Clamp Viewport shadow atlas sizes to improve usability

- Add a range hint to the Viewport `shadow_atlas_size` property.
- Add range steps to the shadow resolution project settings that
  match the lowest allowed values (since lower increments don't
  make sense).

doc/classes/ProjectSettings.xml

@@ -1488,7 +1488,7 @@
 			Subdivision quadrant size for shadow mapping. See shadow mapping documentation.
 		</member>
 		<member name="rendering/quality/shadow_atlas/size" type="int" setter="" getter="" default="4096">
-			Size for shadow atlas (used for OmniLights and SpotLights). See documentation.
+			Size for shadow atlas (used for OmniLights and SpotLights). The value will be rounded up to the nearest power of 2. See shadow mapping documentation.
 		</member>
 		<member name="rendering/quality/shadow_atlas/size.mobile" type="int" setter="" getter="" default="2048">
 			Lower-end override for [member rendering/quality/shadow_atlas/size] on mobile devices, due to performance concerns or driver support.

doc/classes/Viewport.xml

@@ -268,7 +268,7 @@
 		</member>
 		<member name="shadow_atlas_size" type="int" setter="set_shadow_atlas_size" getter="get_shadow_atlas_size" default="0">
 			The shadow atlas' resolution (used for omni and spot lights). The value will be rounded up to the nearest power of 2.
-			[b]Note:[/b] If this is set to 0, shadows won't be visible. Since user-created viewports default to a value of 0, this value must be set above 0 manually.
+			[b]Note:[/b] If this is set to [code]0[/code], both point [i]and[/i] directional shadows won't be visible. Since user-created viewports default to a value of [code]0[/code], this value must be set above [code]0[/code] manually (typically at least [code]256[/code]).
 		</member>
 		<member name="sharpen_intensity" type="float" setter="set_sharpen_intensity" getter="get_sharpen_intensity" default="0.0">
 			If set to a value greater than [code]0.0[/code], contrast-adaptive sharpening will be applied to the 3D viewport. This has a low performance cost and can be used to recover some of the sharpness lost from using FXAA. Values around [code]0.5[/code] generally give the best results. See also [member fxaa].

scene/main/viewport.cpp

@@ -3328,7 +3328,7 @@ void Viewport::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "gui_disable_input"), "set_disable_input", "is_input_disabled");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "gui_snap_controls_to_pixels"), "set_snap_controls_to_pixels", "is_snap_controls_to_pixels_enabled");
 	ADD_GROUP("Shadow Atlas", "shadow_atlas_");
-	ADD_PROPERTY(PropertyInfo(Variant::INT, "shadow_atlas_size"), "set_shadow_atlas_size", "get_shadow_atlas_size");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "shadow_atlas_size", PROPERTY_HINT_RANGE, "0,16384,256"), "set_shadow_atlas_size", "get_shadow_atlas_size");
 	ADD_PROPERTYI(PropertyInfo(Variant::INT, "shadow_atlas_quad_0", PROPERTY_HINT_ENUM, "Disabled,1 Shadow,4 Shadows,16 Shadows,64 Shadows,256 Shadows,1024 Shadows"), "set_shadow_atlas_quadrant_subdiv", "get_shadow_atlas_quadrant_subdiv", 0);
 	ADD_PROPERTYI(PropertyInfo(Variant::INT, "shadow_atlas_quad_1", PROPERTY_HINT_ENUM, "Disabled,1 Shadow,4 Shadows,16 Shadows,64 Shadows,256 Shadows,1024 Shadows"), "set_shadow_atlas_quadrant_subdiv", "get_shadow_atlas_quadrant_subdiv", 1);
 	ADD_PROPERTYI(PropertyInfo(Variant::INT, "shadow_atlas_quad_2", PROPERTY_HINT_ENUM, "Disabled,1 Shadow,4 Shadows,16 Shadows,64 Shadows,256 Shadows,1024 Shadows"), "set_shadow_atlas_quadrant_subdiv", "get_shadow_atlas_quadrant_subdiv", 2);

servers/visual_server.cpp

@@ -2618,12 +2618,12 @@ VisualServer::VisualServer() {
 
 	GLOBAL_DEF("rendering/quality/directional_shadow/size", 4096);
 	GLOBAL_DEF("rendering/quality/directional_shadow/size.mobile", 2048);
-	ProjectSettings::get_singleton()->set_custom_property_info("rendering/quality/directional_shadow/size", PropertyInfo(Variant::INT, "rendering/quality/directional_shadow/size", PROPERTY_HINT_RANGE, "256,16384"));
+	ProjectSettings::get_singleton()->set_custom_property_info("rendering/quality/directional_shadow/size", PropertyInfo(Variant::INT, "rendering/quality/directional_shadow/size", PROPERTY_HINT_RANGE, "256,16384,256"));
 	GLOBAL_DEF_RST("rendering/quality/shadow_atlas/size", 4096);
 	GLOBAL_DEF("rendering/quality/shadow_atlas/size.mobile", 2048);
-	ProjectSettings::get_singleton()->set_custom_property_info("rendering/quality/shadow_atlas/size", PropertyInfo(Variant::INT, "rendering/quality/shadow_atlas/size", PROPERTY_HINT_RANGE, "256,16384"));
+	ProjectSettings::get_singleton()->set_custom_property_info("rendering/quality/shadow_atlas/size", PropertyInfo(Variant::INT, "rendering/quality/shadow_atlas/size", PROPERTY_HINT_RANGE, "256,16384,256"));
 	GLOBAL_DEF_RST("rendering/quality/shadow_atlas/cubemap_size", 512);
-	ProjectSettings::get_singleton()->set_custom_property_info("rendering/quality/shadow_atlas/cubemap_size", PropertyInfo(Variant::INT, "rendering/quality/shadow_atlas/cubemap_size", PROPERTY_HINT_RANGE, "64,16384"));
+	ProjectSettings::get_singleton()->set_custom_property_info("rendering/quality/shadow_atlas/cubemap_size", PropertyInfo(Variant::INT, "rendering/quality/shadow_atlas/cubemap_size", PROPERTY_HINT_RANGE, "64,16384,64"));
 	GLOBAL_DEF("rendering/quality/shadow_atlas/quadrant_0_subdiv", 1);
 	GLOBAL_DEF("rendering/quality/shadow_atlas/quadrant_1_subdiv", 2);
 	GLOBAL_DEF("rendering/quality/shadow_atlas/quadrant_2_subdiv", 3);