Easing Curves Cross-Platform

Easing curves define how animation values change over time, controlling acceleration and deceleration to create natural-feeling motion. Cross-platform design systems must translate easing curve definitions into platform-specific formats that produce visually equivalent results across iOS, Android, and web implementations.

What Are Easing Curves Cross-Platform

Easing curves mathematically describe animation timing. Linear easing moves at constant speed. Ease-in starts slow and accelerates. Ease-out decelerates toward the end. Ease-in-out combines both for smooth acceleration and deceleration.

Cubic bezier curves are the standard representation. Four control points define the curve shape. CSS, iOS, and Android all support cubic bezier specification, though syntax differs. This shared mathematical basis enables cross-platform consistency.

Platform conventions establish expected motion feel. Material Design defines specific easing curves for standard motion. iOS animations use characteristic curves that feel native to Apple platforms. Cross-platform design systems choose whether to follow platform conventions or maintain consistent custom curves.

How Easing Curves Work Across Platforms

Cubic bezier notation uses four values representing control point coordinates. The format (x1, y1, x2, y2) describes how the curve bends between start (0,0) and end (1,1) points.

Easing Curve Platform Syntax:

Standard Easing: cubic-bezier(0.4, 0, 0.2, 1)

CSS:
transition: all 200ms cubic-bezier(0.4, 0, 0.2, 1);
/* or predefined */
transition: all 200ms ease-in-out;

iOS (Core Animation):
let timing = CAMediaTimingFunction(controlPoints: 0.4, 0, 0.2, 1)

iOS (SwiftUI):
.animation(.timingCurve(0.4, 0, 0.2, 1, duration: 0.2))

Android (View Animation):
PathInterpolator(0.4f, 0f, 0.2f, 1f)

Android (Compose):
CubicBezierEasing(0.4f, 0f, 0.2f, 1f)

Common Curves:
- Standard (Material): (0.4, 0, 0.2, 1)
- Decelerate (entrance): (0, 0, 0.2, 1)
- Accelerate (exit): (0.4, 0, 1, 1)
- Linear: (0, 0, 1, 1)

Platform-specific APIs accept bezier values. CSS uses cubic-bezier() function. iOS CAMediaTimingFunction accepts control points. Android PathInterpolator and Compose CubicBezierEasing work similarly. The same four values produce equivalent curves.

Spring animations provide an alternative to bezier curves. Spring physics (mass, stiffness, damping) creates organic motion. iOS and Android support spring animations, but parameters do not map directly between platforms. Web spring support is more limited.

Key Considerations

• Same bezier values produce equivalent curves across platforms
• Spring animation parameters do not translate directly
• Platform conventions may prefer different curve characteristics
• Predefined platform curves simplify implementation
• Testing validates perceptual equivalence
• Documentation should include visual curve representations

Common Questions

How do design systems choose easing curves?

Material Design curves provide well-tested starting points. Standard, accelerate, and decelerate curves serve most animation needs. Using established curves leverages existing research.

Brand motion guidelines may specify custom curves. Organizations with distinctive motion identity may define proprietary curves that express brand personality.

Testing validates curve appropriateness. Curves should feel natural and serve animation purpose. User testing reveals whether easing aids or hinders comprehension.

Consistency within the design system matters more than specific curve choice. Using the same curves throughout creates cohesive motion feel.

Should cross-platform systems use platform-specific curves?

Platform-specific curves align with user expectations. iOS users expect iOS-native motion. Android users expect Material-style motion. Platform curves feel natural to platform users.

Unified curves provide consistent brand experience. Users encounter the same motion regardless of platform. This approach prioritizes brand over platform nativeness.

Hybrid approaches use platform curves for system-like interactions (navigation, feedback) and brand curves for distinctive branded moments.

Testing with platform users reveals preferences. Some users may not notice curve differences; others may find non-native curves jarring.

How do teams handle spring animation curves cross-platform?

Spring animation parameters (mass, stiffness, damping, initial velocity) do not translate directly. iOS and Android spring systems use similar concepts but different implementations.

Intent-based specification works better than parameter matching. Describe the desired feel (“bouncy with quick settle”) and tune parameters per platform to achieve that feel.

Comparative testing aligns platform implementations. Animate similar content on each platform, adjusting parameters until spring motion feels equivalent.

Some design systems avoid spring animations for cross-platform consistency, using bezier curves that translate directly. This trades natural feel for exact consistency.

Summary

Easing curves defined with cubic bezier control points translate directly across CSS, iOS, and Android platforms. Design systems should define standard curves as tokens that transform to platform-appropriate syntax. Spring animations require platform-specific parameter tuning to achieve perceptual equivalence. Consistent easing throughout the design system creates cohesive motion feel regardless of specific curve choice.