Proportions Trick is a method of bypassing forced skeleton alignment with the default animation set featured in many Source engine games such as Half-Life 2, Garry's Mod and Left 4 Dead 2. Originally discovered by CaptainBigButt during her 2014/2015 era of porting MikuMikuDance (MMD) models, the purpose of utilising the Proportions Trick is to use an existing set of animations for a custom model, without the need to make the animation set completely from scratch due to skeleton and mesh differences. In other words, if the model you're porting is shorter or taller in height, or even in a different mesh size (whether it may be shorter arms or legs), without the Proportions Trick, the custom model mesh will be distorted due to the skeleton being forced to the default positions and rotation.




(animation seen in the screenshots is the "idle_melee" animation)

Since implementing the Proportions Trick isn't the main focus of this guide, I won't be going in-depth. If you want to know how to implement it, I highly recommend you to check out a well written and summarised guide made by ZeqMacaw (author of Crowbar), which can be found here: https://sites.google.com/site/zeqmacaw/tutorials/proportion-trick

When decompiling a custom playermodel implemented with the Proportions Trick, you'll most likely end up with broken QC lines, particularly the $sequence lines due to the Proportion Trick utilising predelta options. Depending on the version of Crowbar you're using, the decompiled code lines can vary.

For example




(For me personally, I tend to favour Crowbar 0.24 for decompiling and compiling GMod models. In contrary, Crowbar 0.56 for decompiling and compiling L4D2 models.)



Furthermore, the playermodel you just decompiled will also have these files within the "anims" folder.


The file names can potentially vary depending on the author who initially ported the model with implemented Proportion Trick. Decompiling Dewobedil's ported playermodels for example:

When recompiling the decompiled files of the custom playermodel implemented with the Proportion Trick, there are a few things you'll have to change, check and look out for.

1) $sequence codes in the QC file
2) animation files within the "anims" folder
3) Hitboxes


Firstly, you'll want to replace the following highlighted QC codes situated underneath "// $definebones"...


... with these codes:
(replace "modelname" with the file names of the custom playermodel)


Next, you'll want to go into the "anims" folder, delete "a_proportions" (file name can vary), copy and paste "ragdoll" into the root decompiled folder, rename "ragdoll" to "a_proportions", and move it back into the "anims" folder.


If you don't delete the decompiled "a_proportions" file and then recompile the playermodel, you'll get this abomination since the "a_proportions" animation file is somehow broken during the process of decompiling:


If done correctly, the model should compile to it's original size proportions without stretching limbs and other errors.



When using Crowbar 0.24 to decompile GMod playermodels, hitbox codes in the QC may be commented out by the "//", thus recompiling the model will result in Crowbar automatically generating the hitboxes as shown in the following screenshots:




Just simply remove the "//" from the hitboxes and it'll fix the issue.




If you're planning on fixing a few broken hitboxes for your server, you can use Half-Life Model Viewer's (HLMV) "Bones" tab to do the alteration. Once done, just click "Generate QC", copy and paste it over the old hitbox codes in the QC file.

In summary, this guide should cover the basics of recompiling GMod playermodels that are implemented with the Proportions Trick. The methods and procedures covered in this guide are all from my own personal experience in overcoming decompiling issues with custom GMod playermodel. It may not 100% work simply due to different Crowbar versions, so I do highly suggest using Crowbar 0.24 when you're following this guide.

Additionally, if you don't want to follow my guide, you can check out ZeqMacaw's guide on overcoming decompiling issues, particularly on the topics of fixing glitched jigglebones with newer Crowbar versions: https://ad.gamersky.info/@steamcommunity.com/sharedfiles/filedetails/?id=1774302855

If you want to learn how to implement proportions from the ground up, MSF wrote a pretty in-depth guide on it for L4D2. The same concept can be applied for Gmod as well: https://ad.gamersky.info/@steamcommunity.com/sharedfiles/filedetails/?id=887935033

CaptainBigButt's very in-depth guide on implementing Proportions Trick is now available as well:
https://ad.gamersky.info/@steamcommunity.com/sharedfiles/filedetails/?id=2308084980