From 1a2b1a3bfad7ce48e2a025d3a3dab7103fd0039c Mon Sep 17 00:00:00 2001
From: Jean-Marc Lasgouttes <lasgouttes@lyx.org>
Date: Mon, 20 May 2019 18:36:24 +0200
Subject: [PATCH] backing store

---
 src/frontends/qt4/GuiWorkArea.cpp       | 63 ++++++++++++++++++++++---
 src/frontends/qt4/GuiWorkArea_Private.h | 50 ++++----------------
 2 files changed, 65 insertions(+), 48 deletions(-)

diff --git a/src/frontends/qt4/GuiWorkArea.cpp b/src/frontends/qt4/GuiWorkArea.cpp
index 7955731ad3..5c0ae40e22 100644
--- a/src/frontends/qt4/GuiWorkArea.cpp
+++ b/src/frontends/qt4/GuiWorkArea.cpp
@@ -235,13 +235,27 @@ SyntheticMouseEvent::SyntheticMouseEvent()
 
 
 GuiWorkArea::Private::Private(GuiWorkArea * parent)
-: p(parent), buffer_view_(0), lyx_view_(0),
-  caret_(0), 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)
-{
+: p(parent), buffer_view_(0), lyx_view_(0), caret_(0),
+  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)
+{
+/* Qt on macOS and Wayland does not respect the
+ * Qt::WA_OpaquePaintEvent attribute and resets the widget backing
+ * store at each update. Therefore, we use our own backing store in
+ * these two cases. */
+#if QT_VERSION >= 0x050000
+	use_backingstore_ = guiApp->platformName() == "cocoa"
+	                    || guiApp->platformName() == "wayland";
+#else
+#  ifdef Q_OS_MAC
+	use_backingstore_ = true;
+#  else
+	use_backingstore_ = false;
+#  endif
+#endif
+
 	int const time = QApplication::cursorFlashTime() / 2;
 	if (time > 0) {
 		caret_timeout_.setInterval(time);
@@ -1261,6 +1275,41 @@ void GuiWorkArea::Private::paintPreeditText(GuiPainter & pain)
 }
 
 
+void GuiWorkArea::Private::resetScreen()
+{
+	if (use_backingstore_) {
+		int const pr = p->pixelRatio();
+		screen_ = QImage(static_cast<int>(pr * p->viewport()->width()),
+		                 static_cast<int>(pr * p->viewport()->height()),
+		                 QImage::Format_ARGB32_Premultiplied);
+#  if QT_VERSION >= 0x050000
+		screen_.setDevicePixelRatio(pr);
+#  endif
+	}
+}
+
+
+QPaintDevice * GuiWorkArea::Private::screenDevice()
+{
+	if (use_backingstore_)
+		return &screen_;
+	else
+		return p->viewport();
+}
+
+
+void GuiWorkArea::Private::updateScreen(QRectF const & rc)
+{
+	if (use_backingstore_) {
+		QPainter qpain(p->viewport());
+		double const pr = p->pixelRatio();
+		QRectF const rcs = QRectF(rc.x() * pr, rc.y() * pr,
+		                          rc.width() * pr, rc.height() * pr);
+		qpain.drawImage(rc, screen_, rcs);
+	}
+}
+
+
 void GuiWorkArea::paintEvent(QPaintEvent * ev)
 {
 	// Do not trigger the painting machinery if we are not ready (see
diff --git a/src/frontends/qt4/GuiWorkArea_Private.h b/src/frontends/qt4/GuiWorkArea_Private.h
index 83012fa99f..6342eaba4a 100644
--- a/src/frontends/qt4/GuiWorkArea_Private.h
+++ b/src/frontends/qt4/GuiWorkArea_Private.h
@@ -20,14 +20,6 @@
 #include <QMouseEvent>
 #include <QTimer>
 
-#ifdef Q_OS_MAC
-/* Qt on macOS does not respect the Qt::WA_OpaquePaintEvent attribute
- * and resets the widget backing store at each update. Therefore, we
- * use our own backing store in this case */
-#define LYX_BACKINGSTORE 1
-#include <QPainter>
-#endif
-
 namespace lyx {
 
 class Buffer;
@@ -107,37 +99,12 @@ struct GuiWorkArea::Private
 
 	void paintPreeditText(GuiPainter & pain);
 
-	void resetScreen() {
-#ifdef LYX_BACKINGSTORE
-		int const pr = p->pixelRatio();
-		screen_ = QImage(static_cast<int>(pr * p->viewport()->width()),
-		                 static_cast<int>(pr * p->viewport()->height()),
-		                 QImage::Format_ARGB32_Premultiplied);
-#  if QT_VERSION >= 0x050000
-		screen_.setDevicePixelRatio(pr);
-#  endif
-#endif
-	}
-
-	QPaintDevice * screenDevice() {
-#ifdef LYX_BACKINGSTORE
-		return &screen_;
-#else
-		return p->viewport();
-#endif
-	}
-
-#ifdef LYX_BACKINGSTORE
-	void updateScreen(QRectF const & rc) {
-		QPainter qpain(p->viewport());
-		double const pr = p->pixelRatio();
-		QRectF const rcs = QRectF(rc.x() * pr, rc.y() * pr,
-		                          rc.width() * pr, rc.height() * pr);
-		qpain.drawImage(rc, screen_, rcs);
-	}
-#else
-	void updateScreen(QRectF const & ) {}
-#endif
+	/// Prepare screen for next painting
+	void resetScreen();
+	/// Where painting takes place
+	QPaintDevice * screenDevice();
+	/// Put backingstore to screen if necessary
+	void updateScreen(QRectF const & rc);
 
 	///
 	GuiWorkArea * p;
@@ -146,10 +113,11 @@ struct GuiWorkArea::Private
 	///
 	GuiView * lyx_view_;
 
-#ifdef LYX_BACKINGSTORE
+	/// Do we need an intermediate image when painting (for now macOS and Wayland)
+	bool use_backingstore_;
 	///
 	QImage screen_;
-#endif
+
 	///
 	CaretWidget * caret_;
 	/// is the caret currently displayed
-- 
2.39.2