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

[Carlos Pita <carlosjosepita@gmail.com>]

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> This commit message doesnʼt use the ChangeLog format.

Ahh, I was just informally pattern matching other commit messages I
had seen in your repo. Now I've read [1] (I really like those rules,
will adopt them for other projects too). Nevertheless I'm still unsure
about how to format the notes that go below the actual changes.

Please, tell me what do you think about the new commit message.

> For the rest, it looks ok. Do you plan to make the changes to actually
> use the rif interface as part of the same patch?

No, those are part of bug#37689 [2].

---

[1] https://www.gnu.org/prep/standards/html_node/Change-Logs.html#Change-Logs
[2] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=37689

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From 6da098e0ebfbe8e17ad0fa860245222d12497889 Mon Sep 17 00:00:00 2001
From: memeplex <carlosjosepita@gmail.com>
Date: Tue, 15 Oct 2019 19:14:03 -0300
Subject: [PATCH] Expose scale factor through the redisplay interface

* 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