In the context of Counter-Strike 1.6 OpenGL wallhack is a client-side modification that allows players to see enemies, weapons, and other objects through solid surfaces by manipulating how the graphics library renders the game. How it Works

: Highlighting player skeletons (bones) through walls to make them easier to track. Lambert/NoFlash

The OpenGL wallhack eventually met its match as Valve improved VAC and third-party services like ESEA and CAL (Cyberathlete Amateur League) developed more intrusive anti-cheat clients. Modern games now use much more complex rendering techniques that make simple "depth-test" bypasses nearly impossible.

now use sophisticated kernel-level checks, making these old-school "DLL swaps" instantly detectable on official servers.

• Simpler pipeline: The fixed-function pipeline and predictable draw sequences made it tractable to identify which calls rendered player models and where to intervene.
• Global state model: OpenGL’s global state model meant a single state change could affect subsequent draws; intercepting a few calls could influence many renderables.
• Client-side model drawing: The game performed significant client-side processing of models; trusting the client to perform final rendering enabled visual-only cheats that required no authoritative server changes.
• Accessibility of hooks: Many community tools and wrappers made hooking into OpenGL calls straightforward on Windows builds at the time.