fix(client): fallback to full border recompute on massive tile changes

[blontd6]

Add approved & assigned issue number here:

Resolves #3604
(related)

Description:

Fixes severe client-side lag spikes (framerate dropping to single digits) when multiple nuclear bombs detonate close to each other with "isWaterNukes": true enabled.

• Water nukes convert land to water on detonation. For an Atom Bomb (radius 30), this changes up to 2,800 tiles.

• The client splits these changes across 16 frames (dripBuckets), processing ~150 tile changes per frame.

• For each tile change, BorderComputePass.patchTile computes updates. If the victim's territory is highlighted, the pass expands the repaint area of each tile change to a highlightThicken Chebyshev box of radius 4 (meaning 9x9 = 81 points).

• This forces the CPU to calculate and push up to 150 * 81 = 12,150 points per frame to the border scatter buffer, uploading it, and rendering it as thousands of overlapping GPU POINTS using the complex border shader.

• Under consecutive detonations, this completely freezes the client rendering thread, leading to disconnections.

• Optimizes BorderComputePass.ts to fallback to a full-screen quad border recompute if the scatter point count exceeds a threshold of 2,048 points.

• Bypasses the expensive CPU coordinate expansions and array resizing for subsequent tile updates in the same frame.

• The GPU renders a simple fullscreen quad to rebuild all borders, which is extremely parallelized and executes in <0.1ms, keeping gameplay smooth.

Please complete the following:

• I have added screenshots for all UI updates (N/A)
• I process any text displayed to the user through translateText() and I've added it to the en.json file (N/A)
• I have added relevant tests to the test directory (N/A)

Please put your Discord username so you can be contacted if a bug or regression is found:

blontd6

[coderabbitai]

Walkthrough

BorderComputePass.patchTile now avoids incremental updates during full recomputes and falls back to a full recompute when the scatter queue exceeds 2048 items.

Changes

Border compute safeguards

Layer / File(s)	Summary
Scatter queue safeguards src/client/render/gl/passes/BorderComputePass.ts	patchTile returns when globalDirty is set and marks a full recompute while clearing scatter when its count exceeds 2048.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• openfrontio/OpenFrontIO#4166: Introduced the incremental border scatter and globalDirty logic extended here.
• openfrontio/OpenFrontIO#4303: Also changed neighbor-region queuing in BorderComputePass.patchTile.

Poem

Scatter queues grow, then clear the way,
Full recomputes step in to stay.
Borders refresh with steady light,
Neighbors wait for a cleaner flight.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The patch only adds a border-update fallback and does not deliver the waterNukes terrain, minimap, navigation, and packet-sync work described in #3604.	If this is meant to close #3604, include the waterNukes feature work or retarget this PR to the follow-up performance fix.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: falling back to a full border recompute on large tile-update bursts.
Description check	✅ Passed	The description matches the change and stays on-topic, describing the lag fix and border recompute fallback.
Out of Scope Changes check	✅ Passed	The only code change is a border recompute safeguard, which stays aligned with the performance goal and adds no unrelated behavior.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[coderabbitai]

🧹 Nitpick comments (1)

src/client/render/gl/passes/BorderComputePass.ts (1)

200-200: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Consider extracting the 2048 threshold into a named constant.

A named constant such as SCATTER_FULL_RECOMPUTE_THRESHOLD would make the intent self-documenting and simplify future tuning.

♻️ Optional refactor

+private static readonly SCATTER_FULL_RECOMPUTE_THRESHOLD = 2048;
+
   patchTile(x: number, y: number, prevOwner: number, newOwner: number): void {
     if (this.globalDirty) return;
-    if (this.scatter.count > 2048) {
+    if (this.scatter.count > BorderComputePass.SCATTER_FULL_RECOMPUTE_THRESHOLD) {

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/client/render/gl/passes/BorderComputePass.ts` at line 200, Extract the
literal 2048 used in the condition within BorderComputePass into a named
constant such as SCATTER_FULL_RECOMPUTE_THRESHOLD, then use that constant in
place of the literal while preserving the existing comparison behavior.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/client/render/gl/passes/BorderComputePass.ts`:
- Line 200: Extract the literal 2048 used in the condition within
BorderComputePass into a named constant such as
SCATTER_FULL_RECOMPUTE_THRESHOLD, then use that constant in place of the literal
while preserving the existing comparison behavior.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 1858e443-5805-4391-938c-0857d989cb18

📥 Commits

Reviewing files that changed from the base of the PR and between d766913 and bb184fa.

📒 Files selected for processing (1)

• src/client/render/gl/passes/BorderComputePass.ts

[evanpelle]

thanks!