Avoid pointless repaints of the grid when seeking video

Keep track of which lines are displayed on the current video frame so
that video seeks only have to repaint the grid when the set actually
changes. Speeds up video playback on non-fbf stuff by ~15%.

src/base_grid.cpp

@@ -98,7 +98,7 @@ BaseGrid::BaseGrid(wxWindow* parent, agi::Context *context)
 , context(context)
 , columns(GetGridColumns())
 , columns_visible(OPT_GET("Subtitle/Grid/Column")->GetListBool())
-, seek_listener(context->videoController->AddSeekListener([&] { Refresh(false); }))
+, seek_listener(context->videoController->AddSeekListener(&BaseGrid::OnSeek, this))
 {
 	scrollBar->SetScrollbar(0,10,100,10);
 
@@ -276,6 +276,24 @@ void BaseGrid::SelectRow(int row, bool addToSelected, bool select) {
 	}
 }
 
+void BaseGrid::OnSeek() {
+	int lines = GetClientSize().GetHeight() / lineHeight + 1;
+	lines = mid(0, lines, GetRows() - yPos);
+
+	auto it = begin(visible_rows);
+	for (int i : boost::irange(yPos, yPos + lines)) {
+		if (IsDisplayed(index_line_map[i])) {
+			if (it == end(visible_rows) || *it != i) {
+				Refresh(false);
+				return;
+			}
+			++it;
+		}
+	}
+	if (it != end(visible_rows))
+		Refresh(false);
+}
+
 void BaseGrid::OnPaint(wxPaintEvent &) {
 	// Find which columns need to be repainted
 	std::vector<char> paint_columns;
@@ -357,6 +375,7 @@ void BaseGrid::OnPaint(wxPaintEvent &) {
 
 	const auto active_line = context->selectionController->GetActiveLine();
 	auto const& selection = context->selectionController->GetSelectedSet();
+	visible_rows.clear();
 
 	for (int i : agi::util::range(nDraw)) {
 		wxBrush color = row_colors.Default;
@@ -369,8 +388,12 @@ void BaseGrid::OnPaint(wxPaintEvent &) {
 			color = row_colors.Selection;
 		else if (curDiag->Comment)
 			color = row_colors.Comment;
-		else if (OPT_GET("Subtitle/Grid/Highlight Subtitles in Frame")->GetBool() && IsDisplayed(curDiag))
+
+		if (OPT_GET("Subtitle/Grid/Highlight Subtitles in Frame")->GetBool() && IsDisplayed(curDiag)) {
+			if (color == row_colors.Default)
 				color = row_colors.Visible;
+			visible_rows.push_back(i + yPos);
+		}
 		dc.SetBrush(color);
 
 		// Draw row background color

src/base_grid.h

@@ -57,6 +57,9 @@ class BaseGrid final : public wxWindow {
 
 	int active_row = -1;
 
+	/// Rows which are visible on the current video frame
+	std::vector<int> visible_rows;
+
 	agi::Context *context; ///< Associated project context
 
 	std::vector<std::unique_ptr<GridColumn>> columns;
@@ -95,6 +98,7 @@ class BaseGrid final : public wxWindow {
 	void OnSize(wxSizeEvent &event);
 	void OnSubtitlesCommit(int type);
 	void OnActiveLineChanged(AssDialogue *);
+	void OnSeek();
 
 	void AdjustScrollbar();
 	void SetColumnWidths();