From 4b8c402e439f634c9073d2a7ebfadf0785333ef3 Mon Sep 17 00:00:00 2001
From: Gabriel Franco <gabefgonc@gmail.com>
Date: Thu, 10 Sep 2026 12:03:42 -0300
Subject: [PATCH] feat(frontend): add in-match split-view opponent progress
 pane

---
 frontend/index.html               |  15 ++++
 frontend/src/game/opponentView.ts | 109 ++++++++++++++++++++++++++++++
 frontend/src/game/renderer.ts     |  63 +++++++++++++++++
 frontend/src/style.css            |  33 +++++++++
 4 files changed, 220 insertions(+)
 create mode 100644 frontend/src/game/opponentView.ts

diff --git a/frontend/index.html b/frontend/index.html
index c29d298..8713b86 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -59,6 +59,21 @@
         </div>
       </aside>
     </main>
+
+    <section id="split-view" class="split-view hidden" aria-label="Match progress">
+      <div class="split-pane">
+        <div class="split-pane-label">Yours</div>
+        <div class="canvas-wrap split-canvas-wrap">
+          <canvas id="split-your-canvas" class="split-canvas"></canvas>
+        </div>
+      </div>
+      <div class="split-pane">
+        <div class="split-pane-label">Opponent</div>
+        <div class="canvas-wrap split-canvas-wrap">
+          <canvas id="opponent-canvas" class="split-canvas"></canvas>
+        </div>
+      </div>
+    </section>
   </div>
 
   <div id="intro-modal" class="modal-overlay">
diff --git a/frontend/src/game/opponentView.ts b/frontend/src/game/opponentView.ts
new file mode 100644
index 0000000..dfcb6c0
--- /dev/null
+++ b/frontend/src/game/opponentView.ts
@@ -0,0 +1,109 @@
+import { tokenize } from '../engine/tokenizer';
+import { SNIPPETS, pickRandomSnippetIndex } from '../data/snippets';
+import type { CategoryId, Token } from '../types';
+import { FONT_SIZE, FONT_STACK, GUTTER, LINE_HEIGHT, PAD } from './layoutConstants';
+import { drawOpponentFrame } from './renderer';
+
+function requireEl<T extends HTMLElement>(id: string): T {
+  const el = document.getElementById(id);
+  if (!el) throw new Error(`Missing required element #${id}`);
+  return el as T;
+}
+
+/**
+ * Owns the "opponent progress" canvas: a read-only mirror of the shared
+ * match snippet that reveals only a binary "has the opponent assigned
+ * this category yet?" signal, driven by `round:progress` messages
+ * (see PROTOCOL.md — that message carries a bare `CategoryId`, never a
+ * color). `markAssigned` is the only way to light up a category, and it
+ * only ever accepts a `CategoryId`, so a real opponent-chosen hex has no
+ * path into this view by construction.
+ *
+ * Mirrors `ThemeGuessGame`'s canvas-ownership pattern, but far simpler:
+ * no picker, no clicks, no animation loop — every redraw is a flat,
+ * instant swap (see `drawOpponentFrame`).
+ */
+export class OpponentView {
+  private readonly canvas: HTMLCanvasElement;
+  private readonly ctx: CanvasRenderingContext2D;
+
+  private snippetIndex: number;
+  private tokens: Token[] = [];
+  private lineCount = 1;
+  private maxCols = 0;
+  private charWidth = 0;
+  private width = 0;
+  private height = 0;
+  private assigned = new Set<CategoryId>();
+
+  constructor(canvasId: string, snippetIndex: number = pickRandomSnippetIndex()) {
+    this.canvas = requireEl<HTMLCanvasElement>(canvasId);
+    this.ctx = this.canvas.getContext('2d')!;
+    this.snippetIndex = snippetIndex;
+    this.build();
+  }
+
+  /** Forces a specific snippet (by stable `SNIPPETS` index) and clears
+   * progress — mirrors `ThemeGuessGame.setSnippet`, used to keep both
+   * players' panes on the same source file each match. */
+  setSnippet(index: number): void {
+    this.snippetIndex = index;
+    this.assigned = new Set();
+    this.build();
+  }
+
+  /** Marks one category as assigned by the opponent and redraws. Takes
+   * only a `CategoryId` — never a color — so there is no code path for
+   * an opponent's real chosen hex to reach this view. */
+  markAssigned(categoryId: CategoryId): void {
+    this.assigned.add(categoryId);
+    this.draw();
+  }
+
+  /** Clears every progress signal for reuse across matches, without
+   * touching the current snippet/layout. */
+  reset(): void {
+    this.assigned = new Set();
+    this.draw();
+  }
+
+  private build(): void {
+    this.tokens = tokenize(SNIPPETS[this.snippetIndex]);
+
+    this.lineCount = 1;
+    this.maxCols = 0;
+    let col = 0;
+    for (const t of this.tokens) {
+      if (t.type === 'newline') { this.lineCount++; col = 0; }
+      else { col += t.text.length; this.maxCols = Math.max(this.maxCols, col); }
+    }
+
+    this.setupCanvasSize();
+    this.draw();
+  }
+
+  private setupCanvasSize(): void {
+    const dpr = window.devicePixelRatio || 1;
+    this.ctx.font = `${FONT_SIZE}px ${FONT_STACK}`;
+    this.charWidth = this.ctx.measureText('M').width;
+    this.width = GUTTER + PAD * 2 + this.maxCols * this.charWidth;
+    this.height = PAD * 2 + this.lineCount * LINE_HEIGHT;
+    this.canvas.style.width = `${this.width}px`;
+    this.canvas.style.height = `${this.height}px`;
+    this.canvas.width = this.width * dpr;
+    this.canvas.height = this.height * dpr;
+    this.ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
+  }
+
+  private draw(): void {
+    drawOpponentFrame({
+      ctx: this.ctx,
+      width: this.width,
+      height: this.height,
+      charWidth: this.charWidth,
+      lineCount: this.lineCount,
+      tokens: this.tokens,
+      assigned: this.assigned,
+    }, performance.now());
+  }
+}
diff --git a/frontend/src/game/renderer.ts b/frontend/src/game/renderer.ts
index 41ea4ae..483baba 100644
--- a/frontend/src/game/renderer.ts
+++ b/frontend/src/game/renderer.ts
@@ -64,3 +64,66 @@ export function drawFrame(state: RenderState, now: number): void {
 
