[LyX/master] Fixup 5202d44e: make caret geometry update lazy

[Jean-Marc Lasgouttes]

commit dc35f1ddf49f8944001a916ad2bcbf2965401cc4
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Mon Sep 7 15:45:30 2020 +0200

    Fixup 5202d44e: make caret geometry update lazy
    
    Instead of working around crashes in update of caret geometry, only
    request it as needed. The actual computaiton will take place just
    before painting the caret.
    
    It might be that this is overkill and that caret geometry should be
    updated unconditionally. One would have to to some timing while idle to
    ascertain that.
    
    Fixes bug #11912.
---
 src/frontends/qt/GuiWorkArea.cpp       |   22 ++++++++++++++++------
 src/frontends/qt/GuiWorkArea_Private.h |    2 ++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/frontends/qt/GuiWorkArea.cpp b/src/frontends/qt/GuiWorkArea.cpp
index a2af82d..40a98c5 100644
--- a/src/frontends/qt/GuiWorkArea.cpp
+++ b/src/frontends/qt/GuiWorkArea.cpp
@@ -243,7 +243,7 @@ GuiWorkArea::Private::Private(GuiWorkArea * parent)
   caret_visible_(false), need_resize_(false), preedit_lines_(1),
   last_pixel_ratio_(1.0), completer_(new GuiCompleter(p, p)),
   dialog_mode_(false), shell_escape_(false), read_only_(false),
-  clean_(true), externally_modified_(false)
+  clean_(true), externally_modified_(false), needs_caret_geometry_update_(true)
 {
 /* Qt on macOS and Wayland does not respect the
  * Qt::WA_OpaquePaintEvent attribute and resets the widget backing
@@ -487,7 +487,8 @@ void GuiWorkArea::scheduleRedraw(bool update_metrics)
 
 	// update caret position, because otherwise it has to wait until
 	// the blinking interval is over
-	d->updateCaretGeometry();
+	d->needs_caret_geometry_update_ = true;
+	d->caret_visible_ = true;
 
 	LYXERR(Debug::WORKAREA, "WorkArea::redraw screen");
 	viewport()->update();
@@ -587,7 +588,8 @@ void GuiWorkArea::Private::resizeBufferView()
 	buffer_view_->resize(p->viewport()->width(), p->viewport()->height());
 	if (caret_in_view)
 		buffer_view_->scrollToCursor();
-	updateCaretGeometry();
+	needs_caret_geometry_update_ = true;
+	caret_visible_ = true;
 
 	// Update scrollbars which might have changed due different
 	// BufferView dimension. This is especially important when the
@@ -637,18 +639,20 @@ void GuiWorkArea::Private::updateCaretGeometry()
 		&& completer_->completionAvailable()
 		&& !completer_->popupVisible()
 		&& !completer_->inlineVisible();
-	caret_visible_ = true;
 
 	caret_->update(point.x_, point.y_, h, l_shape, isrtl, completable);
+	needs_caret_geometry_update_ = false;
 }
 
 
+
 void GuiWorkArea::Private::showCaret()
 {
 	if (caret_visible_)
 		return;
 
-	updateCaretGeometry();
+	needs_caret_geometry_update_ = true;
+	caret_visible_ = true;
 	p->viewport()->update();
 }
 
@@ -1356,8 +1360,14 @@ void GuiWorkArea::paintEvent(QPaintEvent * ev)
 	d->paintPreeditText(pain);
 
 	// and the caret
-	if (d->caret_visible_)
+	// FIXME: the code would be a little bit simpler if caret geometry
+	// was updated unconditionally. Some profiling is required to see
+	// how expensive this is (especially when idle).
+	if (d->caret_visible_) {
+		if (d->needs_caret_geometry_update_)
+			d->updateCaretGeometry();
 		d->caret_->draw(pain, d->buffer_view_->horizScrollOffset());
+	}
 
 	d->updateScreen(ev->rect());
 
diff --git a/src/frontends/qt/GuiWorkArea_Private.h b/src/frontends/qt/GuiWorkArea_Private.h
index 6342eab..75fad9b 100644
--- a/src/frontends/qt/GuiWorkArea_Private.h
+++ b/src/frontends/qt/GuiWorkArea_Private.h
@@ -169,6 +169,8 @@ struct GuiWorkArea::Private
 	bool clean_;
 	///
 	bool externally_modified_;
+	///
+	bool needs_caret_geometry_update_;
 
 }; // GuiWorkArea