shaka-project · avelad · Sep 12, 2023 · Sep 11, 2023 · Sep 11, 2023 · Sep 12, 2023
diff --git a/lib/text/ui_text_displayer.js b/lib/text/ui_text_displayer.js
@@ -617,7 +617,15 @@ shaka.text.UITextDisplayer = class {
     // TODO: Implement line alignment with line number.
     // TODO: Implement lineAlignment of 'CENTER'.
     if (cue.line != null) {
-      if (cue.lineInterpretation == Cue.lineInterpretation.PERCENTAGE) {
+      let lineInterpretation = cue.lineInterpretation;
+      // HACK: the current implementation of UITextDisplayer only handled
+      // PERCENTAGE, as cue.line=0 is zero, we can interpret it as percentage
+      // safely.
+      if (cue.line == 0 &&
+          lineInterpretation == Cue.lineInterpretation.LINE_NUMBER) {
+        lineInterpretation = Cue.lineInterpretation.PERCENTAGE;
+      }
+      if (lineInterpretation == Cue.lineInterpretation.PERCENTAGE) {
         style.position = 'absolute';
         if (cue.writingMode == Cue.writingMode.HORIZONTAL_TOP_TO_BOTTOM) {
           style.width = '100%';

diff --git a/test/test/assets/screenshots/chrome-Android/webvtt-ui-line-0.png b/test/test/assets/screenshots/chrome-Android/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/chrome-Linux/webvtt-ui-line-0.png b/test/test/assets/screenshots/chrome-Linux/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/chrome-Mac/webvtt-ui-line-0.png b/test/test/assets/screenshots/chrome-Mac/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/chrome-Windows/webvtt-ui-line-0.png b/test/test/assets/screenshots/chrome-Windows/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/firefox-Linux/webvtt-ui-line-0.png b/test/test/assets/screenshots/firefox-Linux/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/firefox-Mac/webvtt-ui-line-0.png b/test/test/assets/screenshots/firefox-Mac/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/firefox-Windows/webvtt-ui-line-0.png b/test/test/assets/screenshots/firefox-Windows/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/msedge-Linux/webvtt-ui-line-0.png b/test/test/assets/screenshots/msedge-Linux/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/msedge-Mac/webvtt-ui-line-0.png b/test/test/assets/screenshots/msedge-Mac/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/msedge-Windows/webvtt-ui-line-0.png b/test/test/assets/screenshots/msedge-Windows/webvtt-ui-line-0.png
diff --git a/test/test/assets/screenshots/safari-Mac/text-displayer-native-basic-cue.png b/test/test/assets/screenshots/safari-Mac/text-displayer-native-basic-cue.png
diff --git a/test/test/assets/screenshots/safari-Mac/webvtt-ui-line-0.png b/test/test/assets/screenshots/safari-Mac/webvtt-ui-line-0.png
diff --git a/test/text/web_vtt_layout_integration.js b/test/text/web_vtt_layout_integration.js
@@ -213,7 +213,6 @@ filterDescribe('WebVTT layout', shaka.test.TextLayoutTests.supported, () => {
       await helper.checkScreenshot('line-negative-2');
     });
 
-    // FIXME: UI version is wrong: not positioned by line
     it('line 0', async () => {
       parseAndDisplay([
         'WEBVTT\n',