feat: structures cosmetic effect (hover-shown gradient/transition recolor) (#4492)

## Description:

Adds a new `structures` cosmetic effect type: an equippable effect that
recolors the owner's structure icons (City, Port, Factory, Defense Post,
SAM Launcher, Missile Silo) with gradient or transition color styles.
The effect is **shown while the owner's territory is hovered** —
structures otherwise keep their normal player colors, so the map stays
readable.

**Cosmetics / selection**
- `StructuresEffectAttributesSchema` (`CosmeticSchemas.ts`): its own
discriminated union (`gradient` / `transition`) — structurally identical
to the trail attributes today, but structures aren't trails, so it's a
separate schema free to diverge.
- Slot = the effectType itself: `effectTypeForSlot` is generalized to
map any non-nukeExplosion effect type to itself, so server privilege
checks (`Privilege.ts`), client selection, and persistence all work with
no per-type code.
- Effects tab, Default tile, and the store preview (shared color swatch)
come from `EFFECT_TYPES`; the only UI addition is the
`effects.type.structures` label in `en.json`.

**Rendering**
- The shared per-player effect palette grows from 2 to 3 blocks
(`EFFECT_PALETTE_BLOCKS`; structures = block 2, pinned by a
build-breaking guard). `syncPlayerEffects` resolves the `structures`
selection through the same `writeEffectEntry` used by trails.
- `StructurePass` binds the effect texture plus `uTime` and
`uHoverOwner` (fed from the existing `HoverHighlightController` →
`setHighlightOwner` path, now forwarded to the pass).
- `structure.frag.glsl` recolors the **fill only** — the border keeps
the player color for ownership legibility; alt view and construction
gray bypass the effect entirely.
- Style semantics:
- `gradient` — the palette spans each icon's diagonal once (a visible
gradient across the shape), sliding one full cycle every `colorSize · 4
· count / movementSpeed` seconds (the trail-equivalent pace; world-space
banding like the trail's would put a whole icon inside one band and read
as a flat color)
- `transition` — the whole icon is one color at a time, cross-fading at
`frequency` colors/s
- Glyph contrast: the inner icon's black/white decision is now a smooth
luminance fade (`smoothstep(0.25, 0.45)`) instead of a hard flip at
0.25, so animated fills cross-fade the glyph instead of snapping it
between black and white.

## Please complete the following:

- [ ] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/client/WebGLFrameBuilder.ts

@@ -8,6 +8,7 @@ import {
   isTrailEffect,
   type NukeExplosionAttributes,
   type NukeExplosionType,
+  type StructuresEffectAttributes,
   TRAIL_EFFECT_TYPES,
   type TrailEffectAttributes,
 } from "../core/CosmeticSchemas";
@@ -26,8 +27,9 @@ import {
 // Value import from the leaf module (not the ./render/gl barrel) so non-Vite
 // consumers don't pull in GPURenderer and its shaders — see note above.
 import {
+  EFFECT_PALETTE_BLOCKS,
   MAX_TRAIL_COLORS,
-  TRAIL_EFFECT_BLOCKS,
+  STRUCTURES_EFFECT_BLOCK,
 } from "./render/gl/utils/ColorUtils";
 import {
   UT_ATOM_BOMB,
@@ -38,15 +40,18 @@ import type { GameView } from "./view";
 
 const PALETTE_SIZE = 4096;
 
-// TRAIL_EFFECT_TYPES order IS the effect-palette block order: index = block (rows
-// block·MAX_TRAIL_COLORS …). The shader (trail.frag.glsl) picks the block from
-// the trail tile's nuke bit — block 0 = transportShipTrail (nuke bit 0), block 1
-// = nukeTrail (nuke bit 1, set by NUKE_TRAIL_BIT in TrailManager). Reordering
-// TRAIL_EFFECT_TYPES in CosmeticSchemas would silently swap the two trails' colors,
-// so this guard fails the build if the shader-coupled order ever drifts.
+// The effect-palette block order: index = block (rows block·MAX_TRAIL_COLORS …).
+// trail.frag.glsl picks its block from the trail tile's nuke bit — block 0 =
+// transportShipTrail (nuke bit 0), block 1 = nukeTrail (nuke bit 1, set by
+// NUKE_TRAIL_BIT in TrailManager) — and structure.frag.glsl reads block
+// STRUCTURES_EFFECT_BLOCK (2). Reordering TRAIL_EFFECT_TYPES in CosmeticSchemas
+// (or moving the structures block) would silently swap effect colors, so these
+// guards fail the build if the shader-coupled order ever drifts.
 const _EFFECT_BLOCK_ORDER: readonly ["transportShipTrail", "nukeTrail"] =
   TRAIL_EFFECT_TYPES;
 void _EFFECT_BLOCK_ORDER;
+const _STRUCTURES_BLOCK_IS_2: 2 = STRUCTURES_EFFECT_BLOCK;
+void _STRUCTURES_BLOCK_IS_2;
 
 // Attribute → render-param mappings:
 //   size      = the ring's final WIDTH (diameter) in world tiles when it fades
@@ -106,10 +111,11 @@ function attributesToExplosionParams(
  */
 export class WebGLFrameBuilder {
   private readonly palette: Float32Array;
-  // Per-player trail-effect palette, keyed by smallID. Layout is
-  // 4096×(MAX_TRAIL_COLORS·TRAIL_EFFECT_BLOCKS): block 0 (rows 0–7) =
-  // transportShipTrail, block 1 (rows 8–15) = nukeTrail. Consumed by TrailPass's
-  // effect texture; the shader picks the block from the trail tile's nuke bit.
+  // Per-player effect palette, keyed by smallID. Layout is
+  // 4096×(MAX_TRAIL_COLORS·EFFECT_PALETTE_BLOCKS): block 0 (rows 0–7) =
+  // transportShipTrail, block 1 (rows 8–15) = nukeTrail, block 2 (rows 16–23)
+  // = structures. Consumed by TrailPass (block from the trail tile's nuke bit)
+  // and StructurePass (block 2).
   private readonly effectPalette: Float32Array;
   private readonly patternMeta: Float32Array;
   private readonly patternData: Uint8Array;
@@ -140,7 +146,7 @@ export class WebGLFrameBuilder {
   constructor(private readonly view: MapRenderer) {
     this.palette = new Float32Array(PALETTE_SIZE * 2 * 4);
     this.effectPalette = new Float32Array(
-      PALETTE_SIZE * MAX_TRAIL_COLORS * TRAIL_EFFECT_BLOCKS * 4,
+      PALETTE_SIZE * MAX_TRAIL_COLORS * EFFECT_PALETTE_BLOCKS * 4,
     );
     this.patternMeta = new Float32Array(PALETTE_SIZE * 4);
     this.patternData = new Uint8Array(PALETTE_SIZE * 1024);
@@ -407,16 +413,21 @@ export class WebGLFrameBuilder {
       if (this.effectResolved.has(smallID)) continue;
       this.effectResolved.add(smallID);
 
-      // Resolve each trail effectType into its own block of the effect palette.
-      // rowBase block*MAX_TRAIL_COLORS must match the shader's block layout
-      // (ship=0, nuke=1) — see _EFFECT_BLOCK_ORDER above and trail.frag.glsl.
-      // Only trail effect types render here; nukeExplosion is not a trail.
-      TRAIL_EFFECT_TYPES.forEach((effectType, block) => {
+      // Resolve each trail-styled effectType into its own block of the effect
+      // palette. rowBase block*MAX_TRAIL_COLORS must match the consumer
+      // shaders' block layout (ship=0, nuke=1 in trail.frag.glsl; structures=2
+      // in structure.frag.glsl) — see _EFFECT_BLOCK_ORDER above. nukeExplosion
+      // is not trail-styled and renders through the FX pass instead.
+      const blockOrder = [...TRAIL_EFFECT_TYPES, "structures"] as const;
+      blockOrder.forEach((effectType, block) => {
         const selected = p.cosmetics.effects?.[effectType];
         if (!selected) return;
         const effect = findEffect(catalog, effectType, selected.name);
         if (!effect || effect.effectType !== effectType) return;
-        if (!isTrailEffect(effect)) return; // narrows attributes to trail attrs
+        // Narrows attributes to trail attrs (structures share the shape).
+        if (!isTrailEffect(effect) && effect.effectType !== "structures") {
+          return;
+        }
         const rowBase = block * MAX_TRAIL_COLORS;
         if (this.writeEffectEntry(smallID, effect.attributes, rowBase)) {
           dirty = true;
@@ -427,9 +438,9 @@ export class WebGLFrameBuilder {
   }
 
