Fractional zoom level in tile URLs. (Edit)

[danallsop]

Migrated from: Leaflet#9930
Original author: danallsop
Original created: 2025-10-06T10:59:11Z

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Checklist

• I've looked at the documentation to make sure the behavior isn't documented and expected.
• I'm sure this is an issue with Leaflet, not with my app or other dependencies (Angular, Cordova, React, etc.).
• I've searched through the current issues to make sure this hasn't been reported yet.
• I agree to follow the Code of Conduct that this project adheres to.

Steps to reproduce

When having non-integer zoomSnap option and calling map.redraw() method, it may result in fractional zoom level in tile URL, like 2.4396229271192125/0/2. It can happen after view is set by setView(), fitBounds() or similar methods. Zooming in and out by mouse wheel normalizes the situation and map is loaded.
Seems this place in code is missing Math.round() call:
https://github.com/Leaflet/Leaflet/blob/2f5594810c26aa87019582d381960f1b10c1bf62/src/layer/tile/GridLayer.js#L235

Expected behavior

Tiles are always requested with integer coordinates.

Current behavior

Tiles may be requested with fractional Z coordinate.

Minimal example reproducing the issue

No response

Environment

• Leaflet version: 1.9.4

[danallsop]

Comments (1 total)

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Comment by: danallsop on 2025-10-06T11:28:40Z

Workaround with monkey-patching if somebody encountered this bug:

    L.GridLayer.prototype.redraw = function() {
        if (this._map) {
			this._removeAllTiles();
			const tileZoom = this._clampZoom(Math.round(this._map.getZoom()));
			if (tileZoom !== this._tileZoom) {
				this._tileZoom = tileZoom;
				this._updateLevels();
			}
			this._update();
		}
		return this;
    }

[devin-ai-integration]

[Automated] Bug qualifies for automated remediation. Starting feasibility assessment...

Orchestrator: https://app.devin.ai/sessions/6661e4e131bf44388042f03afbdb4780
Pipeline: bug_intake ✓ → feasibility_check (in progress) → bug_reproduce → root_cause_analysis → generate_solution → implement_fix (branch push, no PR)

[devin-ai-integration]

[Automated] Feasibility assessment complete.

• feasibility_score: 85
• automation_recommended: true
• complexity: Low
• estimated_effort: minutes
• confidence: High

Proceeding to bug reproduction.

[devin-ai-integration]

[Automated] Unable to reproduce bug. Remediation pipeline stopped.

Details: Already fixed in current main. TileLayer._clampZoom at src/layer/tile/TileLayer.js:288-290 wraps super._clampZoom() in Math.round(), so _tileZoom is always integer and tile URLs are never fractional. Three reproduction variants (zoomSnap 0.25 + setView(2.4), zoomSnap 0.25 + fitBounds, zoomSnap 0 + setView(2.4396229271192125)) all produced integer z in tile URLs.

Environment: Node v24.12.0, Chrome Headless 147, leaflet@2.0.0-alpha.1 on main.

[devin-ai-integration]

[Automated] Starting bug reproduction phase.

Orchestrator: https://app.devin.ai/sessions/b1a0569bc0fe48479aa4a1f3c1acace7
Pipeline: bug_intake ✓ → feasibility_check ✓ → bug_reproduce (in progress) → root_cause_analysis → generate_solution → implement_fix (branch push, no PR)

[devin-ai-integration]

[Automated] Starting bug reproduction phase.

Orchestrator: https://app.devin.ai/sessions/7f293b93d2764929ba61f9617cc4cd48
Pipeline: bug_intake ✓ → feasibility_check ✓ → bug_reproduce (in progress) → root_cause_analysis → generate_solution → implement_fix (branch push, no PR)

[devin-ai-integration]

[Automated] Starting bug reproduction phase.

Orchestrator: https://app.devin.ai/sessions/933d3d12407d477cba67496061e4c558
Pipeline: bug_intake ✓ → feasibility_check ✓ → bug_reproduce (in progress) → root_cause_analysis → generate_solution → implement_fix (branch push, no PR)

[devin-ai-integration]

[Automated] Unable to reproduce bug. Remediation pipeline stopped. Details: On current main (Leaflet 2.0.0-alpha.1), TileLayer overrides _clampZoom to Math.round(super._clampZoom(zoom)) (src/layer/tile/TileLayer.js:288-290), so the fractional value coming from this._map.getZoom() in GridLayer.redraw() (src/layer/tile/GridLayer.js:235) is rounded before it is stored in _tileZoom and before it appears in tile URLs. This fix was introduced in upstream PR Leaflet#8613 (commit 511f8f1, 'TileLayer rounds fractional zoom in url to integer {z}'), which is NEWER than the reporter's Leaflet 1.9.4. Reproduction attempts against current main with zoomSnap: 0.25 (setView to 2.4396), zoomSnap: 0 (setView to 2.4396), direct _zoom manipulation, and setView(2.3) all produced tile requests with integer Z only; 0/52 tile URL computations across the four scenarios had a fractional Z. The underlying GridLayer._clampZoom still does not round, so any subclass of GridLayer that does not override _clampZoom the way TileLayer does could still exhibit the issue, but this is not the case for the standard TileLayer described in the report.

[devin-ai-integration]

[Automated] Starting bug reproduction phase.

Orchestrator: https://app.devin.ai/sessions/85381ea81e72417b99ad59bf2f201e98
Pipeline: bug_intake ✓ → feasibility_check ✓ → bug_reproduce (in progress) → root_cause_analysis → generate_solution → implement_fix (branch push, no PR)