Add font scaling tweak so that it works well with my org-present

configuration

configuration.org

@@ -36,7 +36,7 @@ configuration loading. The threshold will be set lower at the end of
 the configuration to make each GC call faster for normal emacs use.
   
 #+begin_src emacs-lisp
-(setq gc-cons-threshold (* 60 1024 1024))
+(setq gc-cons-threshold (* 100 1024 1024))
 #+end_src
 
 * Personal information
@@ -314,6 +314,8 @@ buffer. I also like to have Emacs show me matching parenthesis. Also do not show
   )
 #+END_SRC
 
+** Fonts
+
 Select the font I will use depending on the system
 
 #+begin_src emacs-lisp
@@ -329,12 +331,36 @@ Select the font I will use depending on the system
     (setq mh-font-variable "DejaVu Sans")
     )
   )
-(set-face-attribute 'default nil :font mh-font-fixed :weight 'normal :height 150)
-(set-face-attribute 'fixed-pitch nil :font mh-font-fixed :weight 'normal :height 150)
-(set-face-attribute 'variable-pitch nil :font mh-font-variable :weight 'normal :height 150)
+(set-face-attribute 'default nil :font mh-font-fixed :weight 'normal :height 160)
+(set-face-attribute 'fixed-pitch nil :font mh-font-fixed :weight 'normal)
+(set-face-attribute 'variable-pitch nil :font mh-font-variable :weight 'normal)
 (set-frame-font mh-font-fixed nil t)
 #+end_src
 
+*** Dynamic size modification
+
+The default action (~text-scale-adjust~), do not affect faces whose font properties have an
+explicity ~:height~ attribute except for /default/ and /header-line/ face. However, when using
+~org-present~, I change some faces and do not use the /default/ one everywhere. So I change the way
+font size is modified. This solution is adapted from
+https://emacs-fu.blogspot.com/2008/12/zooming-inout.html
+
+#+begin_src emacs-lisp
+(defun my/text-zoom (n)
+  "with positive N, increase the font size, otherwise decrease it"
+  (set-face-attribute 'default nil :height 
+                      (+ (face-attribute 'default :height) (* (if (> n 0) 1 -1) 10)))
+  (set-face-attribute 'fixed-pitch nil :height 
+                      (+ (face-attribute 'fixed-pitch :height) (* (if (> n 0) 1 -1) 10)))
+  (set-face-attribute 'variable-pitch nil :height 
+                      (+ (face-attribute 'variable-pitch :height) (* (if (> n 0) 1 -1) 10)))
+  )
+
+(global-set-key (kbd "C-+") #'(lambda nil (interactive) (my/text-zoom 1)))
+(global-set-key (kbd "C--") #'(lambda nil (interactive) (my/text-zoom -1)))
+#+end_src
+
+
 ** Modeline
 
 Tweak how some modeline elements are displayed
@@ -688,7 +714,7 @@ it with =visual-fill-column= to enhance the visual look of the presentation.
                   (org-level-6)
                   (org-level-7)
                   (org-level-8)))
-    (set-face-attribute (car face) nil :font mh-font-fixed :weight 'medium ))
+    (set-face-attribute (car face) nil :font mh-font-fixed :weight 'medium :height 1.0))
 
   ;; Remove the blank line at top of the frame
   (setq header-line-format nil)