# A question about DSPs (plugin and core) when combined with the geometry engine **URL:** \ **Category:** FMOD Engine\ **Tags:** cpp\ **Created:** [March 2, 2025, 3:34am UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648 "2025-03-02T03:34:16Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Ethin](https://avatars.discourse-cdn.com/v4/letter/e/4af34b/32.png) [@Ethin](https://qa.fmod.com/u/Ethin)\ **Post date:** [March 2, 2025, 3:34am UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/1 "2025-03-02T03:34:16Z")
Hi all, I was looking at the FMOD docs, but I couldn’t find anything on this. Say I generate a geometric mesh using MC33[1] or marching cubes. I have a couple questions: 1. Is it safe to just pass in the vertices directly into FMOD? Is there some way of determining if a polygon should be double-or single-sided, or should I just usually do double-sited unless I need to do something special? 2. How does the geometry engine work when combined wit hspatializer DSPs or other plug-ins which take 3D attributes and other data parameters? Does the geometry occlusion occur _before_ being handled by DSPs/effects, or is that something the DSP would need to do? [1]: Vega, D., Abache, J., Coll, D., A Fast and Memory-Saving Marching Cubes 33 Implementation with the correct interior test, Journal of Computer Graphics Techniques (JCGT), vol. 8, no. 3, 1–18, 2019. [http://jcgt.org/published/0008/03/01/](http://jcgt.org/published/0008/03/01/) ---
**Author:** ![Connor\_FMOD](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/connor_fmod/32/3685_2.png) [@Connor\_FMOD](https://qa.fmod.com/u/Connor_FMOD)\ **Post date:** [March 6, 2025, 11:42pm UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/2 "2025-03-06T23:42:08Z")
Hi, > [@Ethin](#): > > Is it safe to just pass in the vertices directly into FMOD? Once you’ve created the geometry ([FMOD Engine | Core API Reference - Geometry](https://fmod.com/docs/2.02/api/core-api-geometry.html)) it will be passed to FMOD using [FMOD Engine | Core API Reference - System::createGeometry()](https://fmod.com/docs/2.02/api/core-api-system.html#system_creategeometry). Passing the same objects to the geometry system and your renderer is the suggested workflow. > [@Ethin](#): > > Is there some way of determining if a polygon should be double-or single-sided, or should I just usually do double-sited unless I need to do something special? - Double sided is fine - Any face that you would expect to apply occlusion should be passed to the system > [@Ethin](#): > > How does the geometry engine work when combined wit hspatializer DSPs or other plug-ins which take 3D attributes and other data parameters? - The geometry system will apply occlusion to the signal which is then passed onto DPS to process. - So any DSP will be working with an occluded signal Hope this helps. ---
**Author:** ![Ethin](https://avatars.discourse-cdn.com/v4/letter/e/4af34b/32.png) [@Ethin](https://qa.fmod.com/u/Ethin)\ **Post date:** [March 7, 2025, 4:21am UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/3 "2025-03-07T04:21:58Z")
> [@Connor\_FMOD](#): > > Hi, > > > [@Ethin](#): > > > > Is it safe to just pass in the vertices directly into FMOD? > > Once you’ve created the geometry ([FMOD Engine | Core API Reference - Geometry](https://fmod.com/docs/2.02/api/core-api-geometry.html)) it will be passed to FMOD using [FMOD Engine | Core API Reference - System::createGeometry()](https://fmod.com/docs/2.02/api/core-api-system.html#system_creategeometry). Passing the same objects to the geometry system and your renderer is the suggested workflow. Isn’t this backward? I create the geometry (with `System::createGeometry`) and then fill it with polygons? And to confirm: I do pass the exact vertices that I’d get from algorithms like MC33, without modification or anything like that, to `Geometry::addPolygon`? The rest of your post was very helpful – thank you! ---
**Author:** ![Connor\_FMOD](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/connor_fmod/32/3685_2.png) [@Connor\_FMOD](https://qa.fmod.com/u/Connor_FMOD)\ **Post date:** [March 11, 2025, 11:41pm UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/4 "2025-03-11T23:41:02Z")
Here is an example of the mesh struct used: ```auto struct Mesh { int numVertices; FMOD_VECTOR *vertices; float (*texcoords)[2]; int numPolygons; Polygon* polygons; int numIndices; int *indices; FMOD::Geometry *geometry; }; ``` which you will then pass the polygons and vertexes to ```auto mesh.geometry->setPolygonVertex(poly, i, &vertex); ``` Then passed to the FMOD system: ```auto fmodSystem->createGeometry(mesh.numPolygons, mesh.numIndices, &mesh.geometry); ``` Hope this helps ---
