Godot 4 源码分析 - 动态导入图片文件

用Godot 4尝试编一个电子书软件，初步效果已经出来，并且通过管道通信接口可以获取、设置属性、调用函数，貌似能处理各种事宜了。

其实不然，外因通过内因起作用，如果没把里面搞明白，功能没有开放出来，则有些需求就不能实现。

比如，现在想动态加载新的图书，这就是一个实际需求。如果每一本电子书，都需要导出一次，那这个软件就太不通用了。

之前加载图片时，GDScript代码：

# 目标对象上加载图片
func loadPng(obj, pngFileName) -> bool:
	var texture = load(pngFileName) as Texture2D;
	if(texture != null):
		obj.set_texture(texture);
		obj.scale.y = get_viewport_rect().size.y / texture.get_height();
		obj.scale.x = obj.scale.y;
		obj.position.y = get_viewport_rect().size.y / 2;	# 垂直居中
		adjustPos();
		return true;
	return false;

直接加载另一图片，结果不成功

这就得研究一下了。

导入import

把这个图片拷贝到Godot开发环境中，发现切换回Godot时，会快速闪过一个import对话框，那想必Godot干了什么事

到资源管理器，看到多了一个对应的.import文件，打开看了一下内容

[remap]

importer="texture"
type="CompressedTexture2D"
uid="uid://rv5gm15xbcaf"
path="res://.godot/imported/DrGraph_Page24.png-1dd935fbb11807a645ea1ea79ec38662.ctex"
metadata={
"vram_texture": false
}

[deps]

source_file="res://Pages/DrGraph_Page24.png"
dest_files=["res://.godot/imported/DrGraph_Page24.png-1dd935fbb11807a645ea1ea79ec38662.ctex"]

[params]

compress/mode=0
compress/high_quality=false
compress/lossy_quality=0.7
compress/hdr_compression=1
compress/normal_map=0
compress/channel_pack=0
mipmaps/generate=false
mipmaps/limit=-1
roughness/mode=0
roughness/src_normal=""
process/fix_alpha_border=true
process/premult_alpha=false
process/normal_map_invert_y=false
process/hdr_as_srgb=false
process/hdr_clamp_exposure=false
process/size_limit=0
detect_3d/compress_to=1

既然是动态生成的，那肯定是代码里写的。到源码中找，从哪里下手呢？查import、.import都是一大堆结果。再试试内容，查找[remap]，结果很少

定位一看，是EditorFileSystem类的两个函数_reimport_group、_reimport_file，那肯定是用_reimport_file。但这个函数是不可访问的。好在源码在手，直接public出来，可以访问了。

但这个要给GDScript调用，还得做一些工作，需要加入到ClassDB中去。

为了简单一些，直接加到DllStream类中【见Godot 4 源码分析 - 增加管道通信_DrGraph的博客-CSDN博客】，增加一个import函数

ClassDB::bind_method(D_METHOD("import", "fileName"), &DllStream::import);

String DllStream::import(String fileName) {
	if (FileAccess::exists(fileName + ".import") == false) 
		EditorFileSystem::get_singleton()->_reimport_file(fileName);
	return fileName;	
}

运行后，还是不成功。调试发现，_find_file(p_file, &fs, cpos)返回false。而_find_file居然要求文件位于"res://"目录以下，也就是说，得在工程目录下。

bool EditorFileSystem::_find_file(const String &p_file, EditorFileSystemDirectory **r_d, int &r_file_pos) const {
	//todo make faster

	if (!filesystem || scanning) {
		return false;
	}

	String f = ProjectSettings::get_singleton()->localize_path(p_file);

	if (!f.begins_with("res://")) {
		return false;
	}
	f = f.substr(6, f.length());
	f = f.replace("\\", "/");

	Vector<String> path = f.split("/");

	if (path.size() == 0) {
		return false;
	}
	String file = path[path.size() - 1];
	path.resize(path.size() - 1);

	EditorFileSystemDirectory *fs = filesystem;

	for (int i = 0; i < path.size(); i++) {
		if (path[i].begins_with(".")) {
			return false;
		}

		int idx = -1;
		for (int j = 0; j < fs->get_subdir_count(); j++) {
			if (fs->get_subdir(j)->get_name() == path[i]) {
				idx = j;
				break;
			}
		}

		if (idx == -1) {
			//does not exist, create i guess?
			EditorFileSystemDirectory *efsd = memnew(EditorFileSystemDirectory);

			efsd->name = path[i];
			efsd->parent = fs;

			int idx2 = 0;
			for (int j = 0; j < fs->get_subdir_count(); j++) {
				if (efsd->name.naturalnocasecmp_to(fs->get_subdir(j)->get_name()) < 0) {
					break;
				}
				idx2++;
			}

			if (idx2 == fs->get_subdir_count()) {
				fs->subdirs.push_back(efsd);
			} else {
				fs->subdirs.insert(idx2, efsd);
			}
			fs = efsd;
		} else {
			fs = fs->get_subdir(idx);
		}
	}

	int cpos = -1;
	for (int i = 0; i < fs->files.size(); i++) {
		if (fs->files[i]->file == file) {
			cpos = i;
			break;
		}
	}

	r_file_pos = cpos;
	*r_d = fs;

	return cpos != -1;
}

这个要求就有些过分了。不过程序处理就两种方法：一是将图片自动拷贝到工程目录下，二是绕过这个。

随便试一种吧，抛个硬币，背面选二。

既然选绕过，那就直接实现EditorFileSystem::_reimport_file函数，这样也省得再把这个私有函数public出来。所谓实现，就是把EditorFileSystem::_reimport_file的代码全部拷贝过来，然后改呗改呗：

