If you are not a programmer, or don't have one in your team, it might present a problem for the development of your mod. The next course of action would be to use other mods as a base (like Featureful or Opposing Force). However, in some cases, you may not be able to use custom code either. This is where this guide comes in: it contains a list of cool Half-Life features and stuff that you can implement in your mod!
Most of these went unused, or are workarounds rather than features themselves. It also contains some cool map tricks (such as the screen tint). These are meant to solve or tackle specific problems.

Caveats

The techniques discussed in this page isn't without gotchas. Here's some of the main problems of no-coding workarounds and dummied out features:

• They tend to be VERY specific. This means that they aim to replace certain problems, like the lack of a special entity that isn't on vanilla Half-Life, a variation of certain models, etc. You are not going to be able to add new weapons, NPCs, or similar to your mod, unfortunately.
• They are also very complicated and time consuming. Implementing them in your mod will be like trying to build a fully functional motorbike out of empty soup cans. Yes, it's possible, but not quite simple, and it can escalate pretty quickly.

UI/Menu

Main menu music

A common feature in a lot of mods. Add an .mp3 file named gamestartup.mp3 to YourMod/media. This file should contain your selected main menu music. It will be played every time the game is launched. However, the music plays in a loop and does not play again when the player leaves the game or disconnects from a server.

Mapping/Level editing

Screen tint

This one was created by the user Mota. The original map presents a México-yellowish tint, but you can change this to other colors to fit your needs. Explanation and steps for achieving this effect is available in the vault entry page, linked below:

Moving sprites

You would have seen sprites that moves through a level in various locations in Half-Life: Opposing Force. It is achieved through a custom entity (func_spritetrain) that are not available in vanilla Half-Life. However, you can use a trick to have a func_train display a sprite. This trick requires that you use some version of ZHLT compile tools (or its derivatives e.g. VHLT) that supports the use of the zhlt_usemodel keyvalue.

The following vault item has an example and the steps of achieving this trick: You can also use this trick to have a simple rotating sprite that doesn't use animation frames (thus saving on filesize), by using the angular velocity (avelocity) keyvalue. To have the sprite rotate in place, make the path_corner entities very close together (e.g. 1u apart) and have the func_train move very slowly e.g. 0.1u speed.

Model-based func_ entities

Using the same zhlt_usemodel keyvalue as mentioned in previous section, you can force a func_ entity, which is usually brush-based (just like func_train in previous section) to use a model. This is actually used in Condition Zero: Deleted Scenes with many of the mounted guns: they are func_tank entities that use a model, that are otherwise identical in function to the vanilla entity.

The tutorial page "Using models for health/HEV chargers in vanilla Half-Life" explores the use case for this workaround with the health and HEV chargers in particular. A vault item is linked in the page, but here's the same thing:

Corpses of monsters without a _dead variant

You may notice that some monsters don't have a _dead variant. Checking the models used by these monsters (See Reference: Entities and their models page) with a model viewer (e.g. Half-Life Asset Manager aka HLAM) would reveal that they don't have any dead poses. But don't fret! You can use the env_sprite entity to display a model, and can display dead poses. Just turn off SmartEdit on J.A.C.K./Hammer and input the path to the monster's model as the model keyvalue. Then, with SmartEdit still turned off, add the following keyvalues:

• sequence = the sequence number of the dying sequence that you want the end pose to be from. (Use HLAM to get this value)
• framerate = 8 - to accelerate the animation. It will freeze at the end, leaving you with a perfectly dead corpse of the monster.

Or, you could just edit the models and add dead sequences (being the last frames of the dying sequences) at the end of the QC file.

Higher-resolution / 3D skybox

The GoldSource skybox has a resolution of 256x256 per side, and unfortunately, the GoldSource game engine doesn't accept higher-resolution images for the skybox.

