This is a short Python script which changes one byte in the pre-Anniversary Update hw.dll from the steam_legacy branch (CRC32 F7DCFFD9), fixing the gl_overbright command in Goldsrc games like Half-Life. Eliminates the need for third party tools like GLIntercept. Might disable detail textures, but they are not used in the base game anyway. Put the .py script in the same folder as hw.dll and launch with python hwpatcher.py in the command line. The original file will be backed up as hw.bak. Would not recommend for online play, just in case.
When hw.dll establishes GL_ARB_multitexture support, it calculates the amount of available texture units. Then, if any texture units are detected, overbright gets disabled. This patch changes one byte to keep gl_overbright available regardless of the amount of texture units. If you want to do it manually, open hw.dll with a hex editor, go to offset 290143, and change 74 to 7D.
The 25th Anniversary Update uses gl_use_shaders to mimic the overbright effect, rendering this script obsolete.