   /**
-   * Encode a player's trail effect into one block of the effect palette. The
-   * block starts at row `rowBase` (0 = transportShipTrail, MAX_TRAIL_COLORS =
-   * nukeTrail). Within the block, row r holds color r's rgb, and the spare alpha
+   * Encode a player's trail-styled effect into one block of the effect palette.
+   * The block starts at row `rowBase` (block · MAX_TRAIL_COLORS; see
+   * _EFFECT_BLOCK_ORDER). Within the block, row r holds color r's rgb, and the spare alpha
    * channels (rows rowBase+0..3 always exist) carry the scalar params —
    *   row 0.a = color count (0 → the shader falls back to the territory color),
    *   row 1.a = styleId (0 = gradient, 1 = transition),
@@ -441,7 +452,7 @@ export class WebGLFrameBuilder {
    */
   private writeEffectEntry(
     smallID: number,
-    attrs: TrailEffectAttributes,
+    attrs: TrailEffectAttributes | StructuresEffectAttributes,
     rowBase: number,
   ): boolean {
     const colors = attrs.colors

src/client/components/CosmeticButton.ts

@@ -188,8 +188,9 @@ export class CosmeticButton extends LitElement {
         </div>`;
       }
       // Nuke explosions preview per visual type (expanding ring or sparkle
-      // burst); every trail effectType (transportShipTrail, nukeTrail) shares
-      // the same attributes shape and previews as a color swatch.
+      // burst); every trail effectType (transportShipTrail, nukeTrail) and the
+      // structures effect share the same attribute shapes and preview as a
+      // color swatch.
       if (isNukeExplosionEffect(c)) {
         if (c.attributes.type === "sparkles") {
           return html`<sparkles-swatch

src/client/components/EffectPreview.ts

@@ -2,6 +2,7 @@ import { html, LitElement, TemplateResult } from "lit";
 import { customElement, property } from "lit/decorators.js";
 import {
   NukeExplosionAttributes,
+  StructuresEffectAttributes,
   TrailEffectAttributes,
 } from "../../core/CosmeticSchemas";
 
@@ -9,7 +10,8 @@ import {
 const EMPTY_BG = "#444";
 
 /**
- * Swatch preview of a transport-ship-trail effect, filling its container.
+ * Swatch preview of a trail-styled effect (trails and the structures effect
+ * share the same gradient/transition attribute shapes), filling its container.
  *
  * - gradient / single color: a static swatch (flat color or left-to-right
  *   gradient — a multi-color list reads as a rainbow).
@@ -20,7 +22,7 @@ const EMPTY_BG = "#444";
 export class TrailSwatch extends LitElement {
   // Named `trail` (not `attributes`) to avoid clashing with Element.attributes.
   @property({ attribute: false })
-  trail: TrailEffectAttributes | null = null;
+  trail: TrailEffectAttributes | StructuresEffectAttributes | null = null;
 
   private animation: Animation | null = null;
 

src/client/render/gl/Renderer.ts

@@ -61,10 +61,10 @@ import { WorldTextPass } from "./passes/WorldTextPass";
 import type { RenderSettings } from "./RenderSettings";
 import { AffiliationPalette } from "./utils/Affiliation";
 import {
+  EFFECT_PALETTE_BLOCKS,
   getPaletteSize,
   hexToRgb,
   MAX_TRAIL_COLORS,
-  TRAIL_EFFECT_BLOCKS,
 } from "./utils/ColorUtils";
 import { renderDpr } from "./utils/Dpr";
 import {
@@ -267,10 +267,11 @@ export class GPURenderer {
       filter: gl.NEAREST,
     });
 