**Author:** ![Ethin](https://avatars.discourse-cdn.com/v4/letter/e/4af34b/32.png) [@Ethin](https://qa.fmod.com/u/Ethin)\ **Post date:** [March 11, 2025, 11:54pm UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/5 "2025-03-11T23:54:01Z")
It… Kind of does.It sort of does, I just need to figure out the best way to transform the grid into a mesh (I thought I had it nailed down but… Apparently I didn’t :-(). ---
**Author:** ![Ethin](https://avatars.discourse-cdn.com/v4/letter/e/4af34b/32.png) [@Ethin](https://qa.fmod.com/u/Ethin)\ **Post date:** [August 30, 2025, 4:48pm UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/6 "2025-08-30T16:48:37Z")
Sorry to bump this topic, but I’m getting confused again. (It might be helpful to maybe expand the docs with a lot more info on how geometries work to get rid of this confusion in future, perhaps.) When looking at third-party spatializers, they all have occlusion and similar parameters. Ones like SteamAudio do their own geometric occlusion. In my confusion I reached out to atmoky (since I’m very interested in getting the most out of their plug-in) to try to understand things better and I got this response: > > If I want to, for example, simulate geometric/acoustic occlusion, do I need to (manually) feed those values to the atmoky Spatializer plug-in’s Occlusion parameter (parameter 12)? > > FMOD does not currently offer a builtin way to pass geometry information to a plugin, apart from listener and source coordinates. For this reason, the plugin can only perform the audio processing, any geometric occlusion/ray tracing calculations have to be done on the game engine side and mapped down to a float value. We do have some scripts in our trueSpatial FMOD Unity integration that we consider blueprints/starters on how to perform these calculations, but as there are a lot of performance/game specific considerations, we can not offer an end-all solution for this. If you need a place to start though, the Occlusion Probe Group system we implemented in the trueSpatial FMOD Unity integration would probably be a good place to start. So I’m just confused on which is accurate. If occlusion is done on the audio signal _before_ the DSP receives it, then are occlusion parameters only for custom ray-tracing or for adding extra occlusion? Again, sorry for bumping this topic, I really hope I can at least master this somewhat soon-ish! And thank you for all the help! ---
**Author:** ![Connor\_FMOD](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/connor_fmod/32/3685_2.png) [@Connor\_FMOD](https://qa.fmod.com/u/Connor_FMOD)\ **Post date:** [September 2, 2025, 7:20am UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/7 "2025-09-02T07:20:14Z")
Hi, Thank you for the information. > [@Ethin](#): > > If occlusion is done on the audio signal _before_ the DSP receives it, then are occlusion parameters only for custom ray-tracing or for adding extra occlusion? Apologies, I am slightly confused on your question. What are the parameters you are referencing here? Where are you getting confused? ---
**Author:** ![Ethin](https://avatars.discourse-cdn.com/v4/letter/e/4af34b/32.png) [@Ethin](https://qa.fmod.com/u/Ethin)\ **Post date:** [September 4, 2025, 8:45pm UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/8 "2025-09-04T20:45:00Z")
Hi there, Apologies. I wrote a plug-in introspection tool that dumps all of the parameters for DSP-based plug-ins. For things such as Atmoky TrueSpatial, these plug-ins have their own occlusion parameters. For example, in Atmoky TrueSpatial, my tool outputs, in the parameter list: ```auto 12: Name: occlusion Label: Description: Type: float Range: [0, 1], Default: 0 Mapping: auto ``` So hence my confusion. ---
**Author:** ![Connor\_FMOD](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/connor_fmod/32/3685_2.png) [@Connor\_FMOD](https://qa.fmod.com/u/Connor_FMOD)\ **Post date:** [September 8, 2025, 3:33am UTC](https://qa.fmod.com/t/a-question-about-dsps-plugin-and-core-when-combined-with-the-geometry-engine/22648/9 "2025-09-08T03:33:52Z")
Thanks for the information. In regards to our Unreal Integration. The occlusion parameter is used to drive occlusion on your events: [Unreal Integration | Settings - Occlusion Parameter](https://fmod.com/docs/2.03/unreal/settings.html#occlusion-parameter). However, this is just a value driven by a raycast to the player, the value itself is not applying occlusion. So I believe each implementation would have their own way of using this parameter and what it means specifically for them. In our UE integration that means driving a parameter which you apply in studio and for Atmoky I am not sure how they are using it. Let me know if I have misunderstood.