Yaowei Zheng
49 lines
1.6 KiB
TypeScript
49 lines
1.6 KiB
TypeScript
import { describe, expect, it } from "vitest";
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import { nearestSnap, project, rubberband } from "../src/lib/sheet-physics";
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describe("project", () => {
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it("zero velocity, zero displacement", () => {
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expect(project(0)).toBe(0);
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});
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it("matches the exponential-decay projection formula (1000px/s @ 0.998 ≈ 499px)", () => {
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expect(project(1000, 0.998)).toBeCloseTo(499, 0);
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expect(project(-1000, 0.998)).toBeCloseTo(-499, 0);
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});
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it("a lower decay rate projects shorter (0.99 stops faster than 0.998)", () => {
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expect(Math.abs(project(1000, 0.99))).toBeLessThan(Math.abs(project(1000, 0.998)));
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});
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});
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describe("rubberband", () => {
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it("more overshoot shows more, with diminishing increments (progressive damping)", () => {
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const d = 800;
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const r50 = rubberband(50, d);
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const r100 = rubberband(100, d);
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const r150 = rubberband(150, d);
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expect(r100).toBeGreaterThan(r50);
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expect(r150).toBeGreaterThan(r100);
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expect(r100 - r50).toBeGreaterThan(r150 - r100);
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});
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it("the displayed overshoot is always less than the actual overshoot", () => {
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expect(rubberband(100, 800)).toBeLessThan(100);
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expect(rubberband(1, 800)).toBeLessThan(1);
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});
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});
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describe("nearestSnap", () => {
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it("snaps to the nearest point", () => {
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const snaps = [0, 300, 800] as const;
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expect(nearestSnap(120, snaps)).toBe(0);
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expect(nearestSnap(180, snaps)).toBe(300);
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expect(nearestSnap(540, snaps)).toBe(300);
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expect(nearestSnap(700, snaps)).toBe(800);
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});
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it("exactly at the midpoint takes the earlier candidate", () => {
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expect(nearestSnap(150, [0, 300])).toBe(0);
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});
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});
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