-    // Per-player trail-effect texture: TRAIL_EFFECT_BLOCKS stacked blocks of
-    // MAX_TRAIL_COLORS rows (block 0 = transportShipTrail, block 1 = nukeTrail).
-    // Starts zeroed (color count 0 everywhere = no effect → territory color).
-    const effectRows = MAX_TRAIL_COLORS * TRAIL_EFFECT_BLOCKS;
+    // Per-player effect texture: EFFECT_PALETTE_BLOCKS stacked blocks of
+    // MAX_TRAIL_COLORS rows (block 0 = transportShipTrail, block 1 = nukeTrail,
+    // block 2 = structures). Starts zeroed (color count 0 everywhere = no
+    // effect → territory/player color).
+    const effectRows = MAX_TRAIL_COLORS * EFFECT_PALETTE_BLOCKS;
     this.effectTex = createTexture2D(gl, {
       width: palW,
       height: effectRows,
@@ -511,6 +512,7 @@ export class GPURenderer {
       gl,
       header,
       this.paletteTex,
+      this.effectTex,
       this.settings,
     );
     this.structureLevelPass = new StructureLevelPass(gl, header, this.settings);
@@ -676,7 +678,7 @@ export class GPURenderer {
     this.namePass.refreshPlayerColors(this.paletteData);
   }
 
-  /** Re-upload the per-player trail-effect texture (style + colors by smallID). */
+  /** Re-upload the per-player effect texture (style + colors by smallID). */
   updateEffectPalette(effectData: Float32Array): void {
     const gl = this.gl;
     gl.activeTexture(gl.TEXTURE0);
@@ -687,7 +689,7 @@ export class GPURenderer {
       0,
       0,
       getPaletteSize(),
-      MAX_TRAIL_COLORS * TRAIL_EFFECT_BLOCKS,
+      MAX_TRAIL_COLORS * EFFECT_PALETTE_BLOCKS,
       gl.RGBA,
       gl.FLOAT,
       effectData,
@@ -980,6 +982,7 @@ export class GPURenderer {
     this.borderPass.setHighlightOwner(ownerID);
     this.territoryPass.setHighlightOwner(ownerID);
     this.namePass.setHighlightOwner(ownerID);
+    this.structurePass.setHighlightOwner(ownerID);
   }
   setMouseWorldPos(x: number, y: number): void {
     this.namePass.setMouseWorldPos(x, y);

src/client/render/gl/passes/StructurePass.ts

@@ -25,7 +25,11 @@ import {
 } from "../../types";
 import { DynamicInstanceBuffer } from "../DynamicBuffer";
 import type { RenderSettings } from "../RenderSettings";
-import { getPaletteSize } from "../utils/ColorUtils";
+import {
+  getPaletteSize,
+  MAX_TRAIL_COLORS,
+  STRUCTURES_EFFECT_BLOCK,
+} from "../utils/ColorUtils";
 import { createProgram, shaderSrc } from "../utils/GlUtils";
 
 import { assetUrl } from "src/core/AssetUrls";
@@ -92,12 +96,19 @@ export class StructurePass {
   private uIconAlpha: WebGLUniformLocation;
   private uIconColor: WebGLUniformLocation;
   private uIconDarken: WebGLUniformLocation;
+  private uTime: WebGLUniformLocation;
+  private uHoverOwner: WebGLUniformLocation;
+  // Anchored at construction so the uniform stays small (float32 precision).
+  private readonly startTime = performance.now();
+  /** smallID of the hovered territory's owner (0 = none) — gates the effect. */
+  private hoverOwner = 0;
 
   private vao: WebGLVertexArrayObject;
   private instanceBuf: DynamicInstanceBuffer;
   private ghostInstanceBuf: WebGLBuffer;
 
   private paletteTex: WebGLTexture;
+  private effectTex: WebGLTexture;
   private atlasTex: WebGLTexture;
   private affiliationTex: WebGLTexture | null = null;
   private altView = false;
@@ -120,12 +131,14 @@ export class StructurePass {
     gl: WebGL2RenderingContext,
     header: RendererConfig,
     paletteTex: WebGLTexture,
+    effectTex: WebGLTexture,
     settings: RenderSettings,
   ) {
     this.gl = gl;
     this.settings = settings;
     this.mapW = header.mapWidth;
     this.paletteTex = paletteTex;
+    this.effectTex = effectTex;
 
