Android: some MusicXML files fail to fully render and cursor becomes unusable (works on Web)

[AndreiGorelov]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

On Android, this attached MusicXML file does not render fully, and cursor functionality is not usable because rendering fails.
The same file renders correctly in the Web target (tested on https://alphatab.net/).

score.xml

Expected Behavior

The same MusicXML should render fully on Android, and cursor behavior should work normally (including playback/user interaction scenarios), just like in Web target.

Steps To Reproduce

1. Create a simple Android app screen that hosts alphaTab
2. Enable user interaction and cursor in settings, for example:

val settings = alphaTab.Settings().apply {
            player.playerMode = PlayerMode.EnabledAutomatic
            player.enableCursor = true
            player.enableAnimatedBeatCursor = true
            player.enableUserInteraction = true
            player.scrollMode = ScrollMode.OffScreen
            display.scale = 0.8
        }

3. Load the attached MusicXML file (score.xml).
4. Observe that rendering is incomplete/fails and cursor behavior is broken on Android.

Link to jsFiddle, CodePen, Project

No response

Version and Environment

1. alphaTab version: 1.8.1
2. Platform: Android (Kotlin)
3. Devices: Android 14/16 tablet and phone

Platform

Android (Native)

Anything else?

I got stack traces from AlphaTabApiBase.onError on Android for the same file:

• NullPointerException

 0 = {StackTraceElement@34817} "alphaTab.rendering.utils.AccidentalHelper.getNoteSteps(AccidentalHelper.kt:240)"
 1 = {StackTraceElement@34818} "alphaTab.rendering.ScoreBarRenderer.getNoteSteps(ScoreBarRenderer.kt:383)"
 2 = {StackTraceElement@34819} "alphaTab.rendering.glyphs.ScoreBeatGlyph._createNoteGlyphs(ScoreBeatGlyph.kt:307)"
 3 = {StackTraceElement@34820} "alphaTab.rendering.glyphs.ScoreBeatGlyph._createGlyphs(ScoreBeatGlyph.kt:251)"
 4 = {StackTraceElement@34821} "alphaTab.rendering.glyphs.ScoreBeatGlyph.doLayout(ScoreBeatGlyph.kt:218)"
 5 = {StackTraceElement@34822} "alphaTab.rendering.glyphs.BeatContainerGlyph.doLayout(BeatContainerGlyph.kt:216)"
 6 = {StackTraceElement@34823} "alphaTab.rendering.ScoreBeatContainerGlyph.doLayout(ScoreBeatContainerGlyph.kt:99)"
 7 = {StackTraceElement@34824} "alphaTab.rendering.glyphs.MultiVoiceContainerGlyph.doLayout(MultiVoiceContainerGlyph.kt:335)"
 8 = {StackTraceElement@34825} "alphaTab.rendering.BarRendererBase.createBeatGlyphs(BarRendererBase.kt:641)"
 9 = {StackTraceElement@34826} "alphaTab.rendering.BarRendererBase.doLayout(BarRendererBase.kt:444)"
 10 = {StackTraceElement@34827} "alphaTab.rendering.LineBarRenderer.doLayout(LineBarRenderer.kt:111)"
 11 = {StackTraceElement@34828} "alphaTab.rendering.staves.RenderStaff.addBar(RenderStaff.kt:244)"
 12 = {StackTraceElement@34829} "alphaTab.rendering.staves.StaffSystem.addBars(StaffSystem.kt:232)"
 13 = {StackTraceElement@34830} "alphaTab.rendering.layout.VerticalLayoutBase._createStaffSystem(VerticalLayoutBase.kt:426)"
 14 = {StackTraceElement@34831} "alphaTab.rendering.layout.VerticalLayoutBase._layoutAndRenderScore(VerticalLayoutBase.kt:315)"
 15 = {StackTraceElement@34832} "alphaTab.rendering.layout.VerticalLayoutBase.doLayoutAndRender(VerticalLayoutBase.kt:75)"
 16 = {StackTraceElement@34833} "alphaTab.rendering.layout.ScoreLayout.layoutAndRender(ScoreLayout.kt:143)"
 17 = {StackTraceElement@34834} "alphaTab.rendering.ScoreRenderer._layoutAndRender(ScoreRenderer.kt:279)"
 18 = {StackTraceElement@34835} "alphaTab.rendering.ScoreRenderer.render(ScoreRenderer.kt:244)"
 19 = {StackTraceElement@34836} "alphaTab.rendering.ScoreRenderer.renderScore(ScoreRenderer.kt:153)"
 20 = {StackTraceElement@34837} "alphaTab.rendering.ScoreRendererWrapper.renderScore(ScoreRendererWrapper.kt:159)"
 21 = {StackTraceElement@34838} "alphaTab.AlphaTabApiBase.render(AlphaTabApiBase.kt:556)"
 22 = {StackTraceElement@34839} "alphaTab.AlphaTabApiBase._internalRenderTracks(AlphaTabApiBase.kt:429)"
 23 = {StackTraceElement@34840} "alphaTab.AlphaTabApiBase.renderScore(AlphaTabApiBase.kt:386)"
 24 = {StackTraceElement@34841} "alphaTab.AlphaTabApiBase.renderScore$default(AlphaTabApiBase.kt:348)"
 25 = {StackTraceElement@34842} "alphaTab.AlphaTabView.renderTracks(AlphaTabView.kt:115)"
 26 = {StackTraceElement@34843} "alphaTab.AlphaTabView.setTracks(AlphaTabView.kt:29)"

