config: dpi-aware: remove ‘auto’ value, and default to ‘no’

We now default to scaling fonts using the scaling factor, not monitor
DPI.

The ‘auto’ value for dpi-aware has been removed.

Documentation (man pages and README) have been updated to reflect the
new default.

README.md

@@ -411,27 +411,53 @@ This is not how it is meant to be. Fonts are measured in _point sizes_
 **for a reason**; a given point size should have the same height on
 all mediums, be it printers or monitors, regardless of their DPI.
 
-Foot’s default behavior is to use the monitor’s DPI to size fonts when
-output scaling has been disabled on **all** monitors. If at least one
-monitor has output scaling enabled, fonts will instead by sized using
-the scaling factor.
+That said, on Wayland, Hi-DPI monitors are typically handled by
+configuring a _"scaling factor"_ in the compositor. This is usually
+expressed as either a rational value (e.g. _1.5_), or as a percentage
+(e.g. _150%_), by which all fonts and window sizes are supposed to be
+multiplied.
 
-This can be changed to either **always** use the monitor’s DPI
-(regardless of scaling factor), or to **never** use it, with the
-`dpi-aware` option in `foot.ini`. See the man page, **foot.ini**(5)
-for more information.
+For this reason, and because of the new _fractional scaling_ protocol
+(see below for details), and because this is how Wayland applications
+are expected to behave, foot >= 1.15 will default to scaling fonts
+using the compositor’s scaling factor, and **not** the monitor
+DPI.
 
-When fonts are sized using the monitor’s DPI, glyphs should always
-have the same physical height, regardless of monitor.
+This means the (assuming the monitors are at the same viewing
+distance) the font size will appear to change when you move the foot
+window across different monitors, **unless** you have configured the
+monitors’ scaling factors correctly in the compositor.
 
-Furthermore, foot will re-size the fonts on-the-fly when the window is
-moved between screens with different DPIs values. If the window covers
-multiple screens, with different DPIs, the highest DPI will be used.
+This can be changed by setting the `dpi-aware` option to `yes` in
+`foot.ini`. When enabled, fonts will **not** be sized using the
+scaling factor, but will instead be sized using the monitor’s
+DPI. When the foot window is moved across monitors, the font size is
+updated for the current monitor’s DPI.
+
+This means that, assuming the monitors are **at the same viewing
+distance**, the font size will appear to be the same, at all times.
 
 _Note_: if you configure **pixelsize**, rather than **size**, then DPI
 changes will **not** change the font size. Pixels are always pixels.
 
 
+### Fractional scaling on Wayland
+
+For a long time, there was no **true** support for _fractional
+scaling_. That is, values like 1.5 (150%), 1.8 (180%) etc, only
+integer values, like 2 (200%).
+
+Compositors that _did_ support fractional scaling did so using a hack;
+all applications were told to scale to 200%, and then the compositor
+would down-scale the rendered image to e.g. 150%. This works OK for
+everything **except fonts**, which ended up blurry.
+
+With _wayland-protocols 1.32_, a new protocol was introduced, that
+allows compositors to tell applications the _actual_ scaling
+factor. Applications can then scale the image using a _viewport_
+object, instead of setting a scale factor on the raw pixel buffer.
+
+
 ## Supported OSCs
 
 OSC, _Operating System Command_, are escape sequences that interacts

config.c

@@ -972,17 +972,8 @@ parse_section_main(struct context *ctx)
     else if (strcmp(key, "underline-thickness") == 0)
         return value_to_pt_or_px(ctx, &conf->underline_thickness);
 
-    else if (strcmp(key, "dpi-aware") == 0) {
-        if (strcmp(value, "auto") == 0)
-            conf->dpi_aware = DPI_AWARE_AUTO;
-        else {
-            bool value;
-            if (!value_to_bool(ctx, &value))
-                return false;
-            conf->dpi_aware = value ? DPI_AWARE_YES : DPI_AWARE_NO;
-        }
-        return true;
-    }
+    else if (strcmp(key, "dpi-aware") == 0)
+        return value_to_bool(ctx, &conf->dpi_aware);
 
     else if (strcmp(key, "workers") == 0)
         return value_to_uint16(ctx, 10, &conf->render_worker_count);
@@ -2939,7 +2930,7 @@ config_load(struct config *conf, const char *conf_path,
         .use_custom_underline_offset = false,
         .box_drawings_uses_font_glyphs = false,
         .underline_thickness = {.pt = 0., .px = -1},
-        .dpi_aware = DPI_AWARE_AUTO, /* DPI-aware when scaling-factor == 1 */
+        .dpi_aware = false,
         .bell = {
             .urgent = false,
             .notify = false,

config.h

@@ -137,7 +137,7 @@ struct config {
 
     enum { STARTUP_WINDOWED, STARTUP_MAXIMIZED, STARTUP_FULLSCREEN } startup_mode;
 
-    enum {DPI_AWARE_AUTO, DPI_AWARE_YES, DPI_AWARE_NO} dpi_aware;
+    bool dpi_aware;
     struct config_font_list fonts[4];
     struct font_size_adjustment font_size_adjustment;
 

doc/foot.ini.5.scd

@@ -185,7 +185,7 @@ empty string to be set, but it must be quoted: *KEY=""*)
 	Default: _no_.
 
 *dpi-aware*
-	*auto*, *yes*, or *no*.
+	Boolean.
 	
