[Bf-committers] Engine API

[Ton Roosendaal]

Hi Mitchell,

Interesting project. The recode of Blender's viewport offers opportunities to make
adding external (real time) engines work as well. I'm sure Clement and Dalai keep it
in mind. 

However, let's not have focus drift away to make a pluggable/addon api for the viewport.

Blender is first a 3d creation tool for artists. We will make sure the Blender viewport
gets updated to use advanced shaders and drawing code, and we should ensure that all
of this works satisfying and in real-time with all of the tools we have in Blender.

That's the first focus. Make Blender 2.8 usable (again)! 

-Ton-

--------------------------------------------------------
Ton Roosendaal  -  ton at blender.org   -   www.blender.org
Chairman Blender Foundation, Director Blender Institute
Entrepotdok 57A, 1018 AD, Amsterdam, the Netherlands



> On 23 Dec 2016, at 01:34, Mitchell Stokes <mogurijin at gmail.com> wrote:
> 
> Hello,
> 
> I would like to point out that this new/updated API has a lot of overlap
> with a project I have been working on to bridge Blender with external
> realtime/game engines: BlenderRealtimeEngine (brte) addon[1]. I would love
> to see more of this project (or some of its ideas) get integrated into
> Blender and the stand-alone project made obsolete, and this proposal is a
> good step in this direction. I am fairly confident all of the OpenGL code
> in brte's view_draw could be replaced by the new API. Some problem areas we
> ran into with brte that should be taken into account for this project:
> 
>  * Sending updates to an external engine can be a bit of a pain
>    * The current tagging system is fairly fragile and prone to miss
> updates (e.g., I think removing an object from a scene does not tag the
> scene)
>    * brte currently tries to build deltas to pass to external engines
>    * This may not be as much of an issue for internal engines, but we'll
> need to make sure we don't miss things like material updates that trigger
> shader changes
>  * Realtime engines like to get ticked/updated at a constant rate
>    * Blender only updates the viewport if Blender data has changed
> (sometimes engines need to re-draw even if Blender is not aware of a change)
>    * brte runs an update loop in a separate thread to feed the external
> engine with updates and issue a tag_redraw
>    * An option on the RenderEngine to constantly call the new
> view_realtime could help eliminate some of these issues
>  * brte has to play games with preserving global OpenGL state in order to
> safely draw into Blender's viewport
>    * What are we doing to make sure engines issuing their own OpenGL calls
> are not messing up Blender?
>    * Will we put code around the view_realtime call to protect state
> (could be slow)?
>    * Will we document steps a well-behaving Render Engine has to follow to
> not break Blender (could be fragile)?
>    * We can make use of OpenGL 3.3 features to minimize the amount of
> global state, but I don't think we can eliminate it.
> 
> I would also like to see us explore combining view_realtime and view_draw.
> These seem very similar to me, and I am not sure why an engine would need
> to implement both. As the proposal expands, we will want to see if
> view_realtime is actually different enough to require its own callback. If
> not, I say we remove it and just stick to view_draw.
> 
> Thanks,
> Mitchell
> 
> [1] https://github.com/Kupoman/BlenderRealtimeEngineAddon
> 
> On Thu, Dec 22, 2016 at 1:44 PM, Clément FOUCAULT <foucault.clem at gmail.com>
> wrote:
> 
>> Hi everyone, (cross post from bf-viewport)
>> 
>> I (Clément) and Dalai have laid-out the Proposal of the Render Engine API
>> that will be used to create new viewport "Engines". Things might change but
>> this is the general idea.
>> https://wiki.blender.org/index.php/Dev:2.8/Source/Viewport/EngineAPI
>> 
>> We have also introduced a number of PyNodes changes that are required to
>> support custom GLSL for realtime engines. Thanks Brecht for his insights.
>> https://wiki.blender.org/index.php/Dev:2.8/Source/Viewport/PyNodeGLSL
>> 
>> Insights from others realtime engine developpers are more than welcome :) !
>> 
>> The development of this will start as soon as possible in the 2.8 branch.
>> 
>> Thanks,
>> 
>> Clément
>> _______________________________________________
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>> 
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