Lightmapper: Prevent infinite loop when blitting lightmaps into an atlas

doc/classes/LightmapGI.xml

@@ -137,6 +137,12 @@
 		<constant name="BAKE_ERROR_TEXTURE_SIZE_TOO_SMALL" value="9" enum="BakeError">
 			Lightmap baking failed as the maximum texture size is too small to fit some of the meshes marked for baking.
 		</constant>
+		<constant name="BAKE_ERROR_LIGHTMAP_TOO_SMALL" value="10" enum="BakeError">
+			Lightmap baking failed as the lightmap is too small.
+		</constant>
+		<constant name="BAKE_ERROR_ATLAS_TOO_SMALL" value="11" enum="BakeError">
+			Lightmap baking failed as the lightmap was unable to fit into an atlas.
+		</constant>
 		<constant name="ENVIRONMENT_MODE_DISABLED" value="0" enum="EnvironmentMode">
 			Ignore environment lighting when baking lightmaps.
 		</constant>

editor/plugins/lightmap_gi_editor_plugin.cpp

@@ -110,6 +110,9 @@ void LightmapGIEditorPlugin::_bake_select_file(const String &p_file) {
 			case LightmapGI::BAKE_ERROR_LIGHTMAP_TOO_SMALL: {
 				EditorNode::get_singleton()->show_warning(TTR("Failed creating lightmap images. Make sure all meshes selected to bake have `lightmap_size_hint` value set high enough, and `texel_scale` value of LightmapGI is not too low."));
 			} break;
+			case LightmapGI::BAKE_ERROR_ATLAS_TOO_SMALL: {
+				EditorNode::get_singleton()->show_warning(TTR("Failed fitting a lightmap image into an atlas. This should never happen and should be reported."));
+			} break;
 			default: {
 			} break;
 		}

modules/lightmapper_rd/lightmapper_rd.cpp

@@ -240,7 +240,7 @@ Lightmapper::BakeError LightmapperRD::_blit_meshes_into_atlas(int p_max_texture_
 	max = MAX(max, nearest_power_of_2_templated(atlas_size.height));
 
 	if (max > p_max_texture_size) {
-		return BAKE_ERROR_LIGHTMAP_TOO_SMALL;
+		return BAKE_ERROR_TEXTURE_EXCEEDS_MAX_SIZE;
 	}
 
 	if (p_step_function) {
@@ -254,19 +254,27 @@ Lightmapper::BakeError LightmapperRD::_blit_meshes_into_atlas(int p_max_texture_
 	int best_atlas_memory = 0x7FFFFFFF;
 	Vector<Vector3i> best_atlas_offsets;
 
-	//determine best texture array atlas size by bruteforce fitting
+	// Determine best texture array atlas size by bruteforce fitting.
 	while (atlas_size.x <= p_max_texture_size && atlas_size.y <= p_max_texture_size) {
 		Vector<Vector2i> source_sizes;
 		Vector<int> source_indices;
 		source_sizes.resize(sizes.size());
 		source_indices.resize(sizes.size());
 		for (int i = 0; i < source_indices.size(); i++) {
-			source_sizes.write[i] = sizes[i] + Vector2i(2, 2).maxi(p_denoiser_range); // Add padding between lightmaps
+			source_sizes.write[i] = sizes[i] + Vector2i(2, 2).maxi(p_denoiser_range); // Add padding between lightmaps.
 			source_indices.write[i] = i;
 		}
 		Vector<Vector3i> atlas_offsets;
 		atlas_offsets.resize(source_sizes.size());
 
+		// Ensure the sizes can all fit into a single atlas layer.
+		// This should always happen, and this check is only in place to prevent an infinite loop.
+		for (int i = 0; i < source_sizes.size(); i++) {
+			if (source_sizes[i] > atlas_size) {
+				return BAKE_ERROR_ATLAS_TOO_SMALL;
+			}
+		}
+
 		int slices = 0;
 
 		while (source_sizes.size() > 0) {

scene/3d/lightmap_gi.cpp

@@ -1104,10 +1104,12 @@ LightmapGI::BakeError LightmapGI::bake(Node *p_from_node, String p_image_data_pa
 
 	Lightmapper::BakeError bake_err = lightmapper->bake(Lightmapper::BakeQuality(bake_quality), use_denoiser, denoiser_strength, denoiser_range, bounces, bounce_indirect_energy, bias, max_texture_size, directional, use_texture_for_bounces, Lightmapper::GenerateProbes(gen_probes), environment_image, environment_transform, _lightmap_bake_step_function, &bsud, exposure_normalization);
 
-	if (bake_err == Lightmapper::BAKE_ERROR_LIGHTMAP_TOO_SMALL) {
+	if (bake_err == Lightmapper::BAKE_ERROR_TEXTURE_EXCEEDS_MAX_SIZE) {
 		return BAKE_ERROR_TEXTURE_SIZE_TOO_SMALL;
 	} else if (bake_err == Lightmapper::BAKE_ERROR_LIGHTMAP_CANT_PRE_BAKE_MESHES) {
 		return BAKE_ERROR_MESHES_INVALID;
+	} else if (bake_err == Lightmapper::BAKE_ERROR_ATLAS_TOO_SMALL) {
+		return BAKE_ERROR_ATLAS_TOO_SMALL;
 	}
 
 	// POSTBAKE: Save Textures.
@@ -1711,6 +1713,8 @@ void LightmapGI::_bind_methods() {
 	BIND_ENUM_CONSTANT(BAKE_ERROR_CANT_CREATE_IMAGE);
 	BIND_ENUM_CONSTANT(BAKE_ERROR_USER_ABORTED);
 	BIND_ENUM_CONSTANT(BAKE_ERROR_TEXTURE_SIZE_TOO_SMALL);
+	BIND_ENUM_CONSTANT(BAKE_ERROR_LIGHTMAP_TOO_SMALL);
+	BIND_ENUM_CONSTANT(BAKE_ERROR_ATLAS_TOO_SMALL);
 
 	BIND_ENUM_CONSTANT(ENVIRONMENT_MODE_DISABLED);
 	BIND_ENUM_CONSTANT(ENVIRONMENT_MODE_SCENE);

scene/3d/lightmap_gi.h

@@ -143,6 +143,7 @@ public:
 		BAKE_ERROR_USER_ABORTED,
 		BAKE_ERROR_TEXTURE_SIZE_TOO_SMALL,
 		BAKE_ERROR_LIGHTMAP_TOO_SMALL,
+		BAKE_ERROR_ATLAS_TOO_SMALL,
 	};
 
 	enum EnvironmentMode {

scene/3d/lightmapper.h

@@ -143,9 +143,10 @@ public:
 	};
 
 	enum BakeError {
-		BAKE_ERROR_LIGHTMAP_TOO_SMALL,
+		BAKE_OK,
+		BAKE_ERROR_TEXTURE_EXCEEDS_MAX_SIZE,
 		BAKE_ERROR_LIGHTMAP_CANT_PRE_BAKE_MESHES,
-		BAKE_OK
+		BAKE_ERROR_ATLAS_TOO_SMALL,
 	};
 
 	enum BakeQuality {