 	When set to *yes*, fonts are sized using the monitor's DPI, making
 	a font of a given size have the same physical size, regardless of
@@ -199,12 +199,6 @@ empty string to be set, but it must be quoted: *KEY=""*)
 	instead sized using the monitor's scaling factor; doubling the
 	scaling factor *does* double the font size.
 	
-	Finally, if set to *auto*, fonts will be sized using the monitor's
-	DPI if _all_ monitors have a scaling factor of 1. If at least one
-	monitor as a scaling factor larger than 1 (regardless of whether
-	the foot window is mapped on that monitor or not), fonts will be
-	scaled using the scaling factor.
-	
 	Note that this option typically does not work with bitmap fonts,
 	which only contains a pre-defined set of sizes, and cannot be
 	dynamically scaled. Whichever size (of the available ones) that
@@ -217,7 +211,7 @@ empty string to be set, but it must be quoted: *KEY=""*)
 	to size the font (*dpi-aware=no*), the font's pixel size will be
 	multiplied with the scaling factor.
 	
-	Default: _auto_
+	Default: _no_
 
 *pad*
 	Padding between border and glyphs, in pixels (subject to output

foot.ini

@@ -20,7 +20,7 @@
 # underline-offset=<font metrics>
 # underline-thickness=<font underline thickness>
 # box-drawings-uses-font-glyphs=no
-# dpi-aware=auto
+# dpi-aware=no
 
 # initial-window-size-pixels=700x500  # Or,
 # initial-window-size-chars=<COLSxROWS>

terminal.c

@@ -912,42 +912,6 @@ get_font_subpixel(const struct terminal *term)
     return FCFT_SUBPIXEL_DEFAULT;
 }
 
-static bool
-term_font_size_by_dpi(const struct terminal *term)
-{
-    switch (term->conf->dpi_aware) {
-    case DPI_AWARE_YES:  return true;
-    case DPI_AWARE_NO:   return false;
-
-    case DPI_AWARE_AUTO:
-        /*
-         * Scale using DPI if all monitors have a scaling factor or 1.
-         *
-         * The idea is this: if a user, with multiple monitors, have
-         * enabled scaling on at least one monitor, then he/she has
-         * most likely done so to match the size of his/hers other
-         * monitors.
-         *
-         * I.e. if the user has one monitor with a scaling factor of
-         * one, and another with a scaling factor of two, he/she
-         * expects things to be twice as large on the second
-         * monitor.
-         *
-         * If we (foot) scale using DPI on the first monitor, and
-         * using the scaling factor on the second monitor, foot will
-         * *not* look twice as big on the second monitor.
-         */
-        tll_foreach(term->wl->monitors, it) {
-            const struct monitor *mon = &it->item;
-            if (mon->scale > 1)
-                return false;
-        }
-        return true;
-    }
-
-    BUG("unhandled DPI awareness value");
-}
-
 int
 term_pt_or_px_as_pixels(const struct terminal *term,
                         const struct pt_or_px *pt_or_px)
@@ -2158,7 +2122,7 @@ term_font_dpi_changed(struct terminal *term, int old_scale)
     xassert(term->scale > 0);
 
     bool was_scaled_using_dpi = term->font_is_sized_by_dpi;
-    bool will_scale_using_dpi = term_font_size_by_dpi(term);
+    bool will_scale_using_dpi = term->conf->dpi_aware;
 
     bool need_font_reload =
         was_scaled_using_dpi != will_scale_using_dpi ||

tests/test-config.c

@@ -511,6 +511,7 @@ test_section_main(void)
     test_boolean(&ctx, &parse_section_main, "box-drawings-uses-font-glyphs", &conf.box_drawings_uses_font_glyphs);
     test_boolean(&ctx, &parse_section_main, "locked-title", &conf.locked_title);
     test_boolean(&ctx, &parse_section_main, "notify-focus-inhibit", &conf.notify_focus_inhibit);
+    test_boolean(&ctx, &parse_section_main, "dpi-aware", &conf.dpi_aware);
 
     test_pt_or_px(&ctx, &parse_section_main, "font-size-adjustment", &conf.font_size_adjustment.pt_or_px);  /* TODO: test ‘N%’ values too */
     test_pt_or_px(&ctx, &parse_section_main, "line-height", &conf.line_height);
@@ -524,17 +525,6 @@ test_section_main(void)
 
     test_spawn_template(&ctx, &parse_section_main, "notify", &conf.notify);
 
-    test_enum(
-        &ctx, &parse_section_main, "dpi-aware",
-        9,
-        (const char *[]){"on", "true", "yes", "1",
-                         "off", "false", "no", "0",
-                         "auto"},
-        (int []){DPI_AWARE_YES, DPI_AWARE_YES, DPI_AWARE_YES, DPI_AWARE_YES,
-                 DPI_AWARE_NO, DPI_AWARE_NO, DPI_AWARE_NO, DPI_AWARE_NO,
-                 DPI_AWARE_AUTO},
-        (int *)&conf.dpi_aware);
-
     test_enum(&ctx, &parse_section_main, "selection-target",
               4,
               (const char *[]){"none", "primary", "clipboard", "both"},

wayland.c

@@ -373,11 +373,6 @@ update_terms_on_monitor(struct monitor *mon)
     tll_foreach(wayl->terms, it) {
         struct terminal *term = it->item;
 
-        if (term->conf->dpi_aware == DPI_AWARE_AUTO) {
-            update_term_for_output_change(term);
-            continue;
-        }
-
         tll_foreach(term->window->on_outputs, it2) {
             if (it2->item == mon) {
                 update_term_for_output_change(term);