Error DllStream::_import(String destFileName) {
	HashMap<StringName, Variant> params = HashMap<StringName, Variant>();	
	String importer_name; //empty by default though
	ResourceUID::ID uid = ResourceUID::INVALID_ID;
	Variant generator_parameters;

	Ref<ResourceImporter> importer = ResourceFormatImporter::get_singleton()->get_importer_by_extension(destFileName.get_extension());
	if (importer.is_null()) 
		ERR_FAIL_V_MSG(ERR_FILE_CANT_OPEN, "BUG: File queued for import, but can't be imported, importer for type '" + importer_name + "' not found.");

	//mix with default params, in case a parameter is missing

	List<ResourceImporter::ImportOption> opts;
	importer->get_import_options(destFileName, &opts);
	for (const ResourceImporter::ImportOption &E : opts) {
		if (!params.has(E.option.name)) { //this one is not present
			params[E.option.name] = E.default_value;
		}
	}

	if (ProjectSettings::get_singleton()->has_setting("importer_defaults/" + importer->get_importer_name())) {
		//use defaults if exist
		Dictionary d = GLOBAL_GET("importer_defaults/" + importer->get_importer_name());
		List<Variant> v;
		d.get_key_list(&v);

		for (const Variant &E : v) 
			params[E] = d[E];
	}

	//finally, perform import!!
	String base_path = ResourceFormatImporter::get_singleton()->get_import_base_path(destFileName);

	List<String> import_variants;
	List<String> gen_files;
	Variant meta;
	Error err = importer->import(destFileName, base_path, params, &import_variants, &gen_files, &meta);

	ERR_FAIL_COND_V_MSG(err != OK, ERR_FILE_UNRECOGNIZED, "Error importing '" + destFileName + "'.");

	//as import is complete, save the .import file

	Vector<String> dest_paths;
	{
		Ref<FileAccess> f = FileAccess::open(destFileName + ".import", FileAccess::WRITE);
		ERR_FAIL_COND_V_MSG(f.is_null(), ERR_FILE_CANT_OPEN, "Cannot open file from path '" + destFileName + ".import'.");

		//write manually, as order matters ([remap] has to go first for performance).
		f->store_line("[remap]");
		f->store_line("");
		f->store_line("importer=\"" + importer->get_importer_name() + "\"");
		int version = importer->get_format_version();
		if (version > 0) {
			f->store_line("importer_version=" + itos(version));
		}
		if (!importer->get_resource_type().is_empty()) {
			f->store_line("type=\"" + importer->get_resource_type() + "\"");
		}

		if (uid == ResourceUID::INVALID_ID) {
			uid = ResourceUID::get_singleton()->create_id();
		}

		f->store_line("uid=\"" + ResourceUID::get_singleton()->id_to_text(uid) + "\""); //store in readable format

		if (err == OK) {
			if (importer->get_save_extension().is_empty()) {
				//no path
			} else if (import_variants.size()) {
				//import with variants
				for (const String &E : import_variants) {
					String path = base_path.c_escape() + "." + E + "." + importer->get_save_extension();

					f->store_line("path." + E + "=\"" + path + "\"");
					dest_paths.push_back(path);
				}
			} else {
				String path = base_path + "." + importer->get_save_extension();
				f->store_line("path=\"" + path + "\"");
				dest_paths.push_back(path);
			}

		} else {
			f->store_line("valid=false");
		}

		if (meta != Variant()) {
			f->store_line("metadata=" + meta.get_construct_string());
		}

		if (generator_parameters != Variant()) {
			f->store_line("generator_parameters=" + generator_parameters.get_construct_string());
		}

		f->store_line("");

		f->store_line("[deps]\n");

		if (gen_files.size()) {
			Array genf;
			for (const String &E : gen_files) {
				genf.push_back(E);
				dest_paths.push_back(E);
			}

			String value;
			VariantWriter::write_to_string(genf, value);
			f->store_line("files=" + value);
			f->store_line("");
		}

		f->store_line("source_file=" + Variant(destFileName).get_construct_string());

		if (dest_paths.size()) {
			Array dp;
			for (int i = 0; i < dest_paths.size(); i++) {
				dp.push_back(dest_paths[i]);
			}
			f->store_line("dest_files=" + Variant(dp).get_construct_string() + "\n");
		}

		f->store_line("[params]");
		f->store_line("");

		//store options in provided order, to avoid file changing. Order is also important because first match is accepted first.

