    (switch-to-buffer buffer)
    (org-latex-preview))

still does not show the buffer before org-latex-preview has finished rendering.

Answer 1

The O.P. has indicated in a comment that inserting (redisplay t) following the switch-to-buffer call resolves the issue outlined in the question. Another idea would be to use (sit-for 0), which also forces a redisplay by the display engine. The function redisplay contains a doc-string that states:

redisplay is a built-in function in ‘C source code’.

(redisplay &optional FORCE)

Perform redisplay.

Optional arg FORCE, if non-nil, prevents redisplay from being
preempted by arriving input, even if ‘redisplay-dont-pause’ is nil.
If ‘redisplay-dont-pause’ is non-nil (the default), redisplay is never
preempted by arriving input, so FORCE does nothing.

Return t if redisplay was performed, nil if redisplay was preempted
immediately by pending input.