# Unreal Engine: Game Effects *2025-10-08* > Notes taken from the fifteenth week of Game Programming Foundations After covering the complex but incredibly powerful [Gameplay Ability System]({{< relref "/posts/2025/unreal-engine-14-gameplay-ability-system" >}}) last week, this week **revisited** game effects – a deeper look at [Niagara Systems](https://dev.epicgames.com/documentation/unreal-engine/creating-visual-effects-in-niagara-for-unreal-engine), [Niagara Emitters](https://dev.epicgames.com/documentation/unreal-engine/getting-started-in-niagara-effects-for-unreal-engine), [Sound Effects](https://dev.epicgames.com/documentation/unreal-engine/working-with-audio-in-unreal-engine?lang=en-US), and [MetaSounds](https://dev.epicgames.com/documentation/unreal-engine/metasounds-in-unreal-engine?lang=en-US). --- ## Niagara VFX **Niagara VFX** is the primary tool for particle effects in modern Unreal, using both CPU and GPU resources. C++ manages graphics libraries, threads, and system resources, while procedures and tasks are grouped in **Niagara Emitters**. Each **Niagara System** can run and manage multiple Niagara Emitters. ## Niagara Systems - Adding a Niagara System opens with pre-designed templates - Can also create an **Empty Niagara System** ## Niagara Emitters - Similarly, adding a Niagara Emitter provides templates or an empty emitter to start from ## Opening a Niagara System - The **System Overview** panel includes **Add Emitter** - Pre-designed templates can be added (e.g., `NE_01`) - **Parameters and User Parameters** panels expose programmable values - To add a parameter: click **+** in the User Exposed area, then assign a default value in the User Parameters panel - A vector parameter can be made and its default set the same way – parameters can accept various objects like actors, tools, or subsystems ## Using Parameters and Attributes The Niagara System is an **Actor Component** that gets added to an actor: - In the Details panel → Niagara → Niagara System Asset - The **Activation** dropdown sets activation mode - Use **Activate** and **Deactivate** Blueprint nodes To communicate with Niagara from code, two methods exist for setting vector parameters: 1. Effects/Components/Particle System/Set Vector Parameter 2. Niagara/Set Niagara Variable (Vector2/3/4) **Options from the Niagara category are recommended.** Both require the **Parameter Name** and **InVariable Name** text fields to match exactly with the parameter/attribute from the Niagara system. If the variable name is wrong or doesn't exist, nothing will happen – silently. ## Niagara Emitters (Technical Breakdown) Emitters are where particles are generated – controlling how they're born, how they age, and how they look and behave. Emitter modules execute from top to bottom; the final block defines the render object (sprite, mesh, light, decal, etc.). **Steps in an emitter:** 1. Source of processing sits at the top of the emitter box 2. CPU or GPU (or both) can be customised – useful for scaling down to simple devices like smartphones 3. Set the number of particles rendered per frame – can be tied to a "controlling" attribute based on target hardware 4. Set each particle's properties 5. Add a module to apply particle location 6. Final step: particles must change frame-by-frame as they age **Debugging:** Right-click an emitter → **Watch Emitter in Niagara Debugger** ## Sound Effects and MetaSounds **MetaSounds** is the high-performance audio system replacing Sound Cues: - Offers scripting and DSP graph control - Upgrading to newer engine versions may require rebuilding MetaSounds ### Audio Standards and Concepts - Tempo and Rhythm - Melody Generation - Synthesising - Crossfade - Filtering - Enveloping - Effects Processing ### MetaSound Object Each MetaSound object is its own audio rendering engine, capable of rendering in parallel with potentially independent formats. The pattern mirrors materials: - Animation posts data refresh and rendering each frame - Materials use float vectors (Red, Green, Blue, Alpha) - MetaSound follows the same paradigm The editor provides two triggers and one output: - **Triggers** are equivalent to events in Actor Blueprints - Multiple sound Blueprint nodes can be activated by a single trigger **Creating a trigger:** - Click **+** in the Inputs panel - Change variable to **Trigger** in the Details panel - Activate via Blueprint code or the Simulate button (under Default Value → Default) **Playing sound:** - Right-click → **Wave Player** node - Create and edit variables assigned to each pin - **WaveBank** is an array of audio files **Testing:** 1. Press play button on the editor (fires the default On Play trigger) 2. Spawn a MetaSound object → automatically triggers On Play MetaSounds render **asynchronously** and support: - 16-bit, 24-bit, and PCM-formatted .wav files - Ogg-Vorbis, AIFF, FLAC - Internally converted to 16-bit PCM ## MetaSound Parameters Parameters accept input the same way material instances do: - Send parameter name and value to the MetaSound object - Execute **Trigger Parameter** node with trigger as the In Name pin - Combine triggers using **Trigger Any** - Use **Set [data type name] Parameter** Blueprint node - the parameter name must match the In Name pin value - Use **Play** node to trigger playback ## MetaSound Lifecycle Each MetaSound object has an **OnFinished** output trigger. When activated, the MetaSound stops processing sound and removes itself. Any reference to the object becomes invalid – which can cause error messages or crashes. **Two management strategies:** 1. **Avoiding invalid references:** - Maintain a list of audio files and sound effects - Prioritise based on period of activation (e.g., weapons stay loaded, end-level sounds can unload) 2. **Using other MetaSound objects:** - Right-click → Graphs → Other MetaSound objects - Activate via trigger, pass parameters, mix audio output - Can use **Mixer** Blueprint node to blend sounds --- ## Notes on things that stood out This week felt like the second pass on [Week 11]({{< relref "/posts/2025/unreal-engine-11-visual-and-audio-effects" >}}) – same topics, but the course went deeper into the *how* rather than the *what*. The most useful takeaway was the parameter naming discipline: mismatched names fail silently, which is the worst kind of bug in a system this layered. The MetaSound lifecycle note ("any reference becomes invalid") is genuinely scary – if you're keeping references to MetaSound objects after they finish, you're one frame away from a crash. The prioritisation strategy (keep weapons loaded, unlevel background sounds on demand) is the kind of practical guidance that saves hours of debugging later.