Add LightmapGI min light setting (from godotengine#50572)

Author: permelin

doc/classes/LightmapGI.xml

@@ -47,6 +47,10 @@
 		<member name="environment_custom_sky" type="Sky" setter="set_environment_custom_sky" getter="get_environment_custom_sky">
 			The sky to use as a source of environment lighting. Only effective if [member environment_mode] is [constant ENVIRONMENT_MODE_CUSTOM_SKY].
 		</member>
+		<member name="environment_min_light" type="Color" setter="set_environment_min_light" getter="get_environment_min_light" default="Color(0, 0, 0, 1)">
+			The minimum ambient light to use for all the lightmap texels. This doesn't take into account any occlusion from the scene's geometry, it simply ensures a minimum amount of light on all the lightmap texels. This can be used to avoid overly dark areas or for artistic control on shadow color. However, colors that are too bright will result in dull-looking shadows.
+			[b]Note:[/b] After changing [member environment_min_light], the lightmap must be baked again for the changes to be visible.
+		</member>
 		<member name="environment_mode" type="int" setter="set_environment_mode" getter="get_environment_mode" enum="LightmapGI.EnvironmentMode" default="1">
 			The environment mode to use when baking lightmaps.
 		</member>

scene/3d/lightmap_gi.cpp

@@ -1165,6 +1165,20 @@ LightmapGI::BakeError LightmapGI::bake(Node *p_from_node, String p_image_data_pa
 
 			config->save(texture_path + ".import");
 
+			if (!environment_min_light.is_equal_approx(Color(0, 0, 0))) {
+				// Apply minimum lighting to avoid overly dark areas, if requested by the user.
+				for (int j = 0; j < texture_image->get_height(); j++) {
+					for (int k = 0; k < texture_image->get_width(); k++) {
+						Color c = texture_image->get_pixel(k, j);
+						c.r = MAX(c.r, environment_min_light.r);
+						c.g = MAX(c.g, environment_min_light.g);
+						c.b = MAX(c.b, environment_min_light.b);
+
+						texture_image->set_pixel(k, j, c);
+					}
+				}
+			}
+
 			Error err = texture_image->save_exr(texture_path, false);
 			ERR_FAIL_COND_V(err, BAKE_ERROR_CANT_CREATE_IMAGE);
 			ResourceLoader::import(texture_path);
@@ -1517,6 +1531,14 @@ float LightmapGI::get_environment_custom_energy() const {
 	return environment_custom_energy;
 }
 
+void LightmapGI::set_environment_min_light(Color p_min_light) {
+	environment_min_light = p_min_light;
+}
+
+Color LightmapGI::get_environment_min_light() const {
+	return environment_min_light;
+}
+
 void LightmapGI::set_bounces(int p_bounces) {
 	ERR_FAIL_COND(p_bounces < 0 || p_bounces > 16);
 	bounces = p_bounces;
@@ -1642,6 +1664,9 @@ void LightmapGI::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_texel_scale", "texel_scale"), &LightmapGI::set_texel_scale);
 	ClassDB::bind_method(D_METHOD("get_texel_scale"), &LightmapGI::get_texel_scale);
 
+	ClassDB::bind_method(D_METHOD("set_environment_min_light", "min_light"), &LightmapGI::set_environment_min_light);
+	ClassDB::bind_method(D_METHOD("get_environment_min_light"), &LightmapGI::get_environment_min_light);
+
 	ClassDB::bind_method(D_METHOD("set_max_texture_size", "max_texture_size"), &LightmapGI::set_max_texture_size);
 	ClassDB::bind_method(D_METHOD("get_max_texture_size"), &LightmapGI::get_max_texture_size);
 
@@ -1687,6 +1712,7 @@ void LightmapGI::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::COLOR, "environment_custom_color", PROPERTY_HINT_COLOR_NO_ALPHA), "set_environment_custom_color", "get_environment_custom_color");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "environment_custom_energy", PROPERTY_HINT_RANGE, "0,64,0.01"), "set_environment_custom_energy", "get_environment_custom_energy");
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "camera_attributes", PROPERTY_HINT_RESOURCE_TYPE, "CameraAttributesPractical,CameraAttributesPhysical"), "set_camera_attributes", "get_camera_attributes");
+	ADD_PROPERTY(PropertyInfo(Variant::COLOR, "environment_min_light", PROPERTY_HINT_COLOR_NO_ALPHA), "set_environment_min_light", "get_environment_min_light");
 	ADD_GROUP("Gen Probes", "generate_probes_");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "generate_probes_subdiv", PROPERTY_HINT_ENUM, "Disabled,4,8,16,32"), "set_generate_probes", "get_generate_probes");
 	ADD_GROUP("Data", "");

scene/3d/lightmap_gi.h

@@ -167,6 +167,7 @@ class LightmapGI : public VisualInstance3D {
 	Ref<Sky> environment_custom_sky;
 	Color environment_custom_color = Color(1, 1, 1);
 	float environment_custom_energy = 1.0;
+	Color environment_min_light = Color(0.0, 0.0, 0.0);
 	bool directional = false;
 	bool use_texture_for_bounces = true;
 	GenerateProbes gen_probes = GENERATE_PROBES_SUBDIV_8;
@@ -281,6 +282,10 @@ class LightmapGI : public VisualInstance3D {
 	void set_environment_custom_energy(float p_energy);
 	float get_environment_custom_energy() const;
 
+
+	void set_environment_min_light(Color p_min_light);
+	Color get_environment_min_light() const;
+
 	void set_bounces(int p_bounces);
 	int get_bounces() const;