performance updates

KJamsCloneTests/KJamsCloneTests.swift

@@ -2476,3 +2476,28 @@ extension KJamsCloneTests {
         queue.stop();XCTAssertTrue(system.a.player.playing,"Stopping automation preserves current playback")
     }
 }
+
+
+extension KJamsCloneTests {
+    @MainActor func testSpectrumScrollMovesCachedPixelsWithoutRebuildingEveryFrame() async throws {
+        let file = try XCTUnwrap(Bundle(for:Self.self).resourceURL?.appendingPathComponent("Fixtures/Demo.mp3"))
+        let player = Player(persistsMix:false);defer { player.stop() }
+        try player.load(.init(id:1,title:"Scroll",audio:file.path,cdg:nil,rating:0,plays:0),startPlaying:false)
+        for _ in 0..<100 where player.waveformLoading { try await Task.sleep(nanoseconds:20_000_000) }
+        XCTAssertFalse(player.waveform.isEmpty)
+        let view = DJNativeSpectrumView(frame:NSRect(x:0,y:0,width:600,height:100))
+        view.player = player;view.span = 2;view.spectralWaveforms = true
+        func snapshot() throws -> Data {
+            let bitmap = try XCTUnwrap(view.bitmapImageRepForCachingDisplay(in:view.bounds))
+            view.cacheDisplay(in:view.bounds,to:bitmap)
+            return Data(bytes:try XCTUnwrap(bitmap.bitmapData),count:bitmap.bytesPerRow*bitmap.pixelsHigh)
+        }
+        player.seek(1);let first = try snapshot(),builds = view.waveformTileBuildCount
+        XCTAssertGreaterThan(builds,0)
+        player.seek(1.01);let second = try snapshot()
+        XCTAssertEqual(view.waveformTileBuildCount,builds,"Playback frames translate cached waveform pixels rather than rebinning the spectrum")
+        XCTAssertNotEqual(first,second,"The spectrum must move as source position advances")
+        view.frame.size.width = 640;_ = try snapshot()
+        XCTAssertGreaterThan(view.waveformTileBuildCount,builds,"Changing window size must rebuild sharp waveform tiles")
+    }
+}