     // Build unitType string → atlas column mapping
     for (let i = 0; i < header.unitTypes.length; i++) {
@@ -144,6 +157,8 @@ export class StructurePass {
       shaderSrc(structureFragSrc, {
         PALETTE_SIZE: getPaletteSize(),
         ATLAS_COLS,
+        // First row of the structures block in the shared effect palette.
+        STRUCT_EFFECT_ROW_BASE: STRUCTURES_EFFECT_BLOCK * MAX_TRAIL_COLORS,
       }),
     );
     this.uLocalPlayerID = gl.getUniformLocation(
@@ -182,12 +197,15 @@ export class StructurePass {
     this.uIconAlpha = gl.getUniformLocation(this.program, "uIconAlpha")!;
     this.uIconColor = gl.getUniformLocation(this.program, "uIconColor")!;
     this.uIconDarken = gl.getUniformLocation(this.program, "uIconDarken")!;
+    this.uTime = gl.getUniformLocation(this.program, "uTime")!;
+    this.uHoverOwner = gl.getUniformLocation(this.program, "uHoverOwner")!;
 
     // Texture unit bindings + ghost defaults
     gl.useProgram(this.program);
     gl.uniform1i(gl.getUniformLocation(this.program, "uPalette"), 0);
     gl.uniform1i(gl.getUniformLocation(this.program, "uAtlas"), 1);
     gl.uniform1i(gl.getUniformLocation(this.program, "uAffiliation"), 2);
+    gl.uniform1i(gl.getUniformLocation(this.program, "uEffect"), 3);
     gl.uniform1f(this.uGhostAlpha, 1.0);
     gl.uniform3f(this.uOutlineColor, 0, 0, 0);
     gl.uniform1i(this.uHighlightMask, 0);
@@ -280,6 +298,11 @@ export class StructurePass {
     this.localPlayerID = smallID;
   }
 
+  /** Hovered territory's owner (0 = none) — shows that player's structures effect. */
+  setHighlightOwner(ownerID: number): void {
+    this.hoverOwner = ownerID;
+  }
+
   updateStructures(units: Map<number, UnitState>): void {
     let count = 0;
 
@@ -384,6 +407,9 @@ export class StructurePass {
     gl.uniform1f(this.uIconAlpha, ss.iconAlpha);
     gl.uniform3f(this.uIconColor, ss.iconR, ss.iconG, ss.iconB);
     gl.uniform1f(this.uIconDarken, ss.iconDarken);
+    // Seconds; drives the structures-effect gradient scroll / transition cycle.
+    gl.uniform1f(this.uTime, (performance.now() - this.startTime) / 1000);
+    gl.uniform1f(this.uHoverOwner, this.hoverOwner);
 
     gl.activeTexture(gl.TEXTURE0);
     gl.bindTexture(gl.TEXTURE_2D, this.paletteTex);
@@ -396,6 +422,9 @@ export class StructurePass {
       gl.bindTexture(gl.TEXTURE_2D, this.affiliationTex);
     }
 
+    gl.activeTexture(gl.TEXTURE3);
+    gl.bindTexture(gl.TEXTURE_2D, this.effectTex);
+
     gl.bindVertexArray(this.vao);
 
