Elisp to increase font-size in indirect buffer

Question

I use org-mode for writing and frequently use a two pane setup, similar to the one described here: Org-mode 2-pane writing setup using indirect buffers (or display-buffer-alist. I have an outline on the left, and can open indirect buffers to work on particular subtrees. This function (which I bind to SHIFT-RETURN), opens up subtrees in a right hand pane, and then resize them, so I have a skinnier outline column on the left, and a writing window on the right.

    (defun org-tree-open-in-right-window ()
      (interactive)
      (org-tree-to-indirect-buffer)
      (windmove-right)
      (window-resize nil (- (truncate (* 0.7 (frame-width))) (window-width)) t)
    )

In addition to opening a subtree in an indirect buffer and changing the window size, I would like to set increase the font size of the right-hand window. That is the skinny, left-hand buffer would have a smaller font size, allowing a view on the whole document, while the right would be larger (in width) and larger in font-size, to facilitate writing.

I've tried: (set-face-attribute 'default nil :height 150) but this changes the font size in both. Is there a value I can pass, instead of nil, that would restrict this function to just a active window?

Answer 1

See the text-scale-increase function:

text-scale-increase is an autoloaded interactive compiled Lisp function in face-remap.el.

(text-scale-increase INC)

Increase the height of the default face in the current buffer by INC steps. If the new height is other than the default, text-scale-mode is enabled.

Each step scales the height of the default face by the variable text-scale-mode-step (a negative number of steps decreases the height by the same amount). As a special case, an argument of 0 will remove any scaling currently active.

Also see text-scale-adjust for interactive use.