Openclaw

OpenClaw

What this is

OpenClaw is an open-source, cross-platform re-implementation of the engine used in the 1997 platformer game "Claw". It is written in C++ and leverages SDL2 to ensure compatibility with modern operating systems while introducing advanced features like Lua scripting for object logic.

Installation

git clone https://github.com/OpenClaw/OpenClaw.git
mkdir build && cd build
cmake ..
make
# Note: Requires original CLAW.REZ file in the execution directory

Key concepts

• REZ Archive: The engine uses a virtual file system to read assets from original .REZ containers. You do not need to extract these files; the engine accesses them directly via internal paths.
• Lua Logic: Unlike the original game, OpenClaw uses Lua for level logic and object behaviors. This allows for runtime modification of enemy AI and interactive elements.
• WAP Maps: Level layouts are stored in .WAP files, which define tile layers, object placement, and logic triggers.
• SDL2 Rendering: The engine utilizes SDL2 for hardware-accelerated rendering, allowing for windowed modes and modern resolution scaling.

Correct usage patterns

• Lua Scripting for Objects: When defining a new object behavior in a Lua script:

  -- Example: A custom health pickup script
  function OnTouch(player, object)
      if player:GetHealth() < 100 then
          player:AddHealth(10)
          object:Destroy()
          PlaySound("GAME_GETHEALTH")
      end
  end
  

• Configuring the Engine: Adjusting settings via config.xml:

  <config>
      <video width="800" height="600" fullscreen="false" vsync="true" />
      <game path="./CLAW.REZ" />
  </config>
  

Common mistakes to avoid

• Case Sensitivity: Linux builds are case-sensitive. Ensure that asset paths requested in code match the case inside the .REZ file (e.g., IMAGES/LEVEL1.PCX vs images/level1.pcx).
• Missing Original Assets: OpenClaw is an engine only. It will fail to launch without the original CLAW.REZ file from the 1997 retail game.
• Lua Syntax: Ensure scripts follow the specific Lua version embedded (typically Lua 5.3). Avoid using platform-specific OS calls within Lua scripts to maintain cross-platform compatibility.

File and folder conventions

• /src: Contains the C++ source code for the engine core and rendering logic.
• /scripts: Directory for Lua-based object behaviors and level logic.
• /assets: Location for external configuration files and non-REZ media.
• config.xml: The primary configuration file for engine behavior and asset paths.