Subject: Re: bug#37770: [PATCH] Expose scale factor through the redisplay interface

From: Carlos Pita <[email-masked]>
Date: Wed, 16 Oct 2019 16:08:47 -0300

I've capitalized changelog entries in the message and also added a
reference to the bug number.

Eli told me that you prefer code comments to long commit messages but
in this case I think the rationale would be lost in fragmentary
comments here and there. It's true that there is still the reference
to this discussion in the commit message, but I believe it's
convenient to quickly get a description of the change using git blame
when browsing the code. If you disagree I will remove the notes from
the commit message and copy them here.

Best regards
--
Carlos
From 01e52de9ce49bc0b3490492891f066d2f9306cf4 Mon Sep 17 00:00:00 2001
From: memeplex <[email-masked]>
Date: Tue, 15 Oct 2019 19:14:03 -0300
Subject: [PATCH] Expose scale factor through the redisplay interface
 (Bug#37770)

* src/dispextern.h (redisplay_interface): Add get_scale_factor API.

* src/xterm.c (x_get_scale_factor): Consolidate with xg_get_scale (see
bug#37752) and export through the rif. Simplify scale inferring
logic (see note 1 below).

* src/w32term.c (w32_get_scale_factor): Likewise simplify logic and
add to the rif.

* src/nsterm.m (ns_get_scale_factor): Add a dummy implementation that
always return 1 to the rif, since there are no uses of any scale
factor here.

Note 1: both x_get_scale_factor and w32_get_scale_factor computed
distinct scales for x and y by taking the ratio between effective
resolution in each direction and a standard 96 dpi resolution.  Since
this ratio is then truncated to an integer (the floor) it seems to me
that there is no sensible possibility that these two numbers
diverge. Moreover, modern toolkits report one number as scale factor
and we need a common interface here. For those reasons I'm arbitrarily
picking the horizontal scale factor as THE scale factor.

Note 2: I decided to let get_scale_factor return a double, even tough
factors currently in use are all integers AFAIK. This is in
anticipation of fractional scaling. I believe it's prudent to keep
the interface general in this regard.
---
 src/dispextern.h |  3 +++
 src/nsterm.m     |  6 ++++++
 src/w32term.c    | 29 +++++++++++------------------
 src/xterm.c      | 41 ++++++++++++++++++-----------------------
 4 files changed, 38 insertions(+), 41 deletions(-)

diff --git a/src/dispextern.h b/src/dispextern.h
index 0615b16..b93e25f 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -2942,6 +2942,9 @@ reset_mouse_highlight (Mouse_HLInfo *hlinfo)
 
 #ifdef HAVE_WINDOW_SYSTEM
 
+  /* Return the scale factor for the screen containing frame F.  */
+  double (*get_scale_factor) (struct frame *f);
+
   /* Draw a fringe bitmap in window W of row ROW using parameters P.  */
   void (*draw_fringe_bitmap) (struct window *w, struct glyph_row *row,
                               struct draw_fringe_bitmap_params *p);
diff --git a/src/nsterm.m b/src/nsterm.m
index 5583c61..6e1b751 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -2957,6 +2957,11 @@ so some key presses (TAB) are swallowed by the system.  */
 
    ========================================================================== */
 
+static double
+ns_get_scale_factor (struct frame *f)
+{
+  return 1;  // TODO do we need to do something else here?
+}
 
 extern int max_used_fringe_bitmap;
 static void
@@ -5087,6 +5092,7 @@ static Lisp_Object ns_string_to_lispmod (const char *s)
   gui_clear_window_mouse_face,
   gui_get_glyph_overhangs,
   gui_fix_overlapping_area,
+  ns_get_scale_factor,
   ns_draw_fringe_bitmap,
   0, /* define_fringe_bitmap */ /* FIXME: simplify ns_draw_fringe_bitmap */
   0, /* destroy_fringe_bitmap */
diff --git a/src/w32term.c b/src/w32term.c
index 9da0845..6d430c6 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -304,20 +304,16 @@ w32_restore_glyph_string_clip (struct glyph_string *s)
     }
 }
 
-static void
-w32_get_scale_factor(struct w32_display_info *dpyinfo, int *scale_x, int *scale_y)
+static double
+w32_get_scale_factor(struct frame *f)
 {
+  struct w32_display_info *dpyinfo = FRAME_DISPLAY_INFO (f);
   const int base_res = 96;
 
-  *scale_x = *scale_y = 1;
-
-  if (dpyinfo)
-    {
-      if (dpyinfo->resx > base_res)
-	*scale_x = floor (dpyinfo->resx / base_res);
-      if (dpyinfo->resy > base_res)
-	*scale_y = floor (dpyinfo->resy / base_res);
-    }
+  if (dpyinfo && dpyinfo->resx > base_res)
+    return floor (dpyinfo->resx / base_res);
+  else
+    return 1;
 }
 
