Introduce comet effect usermod with fire particle system

usermods/PS_Comet/PS_Comet.cpp

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+#include "wled.h"
+#include "FXparticleSystem.h"
+
+unsigned long nextCometCreationTime = 0;
+
+#define FX_FALLBACK_STATIC { SEGMENT.fill(SEGCOLOR(0)); return; }
+// Use UINT32_MAX - 1 for the "no comet" case so we can add 1 later and not have it overflow
+#define NULL_INDEX UINT32_MAX - 1
+
+///////////////////////
+//  Effect Function  //
+///////////////////////
+
+void mode_pscomet() {
+  ParticleSystem2D *PartSys = nullptr;
+  uint32_t i;
+
+  if (SEGMENT.call == 0) { // Initialization
+    // Try to allocate one comet for every column
+    if (!initParticleSystem2D(PartSys, SEGMENT.vWidth())) {
+      FX_FALLBACK_STATIC; // Allocation failed or not 2D
+    }
+    PartSys->setMotionBlur(170); // Enable motion blur
+    PartSys->setParticleSize(0); // Allow small comets to be a single pixel wide
+  }
+  else {
+    PartSys = reinterpret_cast<ParticleSystem2D *>(SEGENV.data); // If not first call, use existing data
+  }
+  if (PartSys == nullptr || SEGMENT.vHeight() < 2 || SEGMENT.vWidth() < 2) {
+    FX_FALLBACK_STATIC;
+  }
+
+  PartSys->updateSystem(); // Update system properties (dimensions and data pointers)
+
+  auto has_fallen_off_screen = [PartSys](uint32_t particleIndex) {
+    return particleIndex < PartSys->numSources
+      ? PartSys->sources[particleIndex].source.y < PartSys->maxY * -1
+      : true;
+  };
+
+  // This will be SEGMENT.vWidth() unless the particle system had insufficient memory
+  uint32_t numComets = PartSys->numSources;
+  // Pick a random column for a new comet to spawn, but reset it to null if it's not time yet or there's already a
+  // comet nearby
+  uint32_t chosenIndex = hw_random(numComets);
+  if (
+    strip.now < nextCometCreationTime
+    || !has_fallen_off_screen(chosenIndex - 1)
+    || !has_fallen_off_screen(chosenIndex)
+    || !has_fallen_off_screen(chosenIndex + 1)
+  ) {
+    chosenIndex = NULL_INDEX;
+  } else {
+    uint16_t cometFrequencyDelay = 2040 - (SEGMENT.intensity << 3);
+    nextCometCreationTime = strip.now + cometFrequencyDelay + hw_random16(cometFrequencyDelay);
+  }
+  uint8_t canLargeCometSpawn =
+    // Slider 3 determines % of large comets with extra particle sources on their sides
+    SEGMENT.custom1 > hw_random8(254)
+    && chosenIndex != 0
+    && chosenIndex != numComets - 1;
+  uint8_t fallingSpeed = 1 + (SEGMENT.speed >> 2);
+
+  // Update the comets
+  for (i = 0; i < numComets; i++) {
+    auto& source = PartSys->sources[i];
+    auto& sourceParticle = source.source;
+
+    if (!has_fallen_off_screen(i)) {
+      // Active comets fall downwards and emit flames
+      sourceParticle.y -= fallingSpeed;
+      source.vy = (SEGMENT.speed >> 5) - fallingSpeed; // Emitting speed (upwards)
+      PartSys->flameEmit(PartSys->sources[i]);
+      continue;
+    }
+
+    bool isChosenComet = i == chosenIndex;
+    bool isChosenSideComet =
+      canLargeCometSpawn &&
+      (i == chosenIndex - 1 || i == chosenIndex + 1);
+
+    // Chosen comets respawn at the top
+    if (isChosenComet || isChosenSideComet) {
+      // Map the comet index into an output pixel index
+      sourceParticle.x = i * PartSys->maxX / (SEGMENT.vWidth() - 1);
+      // Spawn a bit above the top to avoid popping into view
+      sourceParticle.y = PartSys->maxY + (2 * fallingSpeed);
+      if (isChosenComet) {
+        // Slider 4 controls comet length via particle lifetime and fire intensity adjustments
+        source.maxLife = 16 + (SEGMENT.custom2 >> 2);
+        source.minLife = source.maxLife >> 1;
+        sourceParticle.ttl = 16 - (SEGMENT.custom2 >> 4);
+      } else {
+        // Side comets have fixed length
+        source.maxLife = 18;
+        source.minLife = 14;
+        sourceParticle.ttl = 16;
+        // Shift side comets up by 1 pixel
+        sourceParticle.y += 2 * PartSys->maxY / (SEGMENT.vHeight() - 1);
+      }
+    }
+  }
+
+  // Slider 4 controls comet length via particle lifetime and fire intensity adjustments
+  PartSys->updateFire(max(255U - SEGMENT.custom2, 45U));
+}
+static const char _data_FX_MODE_PSCOMET[] PROGMEM = "PS Comet@Falling Speed,Comet Frequency,Large Comet Probability,Comet Length;;!;2;pal=35,sx=128,ix=255,c1=32,c2=128";
+
+/////////////////////
+//  UserMod Class  //
+/////////////////////
+
+class PSCometUsermod : public Usermod {
+ public:
+  void setup() override {
+    strip.addEffect(255, &mode_pscomet, _data_FX_MODE_PSCOMET);
+  }
+
+  void loop() override {}
+};
+
+static PSCometUsermod ps_comet;
+REGISTER_USERMOD(ps_comet);

usermods/PS_Comet/README.md

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+## Description
+
+A 2D falling comet effect similar to "Matrix" but with a fire particle simulation to enhance the comet trail visuals. Works with custom color palettes, defaulting to "Fire". Supports "small" and "large" comets which are 1px and 3px wide respectively.
+
+Demo: [https://imgur.com/a/i1v5WAy](https://imgur.com/a/i1v5WAy)
+
+## Installation
+
+To activate the usermod, add the following line to your platformio_override.ini
+```ini
+custom_usermods = ps_comet
+```
+Or if you are already using a usermod, append ps_comet to the list
+```ini
+custom_usermods = audioreactive ps_comet
+```
+
+You should now see "PS Comet" appear in your effect list.
+
+## Parameters
+
+1. **Falling Speed** sets how fast the comets fall
+2. **Comet Frequency** determines how many comets are on screen at a time
+3. **Large Comet Probability** determines how often large 3px wide comets spawn
+4. **Comet Length** sets how far comet trails stretch vertically

usermods/PS_Comet/library.json

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+{
+  "name": "PS Comet",
+  "build": { "libArchive": false }
+}