     // --- Real structures ---

src/client/render/gl/shaders/structure/structure.frag.glsl

@@ -4,6 +4,15 @@ precision highp float;
 uniform sampler2D uPalette;
 uniform sampler2D uAtlas;
 uniform sampler2D uAffiliation;   // 256×2 RGBA8 — row 1 = unit affiliation
+uniform sampler2D uEffect;        // RGBA32F — shared effect palette, keyed by
+                                  //   ownerID. The structures block starts at row
+                                  //   STRUCT_EFFECT_ROW_BASE; same layout as
+                                  //   trail.frag.glsl (row r = color r's rgb;
+                                  //   row 0.a = count, 1.a = styleId,
+                                  //   2.a = scalar0, 3.a = scalar1)
+uniform float uTime;              // seconds, for animated effect styles
+uniform float uHoverOwner;        // smallID of the hovered territory's owner
+                                  //   (0 = none) — gates the structures effect
 uniform float uDotsThreshold;
 uniform float uGhostAlpha;       // 1.0 = normal, <1.0 = ghost transparency
 uniform vec3  uOutlineColor;     // ghost outline color (vec3(0) = no outline)
@@ -49,6 +58,49 @@ vec3 darken(vec3 rgb, float vScale) {
   return hsv2rgb(hsv);
 }
 
+// The owner's structures cosmetic color, if equipped. Reads the structures
+// block of the shared effect palette; the gradient/transition math mirrors
+// trail.frag.glsl so the same catalog attributes look identical on both.
+// Returns false when the owner has no structures effect (count 0).
+bool structuresEffectColor(int owner, out vec3 color) {
+  const int rowBase = STRUCT_EFFECT_ROW_BASE;
+  int count = int(texelFetch(uEffect, ivec2(owner, rowBase), 0).a + 0.5);
+  if (count <= 0) return false;
+  if (count == 1) {
+    // Single color — flat recolor.
+    color = texelFetch(uEffect, ivec2(owner, rowBase), 0).rgb;
+  } else if (int(texelFetch(uEffect, ivec2(owner, rowBase + 1), 0).a + 0.5) == 1) {
+    // transition — one color at a time, cross-fading through the list.
+    // frequency = color changes per second.
+    float frequency = texelFetch(uEffect, ivec2(owner, rowBase + 2), 0).a;
+    float t = uTime * frequency;
+    int i = int(t) % count;
+    int j = (i + 1) % count;
+    vec3 a = texelFetch(uEffect, ivec2(owner, rowBase + i), 0).rgb;
+    vec3 b = texelFetch(uEffect, ivec2(owner, rowBase + j), 0).rgb;
+    color = mix(a, b, fract(t));
+  } else {
+    // gradient — the palette spans the icon's diagonal once, so the whole
+    // gradient is visible across the shape (world-space banding like the
+    // trail's would put the entire icon inside one band and read as a flat
+    // color). It scrolls along the diagonal at the trail-equivalent pace:
+    // one full slide every colorSize · 4 · count / movementSpeed seconds,
+    // so both knobs keep their trail timing semantics.
+    float colorSize = max(texelFetch(uEffect, ivec2(owner, rowBase + 2), 0).a, 0.001);
+    float movementSpeed = texelFetch(uEffect, ivec2(owner, rowBase + 3), 0).a;
+    float dn = (vLocalPos.x + vLocalPos.y) * 0.5; // icon diagonal, -0.5..0.5
+    float phase =
+      fract(dn - uTime * movementSpeed / (colorSize * 4.0 * float(count)));
+    float f = phase * float(count);
+    int i = int(f) % count;
+    int j = (i + 1) % count;
+    vec3 a = texelFetch(uEffect, ivec2(owner, rowBase + i), 0).rgb;
+    vec3 b = texelFetch(uEffect, ivec2(owner, rowBase + j), 0).rgb;
+    color = mix(a, b, fract(f));
+  }
+  return true;
+}
+
 #define PI 3.14159265
 
 // Signed distance to regular polygon edge.
@@ -119,6 +171,22 @@ void main() {
     borderColor.a = 1.0;
   }
 
+  // structures cosmetic: while the owner's territory is hovered, recolor the
+  // fill with their effect (raw catalog colors, like trails — no darken). The
+  // border keeps the player color so ownership stays readable. Skipped for
+  // alt view and construction gray.
+  bool effectActive = false;
+  if (uAltView == 0 && vUnderConstruction < 0.5) {
+    int effOwner = int(vOwnerID + 0.5);
+    if (effOwner == int(uHoverOwner + 0.5) && effOwner > 0) {
+      vec3 effectRGB;
+      if (structuresEffectColor(effOwner, effectRGB)) {
+        fillColor.rgb = effectRGB;
+        effectActive = true;
+      }
+    }
+  }
+
   vec4 bgColor = mix(borderColor, fillColor, borderMask);
 
