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Documentation Index

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COI Client’s visual effects system renders screen-space overlays directly in the player’s HUD. When the server sends a coi-client:effect plugin message payload, the client’s EffectManager looks up the effect by ID and activates it as an independent layer on top of the game view. Because each effect is its own VisualEffect instance managed in a shared list, multiple effects can run simultaneously — vignette, heartbeat, and cracks can all be active at once with no conflicts.

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Available Effects

vignette

Darkens screen edges for cursed zones, low sanity, or death proximity.

heartbeat

Pulsing vignette that throbs with a realistic lub-DUB rhythm.

cracks

Branching fracture lines that grow from screen corners toward the center.

eyes

Creepy eyes that open from darkness, stare, then slowly close.

glitch

VHS-style horizontal distortion lines strobing in rapid bursts.

bloodrain

Dark red streaks of varying speed and opacity falling down the screen.

frost

Ice crystals and blue-white gradients growing inward from screen edges.

whispers

Cryptic text phrases that fade in and out at random screen positions.

tunnel

Circular vignette that closes inward, shrinking the player’s field of view.

flash

Instant full-screen color wash that rises quickly and fades out.

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Triggering Effects

Effects are triggered from a Paper plugin via the coi-client:effect plugin messaging channel. Write the effect ID and a comma-separated param string into a ByteArrayDataOutput, then send it to the target player: 
// Helper — call from your Paper plugin
void sendEffect(Player player, String effectId, String params) {
    ByteArrayDataOutput out = ByteStreams.newDataOutput();
    out.writeUTF(effectId);
    out.writeUTF(params);
    player.sendPluginMessage(plugin, "coi-client:effect", out.toByteArray());
}

// Example calls
sendEffect(player, "vignette",  "intensity=0.6,duration=10000");
sendEffect(player, "heartbeat", "intensity=0.9,bpm=95");
sendEffect(player, "flash",     "color=FF2200,intensity=0.7,duration=400");
Remember to register the outgoing channel in onEnable before sending any messages: 
getServer().getMessenger().registerOutgoingPluginChannel(this, "coi-client:effect");
For the complete param reference for every effect, see the full integration guide.

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Stopping Effects

Two stop patterns are supported:
  • Stop one effect — set params to "stop" while providing the specific effect ID: 
    effectId = "<id>",  params = "stop"
  • Stop all active effects — use "all" as the effect ID (params are ignored): 
    effectId = "all",  params = "stop"
Triggering an effect that is already running replaces it — the previous instance is removed and the new one starts from scratch with the new params.

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Debug Screen

During development, press F8 to open the Effect Debug screen. It lists every effect registered in EffectManager alongside Test and Stop buttons so you can preview each effect without a running server. The screen’s isPauseScreen() method returns false, so the game world continues to render and all active effects remain fully visible while the screen is open.
Server developers looking for the complete effects API — including all per-effect params, defaults, and combination recipes — should visit the Server Integration tab for the full effects API reference.

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