• ClassCastException

0 = {StackTraceElement@34703} "alphaTab.model.MusicFontSymbol$Companion.fromValue(MusicFontSymbol.kt:621)"
1 = {StackTraceElement@34704} "alphaTab.rendering.LineBarRenderer._paintTupletHelper(LineBarRenderer.kt:371)"
2 = {StackTraceElement@34705} "alphaTab.rendering.LineBarRenderer.paintTuplets(LineBarRenderer.kt:224)"
3 = {StackTraceElement@34706} "alphaTab.rendering.LineBarRenderer.paintTuplets$default(LineBarRenderer.kt:216)"
4 = {StackTraceElement@34707} "alphaTab.rendering.LineBarRenderer.paintContent(LineBarRenderer.kt:137)"
5 = {StackTraceElement@34708} "alphaTab.rendering.BarRendererBase.paint(BarRendererBase.kt:560)"
6 = {StackTraceElement@34709} "alphaTab.rendering.staves.RenderStaff.paint(RenderStaff.kt:368)"
7 = {StackTraceElement@34710} "alphaTab.rendering.staves.StaffSystem.paintPartial(StaffSystem.kt:579)"
8 = {StackTraceElement@34711} "alphaTab.rendering.staves.StaffSystem.paint(StaffSystem.kt:533)"
9 = {StackTraceElement@34712} "alphaTab.rendering.layout.VerticalLayoutBase._paintSystem$lambda$0(VerticalLayoutBase.kt:344)"
10 = {StackTraceElement@34713} "alphaTab.rendering.layout.VerticalLayoutBase$$ExternalSyntheticLambda1.invoke(D8$$SyntheticClass:0)"
11 = {StackTraceElement@34714} "alphaTab.rendering.layout.ScoreLayout._internalRenderLazyPartial(ScoreLayout.kt:179)"
12 = {StackTraceElement@34715} "alphaTab.rendering.layout.ScoreLayout.renderLazyPartial(ScoreLayout.kt:190)"
13 = {StackTraceElement@34716} "alphaTab.rendering.ScoreRenderer.renderResult(ScoreRenderer.kt:195)"
14 = {StackTraceElement@34717} "alphaTab.rendering.ScoreRendererWrapper.renderResult(ScoreRendererWrapper.kt:166)"
15 = {StackTraceElement@34718} "alphaTab.platform.android.AndroidUiFacade.initialize$lambda$0(AndroidUiFacade.kt:123)"
16 = {StackTraceElement@34719} "alphaTab.platform.android.AndroidUiFacade$$ExternalSyntheticLambda6.invoke(D8$$SyntheticClass:0)"
17 = {StackTraceElement@34720} "alphaTab.platform.android.AlphaTabRenderSurface.onLayout(AlphaTabRenderSurface.kt:159)"

[AndreiGorelov]

I’ve made fixes in my fork for this issue:

• NullPointerException in  AccidentalHelper.getNoteSteps AndreiGorelov@bea62a3
  As I understand, the issue on Android stems from the processing order. I suspect my fix doesn’t address the root cause perfectly, but I couldn’t come up with a better solution yet (still getting familiar with the codebase).
• ClassCastException in LineBarRenderer._paintTupletHelper AndreiGorelov@681c64b

  From what I can tell, the attached file contains non-standard tuplets (12:27) that the previous logic didn’t account for. Additionally, Kotlin’s stricter type handling triggered the error. Unfortunately, I don’t have a musical background, so I’m not entirely confident in the quality of my fix.

