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add some pointers for the future about scenegraph cams
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In fact, CompositeViewer is usually needed whenever we have an *independent* entity (where object A may see a completely different part of the scene than object B, so that B may no longer get access to the PagedLOD nodes that A discarded already), but if the camera can be "slaved" to a parent object in the scene, that's probably what should be done? Looking at osgcompositor.cpp, it can combine both kinds of cameras at runtime.--[[User:Hooray|Hooray]] ([[User talk:Hooray|talk]]) 09:53, 16 November 2020 (EST)
 
In fact, CompositeViewer is usually needed whenever we have an *independent* entity (where object A may see a completely different part of the scene than object B, so that B may no longer get access to the PagedLOD nodes that A discarded already), but if the camera can be "slaved" to a parent object in the scene, that's probably what should be done? Looking at osgcompositor.cpp, it can combine both kinds of cameras at runtime.--[[User:Hooray|Hooray]] ([[User talk:Hooray|talk]]) 09:53, 16 November 2020 (EST)
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=== SceneGraph Cameras vs. Prerender Cams ===
 
: Not sure whether this relevant, but Fernando said that Canvas uses scene-graph cameras, and it seemed that the use of scene-graph cameras caused some issues with canvas-view, but it would be quite a lot of work to change canvas to use slave cameras? --[[User:Cgdae|Cgdae]] ([[User talk:Cgdae|talk]]) 10:57, 16 November 2020 (EST)
 
: Not sure whether this relevant, but Fernando said that Canvas uses scene-graph cameras, and it seemed that the use of scene-graph cameras caused some issues with canvas-view, but it would be quite a lot of work to change canvas to use slave cameras? --[[User:Cgdae|Cgdae]] ([[User talk:Cgdae|talk]]) 10:57, 16 November 2020 (EST)
    
:: scene graph cams basically means that canvas based scenes are rendered "redundantly", that's true regardless of Comp/CV. And an obvious optimization for a number of canvas heavy aircraft (think shuttle, airliners). For full context, refer to these comments [[Post_FlightGear_2020.2_LTS_changes#Canvas]]:
 
:: scene graph cams basically means that canvas based scenes are rendered "redundantly", that's true regardless of Comp/CV. And an obvious optimization for a number of canvas heavy aircraft (think shuttle, airliners). For full context, refer to these comments [[Post_FlightGear_2020.2_LTS_changes#Canvas]]:
 
:: Review Tim's original suggestion<ref>https://sourceforge.net/p/flightgear/mailman/message/36659646/</ref>: Another [Canvas] optimization is to use a pre-render camera that isn't in the scene graph to do the Canvas rendering. '''Otherwise the Canvas textures are rendered at least twice, in the near and far cameras'''. <ref>https://sourceforge.net/p/flightgear/mailman/message/36352621/</ref><ref>https://sourceforge.net/p/flightgear/mailman/message/37042457/</ref> Tim Moore’s canvas-rendering-on-a-pre-camera fix, again should give us a nice perf win for Canvas-intensive acft<ref>https://sourceforge.net/p/flightgear/mailman/message/36355833/</ref>, since within each camera pass (far camera, near camera), all the passes of a technique are run.<ref>https://sourceforge.net/p/flightgear/mailman/message/29563353/</ref> Also, Mathias stated once: that it would be good to be able to specify a completely different scenegraph in some subcameras, i.e. for having panel like instruments on an additional screen/display for example.<ref>https://sourceforge.net/p/flightgear/mailman/message/19718354/</ref>
 
:: Review Tim's original suggestion<ref>https://sourceforge.net/p/flightgear/mailman/message/36659646/</ref>: Another [Canvas] optimization is to use a pre-render camera that isn't in the scene graph to do the Canvas rendering. '''Otherwise the Canvas textures are rendered at least twice, in the near and far cameras'''. <ref>https://sourceforge.net/p/flightgear/mailman/message/36352621/</ref><ref>https://sourceforge.net/p/flightgear/mailman/message/37042457/</ref> Tim Moore’s canvas-rendering-on-a-pre-camera fix, again should give us a nice perf win for Canvas-intensive acft<ref>https://sourceforge.net/p/flightgear/mailman/message/36355833/</ref>, since within each camera pass (far camera, near camera), all the passes of a technique are run.<ref>https://sourceforge.net/p/flightgear/mailman/message/29563353/</ref> Also, Mathias stated once: that it would be good to be able to specify a completely different scenegraph in some subcameras, i.e. for having panel like instruments on an additional screen/display for example.<ref>https://sourceforge.net/p/flightgear/mailman/message/19718354/</ref>
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* [https://sourceforge.net/p/flightgear/flightgear/ci/next/tree/src/Canvas/canvas_mgr.cxx#l72 This is how Canvas placements are registered] (the canvas provides a default placement that is added via the gui camera) [https://sourceforge.net/p/flightgear/flightgear/ci/next/tree/src/Canvas/gui_mgr.cxx#l205]
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* [https://sourceforge.net/p/flightgear/flightgear/ci/next/tree/src/Canvas/FGCanvasSystemAdapter.cxx#l68 This is the API used to insert cameras from simgear into fg]
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* [https://sourceforge.net/p/flightgear/flightgear/ci/next/tree/src/Viewer/renderer.cxx#l974 which ends up here]
    
:: --[[User:Hooray|Hooray]] ([[User talk:Hooray|talk]]) 11:20, 16 November 2020 (EST)
 
:: --[[User:Hooray|Hooray]] ([[User talk:Hooray|talk]]) 11:20, 16 November 2020 (EST)

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