Thread by @AlanZucconi

Let's talk about @unity3d, and the execution order of its event functions—such as 𝚂𝚝𝚊𝚛𝚝 and 𝚄𝚙𝚍𝚊𝚝𝚎.

Trust me when I say that ...IT'S WAY MORE COMPLICATED THAN YOU THINK. 😬

#gamedev #unitytips #madewithunity

🧵👇

🔹𝗙𝗶𝗿𝘀𝘁 𝗦𝗰𝗲𝗻𝗲 𝗹𝗼𝗮𝗱

1⃣ 𝙰𝚠𝚊𝚔𝚎: always called before any 𝚂𝚝𝚊𝚛𝚝 & after a prefab is instantiated

2⃣ 𝙾𝚗𝙴𝚗𝚊𝚋𝚕𝚎: called just after a 𝙶𝚊𝚖𝚎𝙾𝚋𝚓𝚎𝚌𝚝 is enabled (including when loaded, created, or a 𝙼𝚘𝚗𝚘𝙱𝚎𝚑𝚊𝚟𝚒𝚘𝚞𝚛 script is added)

🔹𝗕𝗲𝗳𝗼𝗿𝗲 𝘁𝗵𝗲 𝗳𝗶𝗿𝘀𝘁 𝗳𝗿𝗮𝗺𝗲 𝘂𝗽𝗱𝗮𝘁𝗲

3⃣ 𝚂𝚝𝚊𝚛𝚝: called before the first frame update. This happens only if the script is enabled. 𝚂𝚝𝚊𝚛𝚝 can also be made into a coroutine by changing its return type to 𝙸𝙴𝚗𝚞𝚖𝚎𝚛𝚊𝚝𝚘𝚛

🔹𝗣𝗵𝘆𝘀𝗶𝗰𝘀 𝗨𝗽𝗱𝗮𝘁𝗲

4⃣ 𝙵𝚒𝚡𝚎𝚍𝚄𝚙𝚍𝚊𝚝𝚎: often called several times during each frame. This is where the rigid bodies are updated.

This is also where you should call methods that *continuously* affect the physics, such as 𝙰𝚍𝚍𝙵𝚘𝚛𝚌𝚎 (when non-impulsive).

The physics event functions are invoked after each 𝙵𝚒𝚡𝚎𝚍𝚄𝚙𝚍𝚊𝚝𝚎 call:

5⃣ 𝙾𝚗𝚃𝚛𝚒𝚐𝚐𝚎𝚛𝚇𝚇𝚇
6⃣ 𝙾𝚗𝙲𝚘𝚕𝚕𝚒𝚜𝚒𝚘𝚗𝚇𝚇𝚇

They might be out-of-synch with the game logic. To fix this, you can use 𝚢𝚒𝚎𝚕𝚍 𝚆𝚊𝚒𝚝𝙵𝚘𝚛𝙵𝚒𝚡𝚎𝚍𝚄𝚙𝚍𝚊𝚝𝚎 in a coroutine.

🔹𝗨𝗽𝗱𝗮𝘁𝗲 𝗢𝗿𝗱𝗲𝗿

7⃣ 𝚄𝚙𝚍𝚊𝚝𝚎: called once per frame on any active game object. This is where you want to put most of your game logic.

This is also where you should call one-time event input functions such as:

🔸GetKeyDown
🔸GetKeyUp

🔸GetButtonDown
🔸GetButtonUp

That is very confusing! 😖

So this is a quick & overly simplified table to show you which methods should be safe to call from which event functions.

TL;DR:

🔸One-time input events & game logic? ➔ 𝚄𝚙𝚍𝚊𝚝𝚎
🔸Affecting physics over multiple frames? ➔ 𝙵𝚒𝚡𝚎𝚍𝚄𝚙𝚍𝚊𝚝𝚎

8⃣ 𝙻𝚊𝚝𝚎𝚄𝚙𝚍𝚊𝚝𝚎: called after *all* 𝚄𝚙𝚍𝚊𝚝𝚎 functions have been called.

It is pretty handy because you can assume that all game objects have been correctly updated.

🔹𝗦𝗰𝗲𝗻𝗲 𝗥𝗲𝗻𝗱𝗲𝗿𝗶𝗻𝗴

9⃣ 𝙾𝚗𝚁𝚎𝚗𝚍𝚎𝚛𝙸𝚖𝚊𝚐𝚎: called after the scene rendering is complete. This is used to allow for post-processing.

A few years ago I wrote a tutorial about screen shaders, and how to use them for post-processing.
alanzucconi.com/2015/07/08/scr…

There are many more event functions that are called before 𝙾𝚗𝚁𝚎𝚗𝚍𝚎𝚛𝙸𝚖𝚊𝚐𝚎, but those are rarely used.

In case you are interested, they are:

🔸OnWillRenderObject
🔸OnPreCull
🔸OnBecameVisible
🔸OnBecameInvisibile
🔸OnPreRender
🔸OnRenderObject
🔸OnPostRender

🔹 𝗗𝗲𝗰𝗼𝗺𝗺𝗶𝘀𝘀𝗶𝗼𝗻𝗶𝗻𝗴

🔟 𝙾𝚗𝙳𝚒𝚜𝚊𝚋𝚕𝚎: this method mirrors the behaviour of 𝙾𝚗𝙴𝚗𝚊𝚋𝚕𝚎, being called when the 𝙼𝚘𝚗𝚘𝙱𝚎𝚑𝚊𝚟𝚒𝚘𝚞𝚛 becomes disabled or inactive.

There are many more methods I could simply not fit in this thread. 🤯

Most of the info comes from the official Unity documentation. You should definitely have a look at it if you are interested! 📖👇

docs.unity3d.com/Manual/Executi…

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