[CircularProgressIndicator] Full circle track has seam artifact due to cap overlap at 0°

Description

When CircularDrawingDelegate.drawArc() draws a full circle (360°) track, there is a visible seam artifact at the 0° position where the start and end points overlap.

Root Cause

drawArc() always has a start/end point. When cornerRadius > 0:

With Cap.ROUND: Two round caps overlap at 0°, creating a visible bump
With drawRoundedBlock: Two rounded blocks overlap at the same position

The ROUND_CAP_RAMP_DOWN logic extends the arc beyond 360° to hide caps, but anti-aliasing still produces a visible rendering artifact at the seam.

CircularProgressIndicator.mov

Expected Behavior

A full circle track should render as a perfect circle with no visible seam or artifact.

Proposed Fix

When arcDegree >= 360f and the path is not wavy, use canvas.drawOval() instead of canvas.drawArc(). drawOval has no start/end point concept, so the seam artifact is eliminated entirely.

	`drawArc` (current)	`drawOval` (proposed)
Start/end point	Exists (0° seam)	None
Cap needed	ROUND/BUTT + roundedBlock	Unnecessary (BUTT suffices)
360° rendering	Cap overlap artifact	Perfect circle

Partial arcs (indicators) continue to use the existing drawArc logic unchanged.

Affected Component

CircularDrawingDelegate.java - drawArc() method

Additional Context: Reproduction with Theme.Material3.DayNight.NoActionBar

This artifact is reproducible when using Theme.Material3.DayNight.NoActionBar as the app theme with a CircularProgressIndicator configured as follows:

<style name="Widget.App.CircularProgressIndicator" parent="Widget.MaterialComponents.CircularProgressIndicator">
    <item name="indicatorInset">0dp</item>
    <item name="android:indeterminate">true</item>
    <item name="trackCornerRadius">8dp</item>
    <item name="trackColor">#1F000000</item>
</style>

When trackCornerRadius > 0 and the track draws a full 360° circle, the seam becomes visible at the 0° position. The artifact is most noticeable on the track (not the indicator), since the track is always a complete circle.

The higher the trackCornerRadius value, the more prominent the artifact becomes — because larger corner radii produce larger caps/rounded blocks that overlap more visibly at the start/end junction.

This does not depend on the specific theme; any Material3 theme that renders a full-circle CircularProgressIndicator track with a non-zero trackCornerRadius will exhibit this behavior.

[CircularProgressIndicator] Fix full circle track seam artifact

Navigation Menu

Repository navigation

[CircularProgressIndicator] Full circle track has seam artifact due to cap overlap at 0° #5027

Description

Root Cause

Expected Behavior

Proposed Fix

Affected Component

Additional Context: Reproduction with Theme.Material3.DayNight.NoActionBar

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

[CircularProgressIndicator] Full circle track has seam artifact due to cap overlap at 0° #5027

Description

Description

Root Cause

Expected Behavior

Proposed Fix

Affected Component

Activity

Nanamare commented on Mar 18, 2026

Additional Context: Reproduction with Theme.Material3.DayNight.NoActionBar

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions