• An Nvidia RTX card
  
• Half-Life Source https://steamhost.cn/app/280/HalfLife_Source/
  
• Portal RTX (included with Portal) https://steamhost.cn/app/2012840/Portal_with_RTX/

For both Half-Life Source and Portal RTX:

1. Open the games library page
   
2. Press the cog icon
   
3. Under "Manage" select "Browse local files"

Two explorer windows should now be open. On the one named "Half-Life 2" Ctrl+Click on hl2, hl1_hd and hl1. The window should look a bit like this:
Now, do not click with your mouse, and press ctrl+c.
Now, on the "PortalRTX" window, simply press ctrl+v. If you get a warning about files in hl2, press "Skip these files". If all has gone well, the window should look like this:
Congratulations, you are ready for the next step.

At this point, you may notice Portal RTX still opens Portal. We now need to change that.

1. Close out of the "PortalRTX" and "Half-Life 2" explorer windows, they are no longer needed,
   
2. Re-open Steam if you closed it,
   
3. Open Portal RTX's Steam Library page.
   
4. Click the cog,
   
5. Click "Properties"
   
6. Under "Launch Options", type "-game hl1" (if you own Half-Life 2 you can put hl2, although it is buggier)

Your properties window should look like this:

Now, Portal RTX should be configured to launch Half-Life Source.
Launch it and bask in the glory of RTX Half-Life.

• Flashlight does not work properly
  
• Only following maps work:
  
  • Inbound
    
  • Anomalous Materials
    
  • Blast Pit
    
  • Power Up
    
  • On a Rail (only seemed to work once though)
    
  • Questionable Ethics
    
  • Lambda Core
    
  • Endgame
• HL1: Raytraced[github.com] tends to work better, but only works for the GoldSRC version (no widescreen, basic physics)
  
• The Training Room does not work