 /*
@@ -334,12 +330,8 @@ w32_get_scale_factor(struct w32_display_info *dpyinfo, int *scale_x, int *scale_
 static void
 w32_draw_underwave (struct glyph_string *s, COLORREF color)
 {
-  struct w32_display_info *dpyinfo = FRAME_DISPLAY_INFO (s->f);
-
-  int scale_x, scale_y;
-  w32_get_scale_factor (dpyinfo, &scale_x, &scale_y);
-
-  int wave_height = 3 * scale_y, wave_length = 2 * scale_x, thickness = scale_y;
+  double scale = w32_get_scale_factor (s->f);
+  int wave_height = 3 * scale, wave_length = 2 * scale, thickness = scale;
   int dx, dy, x0, y0, width, x1, y1, x2, y2, odd, xmax;
   Emacs_Rectangle wave_clip, string_clip, final_clip;
   RECT w32_final_clip, w32_string_clip;
@@ -348,7 +340,7 @@ w32_draw_underwave (struct glyph_string *s, COLORREF color)
   dx = wave_length;
   dy = wave_height - 1;
   x0 = s->x;
-  y0 = s->ybase + wave_height / 2 - scale_y;
+  y0 = s->ybase + wave_height / 2 - scale;
   width = s->width;
   xmax = x0 + width;
 
@@ -7192,6 +7184,7 @@ w32_make_rdb (char *xrm_option)
   gui_clear_window_mouse_face,
   gui_get_glyph_overhangs,
   gui_fix_overlapping_area,
+  w32_get_scale_factor,
   w32_draw_fringe_bitmap,
   w32_define_fringe_bitmap,
   w32_destroy_fringe_bitmap,
diff --git a/src/xterm.c b/src/xterm.c
index 5d8b148..67253a6 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -3611,21 +3611,21 @@ x_draw_stretch_glyph_string (struct glyph_string *s)
   s->background_filled_p = true;
 }
 
-static void
-x_get_scale_factor(Display *disp, int *scale_x, int *scale_y)
+static double
+x_get_scale_factor(struct frame *f)
 {
+#ifdef USE_GTK
+  return xg_get_scale (f);
+#else
+  Display *disp = FRAME_X_DISPLAY (f);
+  struct x_display_info *dpyinfo = x_display_info_for_display (disp);
   const int base_res = 96;
-  struct x_display_info * dpyinfo = x_display_info_for_display (disp);
-
-  *scale_x = *scale_y = 1;
 
-  if (dpyinfo)
-    {
-      if (dpyinfo->resx > base_res)
-	*scale_x = floor (dpyinfo->resx / base_res);
-      if (dpyinfo->resy > base_res)
-	*scale_y = floor (dpyinfo->resy / base_res);
-    }
+  if (dpyinfo && dpyinfo->resx > base_res)
+    return floor (dpyinfo->resx / base_res);
+  else
+    return 1;
+#endif /* USE_GTK */
 }
 
 /*
@@ -3641,27 +3641,21 @@ x_get_scale_factor(Display *disp, int *scale_x, int *scale_y)
 static void
 x_draw_underwave (struct glyph_string *s)
 {
-  Display *display = FRAME_X_DISPLAY (s->f);
-
   /* Adjust for scale/HiDPI.  */
-  int scale_x, scale_y;
-
-  x_get_scale_factor (display, &scale_x, &scale_y);
-
-  int wave_height = 3 * scale_y, wave_length = 2 * scale_x;
-
+  double scale = x_get_scale_factor (s->f);
+  int wave_height = 3 * scale, wave_length = 2 * scale;
 #ifdef USE_CAIRO
   x_draw_horizontal_wave (s->f, s->gc, s->x, s->ybase - wave_height + 3,
 			  s->width, wave_height, wave_length);
 #else  /* not USE_CAIRO */
-  int dx, dy, x0, y0, width, x1, y1, x2, y2, xmax, thickness = scale_y;;
+  int dx, dy, x0, y0, width, x1, y1, x2, y2, xmax, thickness = scale;
   bool odd;
   XRectangle wave_clip, string_clip, final_clip;
 
   dx = wave_length;
   dy = wave_height - 1;
   x0 = s->x;
-  y0 = s->ybase + wave_height / 2 - scale_y;
+  y0 = s->ybase + wave_height / 2 - scale;
   width = s->width;
   xmax = x0 + width;
 
@@ -10557,7 +10551,7 @@ x_set_offset (struct frame *f, register int xoff, register int yoff, int change_
 {
   int modified_top, modified_left;
 #ifdef USE_GTK
-  int scale = xg_get_scale (f);
+  double scale = x_get_scale_factor (f);
 #endif
 
   if (change_gravity > 0)
@@ -13356,6 +13350,7 @@ x_activate_timeout_atimer (void)
     gui_clear_window_mouse_face,
     gui_get_glyph_overhangs,
     gui_fix_overlapping_area,
+    x_get_scale_factor,
     x_draw_fringe_bitmap,
 #ifdef USE_CAIRO
     x_cr_define_fringe_bitmap,
-- 
2.20.1