Improve waveform selection behaviour

frontend/src/App.tsx

@@ -210,26 +210,26 @@ function App(): JSX.Element {
 
       setPositionFromFrame(newViewport.start);
     },
-    [mediaSet, audio, video]
+    [mediaSet, audio, video, selection]
   );
 
   // handler called when the selection in the main waveform view is changed.
   const handleWaveformSelectionChange = useCallback(
-    (selection: Frames) => {
-      setSelection(selection);
+    (newSelection: Frames) => {
+      setSelection(newSelection);
 
       if (mediaSet == null) {
         return;
       }
 
       // move playback position to start of selection
-      const ratio = selection.start / mediaSet.audioFrames;
+      const ratio = newSelection.start / mediaSet.audioFrames;
       const currentTime =
         (mediaSet.audioFrames / mediaSet.audioSampleRate) * ratio;
       audio.currentTime = currentTime;
       video.currentTime = currentTime;
     },
-    [mediaSet, audio, video]
+    [mediaSet, audio, video, selection]
   );
 
   const handlePlay = useCallback(() => {

frontend/src/Waveform.tsx

@@ -71,30 +71,20 @@ export const Waveform: React.FC<Props> = ({
       setPositionPixels(null);
       return;
     }
-    const logicalPixelsPerFrame =
-      CanvasLogicalWidth / (viewport.end - viewport.start);
-    const positionPixels = (frame - viewport.start) * logicalPixelsPerFrame;
+    const pixelsPerFrame = CanvasLogicalWidth / (viewport.end - viewport.start);
+    const positionPixels = (frame - viewport.start) * pixelsPerFrame;
     setPositionPixels(positionPixels);
   }, [mediaSet, position, viewport]);
 
   // update selectedPixels on viewport change
   useEffect(() => {
-    const start = frameToCanvasX(selectedFrames.start);
-    const end = frameToCanvasX(selectedFrames.end);
-
-    // more verbose than it has to be to make TypeScript happy
-    if (start == null && end == null) {
-      setSelectedPixels({ start: 0, end: 0 });
-    } else if (start == null && end != null) {
-      setSelectedPixels({ start: 0, end: end });
-    } else if (start != null && end == null) {
-      setSelectedPixels({ start: 0, end: CanvasLogicalWidth });
-    } else if (start != null && end != null) {
-      setSelectedPixels({ start, end });
-    } else {
-      console.error('unreachable');
-    }
-  }, [viewport]);
+    const start = Math.max(frameToCanvasX(selectedFrames.start), 0);
+    const end = Math.min(
+      frameToCanvasX(selectedFrames.end),
+      CanvasLogicalWidth
+    );
+    setSelectedPixels({ start, end });
+  }, [viewport, selectedFrames]);
 
   // handlers
 
@@ -112,26 +102,18 @@ export const Waveform: React.FC<Props> = ({
       setSelectedFrames(selectedFrames);
       onSelectionChange(selectedFrames);
     },
-    [viewport]
+    [viewport, selectedFrames]
   );
 
   // helpers
 
   const frameToCanvasX = useCallback(
-    (frame: number): number | null => {
-      if (mediaSet == null) {
-        return null;
-      }
-
-      if (frame < viewport.start || frame > viewport.end) {
-        return null;
-      }
-
+    (frame: number): number => {
       const pixelsPerFrame =
         CanvasLogicalWidth / (viewport.end - viewport.start);
-      return (frame - viewport.start) * pixelsPerFrame;
+      return Math.round((frame - viewport.start) * pixelsPerFrame);
     },
-    [mediaSet, viewport]
+    [viewport]
   );
 
   // render component