		for (const ResourceImporter::ImportOption &E : opts) {
			String base = E.option.name;
			String value;
			VariantWriter::write_to_string(params[base], value);
			f->store_line(base + "=" + value);
		}
	}

	// Store the md5's of the various files. These are stored separately so that the .import files can be version controlled.
	{
		Ref<FileAccess> md5s = FileAccess::open(base_path + ".md5", FileAccess::WRITE);
		ERR_FAIL_COND_V_MSG(md5s.is_null(), ERR_FILE_CANT_OPEN, "Cannot open MD5 file '" + base_path + ".md5'.");

		md5s->store_line("source_md5=\"" + FileAccess::get_md5(destFileName) + "\"");
		if (dest_paths.size()) {
			md5s->store_line("dest_md5=\"" + FileAccess::get_multiple_md5(dest_paths) + "\"\n");
		}
	}
	if (ResourceUID::get_singleton()->has_id(uid)) {
		ResourceUID::get_singleton()->set_id(uid, destFileName);
	} else {
		ResourceUID::get_singleton()->add_id(uid, destFileName);
	}
}

String DllStream::import(String fileName) {
	if (FileAccess::exists(fileName + ".import") == false) 
		_import(fileName);
	return fileName;	
}

运行后，还是失败，再跟进，发现是

importer->import(destFileName, base_path, params, &import_variants, &gen_files, &meta)

失败。单步调试发现，ResourceFormatImporter的importers为空。从源码中找到其add_importer函数会添加ResourceImporter，在EditorNode::EditorNode()构造函数中，添加了多个ResourceImporter。

	{
		// Register importers at the beginning, so dialogs are created with the right extensions.
		Ref<ResourceImporterTexture> import_texture;
		import_texture.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_texture);

		Ref<ResourceImporterLayeredTexture> import_cubemap;
		import_cubemap.instantiate();
		import_cubemap->set_mode(ResourceImporterLayeredTexture::MODE_CUBEMAP);
		ResourceFormatImporter::get_singleton()->add_importer(import_cubemap);

		Ref<ResourceImporterLayeredTexture> import_array;
		import_array.instantiate();
		import_array->set_mode(ResourceImporterLayeredTexture::MODE_2D_ARRAY);
		ResourceFormatImporter::get_singleton()->add_importer(import_array);

		Ref<ResourceImporterLayeredTexture> import_cubemap_array;
		import_cubemap_array.instantiate();
		import_cubemap_array->set_mode(ResourceImporterLayeredTexture::MODE_CUBEMAP_ARRAY);
		ResourceFormatImporter::get_singleton()->add_importer(import_cubemap_array);

		Ref<ResourceImporterLayeredTexture> import_3d;
		import_3d.instantiate();
		import_3d->set_mode(ResourceImporterLayeredTexture::MODE_3D);
		ResourceFormatImporter::get_singleton()->add_importer(import_3d);

		Ref<ResourceImporterImage> import_image;
		import_image.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_image);

		Ref<ResourceImporterTextureAtlas> import_texture_atlas;
		import_texture_atlas.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_texture_atlas);

		Ref<ResourceImporterDynamicFont> import_font_data_dynamic;
		import_font_data_dynamic.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_font_data_dynamic);

		Ref<ResourceImporterBMFont> import_font_data_bmfont;
		import_font_data_bmfont.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_font_data_bmfont);

		Ref<ResourceImporterImageFont> import_font_data_image;
		import_font_data_image.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_font_data_image);

		Ref<ResourceImporterCSVTranslation> import_csv_translation;
		import_csv_translation.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_csv_translation);

		Ref<ResourceImporterWAV> import_wav;
		import_wav.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_wav);

		Ref<ResourceImporterOBJ> import_obj;
		import_obj.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_obj);

		Ref<ResourceImporterShaderFile> import_shader_file;
		import_shader_file.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_shader_file);

		Ref<ResourceImporterScene> import_scene;
		import_scene.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_scene);

		Ref<ResourceImporterScene> import_animation;
		import_animation = Ref<ResourceImporterScene>(memnew(ResourceImporterScene(true)));
		ResourceFormatImporter::get_singleton()->add_importer(import_animation);

		{
			Ref<EditorSceneFormatImporterCollada> import_collada;
			import_collada.instantiate();
			ResourceImporterScene::add_importer(import_collada);

			Ref<EditorOBJImporter> import_obj2;
			import_obj2.instantiate();
			ResourceImporterScene::add_importer(import_obj2);

			Ref<EditorSceneFormatImporterESCN> import_escn;
			import_escn.instantiate();
			ResourceImporterScene::add_importer(import_escn);
		}

		Ref<ResourceImporterBitMap> import_bitmap;
		import_bitmap.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_bitmap);
	}

EditorNode会在编辑器模式下自动创建，但对于最终的运行程序而言，没有ProjectManager，也没有EditorNode，所以，想导入的话，需要自己创建。

从图片导入过程可知，电子书只需要导入png图片，是Texture格式，所以只导入一种即可

		Ref<ResourceImporterTexture> import_texture;
		import_texture.instantiate();
		ResourceFormatImporter::get_singleton()->add_importer(import_texture);

运行，图片成功显示。