[librpbase] IResourceReader: New function lookup_resource_ID().

This function takes a zero-based index and returns a resource ID for
the given resource type if it's within range. Otherwise, it returns
a negative POSIX error code.

[libromdata] PEResourceReader, NEResourceReader: Implement it.

[libromdata] EXE: Use lookup_resource_ID for positive icon indexes.

This fixes thumbnailing for discs whose AUTORUN.INF specify a
positive, non-zero icon index.

TODO: Older discs may have truncated ISO-9660 filenames. Need to
parse Joliet file systems, maybe...

src/libromdata/Other/EXE.cpp

@@ -405,8 +405,11 @@ rp_image_const_ptr EXEPrivate::loadSpecificIcon(int iconindex)
 	} else if (iconindex > 0) {
 		// Positive icon index
 		// This is a zero-based index into the RT_GROUP_ICON table.
-		// TODO: Add IResourceReader function to get a resource ID from a zero-based index.
-		return {};
+		resID = rsrcReader->lookup_resource_ID(RT_GROUP_ICON, iconindex);
+		if (resID < 0) {
+			// Not found.
+			return {};
+		}
 	} else {
 		// Negative icon index
 		// This is an actual resource ID.

src/libromdata/disc/NEResourceReader.cpp

@@ -646,11 +646,13 @@ IRpFilePtr NEResourceReader::open(uint16_t type, int id, int lang)
 
 	// Get the directory for the specified type.
 	auto iter_dir = d->res_types.find(type);
-	if (iter_dir == d->res_types.end())
+	if (iter_dir == d->res_types.end()) {
 		return nullptr;
+	}
 	auto &dir = iter_dir->second;
-	if (dir.empty())
+	if (dir.empty()) {
 		return nullptr;
+	}
 	
 	const NEResourceReaderPrivate::ResTblEntry *entry = nullptr;
 	if (id == -1) {
@@ -781,4 +783,37 @@ int NEResourceReader::load_VS_VERSION_INFO(int id, int lang, VS_FIXEDFILEINFO *p
 	return 0;
 }
 
+/**
+ * Look up a resource ID given a zero-based index.
+ * Mostly useful for icon indexes.
+ *
+ * @param type	[in] Resource type ID
+ * @param index	[in] Zero-based index
+ * @param lang	[in] Language ID (-1 for "first entry")
+ * @return Resource ID, or negative POSIX error code on error.
+ */
+int NEResourceReader::lookup_resource_ID(int type, int index)
+{
+	if (index < 0) {
+		return -EINVAL;
+	}
+
+	// Get the resource directory for this type.
+	RP_D(NEResourceReader);
+	auto iter_find = d->res_types.find(type);
+	if (iter_find == d->res_types.end()) {
+		// Not found.
+		return -ENOENT;
+	}
+
+	const NEResourceReaderPrivate::rsrc_dir_t &type_dir = iter_find->second;
+	if (index >= static_cast<int>(type_dir.size())) {
+		// Zero-based index is out of bounds.
+		return -ENOENT;
+	}
+
+	// Return the ID at this index.
+	return type_dir[index].id;
+}
+
 }

src/libromdata/disc/NEResourceReader.hpp

@@ -116,6 +116,16 @@ public:
 	 * @return 0 on success; non-zero on error.
 	 */
 	int load_VS_VERSION_INFO(int id, int lang, VS_FIXEDFILEINFO *pVsFfi, StringFileInfo *pVsSfi) final;
+
+	/**
+	 * Look up a resource ID given a zero-based index.
+	 * Mostly useful for icon indexes.
+	 *
+	 * @param type	[in] Resource type ID
+	 * @param index	[in] Zero-based index
+	 * @return Resource ID, or negative POSIX error code on error.
+	 */
+	int lookup_resource_ID(int type, int index) final;
 };
 
 }

src/libromdata/disc/PEResourceReader.cpp

@@ -861,4 +861,35 @@ int PEResourceReader::load_VS_VERSION_INFO(int id, int lang, VS_FIXEDFILEINFO *p
 	return 0;
 }
 
+/**
+ * Look up a resource ID given a zero-based index.
+ * Mostly useful for icon indexes.
+ *
+ * @param type	[in] Resource type ID
+ * @param index	[in] Zero-based index
+ * @param lang	[in] Language ID (-1 for "first entry")
+ * @return Resource ID, or negative POSIX error code on error.
+ */
+int PEResourceReader::lookup_resource_ID(int type, int index)
+{
+	if (index < 0) {
+		return -EINVAL;
+	}
+
+	// Get the resource directory for this type.
+	RP_D(PEResourceReader);
+	const PEResourceReaderPrivate::rsrc_dir_t *type_dir = d->getTypeDir(type);
+	if (!type_dir) {
+		return -ENOENT;
+	}
+
+	if (index >= static_cast<int>(type_dir->size())) {
+		// Zero-based index is out of bounds.
+		return -ENOENT;
+	}
+
+	// Return the ID at this index.
+	return type_dir->at(index).id;
+}
+
 }

src/libromdata/disc/PEResourceReader.hpp

@@ -117,6 +117,16 @@ public:
 	 * @return 0 on success; non-zero on error.
 	 */
 	int load_VS_VERSION_INFO(int id, int lang, VS_FIXEDFILEINFO *pVsFfi, StringFileInfo *pVsSfi) final;
+
+	/**
+	 * Look up a resource ID given a zero-based index.
+	 * Mostly useful for icon indexes.
+	 *
+	 * @param type	[in] Resource type ID
+	 * @param index	[in] Zero-based index
+	 * @return Resource ID, or negative POSIX error code on error.
+	 */
+	int lookup_resource_ID(int type, int index) final;
 };
 
 }

src/librpbase/disc/IResourceReader.hpp

@@ -119,6 +119,16 @@ public:
 	 * @return 0 on success; non-zero on error.
 	 */
 	virtual int load_VS_VERSION_INFO(int id, int lang, VS_FIXEDFILEINFO *pVsFfi, StringFileInfo *pVsSfi) = 0;
+
+	/**
+	 * Look up a resource ID given a zero-based index.
+	 * Mostly useful for icon indexes.
+	 *
+	 * @param type	[in] Resource type ID
+	 * @param index	[in] Zero-based index
+	 * @return Resource ID, or negative POSIX error code on error.
+	 */
+	virtual int lookup_resource_ID(int type, int index) = 0;
 };
 
 typedef std::shared_ptr<IResourceReader> IResourceReaderPtr;