gabrielobholz-corner-smoothing

Apple Corner Smoothing

Use path-based geometry when a design asks for Apple/iOS-like corner smoothing, especially the common 60% Figma Corner Smoothing look. CSS border-radius alone cannot express this shape.

Quick Reference

Need	Use
DOM/SVG rectangle	Generate a <path d="..."> from width, height, radius, smoothing
CSS-only component	Use clip-path: path("...") when acceptable, otherwise inline SVG
Canvas/WebGL	Use the same sampled superellipse points as a polygon/path
Figma parity	Treat 60% as the Apple/iOS-style target
Plain rounded corner	Use smoothing: 0

For copy-paste code, read implementation.md.

Core Principles

1. Do Not Fake It With Bigger Radius

Increasing border-radius changes the radius, not the corner transition. Apple-like smoothing keeps the same radius but eases the transition between straight edges and the corner.

2. Prefer Paths

Use SVG path data, clip-path: path(...), Canvas Path2D, or framework-specific vector paths. This avoids layout hacks, nested masks, pseudo-elements, and broken edge cases.

3. Keep Radius Clamped

Always clamp radius to min(width, height) / 2. This prevents self-intersecting paths when components become small or responsive.

4. Make 60% The Apple Target

When a user asks for Apple/iOS-style corners and gives no other value, use smoothing: 60. Use 0% for normal circular border-radius, 100% only for maximum stylization.

5. Preserve Layout

The smoothing path should affect only drawing/clipping. Do not change element width, height, padding, or layout metrics while animating smoothing.

6. Animate The Path, Not The Box

When animating smoothing, keep width, height, and radius stable and update only the generated path. If also animating labels or numbers, use fixed-size containers and tabular numbers.

Implementation Workflow

1. Read the requested width, height, radius, and smoothing percent.
2. If the target can be SVG, render a <path> and set its d attribute.
3. If the target must be HTML/CSS, use clip-path: path(...) only when browser support and scaling are acceptable; otherwise put an SVG behind or in front of the element.
4. Use smoothing: 60 for Apple/iOS-style unless the user specifies another value.
5. Validate at small sizes and at maximum radius.

Common Mistakes

Mistake	Fix
border-radius: 52px and calling it smoothing	Generate a smoothed path
Radius larger than half the box	Clamp radius
Layout changes during smoothing animation	Keep layout fixed and update path only
Using one-off path strings	Use a reusable function with radius and smoothing
Applying 100% by default	Use 60% for Apple/iOS-style
Using CSS masks that blur edges	Prefer SVG path or clean vector clip

Review Checklist

• Radius is clamped to half the smaller side
• smoothing: 60 is used for Apple/iOS-style unless specified otherwise
• The shape is path-based, not a border-radius-only approximation
• Width, height, and layout do not shift during smoothing changes
• The generated path works for square and rectangular shapes
• The component has a fallback or acceptable behavior if clip-path: path() is unsupported