   // Sample icon from atlas (white on transparent)
@@ -143,10 +211,20 @@ void main() {
   // color. When the shape itself is already dark, that darkened glyph blends
   // into the shape (and the dark territory behind it) and becomes unreadable —
   // so flip the glyph to the light icon color when the fill is too dark.
+  // While the structures effect is animating the fill, the flip becomes a
+  // smooth luminance fade so the glyph cross-fades instead of snapping;
+  // without the effect this is the classic hard threshold, pixel-identical
+  // to having no cosmetic equipped.
   vec3 glyphColor = uIconColor;
   if (uIconDarken > 0.0) {
     float fillLum = dot(fillColor.rgb, vec3(0.299, 0.587, 0.114));
-    glyphColor = fillLum < 0.25 ? uIconColor : darken(fillColor.rgb, uIconDarken);
+    if (effectActive) {
+      float t = smoothstep(0.25, 0.45, fillLum); // 0 = dark fill → light glyph
+      glyphColor = mix(uIconColor, darken(fillColor.rgb, uIconDarken), t);
+    } else {
+      glyphColor =
+        fillLum < 0.25 ? uIconColor : darken(fillColor.rgb, uIconDarken);
+    }
   }
   vec3 finalRGB = mix(bgColor.rgb, glyphColor, iconAlpha);
 

src/client/render/gl/utils/ColorUtils.ts

@@ -25,12 +25,16 @@ export function getPaletteSize(): number {
 export const MAX_TRAIL_COLORS = 8;
 
 /**
- * The trail-effect texture stacks one MAX_TRAIL_COLORS-row block per trail
- * effectType: block 0 = transportShipTrail, block 1 = nukeTrail (matching the
- * nuke bit in trail.frag.glsl). Bump this if another trailed effectType is added
- * (and add its rowBase branch to the shader).
+ * The effect-palette texture stacks one MAX_TRAIL_COLORS-row block per
+ * trail-styled effectType: block 0 = transportShipTrail, block 1 = nukeTrail
+ * (matching the nuke bit in trail.frag.glsl), block 2 = structures (read by
+ * structure.frag.glsl). Bump this if another trail-styled effectType is added
+ * (and give its consumer shader the new rowBase).
  */
-export const TRAIL_EFFECT_BLOCKS = 2;
+export const EFFECT_PALETTE_BLOCKS = 3;
+
+/** Block index of the structures effect within the effect-palette texture. */
+export const STRUCTURES_EFFECT_BLOCK = 2;
 
 // ---------- Terrain ----------
 

src/core/CosmeticSchemas.ts

@@ -10,7 +10,8 @@ export type Skin = z.infer<typeof SkinSchema>;
 export type Pack = z.infer<typeof PackSchema>;
 export type Subscription = z.infer<typeof SubscriptionSchema>;
 // An effect cosmetic of any type — discriminated on effectType (today
-// transportShipTrail + nukeTrail + nukeExplosion; gains a member per effectType).
+// transportShipTrail + nukeTrail + nukeExplosion + structures; gains a member
+// per effectType).
 export type Effect = z.infer<typeof EffectSchema>;
 export type EffectType = z.infer<typeof EffectTypeSchema>;
 // Shared by every trail effectType (transportShipTrail, nukeTrail, …).
@@ -19,6 +20,10 @@ export type TrailEffectAttributes = z.infer<typeof TrailEffectAttributesSchema>;
 export type NukeExplosionAttributes = z.infer<
   typeof NukeExplosionAttributesSchema
 >;
+// Attributes of a structures effect (recolors structure icons, not a trail).
+export type StructuresEffectAttributes = z.infer<
+  typeof StructuresEffectAttributesSchema
+>;
 export type PatternName = z.infer<typeof CosmeticNameSchema>;
 export type Product = z.infer<typeof ProductSchema>;
 export type ColorPalette = z.infer<typeof ColorPaletteSchema>;
@@ -106,6 +111,7 @@ export const EFFECT_TYPES = [
   "transportShipTrail",
   "nukeTrail",
   "nukeExplosion",
+  "structures",
 ] as const;
 export const EffectTypeSchema = z.enum(EFFECT_TYPES);
 
@@ -199,11 +205,45 @@ const NukeExplosionEffectSchema = CosmeticSchema.extend({
   url: z.string().optional(),
 });
 
+// Structures-effect attributes, discriminated on `type`. Structurally the
+// same shapes as the trail attributes today, but structures are not trails —
+// separate schema, and the spatial semantics differ:
+//  - "gradient": the palette spans each structure icon's diagonal once (a
+//    visible gradient across the shape), sliding one full cycle every
+//    colorSize · 4 · count / movementSpeed seconds (the trail-equivalent pace).
+//  - "transition": the whole icon is one color at a time, cross-fading through
+//    the list. `frequency` = color changes per second.
+// Colors are unvalidated strings; the renderer drops any it can't parse (and
+// an empty list leaves the structure on its normal player color).
+export const StructuresEffectAttributesSchema = z.discriminatedUnion("type", [
+  z.object({
+    type: z.literal("gradient"),
+    colors: z.array(z.string()),
+    colorSize: z.number(),
+    movementSpeed: z.number(),
+  }),
+  z.object({
+    type: z.literal("transition"),
+    colors: z.array(z.string()),
+    frequency: z.number(),
+  }),
+]);
+
+// Recolors the owner's structures (city, port, factory, defense post, SAM,
+// silo) with gradient / transition styles. Shown while the owner's territory
+// is hovered; structures otherwise keep their normal player colors.
+const StructuresEffectSchema = CosmeticSchema.extend({
+  effectType: z.literal("structures"),
+  attributes: StructuresEffectAttributesSchema,
+  url: z.string().optional(),
+});
+
 // Any catalog effect, discriminated on effectType. Add a member per effectType.
 export const EffectSchema = z.discriminatedUnion("effectType", [
   TransportShipTrailEffectSchema,
   NukeTrailEffectSchema,
   NukeExplosionEffectSchema,
+  StructuresEffectSchema,
 ]);
 
 /**
@@ -226,17 +266,21 @@ export function isNukeExplosionEffect(
 }
 
 /**
- * A player selects one effect per "slot". A slot is the effectType for trails
- * (transportShipTrail, nukeTrail) and the nukeType for nuke explosions (atom,
- * hydro, mirvWarhead) — so a player can equip a distinct explosion per bomb.
- * Returns the effectType a slot resolves to for catalog lookup, or undefined for
- * an unknown/stale slot (e.g. a bare "nukeExplosion" key from before this split).
+ * A player selects one effect per "slot". A slot is the effectType itself for
+ * per-type effects (transportShipTrail, nukeTrail, structures) and the
+ * nukeType for nuke explosions (atom, hydro, mirvWarhead) — so a player can
+ * equip a distinct explosion per bomb. Returns the effectType a slot resolves
+ * to for catalog lookup, or undefined for an unknown/stale slot (e.g. a bare
+ * "nukeExplosion" key from before the per-nukeType split).
  */
 export function effectTypeForSlot(slot: string): EffectType | undefined {
   if ((NUKE_EXPLOSION_TYPES as readonly string[]).includes(slot)) {
     return "nukeExplosion";
   }
-  if ((TRAIL_EFFECT_TYPES as readonly string[]).includes(slot)) {
+  if (
+    (EFFECT_TYPES as readonly string[]).includes(slot) &&
+    slot !== "nukeExplosion"
+  ) {
     return slot as EffectType;
   }
   return undefined;
@@ -330,6 +374,7 @@ export const CosmeticsSchema = z.object({
       ).optional(),
       nukeTrail: lenientRecord(NukeTrailEffectSchema).optional(),
       nukeExplosion: lenientRecord(NukeExplosionEffectSchema).optional(),
+      structures: lenientRecord(StructuresEffectSchema).optional(),
     })
     .optional(),
   currencyPacks: z.record(z.string(), PackSchema).optional(),