[Bf-gamedev] [Bf-committers] game engine scenegraph: design, review and questions

[Jacob Merrill]

here is my file (it's only handling 1 axis)

http://www.pasteall.org/blend/30589

it's a little tricky, but it gives the effect of slow parent,


On Tue, Jul 22, 2014 at 4:00 PM, brita <britalmeida at gmail.com> wrote:

> Ortiz, i meant to thank you for the example you provided, and asked to see
> Jacob's logic brick setup.
>
> Clearing the response for clarity on what I still need feedback:
>
> 3) Parenting types
> When I parent to a vertex, does it mean I am only parenting to the
> position? As a user I am not choosing the specific vertex..
> 3 Vertices/Triangle  -  at the moment this is doing exactly the same as a
> normal parent relation
> Shouldn't vertex (and triangle) have the relative/offset/inverse option
> too?
>
> 4) Slowparents
> I think it makes more sense to have an object parented to another
> according to whether it makes sense or not for the object to be in the
> other's transform space (following it's scale, orientation..). I think of
> this as a 'tight' connection, as if the child totally belongs to / is part
> off the parent. If the child is instead meant to track another object, it
> should not be it's child, it should follow it according to some
> function/logic.
>
> Slow parenting is currently calculated in the scene graph as a slerp.
> I think this would be better implemented with a 'constraint' controller,
> allowing:
> - a better user interface: the current one is quite hidden and not very
> flexible
> - more constraint types and tweaking
> - more flexibility in the code as well by having this out of the scene
> graph and instead on a step meant to update an object's location relative
> to others.
> - more accuracy - currently, the slerp is not using a time delta and may
> be run several times per frame according to scene graph needs
>
> What I am proposing here is 1) move slow parent out of the scene graph 2)
> implement a new controller that reproduces this functionality and more
> Does this make sense? Is it a good idea? Does it have enough priority?
>
>
> 5) what are those 'depsgraph hacks' checkboxes at object properties panel
> > Relations Extras ?
>
> >Ton added these as a way of telling to depsgraph to tag objects or their
> object-data block to get calculated one more time. It's a quick hack aimed
> at providing an optional way to fix a very limited number of pseudo-cyclic
> scenarios. Does it work? Only in a very limited number of cases, but
> hopefully enough to tide us over until the real problem gets solved...
> -> Can you give me a concrete example? should I check if the GE scenegraph
> is also respecting this checkboxes or it doesn't apply?
>
>
>
> 6) method consistency on SG_Spatial.cpp
> There is a SetLocal and SetWorld for Position, Orientation and Scale. So
> far so good.
> Then there is a Relative Translate Rotate and Scale:
> 6.1) I don't really get the point of these functions and they're all
> different, Can someone clarify?
> 6.2) Translate optionally considers the parent, the Rotate and Scale do
> not.
> 6.3) RelativeScale does not have a 'local' flag. Of course that applying a
> scale in local or world coordinates would be the same, but scaling to a
> value would not. Such as scale = 2 instead of scale * 2
>
> The relative translate is used on the Object/Motion Actuator and the
> Steering Actuator with local as false.
> The relative location is used in the Object/Motion Actuator and the
> MouseActuator
> Both are hooked in the python API:
>
> http://www.blender.org/documentation/blender_python_api_2_71_release/bge.types.KX_GameObject.html?highlight=applymovement#bge.types.KX_GameObject.applyMovement
> According to the python API docs, 'not local' should be world space, not
> parent space.
> The relativeTranslate is using the parent if existing, also, the caller
> ensures that the physics also applies the same transform using world space
> and never the parent:
>
>
> https://developer.blender.org/diffusion/B/browse/soc-2014-bge/source/gameengine/Ketsji/KX_GameObject.cpp$594
>
> Should I change this? It can have an impact in previously made games using
> the logic bricks or python.
>
> The relative scaling is not used by logic bricks and does not have a
> python hook. Is it only directly connected in places where I think it can
> be removed.
>
> ---
> Inês Almeida
>
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