Comic Shell Extension for Windows

A Windows shell extension that adds rich tooltips and a preview pane for .cbz and .cbr comic archive files in Explorer.

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Quick Start

Requirements

• Windows 10/11 (x64)
• The pre-built DLL (x64\Release\ComicTooltipExt.dll), or Visual Studio 2022 with C++ ATL to build from source.
• Administrator permissions to copy the DLL into C:\Windows\System32 and register the shell extensions.

Build

1. Open ComicTooltipExt.vcxproj in Visual Studio 2022.
2. Build the project in Release | x64.
3. The output DLL will be generated at x64\Release\ComicTooltipExt.dll.

Installation

1. Build the project in Release x64 or use the existing DLL from x64\Release.
2. Deploy the DLL:
   • For development, run deploy.bat as administrator. It stops prevhost.exe, dllhost.exe, and explorer.exe, copies the DLL to C:\Windows\System32, then restarts Explorer.
   • If you prefer, you can also copy the DLL manually to C:\Windows\System32 using an elevated prompt.
3. Register by right-clicking one of the batch files below and selecting "Run as administrator":

Script	What it does
register_all.bat	Registers both tooltip and preview handlers
register_tooltip.bat	Registers the tooltip handler only
register_preview.bat	Registers the preview pane handler only

Important: All registration scripts must run in an elevated prompt (Run as administrator). They will refuse to run otherwise.

4. If you did not use deploy.bat, restart Explorer or log out/in for changes to take effect.

Uninstallation

Right-click the corresponding script as administrator:

Script	What it does
unregister_all.bat	Removes both handlers
unregister_tooltip.bat	Removes the tooltip handler only
unregister_preview.bat	Removes the preview pane handler only

Usage

• Tooltip: Hover over any .cbz or .cbr file in Explorer to see metadata (title, series, publisher, creative team, summary, etc.).
• Preview Pane: Press Alt+P in Explorer to open the preview pane, then click a comic file. The current page/cover is shown on the left and metadata on the right.
• Page navigation: In the preview pane you can move between pages with the navigation controls or keyboard shortcuts when available.

Troubleshooting

Problem	Solution
Tooltip doesn't appear	Restart Explorer. Verify with reg query "HKCR\.cbz\shellex\{00021500-0000-0000-C000-000000000046}"
Preview shows "No preview available"	Run register_preview.bat as admin. Check that AppID and DisableLowILProcessIsolation are set (the script does this).
DLL can't be replaced / file locked	Close Explorer and kill prevhost.exe and dllhost.exe before copying. deploy.bat automates this for development installs.
Preview shows only the cover (from CDisplay/ComicRack)	The preview handler must also be registered under the ProgID. register_preview.bat handles this.
Build fails with LNK1104 on ComicTooltipExt.dll	The output DLL is still loaded by Explorer or Preview Host. Run deploy.bat or close explorer.exe, prevhost.exe, and dllhost.exe before rebuilding.

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Technical Reference

Features

• Tooltip handler (IQueryInfo): Plain-text tooltip with all ComicInfo.xml v2.1 fields, formatted with Unicode separators and sections.
• Preview handler (IPreviewHandler): GDI+ rendered panel with image/page area (left) and metadata (right) in a light theme. Supports resizing and page navigation.
• Archive support: Custom ZIP and RAR parsers (no external libraries). ZIP supports store entries and the current code includes a best-effort path for deflate-compressed entries. RAR support is limited to the subset currently handled by the internal parser.
• Metadata: Full ComicInfo.xml v2.1 schema support including series, publication, creative team, story arcs, characters, ratings, and more.

Architecture

ComicTooltipExt.dll
├── COM entry points ─────────── dllmain.cpp
├── Tooltip handler (IQueryInfo) ─ ComicTooltipExt.cpp/h
├── Preview handler (IPreviewHandler) ─ ComicPreviewHandler.cpp/h
├── Metadata parser ──────────── ComicInfo.cpp/h
├── CBZ archive reader ────────── ZipArchive.cpp/h
├── CBR archive reader ────────── RarArchive.cpp/h
├── Precompiled headers ───────── pch.h/cpp
└── Resources / IDL / DEF ─────── *.rc, *.idl, *.def, *.rgs

COM Classes

Class	CLSID	Interfaces
CComicTooltipExt	{A1B2C3D4-E5F6-7890-ABCD-EF1234567892}	IPersistFile, IQueryInfo
CComicPreviewHandler	{B5E84A2F-3D71-4C8A-9F20-1A2B3C4D5E6F}	IPreviewHandler, IInitializeWithFile, IOleWindow, IObjectWithSite

Shell Extension GUIDs

Handler	Shell Extension GUID
Tooltip (IQueryInfo)	{00021500-0000-0000-C000-000000000046}
Preview (IPreviewHandler)	{8895b1c6-b41f-4c1c-a562-0d564250836f}

Registry Layout

The tooltip handler registers under:

HKCR\.cbz\shellex\{00021500-...} = {A1B2C3D4-...}
HKCR\.cbr\shellex\{00021500-...} = {A1B2C3D4-...}
HKCR\CLSID\{A1B2C3D4-...}\InprocServer32 = <path to DLL>

The preview handler additionally requires:

HKCR\CLSID\{B5E84A2F-...}\InprocServer32 = <path to DLL>
HKCR\CLSID\{B5E84A2F-...}\AppID = {6d2b5079-2f0b-48dd-ab7f-97cec514d30b}
HKCR\CLSID\{B5E84A2F-...}\DisableLowILProcessIsolation = 1 (DWORD)
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\PreviewHandlers\{B5E84A2F-...} = "Comic Preview Handler"
HKCR\.cbz\shellex\{8895b1c6-...} = {B5E84A2F-...}
HKCR\.cbr\shellex\{8895b1c6-...} = {B5E84A2F-...}

The AppID points to the prevhost.exe surrogate ({6d2b5079-...}), which is required because Windows runs preview handlers out-of-process for security. DisableLowILProcessIsolation allows the handler to read files from the user's drives.

If a ProgID is registered for .cbz/.cbr (e.g. cYo.ComicRack), the preview handler must also be registered under that ProgID's shellex key.

Build Dependencies

• Visual Studio 2022 with C++ ATL/MFC workload
• GDI+ (gdiplus.lib) — for preview handler rendering
• Windows Compression API (Cabinet.lib, compressapi.h) — for ZIP deflate decompression
• No external libraries (no zlib, no UnRAR SDK)

Key Implementation Notes

• ZIP directory detection: The versionMadeByOS byte in the central directory determines how to interpret external attributes. Unix-origin ZIPs use S_IFDIR (0x4000) in the high 16 bits; MS-DOS uses bit 0x10 in the low byte. Trailing slash is always checked as a fallback.
• DPI handling: GDI+ page unit is set to UnitPixel and all fonts use UnitPixel to prevent DPI auto-scaling in RDP or high-DPI scenarios.
• GDI+ Fonts: The Gdiplus::Font class has a deleted copy constructor. All font parameters must be passed as pointers.
• Double buffering: The preview handler renders to an off-screen bitmap and blits to avoid flicker.

Security

• Read-only file access; no writes except temporary files (cleaned up automatically).
• No network access or external dependencies.
• The preview handler runs in the prevhost.exe surrogate process, isolated from Explorer.

License

This project is provided as-is for educational and personal use.