   state.particles.draw(ctx);
 }
+
+/** Flat color used to signal "opponent has assigned this category" in
+ * the opponent-progress pane. Never a real chosen hex — the opponent's
+ * actual color is never transmitted or known here (see PROTOCOL.md
+ * `round:progress`), so this is the only color this view can ever show
+ * for a picked category. */
+export const OPPONENT_ASSIGNED_HEX = '#5fd75f';
+/** Flat grey used for categories the opponent hasn't picked yet. */
+export const OPPONENT_UNASSIGNED_HEX = '#3a3a52';
+
+/** Everything one frame of the opponent-progress canvas needs. Deliberately
+ * narrower than `RenderState`: no per-category colors, no gradients/pulse
+ * animation, no particles — just which `CategoryId`s are "assigned" so far.
+ * Kept DOM-free like `drawFrame`. */
+export interface OpponentRenderState {
+  ctx: CanvasRenderingContext2D;
+  width: number;
+  height: number;
+  charWidth: number;
+  lineCount: number;
+  tokens: Token[];
+  assigned: ReadonlySet<CategoryId>;
+}
+
+/** Draws the same snippet as `drawFrame`, but every category is either
+ * flat `OPPONENT_ASSIGNED_HEX` or flat `OPPONENT_UNASSIGNED_HEX` — an
+ * instant swap with no transition, since this pane only ever receives a
+ * binary per-category signal. */
+export function drawOpponentFrame(state: OpponentRenderState, _now: number): void {
+  const { ctx } = state;
+  ctx.clearRect(0, 0, state.width, state.height);
+
+  ctx.fillStyle = state.assigned.has('background') ? OPPONENT_ASSIGNED_HEX : OPPONENT_UNASSIGNED_HEX;
+  ctx.fillRect(0, 0, state.width, state.height);
+
+  ctx.fillStyle = 'rgba(0,0,0,.16)';
+  ctx.fillRect(0, 0, GUTTER, state.height);
+
+  ctx.fillStyle = '#665c54';
+  ctx.font = `${FONT_SIZE - 3}px ${FONT_STACK}`;
+  ctx.textBaseline = 'alphabetic';
+  for (let l = 0; l < state.lineCount; l++) {
+    ctx.fillText(String(l + 1).padStart(2, ' '), 8, PAD + l * LINE_HEIGHT + FONT_SIZE - 4);
+  }
+
+  // Stroked outline so foreground text stays legible even when a token's
+  // category and the background happen to share the same flat color.
+  ctx.lineWidth = 3;
+  ctx.strokeStyle = 'rgba(10,10,18,.65)';
+  ctx.lineJoin = 'round';
+  for (const t of state.tokens) {
+    if (t.type === 'whitespace' || t.type === 'newline') continue;
+    const cat = t.type as CategoryId;
+    const x = GUTTER + PAD + t.col * state.charWidth;
+    const y = PAD + t.line * LINE_HEIGHT + FONT_SIZE - 4;
+    ctx.font = t.type === 'comment'
+      ? `italic ${FONT_SIZE}px ${FONT_STACK}`
+      : `${FONT_SIZE}px ${FONT_STACK}`;
+    ctx.fillStyle = state.assigned.has(cat) ? OPPONENT_ASSIGNED_HEX : OPPONENT_UNASSIGNED_HEX;
+    ctx.strokeText(t.text, x, y);
+    ctx.fillText(t.text, x, y);
+  }
+}
diff --git a/frontend/src/style.css b/frontend/src/style.css
index c82e754..0bbb9f4 100644
--- a/frontend/src/style.css
+++ b/frontend/src/style.css
@@ -223,6 +223,39 @@ body {
 }
 .panel-actions .btn { width: 100%; }
 
+/* ---------- split view (in-match opponent progress pane) ---------- */
+
+.split-view {
+  flex: 1 1 auto;
+  min-height: 0;
+  display: flex;
+  gap: 14px;
+}
+.split-view.hidden { display: none; }
+
+.split-pane {
+  flex: 1 1 0;
+  min-width: 0;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+}
+
+.split-pane-label {
+  font-family: var(--pixel);
+  font-size: 10px;
+  letter-spacing: .5px;
+  color: var(--fg-dim);
+  flex: 0 0 auto;
+}
+
+.split-canvas-wrap {
+  flex: 1 1 auto;
+}
+
+.split-canvas { display: block; }
+
 .cat-card {
   background: var(--panel-2);
   border: 3px solid var(--ink);