[HELP] Geometry instancing is not working

[StudenteChamp2]

[HELP] Geometry instancing is not working

[svenwoop]

What geometry is the mesh supposed to be? It is likely just the one grass object, which is also seen in the instancing case. I cannot spot any obvious error in your code.

[freibold]

You can also take a look at the instance array geometry tutorial

https://github.com/embree/embree/blob/master/tutorials/forest/forest_device.cpp

that we added in Embree 4.3.0. This tutorial does almost the same as you want to do but with trees instead of grass/herbs.

[StudenteChamp2]

@svenwoop @freibold Thanks for helping.
I updated the question because it could be confusing. So now the scene has only one mesh: the plane.

To recall I have 2 implementations. I don't get why the second is not working.

1) No instancing(WORKS)

Steps:
-->Create the scene(rtcNewScene)
-->Create a RTCGeometry(RTC_GEOMETRY_TYPE_TRIANGLE) for the plane
-->Set the geometry vertex and index buffers(using rtcSetSharedGeometryBuffer).
-->Commit the geometry(rtcCommitGeometry)
-->Attach the geometry to the scene(rtcAttachGeometryByID)
-->Commit the scene.

2) Instancing(DOESN'T WORK)

Steps based on the instanced geometry tutorial :
-->Create the root scene
g_scene = rtcNewScene(g_device)

-->Create the instanced scene
g_scene1 = rtcNewScene(g_device)

-->Create a RTCGeometry for the plane
g_geometry = rtcNewGeometry(g_device, RTC_GEOMETRY_TYPE_TRIANGLE);

-->Set the geometry vertex and index buffers.

-->Commit the geometry
rtcCommitGeometry(g_geometry)

-->Attach the geometry to the instanced scene
rtcAttachGeometryByID(g_scene1, g_geometry, mesh->getFlatId())

--> Commit the instanced scene
rtcCommitScene(g_scene1)

-->Create a geometry instance.
g_instance0 = rtcNewGeometry(g_device, RTC_GEOMETRY_TYPE_INSTANCE)

-->Link the geometry instance to the instanced scene
rtcSetGeometryInstancedScene(g_instance0, g_scene1)

-->Set the instance transform
`
const float transform[] = { 1.0f, 0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f, 0.0f,
0.0f, 0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 0.0f, 1.0f };

rtcSetGeometryTransform(g_instance0, 0, RTC_FORMAT_FLOAT4X4_COLUMN_MAJOR, &transform[0]))`

-->Attach the instance to the root scene
rtcAttachGeometry(g_scene, g_instance0)

-->Commit the root scene
rtcCommitScene(g_scene))

[svenwoop]

Could you please provide a reproducer by modifying the instance geometry tutorial? It is not obvious what is wrong there and we would need a small reproducer to debug this.

[StudenteChamp2]

I managed to have it working by doing the same steps as what it is in the instanced geometry tutorial. So it works but I don't understand why. It look like this:

-->Create the root scene
g_scene = rtcNewScene(g_device)

-->Create the instanced scene
g_scene1 = rtcNewScene(g_device)

-->Create a RTCGeometry for the plane
g_geometry = rtcNewGeometry(g_device, RTC_GEOMETRY_TYPE_TRIANGLE);

-->Set the geometry vertex and index buffers.

-->Commit the geometry
rtcCommitGeometry(g_geometry)

-->Attach the geometry to the instanced scene
rtcAttachGeometryByID(g_scene1, g_geometry, mesh->getFlatId())

-->Release the geometry
rtcReleaseGeometry(g_geometry);

--> Commit the instanced scene
rtcCommitScene(g_scene1)

-->Create a geometry instance.
g_instance0 = rtcNewGeometry(g_device, RTC_GEOMETRY_TYPE_INSTANCE)

-->Attach the geometry instance to the root scene
rtcAttachGeometry(g_scene, g_instance0)

-->Release the geometry instance
rtcReleaseGeometry(g_instance0);

-->Set the instance transform
`
const float transform[] = { 1.0f, 0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f, 0.0f,
0.0f, 0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 0.0f, 1.0f };

rtcSetGeometryTransform(g_instance0, 0, RTC_FORMAT_FLOAT4X4_COLUMN_MAJOR, &transform[0]))`

--> Commit the instance geometry
rtcCommitScene(g_instance0)

-->Commit the root scene
rtcCommitScene(g_scene))

[StudenteChamp2]

@svenwoop How does rtcReleaseGeometry works?
Here we create the instance geometry then we free it inside the same function(device_init ):
https://github.com/embree/embree/blob/master/tutorials/instanced_geometry/instanced_geometry_device.cpp#L123

Then we later use the same geometry(we released) and we commit it:
https://github.com/embree/embree/blob/master/tutorials/instanced_geometry/instanced_geometry_device.cpp#L339

[svenwoop]

The rtcReleaseGeometry decreases the reference counter on the geometry handle, thus you should not use that handle anymore. However, if you previously attach the handle to some scene, then the object itself will still be alive, as the scene itself increases the reference count on that geometry.