Revert to use an image surface for CairoWidgets

This partially reverts 2edbda252619 and is a follow up to 0b266a54f,
to fix performance issues with MS Windows graphics performance.

2 files changed, 35 insertions, 13 deletions

diff --git a/libs/gtkmm2ext/cairo_widget.cc b/libs/gtkmm2ext/cairo_widget.cc
index bbc4452238..b06e443ec0 100644
--- a/libs/gtkmm2ext/cairo_widget.cc
+++ b/libs/gtkmm2ext/cairo_widget.cc
@@ -58,9 +58,9 @@ CairoWidget::CairoWidget ()
 {
 	_name_proxy.connect (sigc::mem_fun (*this, &CairoWidget::on_name_changed));
 #ifdef USE_CAIRO_IMAGE_SURFACE
-	_use_intermediate_surface = true;
+	_use_image_surface = true;
 #else
-	_use_intermediate_surface = NULL != getenv("ARDOUR_IMAGE_SURFACE");
+	_use_image_surface = NULL != getenv("ARDOUR_IMAGE_SURFACE");
 #endif
 }
 
@@ -82,7 +82,8 @@ CairoWidget::set_canvas_widget ()
 	ensure_style ();
 	gtk_widget_set_realized (GTK_WIDGET(gobj()), true);
 	_canvas_widget = true;
-	_use_intermediate_surface = false;
+	_use_image_surface = false;
+	image_surface.clear ();
 }
 
 void
@@ -97,9 +98,13 @@ CairoWidget::use_nsglview ()
 }
 
 void
-CairoWidget::use_intermediate_surface (bool yn)
+CairoWidget::use_image_surface (bool yn)
 {
-	_use_intermediate_surface = yn;
+	if (_use_image_surface == yn) {
+		return;
+	}
+	image_surface.clear ();
+	_use_image_surface = yn;
 }
 
 int
@@ -158,9 +163,14 @@ CairoWidget::on_expose_event (GdkEventExpose *ev)
 		return true;
 	}
 #endif
-	Cairo::RefPtr<Cairo::Context> cr = get_window()->create_cairo_context ();
-	if (_use_intermediate_surface) {
-		cr->push_group ();
+	Cairo::RefPtr<Cairo::Context> cr;
+	if (_use_image_surface) {
+		if (!image_surface) {
+			image_surface = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, get_width(), get_height());
+		}
+		cr = Cairo::Context::create (image_surface);
+	} else {
+		cr = get_window()->create_cairo_context ();
 	}
 
 	cr->rectangle (ev->area.x, ev->area.y, ev->area.width, ev->area.height);
@@ -188,9 +198,15 @@ CairoWidget::on_expose_event (GdkEventExpose *ev)
 
 	render (cr, &expose_area);
 
-	if (_use_intermediate_surface) {
-		cr->pop_group_to_source ();
-		cr->paint ();
+	if (_use_image_surface) {
+		image_surface->flush();
+		/* now blit our private surface back to the GDK one */
+		Cairo::RefPtr<Cairo::Context> window_context = get_window()->create_cairo_context ();
+		window_context->rectangle (ev->area.x, ev->area.y, ev->area.width, ev->area.height);
+		window_context->clip ();
+		window_context->set_source (image_surface, 0, 0);
+		window_context->set_operator (Cairo::OPERATOR_SOURCE);
+		window_context->paint ();
 	}
 
 	return true;
@@ -245,6 +261,11 @@ CairoWidget::on_size_allocate (Gtk::Allocation& alloc)
 		memcpy (&_allocation, &alloc, sizeof(Gtk::Allocation));
 	}
 
+	if (_use_image_surface) {
+		image_surface.clear ();
+		image_surface = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, alloc.get_width(), alloc.get_height());
+	}
+
 	if (_canvas_widget) {
 		return;
 	}
diff --git a/libs/gtkmm2ext/gtkmm2ext/cairo_widget.h b/libs/gtkmm2ext/gtkmm2ext/cairo_widget.h
index 7c7456eaa3..0dbd8fe8a0 100644
--- a/libs/gtkmm2ext/gtkmm2ext/cairo_widget.h
+++ b/libs/gtkmm2ext/gtkmm2ext/cairo_widget.h
@@ -40,7 +40,7 @@ public:
 
 	void set_canvas_widget ();
 	void use_nsglview ();
-	void use_intermediate_surface (bool yn = true);
+	void use_image_surface (bool yn = true);
 
 	/* swizzle Gtk::Widget methods for Canvas::Widget */
 	void queue_draw ();
@@ -143,12 +143,13 @@ protected:
 	static sigc::slot<void,Gtk::Widget*> focus_handler;
 
 private:
+	Cairo::RefPtr<Cairo::Surface> image_surface;
 	Glib::SignalProxyProperty _name_proxy;
 	sigc::connection _parent_style_change;
 	Widget * _current_parent;
 	bool _canvas_widget;
 	void* _nsglview;
-	bool  _use_intermediate_surface;
+	bool _use_image_surface;
 	Gdk::Rectangle _allocation;
 
 };