Improve settings

src/page/eraser-size-control.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from 'vitest';
+
+import { appConfig } from '../config';
+import {
+  getEraserSizeFromSliderRatio,
+  getEraserSliderRatioFromSize,
+} from './eraser-size-control';
+
+describe('eraser size slider mapping', () => {
+  it('maps slider position quadratically to eraser size', () => {
+    const { max, min } = appConfig.toolbar.eraser;
+
+    expect(getEraserSizeFromSliderRatio(0)).toBe(min);
+    expect(getEraserSizeFromSliderRatio(0.5)).toBe(min + (max - min) * 0.25);
+    expect(getEraserSizeFromSliderRatio(1)).toBe(max);
+  });
+
+  it('maps eraser size back to the inverse slider position', () => {
+    const { max, min } = appConfig.toolbar.eraser;
+    const quarterRangeSize = min + (max - min) * 0.25;
+
+    expect(getEraserSliderRatioFromSize(min)).toBe(0);
+    expect(getEraserSliderRatioFromSize(quarterRangeSize)).toBe(0.5);
+    expect(getEraserSliderRatioFromSize(max)).toBe(1);
+  });
+});