[LyX/master] Avoid some full metrics computations related to math previews

[Jean-Marc Lasgouttes]

commit 5e8578837fea0321998eac04222102986261666d
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Mon Nov 27 15:13:56 2023 +0100

    Avoid some full metrics computations related to math previews
    
    When entering/leaving a math hull inset, a Update::Force flag was set,
    in case the metrics of the inset would change because of a switch
    between normal and preview representation.
    
    When entering the inset, this code is now used only when the inset was
    in preview mode.
    
    In both cases, Update::Force is replaced with Update::SinglePar.
    
    This requites in Text::dispatch to honor Update::SinglePar when it has
    been set by some lfun, even when singleparupdate is false.
    
    Part of bug #12297.
---
 src/Text.cpp                 |  2 +-
 src/mathed/InsetMathHull.cpp | 13 ++++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/Text.cpp b/src/Text.cpp
index d5a1069fa1..2684309dec 100644
--- a/src/Text.cpp
+++ b/src/Text.cpp
@@ -6386,7 +6386,7 @@ void Text::dispatch(Cursor & cur, FuncRequest & cmd)
 
 	// FIXME: the following code should go in favor of fine grained
 	// update flag treatment.
-	if (singleParUpdate) {
+	if (singleParUpdate || cur.result().screenUpdate() & Update::SinglePar) {
 		// Inserting characters does not change par height in general. So, try
 		// to update _only_ this paragraph. BufferView will detect if a full
 		// metrics update is needed anyway.
diff --git a/src/mathed/InsetMathHull.cpp b/src/mathed/InsetMathHull.cpp
index 94d293870d..34c319ea5c 100644
--- a/src/mathed/InsetMathHull.cpp
+++ b/src/mathed/InsetMathHull.cpp
@@ -902,7 +902,7 @@ bool InsetMathHull::notifyCursorLeaves(Cursor const & old, Cursor & cur)
 {
 	if (RenderPreview::previewMath()) {
 		reloadPreview(old);
-		cur.screenUpdateFlags(Update::Force);
+		cur.screenUpdateFlags(Update::SinglePar);
 	}
 	return false;
 }
@@ -2273,14 +2273,17 @@ void InsetMathHull::handleFont2(Cursor & cur, docstring const & arg)
 
 void InsetMathHull::edit(Cursor & cur, bool front, EntryDirection entry_from)
 {
+	bool const has_preview = previewState(&cur.bv());
 	cur.push(*this);
 	bool enter_front = (entry_from == Inset::ENTRY_DIRECTION_LEFT ||
 		(entry_from == Inset::ENTRY_DIRECTION_IGNORE && front));
 	enter_front ? idxFirst(cur) : idxLast(cur);
-	// The inset formula dimension is not necessarily the same as the
-	// one of the instant preview image, so we have to indicate to the
-	// BufferView that a metrics update is needed.
-	cur.screenUpdateFlags(Update::Force);
+	if (has_preview) {
+		// The inset formula dimension is in general different from the
+		// one of the instant preview image, so we have to indicate to the
+		// BufferView that a metrics update is needed.
+		cur.screenUpdateFlags(Update::SinglePar);
+	}
 }