One solution is to place a ludicrously large model of an inverted box (i.e. the box textures face inward). The model face is textured with the sky image. It has to be really, really large (e.g. 50,000 units) so as to minimize parallax effect.
In order to have this really large model visible at all times, and not occluded by the engine:

• It should be placed in a small room disconnected from the rest of the map, and has an info_overview_point entity with "Reverse" attribute set to true.
• "Max viewable distance" in the map's worldspawn has to be at least the sum of the map size and the skybox model size. Using the value of 2.5x the model size should suffice.
• The floor of the room is textured with a pure white texlight, because models take their lighting from the lightmap off the floor. Otherwise the skybox model would be dimmer than its full brightness.

Expanding on the idea is 3D skyboxes. Instead of just an inverted box, the model can have detail such as terrain, buildings, etc. Unlike in Source, the details aren't miniatures but closer to the size it would've been if placed on the playable areas of the map. The models can even have animations, simulating a moving cloud layer in the sky. The mods Delta Particles and Half-Life: Enriched use 3D skyboxes.

Difficulty/skill detection

Suppose we want to have different number of monsters spawn depending on difficulty (higher skill == more monsters): Whereas Half-Life entities have a reserved global spawnflag value: 2048 - Not in deathmatch, which removes the entity if the map is run in deathmatch, unfortunately there is no flag to make entities spawn only at certain difficulty/skill level in the vanilla codebase.

One way to get around this is to use a monster with differing health based on skill level (set in the skill.cfg file), detect the monster's health with map logic, and use the result to do some other map logic; in this case removing certain monsters.

Suppose we'll be using the alien grunt, the only monster in vanilla Half-Life with differing health per skill level. The following snippet from skill.cfg sets their health:

// Alien Grunt
sk_agrunt_health1    "60"
sk_agrunt_health2    "90"
sk_agrunt_health3    "120"

In the starting map (i.e. the starting map when you start a new game), place 2 alien grunts in a room, separate from the rest of the map. Then, add two env_global entities that will get triggered if the skill is below a certain level. Next, set up two doors that will crush the monsters, each set to deal damage slightly below the medium and hard health levels, respectively. Now, when the map starts, the doors will try to crush the monsters. In easy mode, both monsters will be crushed. In medium skill, the first monster lives. In hard skill, both survives. Their deaths sets the appropriate global state.

With the env_global's global states set, you can use trigger_auto in the rest of the campaign to killtarget (i.e. remove from the level) monsters that should only appear in medium or hard skills.

Advanced Half-Life FGD

This FGD implements plenty of dummied out features from Half-Life, such as Dynamic Lights, the inclusion of new unused entities like item_sodacan or grenade. Keep in mind, this FGD is meant for Hammer. Other programs, like J.A.C.K. editor, can't really handle some features, and cause bugs.

Models

Different models for a single entity

You can make variations of pickups, monsters, etc. by adding a bodygroup to the model and adding the "body" property in a map editor: You can also add "limitless" body/skingroups to entities that already use them like HECU grunts or scientists. I wrote "limitless" because there is still a limit on every model. According to The303.org, the limits are:

• 32 submodels
• 32 skingroups

A problem with this workaround is that entities that already work with bodygroups and skingroups (like the scientists and security guards) can't have more groups added, since this will break the models.
An example can be found here, by UrbaNebula.

Add/remove melee/ranged attacks or abilities of monsters

In GoldSource, the models themselves can contain a lot of metadata that defines generic as well as specific abilities and behaviours. The relevant ones for this section are the ACTs that can be assigned to sequences/animations. For example, barneys and scientists have walking and running ACTs, alien slaves have ranged and melee attack ACTs, etc.

By adding or removing the ACT tags on the model sequences, one can add or remove the monsters' defined abilities. As an example, the frankenstein monsters in They Hunger is a modified alien grunt with their range (hivehand) attacks removed.

This zombie model has added sequences and ACTs that makes zombie able to be snared by barnacles.

Misc

(LEGACY) Different launch screen

Half-Life uses a single background image both for the menu and when the game is loading. However, you can add different backgrounds for the loading screen and menu. This can be achieved by modifying the file YourMod/resource/BackgroundLoadingLayout.txt, and adding your new background files. A recommended way to organize the backgrounds is putting the files in different folders, rather than putting everything in the background folder: