Easing Functions

The math2d package provides easing and interpolation functions. Import it with:

import "github.com/drpaneas/gosprite64/math2d"

Easing and interpolation

Lerp

Linearly interpolate between two scalar values. Unclamped - values of t outside 0..1 extrapolate.

math2d.Lerp(0, 100, 0.5)   // 50
math2d.Lerp(0, 100, 0.0)   // 0
math2d.Lerp(0, 100, 1.0)   // 100
math2d.Lerp(0, 100, 1.5)   // 150 (extrapolation)

InvLerp

The inverse of Lerp - given a value, find where it falls in a range as a 0..1 ratio:

math2d.InvLerp(0, 100, 50)   // 0.5
math2d.InvLerp(0, 100, 0)    // 0.0
math2d.InvLerp(0, 100, 100)  // 1.0

Remap

Map a value from one range to another. This is InvLerp followed by Lerp:

// Map health (0..100) to a bar width (0..64 pixels)
barWidth := math2d.Remap(health, 0, 100, 0, 64)

Clamp

Restrict a value to a range:

math2d.Clamp(150, 0, 100)  // 100
math2d.Clamp(-5, 0, 100)   // 0
math2d.Clamp(50, 0, 100)   // 50

MoveToward

Move a value toward a target by at most a fixed step. Useful for smooth following that arrives at the target in finite time (unlike lerp which asymptotically approaches).

// In Update(), smoothly move camera X toward player
cam.X = math2d.MoveToward(cam.X, playerX, 3)

If maxDelta is zero or negative, the value does not change. The function never overshoots the target.

Easing curves

Easing functions take a t in 0..1 and return a shaped 0..1 value. Combine them with Lerp to animate anything:

t := float32(frame) / float32(totalFrames)  // 0..1 over time

// Ease in (slow start, fast end)
x := math2d.Lerp(startX, endX, math2d.EaseInQuad(t))

// Ease out (fast start, slow end)
x := math2d.Lerp(startX, endX, math2d.EaseOutQuad(t))

// Ease in-out (slow start, fast middle, slow end)
x := math2d.Lerp(startX, endX, math2d.EaseInOutQuad(t))

Available curves:

SmoothStep

SmoothStep clamps the input to a range and applies Hermite interpolation. Useful for smooth thresholds:

// Fade alpha from 0 to 1 as distance goes from 50 to 100
alpha := math2d.SmoothStep(50, 100, distance)