A custom curve is stored as cubic-bezier(x1, y1, x2, y2). The keyframe inspector provides a visual editor plus numeric fields.
Axis bounds
How evaluation works
For each normalized time x, the evaluator solves the Bézier curve’s parametric X position to find parameter t, then evaluates the Y curve at that t. It uses iterative Newton steps followed by bounded binary refinement, producing a stable value for each frame.
Build a restrained entrance
Start from Smooth (0.16, 1, 0.3, 1). Reduce the early Y control when the layer arrives too abruptly, or move x1 right when it should hold longer before accelerating. Apply the curve, then review at normal speed.
Overshoot implications
Y values below 0 or above 1 can drive a property outside the endpoint range. This can briefly create negative-looking offsets, scale beyond the final value, or opacity that is later clamped. Inspect intermediate canvas bounds and crop.
A visually dramatic curve preview can be almost invisible across a two-frame interval or excessive across a long interval. Curve and duration must be designed together.
