Enable "Allow Hidpi" by default

This fixes window management issues across platforms on hiDPI monitors.

The `--low-dpi` command line argument has been removed as similar
functionality (forcing low-DPI mode on DPI-aware programs) is
already provided by Windows and macOS itself.

doc/classes/ProjectSettings.xml

@@ -480,8 +480,9 @@
 		<member name="display/mouse_cursor/tooltip_position_offset" type="Vector2" setter="" getter="" default="Vector2(10, 10)">
 			Position offset for tooltips, relative to the mouse cursor's hotspot.
 		</member>
-		<member name="display/window/dpi/allow_hidpi" type="bool" setter="" getter="" default="false">
+		<member name="display/window/dpi/allow_hidpi" type="bool" setter="" getter="" default="true">
-			If [code]true[/code], allows HiDPI display on Windows, macOS, and the HTML5 platform. This setting has no effect on desktop Linux, as DPI-awareness fallbacks are not supported there.
+			If [code]true[/code], allows HiDPI display on Windows, macOS, Android, iOS and HTML5. If [code]false[/code], the platform's low-DPI fallback will be used on HiDPI displays, which causes the window to be displayed in a blurry or pixelated manner (and can cause various window management bugs). Therefore, it is recommended to make your project scale to [url=$DOCS_URL/tutorials/viewports/multiple_resolutions.html]multiple resolutions[/url] instead of disabling this setting.
+			[b]Note:[/b] This setting has no effect on Linux as DPI-awareness fallbacks are not supported there.
 		</member>
 		<member name="display/window/energy_saving/keep_screen_on" type="bool" setter="" getter="" default="true">
 			If [code]true[/code], keeps the screen on (even in case of inactivity), so the screensaver does not take over. Works on desktop and mobile platforms.

main/main.cpp

@@ -164,7 +164,6 @@ static bool init_windowed = false;
 static bool init_always_on_top = false;
 static bool init_use_custom_pos = false;
 static Vector2 init_custom_pos;
-static bool force_lowdpi = false;
 
 // Debug
 
@@ -340,7 +339,6 @@ void Main::print_help(const char *p_binary) {
 	OS::get_singleton()->print("  -t, --always-on-top                          Request an always-on-top window.\n");
 	OS::get_singleton()->print("  --resolution <W>x<H>                         Request window resolution.\n");
 	OS::get_singleton()->print("  --position <X>,<Y>                           Request window position.\n");
-	OS::get_singleton()->print("  --low-dpi                                    Force low-DPI mode (macOS and Windows only).\n");
 	OS::get_singleton()->print("  --single-window                              Use a single window (no separate subwindows).\n");
 	OS::get_singleton()->print("  --tablet-driver                              Pen tablet input driver.\n");
 	OS::get_singleton()->print("\n");
@@ -870,9 +868,6 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 				goto error;
 			}
 
-		} else if (I->get() == "--low-dpi") { // force low DPI (macOS only)
-
-			force_lowdpi = true;
 		} else if (I->get() == "--headless") { // enable headless mode (no audio, no rendering).
 
 			audio_driver = "Dummy";
@@ -1365,9 +1360,7 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 	GLOBAL_DEF("internationalization/rendering/force_right_to_left_layout_direction", false);
 	GLOBAL_DEF("internationalization/locale/include_text_server_data", false);
 
-	if (!force_lowdpi) {
+	OS::get_singleton()->_allow_hidpi = GLOBAL_DEF("display/window/dpi/allow_hidpi", true);
-		OS::get_singleton()->_allow_hidpi = GLOBAL_DEF("display/window/dpi/allow_hidpi", false);
-	}
 
 	// FIXME: Restore support.
 #if 0

misc/dist/shell/_godot.zsh-completion

@@ -49,7 +49,6 @@ _arguments \
   '(-t --always-on-top)'{-t,--always-on-top}'[request an always-on-top window]' \
   '--resolution[request window resolution]:resolution in WxH format' \
   '--position[request window position]:position in X,Y format' \
-  '--low-dpi[force low-DPI mode (macOS and Windows only)]' \
   '--headless[enable headless mode (--display-driver headless --audio-driver Dummy). Useful for servers and with --script]' \
   '(-d --debug)'{-d,--debug}'[debug (local stdout debugger)]' \
   '(-b --breakpoints)'{-b,--breakpoints}'[specify the breakpoint list as source::line comma-separated pairs, no spaces (use %20 instead)]:breakpoint list' \

misc/dist/shell/godot.bash-completion

@@ -52,7 +52,6 @@ _complete_godot_options() {
 --always-on-top
 --resolution
 --position
---low-dpi
 --headless
 --debug
 --breakpoints

misc/dist/shell/godot.fish

@@ -59,7 +59,6 @@ complete -c godot -s w -l windowed -d "Request windowed mode"
 complete -c godot -s t -l always-on-top -d "Request an always-on-top window"
 complete -c godot -l resolution -d "Request window resolution" -x
 complete -c godot -l position -d "Request window position" -x
-complete -c godot -l low-dpi -d "Force low-DPI mode (macOS and Windows only)"
 complete -c godot -l headless -d "Enable headless mode (--display-driver headless --audio-driver Dummy). Useful for servers and with --script"
 
 # Debug options: