feat(chart): refine viewport interaction and rendering

src/utils/formatters.test.ts

@@ -40,10 +40,11 @@ describe('waveform number formatters', () => {
     expect(formatScientificAxisExponent(0.0001, 0.0003)).toBe('E-04')
   })
 
-  it('derives the exponent from Math.max(axisMin, axisMax)', () => {
+  it('derives the exponent from the largest absolute endpoint', () => {
     expect(resolveScientificAxisExponent(-9000, -1000)).toBe(3)
-    expect(resolveScientificAxisExponent(-10_000, 3000)).toBe(3)
-    expect(resolveScientificAxisExponent(-1000, 0)).toBeNull()
+    expect(resolveScientificAxisExponent(-100_000, -3000)).toBe(5)
+    expect(resolveScientificAxisExponent(-10_000, 3000)).toBe(4)
+    expect(resolveScientificAxisExponent(-1000, 0)).toBe(3)
     expect(resolveScientificAxisExponent(0, 0)).toBeNull()
   })
 

src/utils/formatters.ts

@@ -42,8 +42,7 @@ export function shouldUseScientificAxisLabel(maxAbsoluteValue: number): boolean
 export function resolveScientificAxisExponent(axisMin?: number, axisMax?: number): number | null {
   if (typeof axisMin !== 'number' || typeof axisMax !== 'number') return null
 
-  const maxValue = Math.max(axisMin, axisMax)
-  const absoluteMaxValue = Math.abs(maxValue)
+  const absoluteMaxValue = Math.max(Math.abs(axisMin), Math.abs(axisMax))
   return shouldUseScientificAxisLabel(absoluteMaxValue)
     ? Math.floor(Math.log10(absoluteMaxValue))
     : null

src/utils/sampling.ts

@@ -37,7 +37,8 @@ export function downsampleLTTB(data: WaveformPoint[], threshold: number): Wavefo
 
   // 确保阈值至少为 3
   const sampledLength = Math.max(3, Math.floor(threshold))
-  const sampled: WaveformPoint[] = new Array(sampledLength)
+  const sampled: WaveformPoint[] = []
+  sampled.length = sampledLength
 
   // 始终保留第一个和最后一个点
   sampled[0] = data[0]!