From 83b0a31b765348116c079b585ee997b1b5c9d355 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fernando=20Garc=C3=ADa=20Li=C3=B1=C3=A1n?=
 <fernandogarcialinan@gmail.com>
Date: Fri, 27 Aug 2021 18:28:16 +0200
Subject: [PATCH] Canvas cameras are slave cameras instead of scene graph
 cameras

This was a long-standing issue where Canvas cameras were rendered
multiple times, once per slave camera. In the case of the Classic
pipeline they were being rendered twice.

Making them slave cameras has the issue of them not being shared
across GraphicsContexts anymore, so it's not possible to see Canvas
displays in extra CameraGroup windows. This is fixed by using OSG
context sharing feature and sharing the initial windows' context
with all subsequent windows.
---
 src/Viewer/WindowBuilder.cxx |  5 +++++
 src/Viewer/renderer.cxx      | 18 ++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/Viewer/WindowBuilder.cxx b/src/Viewer/WindowBuilder.cxx
index 90eaac00a..4bedcd77e 100644
--- a/src/Viewer/WindowBuilder.cxx
+++ b/src/Viewer/WindowBuilder.cxx
@@ -249,6 +249,11 @@ GraphicsWindow* WindowBuilder::buildWindow(const SGPropertyNode* winNode, bool i
             return result;
     }
     auto traits = new GraphicsContext::Traits(*defaultTraits);
+
+    // Attempt to share context with the window that was created first
+    if (!wsa->windows.empty())
+        traits->sharedContext = wsa->windows.front()->gc;
+
     int traitsSet = setFromProperty(traits->hostName, winNode, "host-name");
     traitsSet |= setFromProperty(traits->displayNum, winNode, "display");
     traitsSet |= setFromProperty(traits->screenNum, winNode, "screen");
diff --git a/src/Viewer/renderer.cxx b/src/Viewer/renderer.cxx
index 87c568f47..419c01697 100644
--- a/src/Viewer/renderer.cxx
+++ b/src/Viewer/renderer.cxx
@@ -1106,13 +1106,27 @@ FGRenderer::setEventHandler(FGEventHandler* eventHandler_)
 void
 FGRenderer::addCamera(osg::Camera* camera, bool useSceneData)
 {
-    _viewerSceneRoot->addChild(camera);
+    osg::Camera *guiCamera = getGUICamera(CameraGroup::getDefault());
+    osg::GraphicsContext *gc = guiCamera->getGraphicsContext();
+    camera->setGraphicsContext(gc);
+    if (composite_viewer) {
+        composite_viewer->getView(0)->addSlave(camera, false);
+    } else {
+        viewer->addSlave(camera, false);
+    }
 }
 
 void
 FGRenderer::removeCamera(osg::Camera* camera)
 {
-    _viewerSceneRoot->removeChild(camera);
+    if (composite_viewer) {
+        unsigned int index = composite_viewer->getView(0)
+            ->findSlaveIndexForCamera(camera);
+        composite_viewer->getView(0)->removeSlave(index);
+    } else {
+        unsigned int index = viewer->findSlaveIndexForCamera(camera);
+        viewer->removeSlave(index);
+    }
 }
 
 void