After many years of trial and error, going off of almost zero documentation other than a poorly worded but still somewhat helpful tutorial on the valve developer community, and dota 2 gameinfo.gi on github gametracker, I have stumbled into how to import a source 1.0 vmf, the steps for Half-Life: Alyx are as follows:
Create a default-new "addon" where you'll keep the imported materials / textures / models.
Then the easiest way to batch import source1 content is using https://github.com/AlpyneDreams/source2utils, after you're done with those tools and you have a folder of .vmat and .tga I like use https://www.xnview.com/en/xnviewmp/#downloads to batch convert all the .tga to have a color depth of 32 with 255 alpha, otherwise source2 cant read it, and enable RLE compression, its lossless and reduces OVER 60% of total file size. Move all of your imported content to that normal addon we made earlier.
Now, here's what I believe to be the magic sauce... create a "MOD" (not a addon ) of your original source1 content on the game-side, not content-side, located at for example "E:\SteamLibrary\steamapps\common\Half-Life Alyx\game\source1mod". A very important note, along with your source1 content, you also need to have a normal source1 gameinfo.txt, located right next to your materials / models folders, the one from tf2 for example would work.
Then, (THE Real magic), open up "E:\SteamLibrary\steamapps\common\Half-Life Alyx\game\hlvr" and edit the "gameinfo.gi" file with a text editor, scroll down to find... Source1Import !
Set importmod, and importdir to your source1 content mod you made, like so :
"importmod" "source1mod"
"importdir" "..\source1mod"
NOW before you run off and try and import a .vmf from your desktop, you need to place even the source .vmf in a special location, on the content-side, not game-side, for example "E:\SteamLibrary\steamapps\common\Half-Life Alyx\content\source1mod\maps\ctf_2fort_d.vmf"
Finally using google I was able to find very little parameters for "Source1Import", but I did find a few, how useful they are is yet to be understood, probably best to start with the default no parameters.
"synthesizeMeshNames" "1"
"ignoreParticleManifest" "1"
"getSkinningFromLod0ByDefault" "0"
"createStaticOverlays" "1" // info_overlay entities will be converted to static overlay nodes instead of preserved as Info_overlay entities
Hopefully this made sense, I'll think about making a more detailed FULL tutorial on steam guides or something later, I'll edit this to have a link to that if I do end up making it. Thanks!