[AndreiGorelov]

Maybe these non‑standard “time signatures” don’t need to be displayed at all?

How it looks now:

• https://alphatab.net/

• Android app with my fixes

• MuseScore (similar file)

• Some PDF version

[AndreiGorelov]

This set of fixes will likely resolve the issue:
AndreiGorelov@567cbb0
AndreiGorelov@628c1e3
AndreiGorelov@9684ee7

The fixes affect rendering — I’ve added handling for MusicXML tags that control tuplets’ visibility and updated how visible tuplets are processed (though I’m still consulting with musicians about this).

The screenshot shows the same section of the problematic file after applying my fixes.

Since these changes significantly modify rendering, they also impact test results (test-web).

Snapshot Summary

  1436 passing (27s)
  12 failing

  1) MusicXmlImporterSamplesTests
       FaurReveSample:
     Error: Difference between original and new image is too big: 465/261881 (0.18%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterSamples.test.ts:37:9)

  2) MusicXmlImporterSamplesTests
       SchbAvMaSample:
     Error: Difference between original and new image is too big: 9061/525346 (1.72%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterSamples.test.ts:65:9)

  3) MusicXmlImporterTestSuiteTests
       23a-Tuplets:
     Error: Difference between original and new image is too big: 480/18494 (2.60%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterTestSuite.test.ts:272:9)

  4) MusicXmlImporterTestSuiteTests
       23b-Tuplets-Styles:
     Error: Difference between original and new image is too big: 2061/74202 (2.78%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterTestSuite.test.ts:277:9)

  5) MusicXmlImporterTestSuiteTests
       23c-Tuplet-Display-NonStandard:
     Error: Difference between original and new image is too big: 618/38556 (1.60%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterTestSuite.test.ts:282:9)

  6) MusicXmlImporterTestSuiteTests
       23d-Tuplets-Nested:
     Error: Difference between original and new image is too big: 1410/16630 (8.48%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterTestSuite.test.ts:289:9)

  7) MusicXmlImporterTestSuiteTests
       33a-Spanners:
     Error: Difference between original and new image is too big: 108/54705 (0.20%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterTestSuite.test.ts:382:9)

  8) MusicXmlImporterTestSuiteTests
       33j-Beams-Tremolos:
     Error: Difference between original and new image is too big: 485/13130 (3.69%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterTestSuite.test.ts:438:9)

  9) MusicXmlImporterTestSuiteTests
       34a-Print-Object-Spanners:
     Error: Difference between original and new image is too big: 220/33424 (0.66%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterTestSuite.test.ts:443:9)

  10) MusicXmlImporterTestSuiteTests
       34b-Colors:
     Error: Difference between original and new image is too big: 234/75232 (0.31%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async MusicXmlImporterTestHelper.testReferenceFile (test/importer/MusicXmlImporterTestHelper.ts:85:13)
      at async Context.<anonymous> (test/importer/MusicXmlImporterTestSuite.test.ts:449:9)

  11) EffectsAndAnnotationsTests
       tuplets-advanced:
     Error: Difference between original and new image is too big: 2065/312449 (0.66%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async VisualTestHelper.runVisualTest (test/visualTests/VisualTestHelper.ts:87:9)
      at async Context.<anonymous> (test/visualTests/features/EffectsAndAnnotations.test.ts:123:9)

  12) SpecialTracksTests
       slash:
     Error: Difference between original and new image is too big: 1109/64682 (1.71%)
      at VisualTestHelper._expectToEqualVisuallyAsync (test/visualTests/VisualTestHelper.ts:397:19)
      at async VisualTestHelper.compareVisualResult (test/visualTests/VisualTestHelper.ts:300:13)
      at async VisualTestHelper.runVisualTestFull (test/visualTests/VisualTestHelper.ts:179:21)
      at async VisualTestHelper.runVisualTest (test/visualTests/VisualTestHelper.ts:87:9)
      at async Context.<anonymous> (test/visualTests/features/SpecialTracks.test.ts:20:9)

What you think about it?